Engineering Chemistry Volume 7

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Volume 7 of
Engineering Chemistry

ISSN print 2813-6527
ISSN web 2813-6535

Full text available online at https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

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Table of Contents

Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

Daniel Gbenga Adekanmi, Carlos Rodriguez Garcia, Claudia M. Lopez-Badillo

Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Silas Oseme Okuma, Okiemute Dickson Ofuyekpone, Cynthia Chinasa Nwaeju, Martins Obaseki, Ejovi Okuma Ogagavwodia

Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

Sudibyo Enggar Laksono, Ade Sonya Suryandari, Widiyastuti Widiyastuti, Tantular Nurtono, Heru Setyawan

Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

Rudi Firyanto, Retno Ambarwati, Chelsi Chika

Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

Harmami Harmami, Ita Ulfin, Baswara Gilang Ramadhan, Kartika A. Madurani

Bilayer Solar Steam Generator by Co-Gelation Method

Annisa Nur Fidyanti Pamuji, Juliananda Juliananda, Widiyastuti Widiyastuti, Tantular Nurtono, Heru Setyawan

Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Jauharatul Wardah, Sugeng Winardi, Suci Madhania, Mohammad Irwan Fatkhur Rozy, K. Kusdianto

Highly Porous Ni Electrode Decorated with for Oxygen Evolution Reaction (OER)

Bayu Satria Wardhana, Sheng Wei Lee, Jason Shian Ching Jang

Keywords Index

Authors Index

The original version of this eBook is available on https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 1-24

doi: 10.4028/p-518pjS

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2024-01-15

Revised:
2024-06-01

Accepted:
2024-06-17

Online:
2024-06-26

Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

The original version of this paper is available on https://www.scientific.net/EC.7.1.pdf

Daniel Gbenga Adekanmi , C.R. Garcia , Claudia M. Lopez-Badillo

Facultad de Ciencias Químicas. Universidad Autónoma de Coahuila. Unidad Saltillo. Saltillo, Coahuila, 25280, México.

Facultad de Ciencias Físico Matemáticas, Universidad Autónoma de Coahuila. Unidad Saltillo. Saltillo, Coahuila, 25280, México.

danieladekanmi@uadec.edu.mx, crodriguezgarcia@uadec.edu.mx, cllopezb@uadec.edu.mx

*corresponding author: cllopezb@uadec.edu.mx

Keywords: Carbonate hydroxyapatite, biomaterial, bioceramic, synthesis.

Abstract

Carbonate hydroxyapatite is the common derivative of hydroxyapatite found in living systems. It is the building block of most hard tissues, including the teeth and bones. A vast majority of the applications of this versatile material focus on its biomedical applications, which is attributable to its closeness to biological apatites. Hydroxyapatite is a strong precursor to carbonate apatite in nature, and many experiments show that both are similar in a few respects. A significant divergence point is carbonate's obvious impact on its physicochemical properties and concomitant applications. The inclusion of carbonate ions into the lattice of hydroxyapatite results in morphological and physicochemical changes that vary with the method of synthesis and extent of substitution. The unique crystal structure, improved surface area, and porous morphology of carbonate hydroxyapatites also make it useful for catalysis and environmental remediation as adsorbents for heavy metals. This review briefly examines carbonate hydroxyapatite, its synthesis, its modification, and its characterization. It also highlights its biomedical applications while drawing attention to its nonmedical potential.

Introduction

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Biomaterials play a major role in modern medicine, facilitating the repair, replacement, and augmentation of damaged tissues and organs. Moreover, they are utilized to administer drugs and therapeutic materials to the body in a targeted and controlled manner [1,2]. As the field of biomaterials continues to advance, innovative biomaterials are continuously being developed. One such material is hydroxyapatite and its derivatives, which are closely related to the calcium phosphate compounds found in living organisms. Carbonate hydroxyapatite, specifically, is present in the bones and teeth of vertebrates, as well as some marine organisms like corals and mollusks [3,4]. Due to its bioactive properties and resemblance to biological apatite, it is a preferred material in hard tissue engineering and drug delivery. Additionally, carbonate hydroxyapatite has non-medical uses. This article will provide an overview of biomaterials, the synthesis, and the applications of carbonate hydroxyapatite in medicine and beyond.

Biomaterials and their Classification

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Over the years, the definition of biomaterials has evolved from its earliest mention in 1967 by Dr. Jonathan Cohen. His definition summed up biomaterials to include all materials except drugs and sutures [1]. Although his definition was limited by the knowledge and research available at that time and by his experience as a surgeon, it captured the essence of biomaterials. It also separates biomaterials from aesthetic and beauty-motivated structures [2]. Following recent technological advancements in research, biomaterials are no longer considered inert structures as previously conceived [5]. Modern biomaterials last longer and can be whole or partial replacements of tissues or organs in the body [6]. The success ratings of biomaterials have increased, and the risk of revision
surgeries and related complications has been reduced. Various types of biomaterials have been used to enhance the quality of life of patients on application [2,7,8].
The broadest system of classifying biomaterials is based on their chemical structure and mode of interaction with the living system. Under this classification, structurally, biomaterials can be bioceramics, polymers, metals, or composites (Fig. 1), then inert, bioactive, or bioabsorbable based on the mode of interaction [9]. An oversimplified classification focuses on their origin, that is, natural or synthetic .

Fig 1. Classification of biomaterials

Fig 1. Classification of biomaterials

Bioceramics

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Due to their exceptional properties and versatility, bioceramics are a significant class of biomaterials [12]. Ceramic materials designed for biomedical use exhibit outstanding biocompatibility, chemical stability, and mechanical strength. Bioceramics can be credited with a significant portion of the boom in demand for biomaterials [13]. First-generation bioceramics were bioinert, while second-generation bioceramics are bioactive and can be loaded with therapeutic species for targeted treatment [14, 15]. Examples of bioinert bioceramics are alumina, zirconia, and pyrolytic carbon. Their bioactive counterparts include calcium phosphates, hydroxyapatite, bioactive glasses, and coralline [16]. Compatibility is a major concern when designing biomaterials [8, 15, 17]. The bioactivity of bioceramics drives the production of bone grafts, skeletal implants, and coatings that promote faster healing, thereby improving their performance and reducing recovery time [18, 19], and as carriers of drugs that provide precise and long-lasting delivery of therapeutic substances to target areas [20-22]. Since the 60s, interest in the use of calcium orthophosphate bioceramics has grown, especially hydroxyapatite and its derivatives [23].

Hydroxyapatite (HA) and apatites

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Biomineralization is a typical process in living systems in which bioactive minerals are crystallized and deposited in the form of specialized structures. Common biominerals include silica, calcium carbonate, and hydroxyapatite. Hydroxyapatite is the fundamental component of hard tissues found in vertebrates and is characterized by its hexagonal or monoclinic crystal structure with the main difference being the spatial arrangement of the hydroxyl groups relative to the other groups in the structure [24-26]. Hydroxyapatite crystals with hexagonal crystal structure confirmed through X-ray diffraction have been reported more than their monoclinic counterpart although, Korowash et al. and Prihanto et al. reported that monoclinic have better thermodynamic stability and are often found in nature being formed at lower temperatures and pH of between 5 to 7.5 [25,27]. It has however been observed that the two crystal structures can coexist and possess a dynamic relationship depending on the conditions of synthesis and prevailing conditions [28,29]. Apatites refer to a family of compounds that share similar structures, especially the hexagonal system and space group ( ). Appreciable characterization of apatites began in the 18th century [30]. By 2019, of hydroxyapatite articles were focused on substituted hydroxyapatite, a steady rise from in 2010 [31]. Three main properties of hydroxyapatite include acidity, ion exchange property, and adsorption potential. These
properties have made them effective ion exchangers, sorbents, and carriers of biomolecules, also influencing their applications in many fields as shown in Table 1 [32-35]. Most hydroxyapatites are hydrated salts because water acts as both a stabilizer in their synthesis and ensures the stability of their crystals [36]. Hydroxyapatites, chemically represented as , play a vital role in the composition of mammalian hard tissues [37] and exist in natural phosphate mineral deposits [38]. Hydroxyapatites can be sourced from natural materials such as mammalian bones, shells, fish scales, and minerals [39-46]. Their crystal structure possesses two distinct planes [47, 48]. From a functional and evolutionary perspective, aquatic animals meet their phosphorus demands through the seawater around them; similarly, terrestrial animals depend on the apatites in their hard tissues as a store of phosphorus for metabolic activities. This makes apatite found in the bones and other hard tissues adaptational storage, providing and regulating calcium and phosphorus in the body [49, 50]. Biological apatites, while nonstoichiometric and calcium deficient, exhibit a range of ratios from 1.5 to 1.69 , which significantly impacts their biological and physical characteristics [51,52]. The properties and amorphous behavior of these apatites are contingent upon the type of modification and the extent of substitution [53].

Table 1. Properties of hydroxyapatites and the influencing factors

Properties
Mechanisms and factors
References

Biocompatibility
Composed of ions, they are easily metabolized by the body.
Adequate crystallinity and porosity
Adaptable mechanical properties.
Functional groups, functionalized surfaces, and high surface activity stimulate covalent bonding.
[54-57]

Bioactivity
Composed of ions that stimulate normal cell growth.
Adequate surface area and porosity to support effective attachment of cells and flow of body fluid.
[54, 58]

Bioabsorbable
Slow degradation into Ions that are easily metabolized by the body.
[55, 56, 59]

Therapeutic
Inherent or incorporated ions
Bioactive molecules incorporated into the structure.
[49, 57, 60]

Biostability/Biodegradability
Chemical composition, particle size, and purity.
[54, 58]

Ion exchange
High surface activity.
Precipitation through complexation.
[54, 57, 61, 62]

Adsorption
Functional groups, functionalized surfaces, and high surface activity stimulate covalent bonding.
Physical traps through nanopores.
[54, 57]

Modifications and physicochemical properties

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The structure, composition, and stoichiometry of hydroxyapatite have been successfully modified by the incorporation of other ions [63, 64]. Maximizing the ease of ion replacement in hydroxyapatites can improve their conductivity, crystallinity, solubility, and thermal stability, subsequently enhancing their applicability [65,66]. The flexibility of hydroxyapatite crystal lattice encourages incorporating other ions to enhance their characteristics [49, 67]. Non-native ions found in the bone and tooth enamel hydroxyapatite include carbonate ( . %), sodium ( . %), magnesium, and trace amounts of other elements such as potassium, chloride, and fluoride [68]. Ince et al. [69] and Sridevi
et al. [70] reported that synthesized hydroxyapatite's morphology, stability, solubility, mechanical properties, and biological behavior are influenced by the type of ion, size, and charge. The hydroxyapatite lattice can accommodate ions larger in size than its native ions ( and ), causing a marginal strain [49]. For example, could be replaced with alkali and alkaline earth ions, which alters its basicity, while , and can replace to modify its acidity. Divalent ions like , and have also been used to improve the mechanical performance of hydroxyapatite [67]. Sometimes bioactive organic molecules like citrate or other ions can adsorb functionally to the surface of apatites [49, 71]. Apatites doped with rare-earth elements have been used as biomarkers for tracking scaffolds in situ and other proteins [7274]. Lanthanides replace in hydroxyapatite, yielding photoluminescent products, although Yttrium and Samarium have the potential to promote osteoblast adhesion. Rare elements take up selective positions in the calcium phosphate structure, which produces distinct properties in the products [34, 72, 73]. Fig. 2 summarizes the general effect of cations, anions, and bioactive molecules on hydroxyapatites.

Fig. 2. Properties affected by incorporating cations and anions into hydroxyapatite lattice.

Fig. 2. Properties affected by incorporating cations and anions into hydroxyapatite lattice.

Carbonated hydroxyapatite (CHA)

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CHA has become the important derivative of hydroxyapatite used in hard tissue engineering since natural bones are comprised of 60-70% by mass of carbonated, low-crystalline, calcium-deficient hydroxyapatites. It is the closest to the bioapatite found in bones and dental enamel. Pure stoichiometric hydroxyapatite is seldom found in nature whereas the presence of calcium-deficient hydroxyapatite combined with other ions are common [11, 75]. The introduction of carbonate ions ( ) into the crystal lattice structure of hydroxyapatite, which partially replaces hydroxyl ions or phosphate ions, imparts unique characteristics and complexities to the mineral [67, 76-78].
The inclusion of carbonate in the apatite structure has resulted in different morphological changes, which vary predominantly with the synthesis method. Generally, the inclusion of carbonate ions reduces crystallinity and increases solubility, thereby promoting biocompatibility, biomineralization, bioactivity, and reabsorption [77, 79-82]. CHA exhibits improved homogeneity and capacity, particularly when synthesized at the nanoscale [83]. Usually, when nanosized it offers better surface area, facilitating uniform distribution and interaction with its surrounding environment. However, nanosized apatites are preferred in drug delivery since they offer a higher surface area ratio, whereas bone graft and implant coatings use microsized apatite because they are bulkier [13].

The incorporation of carbonate ions into the apatite structure yields two types of CHA. B-type carbonation, characterized by substituting phosphate groups with carbonate ions, is notably present in young bones. B-type substitution results in CHA with a decrease in crystallinity and increased solubility [84]. B-type CHA mimics the chemical composition of natural bone constituents, though the carbonate content of bones is age-dependent. Interestingly, B-type CHA can be obtained from other sources besides humans [75, 85]. The A-type formed by substituting hydroxyl ions with carbonate is less polar, causing lower cell attachment to osteoblastic cells. Old tissues have been reported to contain more A-type CHA than younger ones [75]. A-type CHA compensates for charge through the loss of OH ions, whereas B-type CHA achieves compensation by the loss of which is energetically favorable [86]. A-type CHA is represented as and B-type is .
Depending on the extent and type of substitution, carbonates can influence the crystal lattice, crystallinity, morphology, and mechanical behavior of apatites [76, 78]. In a study, the incorporation of carbonate resulted in lower bending strength of single-crystal pure hydroxyapatite [89], which aligns with the findings that the elasticity of carbonated apatite increases [76]. The morphological transformation of CHA and their composites is proportional to the concentration of the carbonate included and attributed to the increase in disorder caused by introducing carbonate groups [90, 91]. Synthetic pure hydroxyapatite may be preferred because of its stability during sintering, but recent studies have improved the thermal stability of CHA, making it also available for medical applications [50].
The carbonate content in bone hydroxyapatite, which is about , surpasses that in enamel and dentin which varies between and [92]. Variations in carbonate content exist both within a bone and among different bones in the body, reflecting composition-dependent functionality and this makes CHA a good substitute [93-95]. Spence et al. [96] and Ishikawa [96] confirmed this through in vitro studies on carbonated and pure hydroxyapatite. The study reported that carbonated hydroxyapatite stimulated collagen production in human osteoblasts when compared with pure hydroxyapatite [75, 97, 98]. An investigation into the implications of altered carbonate levels in bone diseases revealed connections between CHA and various pathological conditions. Comparative analyses of healthy bones and bones of patients with conditions such as osteoporosis or renal osteodystrophy revealed distinctive differences in carbonate content. Osteoporotic conditions result in elevated carbonate in bones which may correspond to impaired disruptions in mineralization processes and changes in bone mineral density. Furthermore, various pathological conditions and their extent of progress may be distinguished through comparisons of carbonate levels in the bones of patients [99, 100].
In physiological mediums, leaching is one of the series of processes that results in the formation of CHA and the incorporation of other ions into the apatite structure. The basic environment is formed by the migration of , and within the medium. As ions migrate to the surface, phosphates are formed, and eventually, crystallization occurs, and and are incorporated to form carbonated apatite [101]. The altered crystal lattice due to carbonate substitution can lead to variations in bone load-bearing capabilities and resistance to fractures [102]. Simultaneous inclusion of and increased its release potential. The replacement of Ca with Si resulted in lowered crystallinity and fine particle size [103]. Robin et al. [104] studied the mineralization process of CHA using micro-Raman spectroscopy and solid-state NMR. The process was initiated by the formation of amorphous calcium phosphate, which is then transformed into octacalcium phosphate and eventually into carbonated apatite.

Synthesis methods and characterization

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The ease of adjusting morphology and applications of apatites based on the choice of synthesis route has also favored apatites [13]. Popular biogenic sources of calcium for the synthesis of carbonate apatites include fish bones, shells, cow, and bovine bones [37]. Other standard reagents, such as , and are also used for the synthesis of CHA and its derivatives. The use of natural materials such as shells and salt
of sodium and potassium competitively includes magnesium, sodium, potassium or other elements in the carbonate apatite structure while optimizing the incorporation of carbonate through charge balance. Also, the products obtained from them imitate the natural bone CHA composition which is beneficial for bone tissue engineering [88, 105]. Similarly, halides are liberated when their salts are used. If pure undoped CHA is desired, ammonium and nitrates salts are mostly preferred because their residues are easily washed off after the reaction [106, 107]. Ultimately, the choice of reagents depends on the synthesis method and the desired properties of the hydroxyapatite nanoparticles. The synthesis route then, determines the morphology and size distribution, as shown in Table 2. The synthesis method also influences the mechanical properties, surface chemistry, purity, and bioproperties of the products [4, 108, 109]. Sometimes, nanosizing, nucleation and agglomeration of apatite nanoparticles is desired and facilitated using organic materials that serve as templates [110]. These organic modifiers uniquely influence the morphology and crystal structure of nanoparticles [111]. They are also beneficial in the chemical modification of hydroxyapatite nanoparticles' surface and are achieved through functionalization, which introduces functional groups that enhance the effective attachment of therapeutic materials, targeting, and release [112]. CHA synthesis methods can be grouped into two: wet and dry synthesis methods [4, 113-116].

Table 2. Synthesis methods, reagents, and morphology of carbonate hydroxyapatites.

Reagents | Synthesis method | Morphology | References
Ca(OH)₂, (NH₄)₂HPO₄, CaCO₃, (NH₄)HCO₃ | Microwaved-assisted synthesis precipitation | Microcrystalline powders | [117]
CaO, (NH₄)₃PO₄, (NH₄)₂CO₃ | Microwave-assisted mechanosynthesis | Micro-sized granules | [118]
Ca(NO₃)₂.4H₂O, (NH₄)₃PO₄, (NH₄)HCO₃, EDTA | Hydrothermal | Nanorods | [119]
CaCO₃, CaHPO₄.2H₂O | Mechanosynthesis | Nanocrystalline powder | [120]
Ca(NO₃)₂.4H₂O, (NH₄)₂HPO₄, (NH₄)HCO₃ | Nanoemulsion | Nanosized crystals | [121]
Ca(NO₃)₂.4H₂O, (NH₄)HCO₃, (NH₄)₂HPO₄ | Nanoemulsion | Nanocrystalline | [122]
Ca(NO₃)₂.4H₂O, (NH₄)₂HPO₄, K₂CO₃ | Wet precipitation | Nanocrystalline powder | [98, 123]
Ca(NO₃)₂.4H₂O, K₂CO₃, Urea | KH₂PO₄, Hydrothermal | Nanorods | [124]
Calcium gluconate, Na₂HPO₄, Na₂CO₃, CaNO₃ | wet precipitation | Needle-like nanograins | [125]
Ca(NO₃)₂.4H₂O, (NH₄)₃PO₄, Na₂CO₃ | Wet precipitation | Micro-sized solids | [107]

Dry methods are economically beneficial for the mass production of apatite powders. However, dry synthesis tends to contain impurities in the form of other phases and is therefore not always preferred for medical products [126]. Dry methods for synthesizing CHA include solid-state synthesis and mechanosynthesis [127-129]. Damayanti et al. [129] reported the synthesis of CHA through mechanosynthesis. The thoroughly milled mixture of hydroxyapatite and produced predominantly B-type carbonate apatite. They observed that milling time is a major factor in the incorporation of the carbonate into the apatite structure through mechanosynthesis. Ito et al. [130] synthesized A-type carbonated hydroxyapatite by sintering pure hydroxyapatite in a atmosphere at for 15 hours. An alternative method reported by Nordström et al. [131], which yielded Atype CHA, involved immersing hydroxyapatite in a saturated solution for up to two months.

Wet synthesis methods are particularly effective for tailoring the morphology and particle size of products [132]. For stochiometric hydroxyapatite, a ratio of 1.67 must be achieved during precipitation in wet synthesis. The inclusion of carbonate ion, however, increases the ratio up to 1.8, especially if it is B-type substitution [105]. All wet methods of CHA are carried out in an alkaline medium because at high pH levels, CHA is precipitated and remains stable, as shown in Fig. 3 [106, 127, 133-135]. Another important factor that increases the yield of wet methods, nanocrystallinity, and affects the percentage weight of incorporated carbonate is the aging period of the reaction system. This was explained by the increase in the number of phosphate ions replaced by carbonate ions [105]. Wet methods include sol-gel synthesis, hydrothermal synthesis, and wet precipitation (Fig. 4).

Fig. 3. Stability of calcium phosphate, phosphate ion, and carbonate ion at different pH [124].

Fig. 3. Stability of calcium phosphate, phosphate ion, and carbonate ion at different pH [124].

Sol-gel synthesis involves the formation of a sol-gel of phosphate salt, carbonate salt, and calcium salt solution. The sol obtained must age properly at low temperature and then calcined at a higher temperature [136]. Sol-gel synthesis yields CHA nanoparticles with good homogeneity and biocompatibility [137]. Bang et al. [138] reported phase transformation of calcites prepared through sol-gel synthesis. The immersion of the initially prepared calcites into solution produced nanosized needle-shaped carbonate apatites. Deptuła et al. [139] reported the synthesis of CHA through sol-gel synthesis using calcium acetate and phosphoric acid, calcining at .
Hydrothermal synthesis is carried out under high pressure and temperature usually in an autoclave and can produce carbonate hydroxyapatite, which is adequate for biomedical applications. The closed synthesis system eliminates the need for calcination after synthesis [119, 140, 141]. Hydrothermal method was used to synthesize and hydroxyapatite-carbonate composites from corals. The hydroxyapatite-carbonate composites obtained on application initiated rapid bone differentiation within a year as evidence of the viability of synthetic carbonate apatites [142]. Organic templates have been used to mediate the hydrothermal synthesis of CHA [119, 140].
Wet precipitation is usually carried out with calcium, phosphate, and carbonate salts in alkaline medium at ambient or slightly elevated temperatures. To improve the homogeneity of the products, reaction conditions and material purity must be taken into consideration [141, 143]. Safarzadeh et al. [98] and Furko et al. [125] carried out wet synthesis of CHA using carbonate salts. In another research, Nowicki et al. [144] used a two-step approach to synthesize CHA. The first involves wet precipitation of pure hydroxyapatite followed by sintering in dry .

Fig. 4. Scheme for common CHA wet synthesis routes [145-147].

Fig. 4. Scheme for common CHA wet synthesis routes [145-147].

Other methods for the synthesis of CHA that are derived from wet precipitation include microwaveassisted synthesis, nanoemulsion synthesis and sometimes a combination of two methods. CHA obtained from microwave-assisted synthesis were reported to be less thermally stable although their bioactivity increased [148]. Ezekiel et al. [122] also concluded that CHA prepared through nanoemulsion exhibits a similar level of crystallinity and chemistry to biological apatites. After the incorporation of , and separately and together by nanoemulsion route into CHA, the product remained amorphous and retained its phase purity. However, unlike their initial spherical shapes, the particles became more needle-like [84]. An example of the combination was carried out by Liu et al. [106]. They conducted a two-step process to synthesize CHA. For the first step, they performed stoichiometric synthesis of hydroxyapatite using and . Subsequently, they employed a hydrothermal process for biomimetic CHA synthesis at for 24 h using KOH as a mineralizer and as the carbonate source. Interestingly, carbonation resulted in a reduction in the length of the rod-like hydroxyapatite nanoparticles as the carbonate concentration increased. Sintering also known as thermal treatment, improves mechanical performance, stability, porosity, osteoclastic properties, and granular structure of CHA [17, 75]. It can be carried out at upwards in a dry atmosphere [149]. Thermal stability is attributed to the concentration and type of carbonates used in the synthesis, though there is always significant decomposition of CHA with onset from . Sintering time, temperature, and atmosphere affect carbonate substitution [150].
During thermal treatment, the carbonate content of apatites reduces. However, functional CHA must contain the average carbonate content of bones after sintering. To solve this challenge, Landi et al. [75] proposed residue-controlled sintering or sintering in a controlled atmosphere. Muhammad Syazwan et al. [84] observed that furnaces wear out easily when wet is used for carbonation during sintering. Their proposed alternative was to carry out an intermittent supply of wet during the sintering or to use sintering aids. CHA prepared with sintering aids , KOH , and ) produced samples with improved morphology and better strength [151]. During thermal treatment, B-type CHA may form alongside various other phases, and at extreme temperatures, -tricalcium phosphate is formed [86]. Lovón-Quintana et al. [133] noted that thermal treatment in atmosphere at high temperatures above yields A-type CHA while lower temperature gives B-type. However, they noted that the synthesis route of CHA also influences the type of sintered CHA obtained [149].
X-ray diffraction (XRD) studies serve as a tool to elucidate shifts in the lattice parameters and the position of carbonate ions within the apatite structure. From observation, an increase in the amorphous phase due to the inclusion of carbonate results in broader peaks with lower intensity [88, 119, 152, 153]. Also, Verma et al. [154] explained that the slight shift in to higher values was connected to a compressive microstrain in the lattice structure. This strain leads to the extension of the c-axis and shortening of the a-axis, a characteristic of B-type carbonation of hydroxyapatites. In the study of the effect of ammonium carbonate on the formation of calcium-deficient hydroxyapatite, lower levels of carbonation still maintained the sharper peaks and crystalline structure of
hydroxyapatite. As the degree of carbonation increased, the peaks became broader, and crystallinity reduced [152, 155-157]. Generally, peaks between and represent the (002) plane while those between 31 and represent 211, 213, 222, 300 and 310 planes of apatites (Fig. 5) [41, 119, 154, 158, 159].
Although X-ray diffraction patterns can identify the hydroxyapatite phase, the presence of hydroxyl, phosphate, and carbonate groups is easily confirmed through FTIR [160]. Typically, FTIR spectra of CHA have broad -OH absorption around and , and absorption around representing the and , respectively. Sharp peaks for are recorded at around and . The bands at and are attributed to absorption [160,161]. Usually, the replacement of or by the incorporated ion weakens the intensity peaks for the corresponding ion but according to stoichiometry, the O-H stretching band is usually weaker when compared with P-O (Fig. 5) [161-163].

Fig. 5. XRD diffractograms and FTIR spectra of carbonated hydroxyapatites [163].

Fig. 5. XRD diffractograms and FTIR spectra of carbonated hydroxyapatites [163].

Scanning Electron Microscopy (SEM) reveals the transition in morphology as chemical composition changes or modification occurs with the inclusion of carbonate ions (Fig. 6). The morphology of CHA as confirmed by SEM showed that an increase in carbonation increased amorphous characteristics leading to the formation of "featureless" structures from the previous rod-like shapes of the hydroxyapatite [152]. Moore et al. [157] also confirmed the amorphous structure of carbonate hydroxyapatite prepared through low-temperature precipitation. Frank-kamenetskaya et al. [164] compared the morphology of CHA prepared by precipitation and hydrothermal routes. The hydrothermal route produced more crystalline CHA than the precipitation route although the amorphous characteristics generally increased in both cases as degree of carbonation increased.
Thermal behavior of materials studied through thermogravimetric analysis is crucial to determining the behavior of materials in mild and extreme temperatures (Fig. 6). Usually, CHA obtained from biogenic materials undergoes a refinement in the structure after calcining. This is due to the volatilization of organic matter, resulting in a loss of mass at about [162]. Thermogravimetric analysis of CHA obtained through sol-gel synthesis [165] revealed a loss of mass resulting from the water below and a loss of mass from due to the release of [74, 166, 167].

Fig. 6. TGA spectra [163] and SEM of granular [168] and rod-like [163] CHA.

Fig. 6. TGA spectra [163] and SEM of granular [168] and rod-like [163] CHA.

Biomedical applications and biomaterial design

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CHA has significant relevance in biomedical applications due to its distinctive properties derived from carbonate substitution within the hydroxyapatite lattice (Fig. 7). It is a better substitute for pure synthetic hydroxyapatite [17]. Hard tissues in orthopedics and dentistry have been repaired or replaced using CHA [169]. The porous microstructure obtained after sintering CHA confers osteoconductive, osteoinductive, and osteointegrative properties [170]. The context of application determines whether CHA is used in its pure form or as a composite with other materials or bioactive molecules. Carbonate apatite products can be incorporated into living systems as a solid body with low porosity, porous structures, sponges, or alloy and metal implant coatings [49, 171, 172].
Studies have demonstrated that CHA nanoparticles surpass their micron-sized counterparts in terms of mechanical properties [102]. The CHA layer formed on the surface of implants facilitates the attachment of the implant to the living bone and the surrounding tissues [173]. The dense network formed by the porous CHA allows the diffusion of cells responsible for the deposition of bone tissue (osteoconduction), ultimately improving biointegration and mechanical stability. These pores are interconnected and have dimensions ranging from to [174]. CHA also works as a scaffold that supports biomineralization [82]. Porous scaffolds made through CHA incorporated into sponges are like those found in bones. The best scaffolds are made through optimal slurry concentration and sintering conditions. Porous bodies of B-type CHA prepared by impregnating cellulose sponge with CHA are usually sintered in air and to determine their thermal stability. Compared with pure hydroxyapatite, the CHA-based materials displayed good osteoconductive and biosorption properties [75]. Sintered CHA coatings are effective anti-corrosion materials [100]. Hiromoto et al. (2020) asserted that insoluble materials with good osteoclastic resorption have good anti-corrosion properties. Upon examination, the CHA coating dissolved in the presence of osteoclasts, which makes it a possible bioabsorbable material for corrosion control of biodegradable Mg alloys.
Carbonate ions and other ions in the CHA structure influence the formation and growth of hydroxyapatite crystals within the bone tissue by maintaining the acid-base balance needed to ensure uninterrupted metabolic processes. Additionally, carbonate ions enhance the absorption of and other cations to maintain the balance of ions within the apatite structure [49]. Calcium ion is released
through the breakdown of apatites in living systems, a factor known to induce apoptosis in tumor cells, contributing to their efficiency in tumor treatment [175]. The inherent cancer-inhibitory attributes of CHA [112] further support its use as a vehicle for drug delivery, dental enamel repair [176], and injectable bone cement [177]. CHA has been used in the presence of organic phases, for example, CHA-chitosan membranes and their microporous surface aided adhesion to living tissue when used as coatings for exoskeletons. The organic phase (chitosan) also aided agglomeration and biocompatibility of the composite membrane [178]. Biomimetic mineral coatings made of CHA can be used as alternatives to typical fluoride compounds. When applied, nanocrystalline CHA acts as a self-distributing filler for the surface dents and scratches in enamels [179] and when doped with specific cations, controls the growth of some microbes. On its own, carbonated hydroxyapatite (CHA) exhibits limited antimicrobial inhibitory properties, with a minimum inhibitory concentration of which supports its doping with ions with known antimicrobial properties [119, 154, 180]. Aziz et al. [107] reported the use of Ag-doped CHA for the inhibition of bacterial growth on peri-implants.

Non-Biomedical Applications of CHA Nanoparticles

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The tunable surface chemistry of CHA nanoparticles allows for modifications that increase their selectivity toward specific contaminants, making them versatile tools for addressing environmental pollution (Fig. 7) [181]. The high surface area-to-volume ratio of nanosized CHA enhances their adsorption capacity, making them effective in removing heavy metal ions from polluted water and soil [182]. The dispersal leading to toxicity of Au, Ag, and graphene nanoparticles when used in water treatment is a limitation [183]. Asimeng et al. [184] reported the use of CHA synthesized from snail shells as nontoxic removal material from wastewater. An efficiency of was reported compared with for pure hydroxyapatite [185]. Sometimes CHA forms insoluble phosphates with toxic ions when used in water treatment [109]. CHA is very effective in water treatment because of its adsorption affinity, ion exchange, complexation, and coprecipitation properties [186, 187]. CHA removes lead ions from contaminated water through adsorption and dissolution-precipitation models [188]. Liao et al. [160] determined the uptake of lead (II) ion by CHA as a pseudo-second-order reaction and takes place optimally at pH 6 . Xing et al. [189] also reported rapid adsorption of by CHA flakes synthesized through ureolytic bacteria. The nanomaterial had large adsorption capacity ( ). Municipal wastewater is known to be rich in phosphorus, and phosphorus is removed through precipitation as part of the purification process [190]. Struvite is the major precipitate obtained in the anaerobic process. However, Sarria et al. [61] and Castro et al. [62] observed that other forms of hydroxyapatite including carbonated apatite can be obtained through pH adjustments in the purification process.

Fig. 7. Biomedical and non-biomedical application of CHA

Fig. 7. Biomedical and non-biomedical application of CHA

Moore et al. [157] exploited the affinity of selenite for Ca-based materials to remediate soils polluted with selenium using CHA. Smart spongy fertilizers were synthesized using CHA. The ecofriendliness was verified by application on water spinach plants, and it had no adverse effect on their growth. Also, the cationic exchange properties of apatites come into play in their use as fertilizers [109]. CHA also simultaneously adsorbs organic pollutants like glyphosate and radionuclides [191]. Nanofertilzers doped with bioorganic molecules and ions can perform better due to increased surface area, porosity, and easy degradability [192]. A surface coating for stonework made of CHA doped with zinc, strontium, and magnesium increased their mechanical strength and decreased water absorption, ultimately improving their surface durability [193].
Catalysis is important in many processes because it reduces cost in terms of energy and time. With rising awareness of the impact of unfettered consumption of energy on the environment, studies to diversify and obtain efficient catalysts have not spared the use of hydroxyapatite [194]. Ethanol is one of the major additives in gasoline and could become an alternative energy source. CHA is being investigated as an alternative catalyst with better results in the synthesis of ethanol and biodiesel and the detection of glucose and hydrogen peroxide [115]. Some defects in B-type CHA microstructure have been reported to promote its catalytic performance in ethanol-to-hydrocarbon conversion. Ethanol was also successfully synthesized using CHA as a catalyst. The acid-basic sites of CHA make it a potential bifunctional catalyst. [133]. The unique chemical composition and surface morphology of CHA nanoparticles make them potential candidates for heterogeneous catalysis [109]. Active surface sites on these nanoparticles can participate in various catalytic reactions, including biodiesel production through transesterification [195]. The presence of carbonate groups enhances acidity and modifies the electronic structure of the apatite, thereby influencing its catalytic activity [72]. Apatite catalysts are produced through anionic and cationic modifications.
The catalytic properties of apatites and their use as detectors have also been enhanced by introducing various transition metals, such as nickel [196] or iron [64]. When preparing doped apatites for catalytic or ion exchange purposes, it is necessary to recognize the nature of the mechanism of the surface reaction. In the case of dope or impregnated apatite, catalyst synergistic effect is a common phenomenon [109].
Self-hardening cement was made from a mixture of and . When the CHA component was increased, the rate of resorption increased. An increase in acidity of the environment also increases the ease of absorption of the cement [197].

Conclusion

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Carbonate hydroxyapatite (CHA) is a common derivative of hydroxyapatite, with a morphology and properties that can be tailored through the choice of synthesis method and conditions. CHA can be synthesized via dry methods like mechanosynthesis and solid-state synthesis; however, when nanosized CHA is desired, wet methods such as hydrothermal, precipitation, and microwave-assisted synthesis are preferred. CHA is a versatile ceramic with increased porosity compared to stoichiometric hydroxyapatite, resulting in a high surface area. CHA has been extensively exploited in various medical applications, including use as a scaffold, bone filler, biomarker, and drug delivery material. Doping CHA with specific biogenic ions like strontium and silver has further enhanced its antibacterial and anticancer properties for biomedical applications. Beyond medicine, CHA has the potential to be used as a catalyst, fertilizer, and water purifier. As research progresses, additional nonmedical applications of CHA are likely to emerge.

Acknowledgments

The original version of this paper is available on https://www.scientific.net/EC.7.1.pdf

Daniel Gbenga Adekanmi is grateful for the CONAHCYT Scholarship awarded to him to conduct his research.

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Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 25-40

doi: 10.4028/p-nwJaI5

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Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

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Silas Oseme Okuma , Okiemute Dickson Ofuyekpone , Cynthia Chinasa Nwaeju , Martins Obaseki , Ejovi Okuma Ogagavwodia

¹Department of Mechanical Engineering, Faculty of Engineering, Nigeria Maritime University, Okerenkoko, Nigeria

Department of Materials and Metallurgical Engineering, Faculty of Engineering, Delta State University of Science and Technology, Ozoro, Nigeria

Department of Mechanical Engineering, River State University, Port Harcourt, Nigeria

silasoseme@gmail.com, okedickbest@yahoo.com, cynthianwaeju@gmail.com, martins.obaseki@nmu.edu.ng, ogagaejovi@yahoo.com

Keywords: Inhibitor, Biodegradability, Optimization, Lasienthera africanum, Phytochemicals, Model

Abstract

In this study, the CCD response surface methodology was used to model and optimise the performance of Lasienthera africanum leaves extract (LALE) as a corrosion inhibitor on mild steel. The experimental parameters were assessed at different immersion time and inhibitor concentration to determine the optimum conditions for corrosion mitigation. Using experimental results of the corrosion characteristics such as the weight loss, corrosion rate, and inhibition efficiency of LALE, new models were developed, the significance of which was tested using variance analysis. The developed RSM models of WL, CR, and IE were accurate and reliable, and their P-values were 0.0001 , which is less than 0.05 . Likewise, the -statistics ( , adjusted- , and predicted- ), adequate precision, and diagnostic plots were also used as a means to ascertain the degree of accuracy and adequacy of the WL, CR, and IE models. In addition, optimization of the corrosion inhibition process for LALE revealed that the optimum conditions for maximum IE, minimum WL, and CR were achieved at a concentration of 93.93 ppm and an immersion time of 228 hrs . Under these settings, the inhibition efficiency, weight loss, and corrosion rate were and , respectively. Therefore, the models are considered ideal for prediction with a confidence level of , and the optimal combination is suitable for the corrosion inhibition process design. Hence these models can be recommended for applications such as oil well acidizing and pickling pipelines.

1. Introduction

The original version of this paper is available on https://www.scientific.net/EC.7.25.pdf

Hydrochloric acids are frequently employed in various industrial applications such as oil well cleaning, pickling, acid descaling, and acidification. However, it is important to note that these acids exhibit a high level of corrosiveness towards mild steels [1]. The mitigation of corrosion in steel holds significant importance in several industrial applications. One effective method for alleviating the challenges posed by corrosion is the use of corrosion inhibitors [2]. Corrosion inhibitors are available in a diverse range of types [3-6], encompassing inorganic salts, rare earth compounds, organic molecules, and plant-derived natural substances. Natural compounds formed from vegetable and plant components possess numerous advantages in comparison to synthetic chemicals. These advantages include low cost, biodegradability, abundance, and eco-friendliness [6]. The development of chemical corrosion inhibitors has resulted in increased costs, adverse environmental impacts, and potential risks to human health [7].
In the oil and gas industry, mild steel is widely used in constructions and applications such as upstream platforms, transportation pipelines, processing facilities, and fuel storage facilities. Mild steel is widely used because of its affordability, durability, and versatility [8]. Nevertheless, an increase in pH levels in the environment in use, would result in an increased rate of precipitation and
the formation of deposits, eventually leading to under deposits corrosion. The key factor contributing to corrosion in mild steel inside a moist environment is a reduction in pH value, whereas conversely, an increase in pH value would result in a mitigating impact. Hence, mild steel continues to be the preferred material for a significant majority of applications, although the existence of other corrosionresistant materials manufactured by contemporary industry. Nevertheless, corrosion-resistant materials lack the economic viability to completely replace mild steel as the preferred material.
One of the most common precautionary measures against corrosion is the use of an inhibitor [9-10]. It is common knowledge that one way to shield metal from the corrosive effects of its surrounding environment is to take preventative measures against the corrosion process [11]. It has been postulated that organic molecules containing oxygen, nitrogen, and phosphorus are especially efficient at militating against corrosion related effects on metals when exposed to an acidic environment [12]. Extensive research has been conducted to investigate the anticorrosion capabilities of plant extracts derived from a wide range of different plant sources. The utilisation of plant extracts for corrosion control has demonstrated efficacy due to the presence of phytochemical constituents [13-19]. Scientists are continually investigating the potential benefits of plant species for their ability to serve as environmentally benign metal inhibitors in both alkaline and acidic environments [20-21].
Several plants have been shown to be effective inhibitors in corrosion control and mitigation. Organic inhibitors have been extracted from plants such as Eucalyptus camaldulensis [22], Ricinus communis [23], Artemisia herba alba [24], Ginko leaves [25], Thyme leaves [26], Carica papaya [27], Irvingia gabonensis [28], and Coffee senna [29]. All of them were shown to have components whose interactions enhance inhibition on the surface of mild steel.
Lasienthera africanum ("Editan") is a member of the order Celestrales, which consists of thirteen fundamental tree and shrub families. It belongs to the Icacinaceae family. These specific plants and shrubs have both medicinal and edible potential. It is consumed as a vegetable in the southern part of Nigeria [30]. However,there has been no investigation into whether the plant's essential leaves can be utilised to control and minimize the corrosion rate of mild steel in hydrochloric solution. Various researchers have explored the use Lasienthera africanum extract (LAE) for corrosion control under diverse conditions. Akinyemi [31] investigated LAE as an organic inhibitor for aluminium and mild steel in HCl medium. Their study revealed impressive corrosion inhibition efficiencies of for aluminium and for mild steel at an extract concentration of , employing the Weight Loss method. Okuma et al. [19] also explored LAE's inhibitive effect on HCl medium and found a substantial inhibition efficiency for mild steel. Fayomi et al. [32] delved into the impact of temperature variation on LAE's inhibitive absorption in 0.5 M HCl , establishing inhibition efficiencies of at 303 K and at 313 K . These studies collectively highlight LAE's potential in preventing corrosion in carbon steel samples, considering various influencing parameters. Experimental design methods prove invaluable in optimizing the number of experiments, yielding more accurate results for key responses (WL, CR, and IE) and the interactions among studied variables or parameters. Consequently, the concurrent assessment of various parameters on WL, CR, and IE can be expedited through these design methods, facilitating a comprehensive understanding of LAE's performance in corrosion control. A valuable and practical approach in this context is the utilization of the Response Surface Method (RSM) [33-35]. RSM comprises a collection of statistical and mathematical techniques highly useful for simulating and assessing problems where the response variable is influenced by numerous independent parameters, with the ultimate goal of optimizing these responses [36]. A key advantage of RSM lies in its ability to significantly reduce the number of required tests when evaluating multiple variables and their interrelationships. Furthermore, RSM proves advantageous for developing predictive models for corrosion rate (CR) and inhibition efficiency (IE) associated with specific inhibitors [37,38].This review will delve into the application of RSM and Analysis of Variance (ANOVA) in the exploration of an inhibitor's effectiveness in mitigating the corrosion process.
Chung et al. [39] employed the Response Surface Method (RSM) to assess changes in corrosion current density for carbon steel samples across different media. They conducted electrochemical experiments, analysing corrosion current density at varying pH values, chloride, and sulphate
concentrations. Using experimental data, the authors constructed a mathematical model to determine corrosion current density. Their findings indicated the model's success within the studied parameter ranges, with chloride concentration identified as the primary factor influencing the corrosion process. Yamin et al. [38] delved into the inhibition efficiency (IE) of a novel organic corrosion inhibitor featuring oxygen, sulphur, and nitrogen heteroatoms in its structure for mild steel samples immersed in 1 M HCl solution, employing RSM. They leveraged laboratory data from weight loss experiments at different reagent concentrations, temperatures, and times to develop a quadratic formula for predicting corrosion prevention effectiveness. Their analysis underscored immersion time and temperature as two pivotal parameters significantly impacting the corrosion inhibitor's efficiency.
Kumari and Lavanya [40] optimized the corrosion inhibition performance of a Schiff base in HCl solution for mild steel samples through electrochemical tests and RSM. They conducted tests at varying acid concentrations, temperatures, and reagent concentrations, measuring experimental data on corrosion rate (CR) and IE. Their regression model for corrosion inhibition efficiency proved valuable for prediction, closely aligning with laboratory data. Omran et al. [34] harnessed RSM to optimize corrosion inhibition using green inhibitors for mild steel in sulfuric acid. Their approach involved electrochemical testing and modelling based on experimental data, supported by Analysis of Variance (ANOVA). The authors identified pH and reagent concentration as key parameters for corrosion inhibition, with the proposed model demonstrating high accuracy. Drawing from this literature review, it becomes evident that temperature, inhibitor concentration, and exposure time in aggressive environments significantly influence weight loss (WL), CR, and IE. Consequently, this study aims to experimentally assess these parameters' impact on LALE's IE in 0.5 M hydrochloric acid solution for mild steel samples, involving the measurement of WL, CR, and IE values. The resulting experimental data will undergo RSM analysis to formulate mathematical models for predicting WL, CR, and IE across a wide range of influencing factors. This work introduces novelty by developing a new model for predicting the effectiveness of LALE corrosion inhibition, considering time and inhibitor concentration simultaneously. While LALE has received substantial attention in the literature, a predictive model for its inhibitory effectiveness has not yet been established, making this study a significant contribution to the field.

2. Materials and Methods

The original version of this paper is available on https://www.scientific.net/EC.7.25.pdf

2.1 Data collection

The data utilised for the analysis and development of the design was derived from experimentally generated data. Gravimetric methods were employed to acquire the experimental corrosion data [41]. The anti-corrosion efficiency of Lasienthera africanum was evaluated by subjecting it to 0.5 M hydrochloric acid solutions at room temperature. The concentrations of the solutions were varied at , and 100 parts per million ( ppm ). The experiments were conducted at a temperature of . In order to assess weight loss, test coupons made of mild steel with dimensions of 9 mm by 18 mm by 3 mm were prepared. These specimens were measured and afterwards submerged in a beaker containing a test media. The immersion durations were set at 48,96 , 144, 192, 240, and 288 hours. The test media was used both with and without the inclusion of Lasienthera africanum extract. Following the designated duration, they were retrieved. The corrosion products were removed with the application of distilled water, acetone, and a subsequent air-drying procedure. The specimens underwent additional weighing procedures to ascertain their mass reduction. Subsequently, the weight loss of the specimen was recorded and calculated at each predetermined time interval. The experimental data were collected and analysed using equations (1) to (3) as derived from previous research [41].

and represent the coupon's initial and final weights, respectively. and represent, respectively, the weight loss values for the blank and inhibited conditions.

2.2 Corrosion inhibitor

In this study, Lasienthera africanum leaf extract (LALE) was used to study corrosion rate and inhibition effectiveness in a 0.5 M HCl solution at various values of exposure time, and inhibitor concentration. The Phytochemicals organics compounds of LALE is presented in Table 1. As shown in the Table, the inhibitor contains alkaloids, tannins, flavonoids and saponins, which can provide high inhibition performance [19,22,28]. The application of LALE inhibitor for corrosion control by various researchers was reviewed in the Introduction section.

Table 1 Phytochemicals present in LALE inhibitor [19]

Phytochemical | Occurrence
Alkaloids | ++
Tannins | ++
Flavonoids | ++
Saponins | ++

++ = Present in appreciable quantity

2.3 Optimization Study with Response Surface Methodology

The application of the Response Surface Methodology (RSM) in conjunction with central composite design (CCD) tool of Design Expert (DOE) software version 11 facilitated the process of modelling and improved the inhibitory efficiency (IE) as well as other experimental corrosion metrics. The study employed a quadratic layout model. The independent factors in this study were the concentrations of inhibitors (20, 40, 60, 80, and 100 ppm ) and the duration of immersion time (48, 96, 144, 192, and . The dependent variables measured were weight loss (WL), corrosion rate (CR), and inhibition efficiency (IE). A total of 30 independent experiments were done in order to gather data pertaining to the dependent variable. The factors levels is presented in Table 2.

Table 2 Variables level of independent parameter for central composite Design (CCD)

Phytochemical | Occurrence
Alkaloids | ++
Tannins | ++
Flavonoids | ++
Saponins | ++

3 Results and Discussion

The original version of this paper is available on https://www.scientific.net/EC.7.25.pdf

3.1 Response Surface Analysis

The Response surface analysis of mild steel in the induced acid corrosion is presented in Table 3. A total of 30 experimental runs were analysed from the design tool.

Table 3 Experimental results design layout

|  | Factor 1 | Factor 2 | Response 1 | Response 2 | Response 3
Std | Run | A:Immersion time | B:Inhibitor Concentration | WL | CR | IE
|  | hours | ppm | g | mm/yr | %
14 | 1 | 48 | 20 | 0.0493 | 2.547 | 57.4
3 | 2 | 48 | 40 | 0.0438 | 2.2628 | 62.18
6 | 3 | 48 | 60 | 0.0312 | 1.6119 | 73.1
24 | 4 | 48 | 80 | 0.0285 | 1.4723 | 97.4
15 | 5 | 48 | 100 | 0.0221 | 1.1418 | 98.6
8 | 6 | 96 | 20 | 0.0822 | 2.7547 | 86.8
16 | 7 | 96 | 40 | 0.0974 | 2.516 | 84.3
1 | 8 | 96 | 60 | 0.0898 | 2.3197 | 85.6
29 | 9 | 96 | 80 | 0.0815 | 2.1053 | 95.8
22 | 10 | 96 | 100 | 0.0695 | 1.7952 | 96.8
20 | 11 | 144 | 20 | 0.1313 | 2.2611 | 87.2
26 | 12 | 144 | 40 | 0.1389 | 2.392 | 86.5
11 | 13 | 144 | 60 | 0.1149 | 1.9786 | 88.8
5 | 14 | 144 | 80 | 0.1382 | 2.3799 | 94.7
28 | 15 | 144 | 100 | 0.1732 | 2.9827 | 95.1
4 | 16 | 192 | 20 | 0.2676 | 3.4563 | 76.3
19 | 17 | 192 | 40 | 0.3861 | 4.9867 | 65.8
13 | 18 | 192 | 60 | 0.3641 | 4.7026 | 67.8
21 | 19 | 192 | 80 | 0.2561 | 3.3077 | 92.1
25 | 20 | 192 | 100 | 0.2712 | 3.5027 | 90.1
27 | 21 | 240 | 20 | 0.4783 | 4.9421 | 57.8
2 | 22 | 240 | 40 | 0.4326 | 4.214 | 61.8
30 | 23 | 240 | 60 | 0.4526 | 4.6755 | 60.1
18 | 24 | 240 | 80 | 0.3131 | 3.2351 | 92.6
9 | 25 | 240 | 100 | 0.3131 | 3.1318 | 93.3
17 | 26 | 288 | 20 | 0.4997 | 4.3027 | 57.68
23 | 27 | 288 | 40 | 0.4894 | 4.2139 | 58.6
12 | 28 | 288 | 60 | 0.4954 | 4.2657 | 58
7 | 29 | 288 | 80 | 0.3752 | 3.2307 | 92.4
10 | 30 | 288 | 100 | 0.3612 | 3.1101 | 93.1

3.2 Statistical Analysis of Variance (ANOVA)

Table 4 showcase the output of the analysis of variance (ANOVA), which indicates that quadratic model is adequate for analysing experimental data. Statistically, the model is significant, with an Fvalue of 11.17. This "model F -value" has a possibility occurrence probability of . Additionally, model terms are significant if their "Prob " values are less than 0.0500 . In this instance, the letters , and are significant model terms. If a model term's value is greater than 0.1000 .This reported model shows that the signal is strong enough to move around the design space [42-43]. This model can also predict the corrosion inhibition efficiency of mild steel in a hydrochloric acid environment when treated with Lasienthera Africanum leaf extract (LALE) This indicates that the findings can be relied upon statistically. The model equation is represented by Equation (4) in terms of the coded values of the process variables.

Table 4 ANOVA results for inhibition efficiency on mild steel in 0.5 M HCl with LALE

Source | Sum of Squares | df | Mean Square | F-value | p-value |
Model | 4451.09 | 5 | 890.22 | 9.5 | < 0.0001 | significant
A-Immersion time | 17.87 | 1 | 17.87 | 0.1907 | 0.6663 |
B-Inhibitor Concentration | 2526.68 | 1 | 2526.68 | 26.96 | < 0.0001 |
AB | 44.2 | 1 | 44.2 | 0.4717 | 0.4988 |
A² | 482.57 | 1 | 482.57 | 5.15 | 0.0325 |
B² | 199.28 | 1 | 199.28 | 2.13 | 0.1577 |
Residual | 2248.99 | 24 | 93.71 |  |  |
Cor Total | 6700.08 | 29 |  |  |  |
Std. Dev. | 9.68 |  | R² |  | 0.6643 |
Mean | 80.26 |  | Adjusted R² |  | 0.5944 |
C.V. % | 12.06 |  | Predicted R² |  | 0.441 |
|  |  | Adeq Precision |  | 11.1727 |

Likewise, from Table 5, the p-value for the mathematical model for corrosion rate is less than 0.05 (0.0001), so it is a significant model. The F-value of 9.5 also indicate the significance of this model. This revealed that the input factors such as immersion time, and extract concentration have a significant effect on the corrosion rate. The second-order polynomial model obtained for corrosion rate is expressed in Eq. (5).

Table 5 ANOVA results for corrosion rate of mild steel in 0.5 HCl with LALE

Source | Sum of Squares | df | Mean Square | F-value | p-value |
Model | 24.79 | 5 | 4.96 | 12.83 | < 0.0001 | significant
A-Immersion time | 16.21 | 1 | 16.21 | 41.92 | < 0.0001 |
B-Inhibitor Concentration | 2.53 | 1 | 2.53 | 6.55 | 0.0172 |
AB | 0.1072 | 1 | 0.1072 | 0.2774 | 0.6033 |
A² | 0.8322 | 1 | 0.8322 | 2.15 | 0.1553 |
B² | 0.1516 | 1 | 0.1516 | 0.392 | 0.5372 |
Residual | 9.28 | 24 | 0.3866 |  |  |
Cor Total | 34.07 | 29 |  |  |  |
Std. Dev. | 0.6218 | R² | 0.7277 |  |
Mean | 3.06 | Adjusted R² | 0.6709 |  |
C.V. % | 20.32 | Predicted R² | 0.5979 |  |
|  | Adeq Precision | 12.0539 |  |

Table 6 shows the ANOVA results on the response of weight loss to the process variable at the confidence level and significance level. As indicated, the probability for the linear model is 0.0001 , which is less than 0.05 . It is evident from this that the variables directly influencing weight loss are significant. In addition, the F-value of 12.83 indicates that the model is significant, since noise can only account for of such a high F -value. The second-order polynomial model obtained for WL is expressed in Eq. (6).

Tables 4, 5, and 6 predict values that are in agreement with the adjusted values. As their variances are less than 0.2 and the nears 1, the fitted model considered ideal for the process [44]. The signal-to-noise ratio is measured by Adeq Precision. It is considered acceptable and desirable to have a ratio of 4 or higher. The ratios of , and 24.9089 indicate adequate signals in Tables 4, 5, and 6. The design space can therefore be navigated successfully using these models [45].

Table 6 ANOVA results for weight loss of mild steel in 1.0 HCl with LALE

Source | Sum of Squares | df | Mean Square | F-value | p-value |
Model | 0.7448 | 5 | 0.149 | 63.89 | < 0.0001 | significant
A-Immersion time | 0.3869 | 1 | 0.3869 | 165.93 | < 0.0001 |
B-Inhibitor Concentration | 0.0065 | 1 | 0.0065 | 2.8 | 0.1074 |
AB | 0.0132 | 1 | 0.0132 | 5.66 | 0.0257 |
A² | 0.0009 | 1 | 0.0009 | 0.3707 | 0.5483 |
B² | 0.0023 | 1 | 0.0023 | 0.9859 | 0.3307 |
Residual | 0.056 | 24 | 0.0023 |  |  |
Cor Total | 0.8007 | 29 |  |  |  |
Std. Dev. | 0.0483 |  | R² | 0.9301 |  |
Mean | 0.2349 |  | Adjusted R² | 0.9156 |  |
C.V. % | 20.55 |  | Predicted R² | 0.8942 |  |
|  |  | Adeq Precision | 24.9089 |  |

3.3 Diagnostic fitness plots

The diagnostic fitness plot presented in Fig 1(a-c) are the normal distribution plots for inhibition efficiency, corrosion rate and weight loss. In the depicted Figures, it can be observed that the plots points are clustered around the line of best fit. This showed that fitted models can accurately be used to represent the data for each of the responses [46].

Fig.1. Normal distribution plots for responses (a) inhibition efficiency (b) corrosion rate (c) weight loss

Fig.1. Normal distribution plots for responses (a) inhibition efficiency (b) corrosion rate (c) weight loss

The fitness model is illustrated in Fig. 2(a-c), which show the interaction between the actual and predicted results of inhibition efficiency, corrosion rate, and weight loss of mild steel in 0.5 M HCl with LALE. The fitness model showed the level of fit between the model's predicted and experimental values. From the figures, it revealed a good fit result was obtained from the data points as the plot randomly clustered around the points of intersection for all responses [47]. These trends show that the achieved design model is adequate to predict the studied corrosion characteristics of mild steel in the LALE inhibited environment. There is also a strong correlation between the predicted and actual values of the IE, CR, and WL.

Fig. 2. Model graph of predicted versus actual for (a) inhibition efficiency; (b) corrosion rate (c) weight loss

Fig. 2. Model graph of predicted versus actual for (a) inhibition efficiency; (b) corrosion rate (c) weight loss

Figures 3(a-c) highlight a three-dimensional (3D) surface plot that display the surface interaction between the dependent responses (inhibition efficiency, corrosion rate and weight loss) and some of the independent factors (immersion time and inhibition concentration). It can be observed from the figures that the responses are affected by the independent variables. The surface plots further depict that increasing both the extract concentration of LALE and immersion time enhances the inhibition efficiency reduces the weight loss and corrosion rate, and, also has a significant effect on the expected response due to the increase in environmental conditions. Thus, electrochemical reaction would readily occur when the average atmospheric temperature rises [45]. The model surface 3D results were discovered to be consistent with the experimental results, suggesting LALE is a suitable plant extract for surface treatment of mild steel in aggressive environments.

Fig.3. Three-dimensional surface interaction plots for (a) Inhibition efficiency (b) Corrosion rate; (c) weight loss

Fig.3. Three-dimensional surface interaction plots for (a) Inhibition efficiency (b) Corrosion rate; (c) weight loss

3.4 Optimization of the Corrosion Inhibition process

In the study, the main focus was to obtain the optimum conditions of parameters that the maximum corrosion control of mild carbon steel in the evaluated environment can be achieved. For this reason, optimization of the process was completed using Design-Expert-Software based on the established IE, CR and WL models [46]. The main objectives (optimization criteria) of the present work here to minimize CR, WL and maximize IE at the same time. The characteristics and pre-set optimization goals are presented in Table 6. From the report shown in Fig. 4, it was depicted that out of 9 solutions generated from the procedure with a near desirability value of 0.653 , the numerical optimal solution for the independent factors (immersion time, and inhibition concentration) was 228 hrs , and 93.93ppm respectively. The optimal responses of the corrosion characteristics are , and for weight loss, corrosion rate, and inhibition efficiency under the same desirability. The optimum conditions are reliable in determining the significance of individual responses. Also, this optimization solution was chosen and presented in the overlay plot after meeting the given conditions (Fig. 5). Figure 7 highlight the optimization desirability chart that shows the degree of desirability for each optimal solution for the factor response variables. The best factor conditions are presented by a red bar, while the best response predictions value is described with a blue bar [43]. The chart revealed how well each parameters satisfied the conditions with values near to unity being accepted as satisfactory [47].

Table 7 Pre-set optimisation goals for desirability

Name | Goal | Lower Limit | Upper Limit | Lower Weight | Upper Weight | Importance
A: Immersion time | is in range | 48 | 228 | 1 | 1 | 3
B: Inhibitor Concentration | is in range | 20 | 100 | 1 | 1 | 3
WL | is in range | 0.0221 | 0.4997 | 1 | 1 | 3
CR | maximize | 1.1418 | 4.9867 | 1 | 1 | 3
IE | maximize | 57.4 | 98.6 | 1 | 1 | 3

Fig.4. Optimization Ramp

Fig.4. Optimization Ramp

Fig. 5. Optimization Overlay

Fig. 5. Optimization Overlay

Fig.6. Optimization desirability values chart for factors, responses and combined

Fig.6. Optimization desirability values chart for factors, responses and combined

3.5 Validation of Predicted Models

An additional experiment to validate the model's prediction was done with the predicted optimum conditions. Duplicate samples of mild steel were machined for each test, and the mean result obtained was recorded. The results are shown in Table 8. As presented in this table, the predicted and experimental values are close to each other, and the uncertainty errors between them are , and for WL, CR, and IE, respectively. Therefore, we establish that the models are statistically fit in the prediction of the corrosion parameters responses. Hence these models can be recommended for applications such as oil well acidizing and pickling pipelines.

Table 8 Comparative validation of predicted and experimental values of LALE corrosion parameters

Parameters | Inhibitor Concentration | Immersion time | Predicted values | Experimental Values | Uncertainty error
| ppm | hours |  |  | %
WL | 93.93 | 228 | 0.29 | 0.31 | 0.02
CR |  |  | 3.271 | 3.356 | 0.085
IE |  |  | 93.85 | 94.12 | 0.27

Conclusions

The original version of this paper is available on https://www.scientific.net/EC.7.25.pdf

The central composite design (CCD) of response surface methodology was adopted in analysing and optimization of the LALE corrosion inhibitor performance on mild steel in hydrochloric induced environment. The main findings from the study are as follows:

Response surface methodology (RSM) via variance analysis in three significance regression models were developed to predict WL, CR and IE. The coefficient of determination and RSM diagnostic plots were also use to assess the accuracy and adequacy of the models. The results showed that the models were significant and suitable to navigate the design space.

The model developed for each corrosion characteristics response was reaffirmed to be statistically significant and ideal for predicting the responses. Also, the interaction between each response is dependent on the factors as shown from the three-dimensional plots.

The optimal optimization of the corrosion characteristic process for LALE showed that the optimum settings for maximum IE ( ), minimum WL ( 0.294 g ) and CR ( ) were obtained at a concentration of 93.93 ppm and immersion time of 228 hours.

The validation experiment done at the optimal conditions established for IE, 3.356 for CR and 0.31 for WL respectively. Since the uncertainty error is less than , the models are therefore validated to be statistically fit for the prediction of corrosion characteristic responses.

Declaration of Conflicting Interests

The original version of this paper is available on https://www.scientific.net/EC.7.25.pdf

The authors confirm that there is no potential conflict of interest involved in the research, the authoring, or the publication of this article.

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The original version of this eBook is available on https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 41-50

doi: 10.4028/p-pyQFX5

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2023-12-06

Revised:
2023-12-28

Accepted:
2023-12-29

Online:
2024-06-26

Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

The original version of this paper is available on https://www.scientific.net/EC.7.41.pdf

Sudibyo Enggar Laksono , Ade Sonya Suryandari , W. Widiyastuti , Tantular Nurtono , and Heru Setyawan

Department of Chemical Engineering, Faculty of Industrial Technology and System Engineering, Sepuluh Nopember Institute of Technology, Kampus ITS Sukolilo, Surabaya 60111, Indonesia

Department of Chemical Engineering, Politeknik Negeri Malang, JI. Soekarno-Hatta No. 9, Malang 65141, Indonesia

sudibyoenggar21@gmail.com, ade.sonya@polinema.ac.id, widi@chem-eng.its.ac.id, tantular@chem-eng.its.ac.id, sheru@chem-eng.its.ac.id

Keywords: Biodiesel, Cellulose Aerogel, Coir Fiber, Solid Acid Catalyst.

Abstract

Abstarct. The effect of sulfonic agents on the performance of solid acid catalysts in esterification reactions of long-chain fatty acids has been studied. Herein, sulfonated activated carbon with sulfanilic acid (SAC-SA) and sulfuric acid (SAC-SO4) as a sulfonic agent were prepared and used for esterification reaction to convert long-chain fatty acids into methyl esters within 5 h at . The obtained SAC-SA has a higher surface area than SAC-SO4 of 1301.981 and , respectively. When SAC-SO4 and SAC-SA catalysts were applied to the esterification reaction, the FAME product conversion results were 74.47 and , respectively. The physical property of SAC-SO4 has more macropores size distribution than mesopores size based on the BJH method. Large pore size on the catalyst will support the diffusion of large organic molecules to improve catalytic ability. The pore size determines the performance of solid acid catalysts, especially in longchain fatty acid reactants for biodiesel production.

Introduction

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Biodiesel is a monoalkyl ester composed of lipids ( , and ) such as vegetable oil, waste cooking oil, microalgae, and animal fat [1]. The cetane number, energy content, viscosity, and phase change of biodiesel are like those of fossil diesel so that biodiesel can be mixed with a specific composition with petroleum (diesel) to become a biofuel that can be used as an alternative fuel for diesel engines. Biodiesel is produced through a transesterification reaction between triglycerides contained in fats or oils and alcohol. Oil as biodiesel feedstock with an FFA content of more than will react with base catalysts in the transesterification reaction, causing a saponification reaction, so it is necessary to carry out an esterification reaction to reduce the FFA content of the raw material [2], [3]. Thus, an esterification reaction is necessary to reduce the FFA content below as a pretreatment step of the transesterification process. In esterification reactions, homogeneous catalysts such as phosphoric acid and sulfuric acid are often used. However, homogeneous catalysts have drawbacks, such as toxic and environmentally harmful properties, as well as corrosion of metal industrial equipment. They are also difficult to recycle because they have the same physical form as the products and reactants [4].

Previous research has been conducted on using support materials in heterogeneous catalysts to improve the stability of the catalyst structure and expand the surface area through high porosity. Some materials that are commonly used as catalyst supports are , zeolite, and biochar [5]. Recently, biochar has been the focus of research in heterogeneous catalysis. Biochar has advantages in terms of easy availability from biomass waste at low cost, large surface area, controllable pore size, and good stability [6]. For acid catalysis, under severe reaction conditions, groups can be successfully grafted on biochar by direct sulfonation methods, such as the direct sulfonation of and [4], [7], [8]. Previous research by Fauziyah et al. (2020) reported the synthesis of carbon aerogel-based heterogeneous acid catalyst derived from coir fiber through the carbonization method
and continued sulfonation with sulfuric acid as a sulfonic agent and catalytic activity test through the esterification of acetic acid with ethanol. This catalyst can provide an esterification conversion with a molar ratio of ethanol to acetic acid of , adding wt heterogeneous acid catalyst, esterification temperature of , and esterification time for 3 hours [4]. However, the biochar-based sulfonic acidic catalyst can not have hydrophobicity due to the hydrophilicity of .

On the other hand, esterification reactions for biodiesel production produce by-products in the form of water; the water will cover with the active side of the catalyst, resulting in poor catalytic activity. In addition, hydrophobic and non-polar reactants will find it challenging to approach the hydrophilic surface to interact with the active sites of the catalyst and consequently decrease the catalytic activity. [9]. Therefore, solid catalysts with strong hydrophobicity and acidity are exciting topics to be researched for enhancing catalytic activity in esterification or transesterification reactions [10]. Recently, sulfonation with 4-benzenediazoniumsulfonate (sulfanilic acid) as the sulfonating agent has more efficient results than its sulfonating agent due to the high sulfonation rate and increased catalyst reuse due to the stable bond due to the benzene structure in sulfanilic acid which causes the hydrophobic properties of the catalyst to increase [11].

Furthermore, sulfonated carbons generated by direct sulfonation are prone to substantial deactivation, with a loss of of initial activity, primarily due to group leaching, limiting their effectiveness [11]. The present work focused on using coir fiber waste as a raw material for preparing sulfonated hydrophobic carbon aerogels applied as solid acid catalysts in the esterification reaction of long-chain fatty acids. The characteristics of the solid acid catalyst were studied by varying the sulfonating agent used in the sulfonation process. Catalysts with hydrophobic characteristics are expected to increase the conversion of long-chain fatty acid esterification reaction.

Experimental Method

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Materials

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The materials used in this study were: Coir fiber was collected from a coconut milling facility in Tulungagung, Indonesia. sodium hydroxide ( NaOH ; 99% p.a.), sulfanilic acid ( , p.a.), and sodium nitrite ( , p.a.), were obtained from Merck. Urea was obtained from PT Petrokimia Gresik Indonesia. 4-tert-Butylaniline ; p.a.), ethanol , and oleic acid were obtained from Sigma Aldrich. Sulfuric acid , reagent grade) and hydrochloric acid ( , reagent grade) were purchased from Mallinckrodt. Hydrogen peroxide ( ) was obtained from PT Peroksida Indonesia Pratama. All chemicals/materials were used as received without further purification.

Catalyst preparation

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In the present study, carbon aerogel was used as catalyst support; the preparation of carbon aerogel itself consists of two main steps, the preparation of cellulose aerogel from coir fiber and carbonization. Coir fiber was ground and sieved with a mesh sieve and then digested in NaOH at coir fiber under atmospheric reflux for 2 h . Then the coir pulp was bleached with a solution of at pulp at for 1 h . Two grams of pulp (dry basis) was mixed into a solution containing 4 g urea and 1 g NaOH in 10 mL demineralized water using a stirrer in an ice bath for 30 minutes. The mixture was then refrigerated at for 24 h to form a gel and continued thawing at room temperature. It was then immersed in ethanol for 24 h for coagulation. The ethanol in the gel was then exchanged with demineralized water and frozen at for 24 h prior to freeze-drying. The freeze-drying (FDU-1200, EYELA) was carried out at a temperature of under a vacuum pressure of 20 Pa for 24 h to obtain the cellulose aerogel. The cellulose aerogel was carbonized by pyrolyzing in a furnace under flowing nitrogen at . The pyrolysis temperature was initially set at for 30 min to remove the moisture content and then increased to for 30 min to decompose the cellulose compound and evaporate any other volatile matter. The temperature was increased to and held for 2 h to allow carbonization to occur, increasing the temperature at rate of . Next, the carbon aerogel was neutralized using 0.5 M HCl
solution. Then the carbon aerogel was crushed and sieved with a 45-mesh sieve. The sulfonation process with two different methods:

Sulfonation method 1

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Sulfonic acid was used for sulfonated by immersed carbon aerogel under a nitrogen atmosphere. 1 gram of carbon aerogel was spread in 25 mL of , and the resulting mixture was then heated with continuous stirring for 5 hours at . After cooling to room temperature, the mixture was diluted with demineralized water and filtered, and the sulfonated carbon aerogel product was thoroughly washed with demineralized water to remove any remaining . The successful removal of was indicated by the absence of white precipitates upon introducing the washing solution to a solution. The material was subsequently dried in an oven for 3 hours [4]. The sample of activated carbon aerogel with sulfuric acid will be referred to as SAC-SO4.

Sulfonation method 2

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4-Benzenediazoniumsulfonate was synthesized by diazotization using sulfanilic acid. Sulfanilic acid was dispersed within a three-necked round-bottom flask containing 300 mL of 1 M HCl aqueous solution. The flask was transferred to an ice water bath, and the temperature was carefully maintained between while continuously stirring the mixture. Subsequently, a excess of , aqueous solution) was incrementally introduced, resulting in the formation of a clear solution once all the had been added. Following an additional 1-hour stirring at the same temperature, the ensuing white precipitate of 4-benzenediazoniumsulfonate was separated through filtration. Then, the isolated precipitate was transferred to another three-necked round-bottom flask containing 200 mL of deionized water and 120 mL of ethanol. At a temperature of of aerogel carbon was introduced. Subsequently, a aqueous solution of was added into the mixture. After stirring for 30 minutes, an additional 50 mL of aqueous solution was added, and the mixture was allowed to stand for an additional hour with occasional strirring. The resulting sulfonated aerogel carbon was washed with acetone and distilled water before being dried overnight [11]. The sample of activated carbon aerogel with sulfanilic acid will be referred to as SACSA.

Catalyst characterization

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The density ( ) of the cellulose aerogel and carbon aerogel was determined by dividing the mass of the measured sample by the volume of the measured aerogel. The porosity of the aerogels was calculated by equation :

where is the original density of cellulose and carbon particle are and , respectively [12], [13]. Fourier Transform Infra-Red spectra (FTIR spectroscopy; Thermo Scientific Nicolet iS10) recorded in the wavelength range of were used to identify the formation of groups on carbon aerogels and sulfonate functional groups on solid acid catalyst samples. Specific Surface Area (SSA) was measured quantitatively with an adsorption-desorption instrument (Nova 1200, Quantachrome). Previously, the samples were degassed at for 5 hours for cellulose aerogel samples and for 3 hours for carbon aerogel samples before analysis. SSA was calculated using the Bruanuer-Emmet-Teller (BET) method at relative pressure ( ) . The pore size distribution was quantitatively invetigated using the Barret-Joyner-Halenda (BJH) method. Sample morphology was analysed by scanning electron microscope (SEM; Hitachi FlexSEM 1000). The hydrophobicity of the samples has been characterised by measuring the contact angle to water droplets on the catalyst surface and dispersed into water.

The acid-base titration method was used to calculate the total acid density 0.05 g of catalyst was mixed with 30 mL of 0.02 M NaOH solution and ultrasonicated for 1 hour to replace hydrion with sodion. Then the sample was filtered and titrated with 0.01 M HCl solution with phenolphthalin
indicator. The concentration of ions remaining from the NaOH solution is identified from the amount of ions supplied from HCl equivalent to the amount of ions consumed from the NaOH solution. Thus, acid density is calculated as the amount of consumed (mmol) divided by the weight of the catalyst sample (grams) [14].

Catalytic test

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An evaluation was made of the catalytic performance of the sulfonated carbon aerogel in the esterification of oleic acid with methanol to produce methyl oleat. The esterification was performed in a three neck flask with a volumetric ratio of oleic acid to methanol of and catalyst loading of of oleic acid. The temperature was set at a constant of and the reaction was carried out for 5 hours. The methyl oleate concentration was quantitatively analyzed using gas chromatography (GC Trace 1310; Thermo Scientific). The GC instrument was equipped with a flame ionization detector (FID), and the column of Thermo Scientific TG-5MS type . Helium gas as a carrier gas constantly flowed at a minute flow rate during analysis with an injector inlet temperature of with a split ratio of 1:150. Sample analysis began at , then the temperature was held for 3 minutes, then increased to with a heating rate of minute. The sample was then cooled to . The mass of amyl alcohol and methyl oleate was determined using an internal calibration, where the calibration curve was made by dissolving methyl oleate into amyl alcohol at various concentrations.

Result and Discussion

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Characterization of carbon aerogels

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Carbon aerogel produced from the pyrolysis treatment of cellulose aerogel made from coconut fiber, cellulose aerogel has a light brown color, bulk density, and porosity of and , respectively, as show in Fig. 1(a). In comparison, the carbon aerogel produced has bulk density and porosity of and , respectively. Pyrolysis treatment produced carbon aerogel with a yield of . Fig. 1(b) shows the FTIR data of cellulose aerogels and carbon aerogels. Wavenumber peak values on cellulose aerogel show the characteristics of the functional groups of cellulose aerogels; the peak at wavenumber shows the stretch functional group. The group comes from intramolecular hydroxyl cellulose. The wavenumber peak shows a stretch group derived from in cellulose. The functional group at the peak of wavenumber shows an amide group that binds to the carbon atom in the carbonyl group; this comes from urea which acts as a crosslinking. At the peak of wavenumber , there is a stretch functional group that overlaps with the group; the functional group can come from the bond in cellulose, while the functional group comes from the bond in urea. However, wavenumber was previously an stretch functional group, strengthening the conjecture that wavenumber is a functional group derived from cellulose [12], [15]. Pyrolysis treatment at significantly impacts the characterization of the resulting carbon aerogel; there are two aromatic groups, and , at wavenumbers 1428 and , respectively. Pyrolysis treatment on aerogel causes dehydration and dissociation of carbonyls. It triggers the formation of aromatic groups on cellulose aerogel so that and groups on cellulose aerogel are lost due to the heating effect during pyrolysis treatment, and stretch and stretch groups on cellulose aerogel turn into aromatic and groups on carbon aerogel [15].

Fig. 1. (a) Picture of cellulose aerogel (left) and aerogel carbon (right); (b) FTIR Spectra of cellulose aerogel and aerogel carbon

Fig. 1. (a) Picture of cellulose aerogel (left) and aerogel carbon (right); (b) FTIR Spectra of cellulose aerogel and aerogel carbon

Fig. 2. SEM Image of (a) cellulose aerogel and (b) carbon aerogel

Fig. 2. SEM Image of (a) cellulose aerogel and (b) carbon aerogel

Figure 2 shows cellulose aerogel and carbon aerogel SEM images after pyrolysis. The SEM image results show that the aerogels have fibers in the form of thick lines and open pores. The cavity and pore size produced in carbon aerogels is more significant than in cellulose aerogels due to the pyrolysis treatment. The increase was also proven by the surface area analyzer (SAA) using the BET method. Table 1 shows cellulose aerogel and carbon aerogel BET SSA and pore volume. The surface area of aerogel increased from 430.522 to ; pyrolysis treatment can increase the surface area of carbon aerogel more than three times. The increase in surface area is due to the decomposition of cellulose compounds and the evaporation of volatile matter contained in cellulose aerogels [16]. Pyrolysis treatment also increased total pore volume of aerogel carbon from 0.367 to , the increase is due to the accelerated release of volatile matter, as depicted in the SEM image (Fig. 2) [17].

Table 1. Specific surface areas of cellulose aerogel and carbon aerogel.

Sample | SBET (m²/g) | Vtotal (cm³/g)
Cellulose aerogel | 430.522 | 0.367
Carbon aerogel | 1655.099 | 1.449

Characterization of sulfonated carbon aerogels

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From the results of the FTIR analysis shown in Fig. 3, information was obtained about the constituent groups of sulfonated carbon aerogel from the sulfonation method previously described. The vibration peaks near 668 and are assigned to the stretching and asymmetric stretching, respectively, of the group. The functional groups read from the analysis indicate that the sulfonate process was successful due to the presence of C groups bonding with and S groups bonding with O [4], [18]. The characteristics of the carbon aerogel content were indicated by the presence of aromatic, which appeared at . Acid density analysis was performed on SAC-SA and SAC-SO4 with acid density values of 2.30 and , respectively (Table 2). The two analyses showed that although the peak of the group was less sharp in the FTIR analysis, the acid density analysis showed the successful grafting of the group on the carbon aerogel. The nature of sulfonate has an effect on the acid density value of sulfonated carbon aerogel catalyst, where sulfuric acid as a strong acid has a higher acid density value compared to SAC-SA which uses sulfanilic acid which is a weak acid, this indicates the use of sulfuric acid as a strong acid that has high reactivity so that it is able to form sulfonate ions by replacing hydrogen groups from carbon aerogel better than using sulfanilic acid. It also shows the use of sulfuric acid as an effective sulfonating agent and validates the efficiency of the sulfonation process by producing high acid density values [19].

Fig. 3. FTIR spectra of (a) carbon aerogel an sulfonated carbon prepared using (b) sulfuric acid and (c) sulfanilic acid.

Fig. 3. FTIR spectra of (a) carbon aerogel an sulfonated carbon prepared using (b) sulfuric acid and (c) sulfanilic acid.

Table 2. Specific surface areas of solid acid catalyst with sulfuric acid and sulfanilic agent.

Sample Code | Surface area (m²/g) | Acid density (mmol/g)
SAC-SA | 1301.981 | 2.30
SAC-SO4 | 1182.096 | 3.58

Fig. 4. (a) Effect of sulfonation agent on spesific surface area and pore volume; and (b) pore size distribution of carbon aerogel and sulfonated carbon with variation of sulfonat agent.

Fig. 4. (a) Effect of sulfonation agent on spesific surface area and pore volume; and (b) pore size distribution of carbon aerogel and sulfonated carbon with variation of sulfonat agent.

After the sulfonation process, the BET surface area and pore volume for the solid acid catalyst samples with sulfonic agents sulfanilic acid and sulfuric acid decreased from the values in the initial carbon aerogel from to 1301.981 and to 1.159 and 1.053 , respectively. The decrease in surface area is due to the groups grafted on the cellulose groups in the carbon aerogel, as shown in Fig. 4(a). Fig. 4(b) about pore distribution analysis with the BJH method provides information on the pore size distribution before and after sulfonation. Using sulfanilic acid as a sulfonating agent resulted in the particle size distribution in SAC-SA being more dominantly mesoporous than macroporous, as seen from the graph with diameters less than 50 nm . However, when sulfonation uses sulfuric acid as a sulfonic agent, the particle size of SAC-SO4 is distributed towards macropores, as seen from the diameter produced in BJH analysis, which is more dominant above 50 nm . Apart from being a sulfonating agent, high concentrations of sulfuric acid are corrosive so that they can erode and damage the pore structure of carbon aerogels. Erosion or physical changes to the pore structure can increase overall pore size, including forming larger or combining tiny pores into larger pores [20], [21].

Fig. 5. (a) water contact angles of catalysts and (b) dispersion of prepared catalysts into water.

Fig. 5. (a) water contact angles of catalysts and (b) dispersion of prepared catalysts into water.

The hydrophobicity of the catalyst was evaluated by dripping water on the catalyst surface; the result of the contact angle of the two catalysts was still below , which indicated that the catalyst was still hydrophilic, as shown in Fig. 4(a). The catalyst is hydrophobic when water drips on the catalyst and forms a contact angle of more than [4]. A small amount of sulfonated catalyst was dispersed into water to test the hydrophilicity of the catalyst; both catalysts would eventually sink to the bottom of the beaker. This indicates the catalyst hydrophilic characteristics, shown in Fig. 4(b).

Catalyst application in esterification reaction

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In our study, the performance of sulfonated carbon catalyst has been tested for the underreflux esterification reaction between oleic acid and methanol to produce fatty acid methyl ester (FAME) and water. As the result, SAC-SO4 produced higher conversion than SAC-SA after the esterification reaction for 5 hours under reflux, as seen in Fig. 6. Although SAC-SA contains a nonpolar sulfonic group, causing the catalyst to be more hydrophobic than SAC-SO4 after the contact angle test, SAC-SA still produces a small conversion compared to SAC-SO4. Pore size is another factor for the catalytic application of mesoporous materials in reactions using solid catalysts, especially when synthesizing biodiesel with large organic molecules. Although the surface area and acid density values of SAC-SO4 used in the catalytic reaction were lower than those of SAC-SA, the significantly different conversion results between SAC-SO4 and SAC-SA after the esterification reaction can be attributed to the fact that the SAC-SO4 catalyst has a material with a micropore size that is more dominant than the mesopore size, Fig. 3(b). The influence of pore size on catalytic performance suggests that factors favoring the diffusion of large organic molecules contribute to improving catalytic properties.

Fig. 6. Catalytic performance of sulfonated carbon aerogel in esterification reaction

Fig. 6. Catalytic performance of sulfonated carbon aerogel in esterification reaction

Conclusion

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Preparation of solid acid catalysts for esterification reaction has been reported in long-chain fatty acids. Heterogeneous solid acid catalysts have been successfully prepared from coir fiber using different sulfonic agents, with sulfanilic acid and sulfuric acid. Surprisingly, although SAC-SA has higher surface area than SAC-SO4, it was found that the conversion of FAME products was higher when SAC-SO4 was applied as a catalyst in esterification reaction with the property that SAC-SO4 has more macropore size distribution than mesopores. The large pore size (macropores) on the catalyst will support the diffusion of large organic molecules to improve catalytic ability.

Acknowledgments

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The authors also want to thank Mrs. Devidha Halida Vinkyrisma and Mrs. Prasasti Mahanani Niken Pinakesti for their assistance in the experiments.

References

The original version of this paper is available on https://www.scientific.net/EC.7.41.pdf

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Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 51-59

doi: 10.4028/p-d4sMSP

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2024-01-05

Revised:
2024-04-29

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2024-04-29

Online:
2024-06-26

Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

The original version of this paper is available on https://www.scientific.net/EC.7.51.pdf

Rudi Firyanto , Retno Ambarwati Sigit Lestari and Chelsi Chika Zeruya

¹Chemical Engineering Department in Universitas 17 Agustus 1945 (UNTAG) Semarang JI.Pawiyatan Luhur Bendan Duwur, Semarang 50233, Indonesia

rudi-firyanto@untagsmg.ac.id, retnotengaran@gmail.com, chelsicz@gmail.com

Keywords: Ketapang seed outer shell, Adsorbent, Activated charcoal, Lead metal, Adsorption

Abstract

Lead is a heavy metal that is dangerous if it enters the environment through industrial waste, mining, waste from the electroplating process, burning fuel oil and so on which is carried by streams. Therefore, it is necessary to limit the lead metal content. Efforts to reduce the impact of lead metal pollution can be done in several ways, one of which is by adsorption using adsorbents. Adsorption has been proven to be a fairly effective method for treating liquid waste and is the most commonly used method because it has a simpler concept and can be regenerated and is economical. One of the natural resources around us that contains cellulose that is not utilized is the outer shell of ketapang seeds. The outer shell of ketapang seeds which contains cellulose is a good alternative for utilizing this waste so as not to pollute the environment. To reduce lead metal levels, you can use a natural adsorbent from activated charcoal on the outer shell of ketapang seeds. The adsorption process uses activated charcoal adsorbent, which is one of the most frequently used non-polar adsorbents because it has better adsorption power and surface area than other types of adsorbent. This research aims to determine the variables that influence and the optimum conditions for natural adsorbents from activated charcoal in the outer shell of Ketapang seeds to reduce metal levels. The research method used is an experimental method with a two-level factorial design. The research results showed that adsorption temperature was the most influential variable in this research with an optimum yield presentation of . The activated charcoal produced has a water content of , an ash content of and a methylene blue absorption capacity of .

Introductions

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Indonesia as a developing country is currently filled with various industries. Waste disposal from the industry can pollute the environment, especially waste disposal of heavy metals. Lead is one of the dangerous heavy metals when it enters the environment through industrial waste, mining, waste from electroplating processes, burning fuel oil and so on which is carried away. Therefore it is necessary to limit the content of lead metal [1].

Efforts to reduce the impact of lead metal pollution can be done in several ways, one of which is adsorption using an adsorbent. Adsorption has been proven to be a fairly effective method for treating wastewater and is the most commonly used method because it has a simpler concept and can be regenerated and economical [1]. Along with the development of science, research is currently being developed which aims to find alternative adsorbents based on natural ingredients. One of the natural resources around us that contains cellulose that is not utilized is the outer skin of ketapang seeds. The outer shell of the ketapang seed is produced from the ketapang tree which is found in several regions in Indonesia. The large number of ketapang seeds that fall from the ketapang tree which is used as a shade causes waste in the environment. So far, there are quite a number of ketapang seeds that fall from the ketapang tree, so using the outer shell of the ketapang seeds which contain cellulose is a good alternative for utilizing this waste so it doesn't pollute the environment.

Metal pollution basically does not stand alone, but can be carried by water, soil and air. If all of these components have been contaminated by inorganic compounds, then they may contain various heavy metals such as and so on. Lead has a negative impact on health, especially if the levels exceed the levels required by body. Even at low concentrations, the effects of
heavy metal ions can have a direct effect and accumulate in the food chain. like other sources of environmental pollution, these heavy metals can be transferred over very long distances in the environment [2].

Several methods that can be used to reduce the concentration of heavy metal ions in liquid waste include adsorption, precipitation, ion exchange using resin, filtration, and by absorbing pollutant materials by adsorbents in the form of synthetic resins. and activated carbon [3]. Among these methods, adsorption is the most commonly used method because it has a simpler concept and can be regenerated and is economical.

Adsorption techniques for heavy metals have been widely carried out using various kinds of adsorbents, namely [4] conducted research on making active carbon from rice husks with activator, [5] also conducted research on guava bark as an adsorbent for lead metal.

Furthermore, [6] researched the manufacture of adsorbents through the use of corn stalks as activated charcoal using sulfuric acid activator with its use in the absorption of copper (II) ions and the use of palm oil shells as an adsorbent through physicochemical activation [7].

So far, there are ketapang fruit that use the seeds as a substitute for almonds in making cakes [8] and there are also those who use them to extract oil from ketapang seeds as a basic ingredient for biodegradable monodiglyceride surfactants [9] so that the outer skin is wasted. To increase the economic value of the outer skin of ketapang seeds, this can be used as activated carbon because organic waste from plants is a source of carbon such as cellulose, hemicellulose and lignin.

Several studies on the manufacture of ketapang adsorbents have been carried out, including by examining ketapang leaves as an adsorbent [10]. The way of working in the research was carried out with 3 procedures. The first is the preparation of bioarang by cleaning the ketapang leaves and drying them, then pulverizing them using a blender and sifting them with a mesh sieve, after that the carbonization process is carried out in the furnace at a temperature of with time variations of 30,60 and 120 minutes.

The second way of working is to determine the moisture content and ash content, the water content is determined by weighing the charcoal weighing 1 gram after that it is placed in the oven at for 4 hours, then the charcoal is cooled in a desiccator and weighed until a constant weight. The ash content is determined by weighing 1 gram of charcoal and then placing it in the furnace at for 6 hours, when all the charcoal has turned to ash, then cool it in a desiccator and then weigh it.

The third way of working is adsorption of methylene blue by bioarang from ketapang leaf waste, at the time of contact absorption as much as 0.1 gram of bioarang is put into Erlenmeyer and added 20 mL of 10 ppm methylene blue solution and stirred using a water bath shaker at at 120 rpm speed with varying times of , and 20 minutes, then the stirring solution was centrifuged for 10 minutes at a speed of 3000 rpm after that the filtrate was allowed to stand for 30 minutes and after the charcoal had settled, a number of the filtrate was taken and the adsorption was measured using a spectrophotometer.

The results of this study indicate that the adsorption capacity is not affected by the water content but the ash content because the lower the ash content the greater the adsorption capacity [10].

In this research, the outer shell of ketapang seeds will be examined as an adsorbent. In contrast to previous studies, namely using ketapang leaf adsorbents to remove pollution from dyes using methylene blue. In this study, the outer shell of ketapang seeds was used as an adsorbent to reduce levels of metal. The ketapang seed outer shell adsorbent can be obtained by chemical activation with HCl activator, and physically obtained by carbonization.

This substance will activate the carbon atoms which will enter the pores and open the closed surface of the charcoal, so that the impurity compounds in the pores become more easily absorbed and the surface area of activated carbon increases to increase its absorption power. The advantage of this process is that it can reduce environmental pollution because the residues in the form of oxides that are not soluble in water when washing are neutralized with NaOH to bind back chemical residues attached to the surface of activated charcoal and the ash content contained in activated charcoal.

The aims of this study were: (i) to find out the variables that most influenced the reduction of metal levels, (ii) to determine the optimum conditions of the variables that affected the process
of implementing the natural adsorbent of the outer shell of ketapang seeds on decreasing levels of metal , (iii) To determine the activated charcoal produced according to the Indonesian National Standard (SNI) with the parameters of water content, ash content, and absorption capacity of methylene blue.

Ketapang. Ketapang (Terminalia cattapa) is a tropical almond tree that is widely distributed in tropical climates and is often used as a shade tree in parks, on roadsides and on beaches. Ketapang trees can grow to a maximum height of 25 meters and a leaf canopy width of 9 meters. The leaves of the ketapang tree are oval-shaped, green in color, turn yellow and brown when they fall [11].

Fig. 1. Ketapang Seed Skin [12]

Fig. 1. Ketapang Seed Skin [12]

Ketapang seed coat is divided into 2, namely the outer skin layer (testa) and the inner skin layer (tegmen). The outer skin layer on the ketapang seeds is hard like wood. This layer is the main protector for the part of the seed inside. The outer shell of the ketapang seed or the shell of the ketapang seed can be used to make briquettes or activated charcoal because it has a carbon element.

Table 1. Composition of Ketapang Seed Outer Skin [13]

Komposisi | Presentase
Selulosa | 16,60%
Hemiselulosa | 24,70%
Lignin | 43,46%

Lead (II) Nitrate. Lead (II) Nitrate is an inorganic compound with the chemical formula . This compound is generally found as colorless crystals or white powder [14] and is toxic to the human body because lead at a temperature of can evaporate and react with oxygen [15]. Lead in the elemental arrangement is a heavy metal that occurs naturally in the earth's crust [16]. Lead metal is a type of heavy metal that is usually contained in industrial wastewater and can cause serious problems because of its toxic nature [17], so it is categorized as a heavy metal that has the highest affinity [18]. Lead metal is more widespread than most other toxic metals [14], so it is very dangerous if it enters the human body.

Adsorbents. Adsorbents are solid substances that can absorb certain components of a fluid phase. Most adsorbents are in the form of highly porous materials so that adsorption takes place on the pore walls or at certain locations within the particle [19]. A good adsorbent has a variety of requirements as follows: has great dissolving power, has a low vapor pressure, as far as possible not corrosive, has a relatively low viscosity, thermally stable, affordable prices. From the requirements above, it can be concluded that the adsorbent is used as an absorbent for unwanted substances. Adsorbents used commercially can be grouped into two groups, namely polar and non-polar groups. Types of adsorbents belonging to the polar adsorbent group are silica gel, activated alumina, and zeolite. While the types of adsorbents included in the non-polar adsorbent group are adsorbent polymers and activated charcoal [19].

Activated charcoal. Activated charcoal is an amorphous compound produced from an adsorbent containing carbon or charcoal which is specially treated to obtain high adsorption power. Activated charcoal is one of the most frequently used adsorbents in the adsorption process because it has better adsorption power and surface area than other types of adsorbents, so it can adsorb certain gases and
chemical compounds depending on the size of the pore volume and surface area. The absorption capacity of activated charcoal is very large, which is by weight of activated charcoal [20]. The adsorption properties of activated charcoal are influenced by several factors including; size of adsorbate molecules, influence of temperature, characteristic of adsorbent, contact time and agitation speed. The types of activated charcoal are differentiated according to their functions, namely activated charcoal in gas and liquid phases. Gas phase activated charcoal is a carbon adsorbent gas absorbent, this type of charcoal is used to adsorb materials in the form of vapor or gas. This type of carbon can be found in coconut shell carbon. Meanwhile, liquid phase activated charcoal is used to absorb unwanted impurities from liquids or solutions. This type of charcoal usually comes from coal and cellulose.

Research Methodology

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Methods this research was carried out experimentally in the laboratory. The experimental design method means a set of experiments designed to obtain real data to prove a hypothesis. In the experimental design, each variable is tested by being determined at several prices. Usually two values are used for the independent variables, then the independent variables are combined for several possibilities. From the combination obtained, it is used for drawing conclusions. So that the experimental design method is very possible to obtain more accurate results and conclusions.

Experimental design is a method of calculation that is often used compared to other methods that are considered conventional, because experimental design only requires fewer runs to find out the side effects on all variables. Optimum conditions obtained can be more precise because it includes interactions. Decision making can be more certain because it is supported by easy and simple statistical calculations. Experimental design consists of several ways, one of which is the factorial design method with two levels, namely low level and high level. This factorial design method is used to prove or strengthen the conclusions from conventional methods.

Experiments carried out on experimental designs with n variables use the equation formula, for 3 variables a total of or 8 experiments are needed. In this study the variables used were absorption temperature (A), absorption time (B) and adsorbent size (C). Next, a two-level experimental design (low level and high level) was created, with 3 variables. Variance analysis was carried out by calculating the main effect, interaction effect and calculating the yield equation. Determining influential variables using normal probability charts. The interaction effect point furthest from the approach line is the most influential variable. An approach line is a line created by passing the line over many interaction effect points.

Determination of variables in the experimental design method includes fixed and changing variables. The fixed variable used was heavy metal adsorbed , with weight was 2 grams, the concentration of was 5 ppm . While the changing variables used are adsorption temperature of and , adsorption time of 60 and 90 minutes, size of adsorbent mesh and 60-80 mesh.

The research materials used were: ketapang seed shell (ketapang seed shell) obtained in the area around Semarang. , methylene blue, and aquadest purchased from The Indrasari chemical shop, Semarang Indonesia. Meanwhile, the research tools used were: beaker glass, erlenmeyer, measuring flask, furnace, filter paper, oven, blender, pH indicator, statives, clamps, desiccator, analytical balance, magnetic stirrer, Sieve 60, 80, 100 and 120 mesh, hot plate stirrer, thermometer , Spectrophotometry Atomic Absorption (SSA), shakers.

Research procedure

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Adsorbent preparation. The outer skin of the ketapang seeds or ketapang shells is cleaned and cut then dried in the sun for 2 days until the raw material is dry or loses its water content. After the dehydration process, the raw material is carbonized into the furnace for 15 minutes at a temperature of . Then blended until smooth and sieved using 60-80 mesh and 100-120 mesh size sieve.

Activation of the adsorbent with HCl. As much as 25 grams of ketapang seed outer shell powder measuring 60-80 mesh and 100-120 mesh were put into 250 ml of 2.5 N HCl and stirred for 1 hour at room temperature. Then allowed to stand for 24 hours and filtered after that neutralized with 1 N NaOH to pH 7 and dried in an oven at for 4 hours.

Adsorption Process. 25 ml of solution was added to 2 grams of adsorbent size 60-80 mesh mesh then stirred at and for 60 and 90 minutes using a magnetic stirrer. Then filtered to separate the adsorbed solution from the adsorbent.

Analysis of levels reduction using Atomic Absorption Spectrophotometry. The adsorbed solution on the filtering results was measured for its absorption at a wavelength of 283 nm to determine the decrease in its levels.

Analysis of the reduction of metal levels of using Scanning Electrone Magnetic. solution before and after adsorption with the highest decrease in metal content, was analyzed using Scanning Electrone Magnetic to determine its morphological picture.

Result and Discussion

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Determination of the Most Influential Variable. Determination of the most influential variable, using the normal probability chart as shown in Fig. 2. The symbols in the figure, IA are temperature interactions, IB are time interactions, IC are adsorbent size interactions. Meanwhile, IAB states the interaction between temperature and time, IAC is the interaction of temperature with the size of the adsorbent, IBC is the interaction of time with the size of the adsorbent and IABC is the interaction of temperature-time-size of the adsorbent.

Fig. 2. Normal probability chart

Fig. 2. Normal probability chart

Fig. 2 shows that the temperature variable (IA) is located farthest from the approach line, thus indicating that the temperature variable greatly affects the adsorption power of the active charcoal adsorbent on the outer shell of ketapang seeds on decreasing levels of metal . This is because when the adsorbate molecules attach to the adsorbent, energy is released so that the adsorption rate will increase with increasing temperature [21].

Optimization of influential variables. Optimization was carried out at a temperature range of with an adsorbent weight of 2 grams, a concentration of 5 ppm , an adsorption time of 60 minutes, and an adsorbent size of mesh. The results of the optimization experiments show that the higher the adsorption temperature, the greater the adsorption power as shown in Fig. 3.

Fig. 3. Optimization of temperature

Fig. 3. Optimization of temperature

This happens because temperatures that are too high can cause desorption or re-release of ions or molecules that have bound to the active group on the adsorbent [15], so that it only reaches the optimum point, namely at and after reaching the optimum point, the % decrease in metal will decrease with increasing temperature. The optimum condition was reached at with a reduction level of metal by .

Testing the water content, ash content and absorption capacity. Testing the water content aims to determine the hygroscopic nature of activated charcoal. The hygroscopic nature causes activated charcoal under certain conditions and humidity to reach an equilibrium moisture content which is a measure of hygroscopicity. The method used is oven drying. The sample was placed in an oven at for some time, until a constant weight was obtained. then the weight is measured before and after drying. The difference between the initial and final weights indicates the water content in the sample. The result of measuring the water content is .

Testing the ash content aims to determine the mineral content of activated charcoal, because activated charcoal made from natural ingredients does not only contain carbon compounds. The lower the ash content in activated charcoal, the greater the ability of the adsorbent to absorb metal ions. This is because the ash content is an impurity that is not expected to exist in the adsorbent. The sample to be tested is cleaned of dirt and other foreign matter. Then, the sample is fired at high temperature, usually in a furnace at , for several hours until ash is formed. After the ash is formed, the ash is taken from the furnace and cooled to room temperature. Then, the ashes were weighed. After that, the ashes were burned again in the furnace at the same temperature as before for 1 hour, then cooled down to room temperature. Then, the ashes were weighed again. The ash content can be calculated by subtracting the weight of the ash after the first burning by the weight of the ash after the second burning, then dividing by the initial weight of the sample and multiplying by to get the ash content in percent. The results of measurement of ash content obtained .
Testing the absorption capacity of methylene blue aims to determine the surface area of activated charcoal and its ability to absorb colored solutions. This test was carried out by adsorption using a shaker with a speed of 100 rpm without immersion time and the absorbance was measured using atomic absorption spectrophotometry with a wavelength of 664 nm . The measurement results obtained adsorbent absorption of methylene blue with a surface area of . Calculation of surface area using the following equation [22]:

30 | 62
35 | 63.5
40 | 64.5
45 | 65.5
50 | 66.77
55 | 66.3
60 | 65.8

Scanning Electrone Microscope (SEM) Analysis. SEM analysis aims to determine the microstructure (including porosity and crack shape) of solid objects. The results of the SEM analysis can be seen in Fig. 4.

Fig. 4. SEM Analysis Results: (a), (c) before adsorption; (b), (d) after adsorption

Fig. 4. SEM Analysis Results: (a), (c) before adsorption; (b), (d) after adsorption

The results of SEM analysis before adsorption, Fig. 4(a) and 4(b), show pores after activation using HCl . The pores formed are mesoporous, the mesoporous material is activated carbon which consists of carbon skeletons with mesoporosity and microporosity due to a diameter of 2 to 50 nm . The small pores which are the structure of the cellulose of the ketapang seed coat indicate that there are bonds in the form of cellulose OH ions which can cause the adsorption process to occur. For the results of SEM analysis after adsorption, Fig. 4(c) and 4(d), it appears that there are deep holes which have absorbed the metal attached to the pore surface, this is because the adsorbent has reacted with the adsorbate through adsorption process.

Several factors that influence adsorption kinetics include: nature of the adsorbant and adsorbate, adsorbant concentration, temperature, surface area of the adsorbent, relative humidity, agitation or mixing, pH level. These factors can interact with each other and influence the overall adsorption kinetics.

Several factors that influence adsorption kinetics include: nature of the adsorbant, adsorbant concentration, temperature, surface area of the adsorbent, relative humidity, agitation or mixing, pH
level. These factors can interact with each other and influence the overall adsorption kinetics. Several factors that influence adsorption thermodynamics include: adsorption energy, adsorption enthalpy, adsorption entropy, temperature, pressure, adsorbant concentration, adsorbent surface properties. These factors together influence the thermodynamics of adsorption and determine the thermal and energetic properties of the process

Conclusion

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Adsorption temperature is the most influential variable in the implementation of natural adsorbents from activated charcoal outer shell of ketapang seeds on decreasing levels of metal . Optimum conditions achieved at adsorption time of 60 minutes, adsorbent size of 60-80 mesh is at with a maximum yield of .

Activated charcoal from the outer shell of ketapang seeds can be used to reduce levels in the solution. The adsorption process on activated charcoal will capture ions in solution, reducing their concentration and thereby reducing levels. Activated charcoal has a large pore structure and surface area which allows it to absorb and bind heavy metal ions such as effectively. Therefore, the use of activated charcoal from the outer shell of ketapang seeds can be an effective option in reducing levels in the solution.

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This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 61-70

doi: 10.4028/p-UqJ3In

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2023-12-13

Revised:
2023-12-29

Accepted:
2024-01-02

Online:
2024-06-26

Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

The original version of this paper is available on https://www.scientific.net/EC.7.61.pdf

Harmami , Ita Ulfin , Baswara Gilang Ramadhan and Kartika A. Madurani

Chemistry Department, Faculty of Science and Data Analytics, Institut Teknologi Sepuluh Nopember, Indonesia

a*harmami@chem.its.ac.id, itau@chem.its.ac.id, baswara.18012@mhs.its.ac.id, kartika.madurani@its.ac.id

Abstract

In this study, we utilized an adsorbent based on rice straw for reducing hexavalent chromium ions ( ) in an aqueous solution. The rice straw as adsorbent raw material was washed, dried, and powdered. Rice straw powder was heated at for 2 hours to obtain rice straw adsorbent. The adsorbent was activated with for 4 hours. Characterization of the adsorbent was done using Fourier Transform Infra-Red (FTIR) method. FTIR spectra showed the presence of hydroxy, carboxylic, aromatic, and ether groups on the surface of the rice straw and the made adsorbent. The reduction of ions in aqueous solutions was carried out using the adsorption batch method. The adsorption process was conducted in various the solutions pH for 1-5 and variations in contact time for 5-720 minutes. The highest percentage reduction of reached . It has occurred at pH 2 and equilibrium at 600 minutes of contact time.

Introduction

The original version of this paper is available on https://www.scientific.net/EC.7.61.pdf

Chromium ( Cr ) are famous compounds in various industries such as dyes, coating, catalysts, corrosion inhibitors, etc. [1]. This condition makes the main industrial waste contain Cr compounds. Cr compounds in wastewaters is primarily encountered in oxidation stages III and +6 [Cr(VI)]. Recent research suggests that Cr (VI) compounds are more toxic dan reactive than Cr (III) [2]-[4]. These properties combined with sufficient solubility and mobility of VI in the environment, makes the issue of utilization and disposal of chromium-containing waste relevant to many countries. To cover this problem, the possible thing to do is improve the technology for its removal from industrial waste. The most common technology for removal is adsorption. Adsorption is cost-effective and easy operating method [2]. The important part of adsorption method is the adsorbent used [3]. The conventional choice for adsorbent is commercial activated carbon. Unfortunately, this adsorbent is not cheap due to the high-cost raw materials for production. Therefore, developing low-cost activated carbon from inexpensive and sustainable raw materials is important.

Rice straw is byproducts of rice harvest. Rice straws reached 415,970.61 ton in East Java, Indonesia, in 2018 [5]. Besides being used for material production and as a source of renewable energy, rice straw is often utilized as an adsorbent for reducing heavy metals in aqueous solutions. There are various types of adsorbents that can be obtained from rice straw, such as bio sorbents, nanomaterials, and activated carbon [6]-[9]. Adel et al. made an adsorbent based on heated rice straw at temperatures ranging from 300 to for 30 to 120 minutes, followed by activation with 1 M HCl and NaOH [10]. The results showed that heating at for 120 minutes produced adsorbents with the highest adsorption capacity for reducing Pb (II) in aqueous solutions. The heating temperature can affect the functional groups on the adsorbent. Heating above can increase the amount of aromatic compounds and reduce the polarity of the adsorbent, which has a negative impact on the heavy metals adsorption [11], [12]. Rice straw, which is a lignocellulosic compound, is a suitable raw material for the production of carbon-based adsorbents.

Zhou et al. [13] used activated carbon derived from rice straw, activated with HCl and NaOH , as an adsorbent for the removal of from aqueous solutions. They found that the optimum condition for adsorption was pH 2 , with equilibrium reached after a contact time of 1440 minutes, resulting in a reduction of and for HCl and NaOH activators, respectively. Farahmand et al. utilized activated carbon from rice straw with an activator for the removal of Ce (IV) [14]. The optimum pH for Ce (IV) adsorption occurred at pH 4 , with equilibrium achieved after 500 minutes of contact time. The maximum adsorption capacity for Ce (IV) obtained was . In the research conducted by Sakhiya et al., carbon adsorbent from rice straw was used for the reduction of Pb (II) and Zn (II) metal ions in aqueous solutions [9]. The optimum pH for adsorption of both metals was pH 6 , with equilibrium achieved after a contact time of 150 minutes. The adsorption capacity for Pb (II) was found to be , and for Zn (II), it was .

Research on the adsorption of from aqueous solutions continues to be a topic of investigation. Fan et al. used a mixed adsorbent of rice straw and sewage sludge activated with to reduce in aqueous solutions [15]. The optimum pH for adsorption was pH 2 , and equilibrium was reached after a contact time of 1440 minutes. The adsorption capacity for VI obtained was . Gao et al. employed rice straw bio sorbent activated with for the reduction of in aqueous solutions [16]. The optimum pH for adsorption was 2, with a contact time ranging from 0 to 3600 minutes. The highest percentage reduction of occurred at a contact time of 2880 minutes. The study of Ma et al. reported that activated carbon from corn straw, activated with KOH, was used to adsorb at a capacity of with a contact time of 480 minutes [17]. Despite various studies investigating the reduction of from aqueous solutions using straw-based adsorbents activated with different agents, it appears that has not yet been used as an activator.

The use of as an activator can indeed enhance the adsorption capacity of activated carbon obtained from various raw materials. plays a crucial role in the pyrolytic transformation of the raw material and contributes to the formation of cross-linked carbonaceous structures [18], [19]. In this study, rice straw adsorbents were made and activated with for the reduction of in aqueous solutions. The research aims to determine the optimum pH and equilibrium contact time for the adsorption process.

Materials and Methods

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Materials. The semi-dried rice straw was obtained from local paddy fields in Malang, East Java, Indonesia. Phosphoric acid , chloride acid , and sodium hydroxide were purchased from local market. Demineralized water was bought from a local market and used for cleaning and chemical preparation. All chemicals were used without any purification. 1 M solution as adsorbent activator and 1 M HCl solution were prepared in Laboratory of Instrumentation and Analytical Sciences, Chemistry Department, Faculty of Sciences and Data Analytics, Institut Teknologi Sepuluh Nopember. The standard solutions of in various concentration (10-50 ) were prepared by diluting potassium dichromate (VI) with demineralized water. The standard solutions were measured by Atomic Absorption Spectrophotometry (AAS, Thermo Fisher) at 357.9 nm to obtain calibration curve. The working solution is wastewater that containing . The working solution was prepared from dilution of potassium dichromate (VI) and demineralized water.

Preparation of Rice Straw Adsorbent. Rice straw was cut into pieces and washed until the rinsed water became clear. The straw was then air-dried at room temperature for approximately 24 hours before being heated in an oven at for 24 hours. The dried straw was finely ground to obtain a powder, which was subsequently heated to with a retention time of 2 hours and a heating rate of minute, resulting in the rice straw adsorbent [9], [20]. The rice straw adsorbent was washed with 1 M HCl and deionized water until it reached a pH of 6-7, and then it was dried in
an oven at for 12 hours. Prior to use, the rice straw adsorbent was sieved through a 120 -mesh sieve to obtain uniform particles with a size below and stored in the desiccator [21].

The activated rice straw adsorbent was prepared by mixing it ( 5 g ) with 100 mL of activator solution. The mixture was stirred for 4 hours [10]. Subsequently, it was filtered and washed with demineralized water to obtain a pH of 6-7. Then, it was dried in an oven at for 12 hours until a constant weight. The activated adsorbent was sieved through a 120 -mesh sieve and stored in the desiccator.

Batch Experiments. The batch adsorption method was employed to determine the optimum pH and contact time using an adsorbent dosage of [22]. A total of 0.1 g of rice straw activated carbon was mixed with 25 mL of a wastewater containing of . The mixture was stirred for a specified period [15]. The mixture was filtered, and the resulting filtrate was analyzed using AAS technique. The removal percentage was calculated using Eq. 1, where refers to the initial concentration of the adsorbate in the solution, and represents the concentration of the adsorbate after the adsorption process has taken place.
Removal Percent

The testing of the adsorbate's pH influence was conducted using a working solution adjusted to pH values of , and 5 , with each test having a contact time of 100 minutes [23]. The pH variation that resulted in the highest percentage reduction was determined as the optimum pH and will be used in the following experiments. The effect of contact time was conducted by varying the contact time between the adsorbent and adsorbate, starting from 5 minutes and continuing until a constant percentage reduction was obtained. This was done using a working solution containing at a concentration of , each at the previously determined optimum pH .

FTIR Characterization. The KBr pellet method was employed for FT-IR characterization. The samples were mixed with KBr at a ratio of 1:100 and finely ground and pulverized. The mixture of powders was then placed into a press apparatus to form pellets, which were subsequently loaded into a sample holder for FT-IR analysis. This analysis was carried out for the following samples: dried rice straw powder, rice straw activated carbon, -activated rice straw adsorbent, and activated rice straw adsorbent after adsorption.

Results and Discussions

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Fabrication of Rice Straw Adsorbent. Fig. 1A shows the cut and washed rice straw and the powdered rice straw is depicted in Fig. 1B. The rice straw powder displayed a brown color throughout, indicating the degradation of chlorophyll during the heating process [24]. The heating of the rice straw powder was carried out in an electric furnace at for 2 hours with a heating rate of minute to obtain rice straw adsorbent. The result of this heating process showed a color change in the powder to black, with a small amount of ash on the surface. The formation of ash is attributed to the rice straw powder reacting with oxygen inside the crucible, resulting in complete combustion. The appearance of the rice straw powder after heating can be seen in Fig. 2A. The obtained rice straw adsorbent was washed with 1 M HCl and demineralized water until pH of 6-7 to remove residual ash from carbonization. After activating and sieving, there were no significant differences observed in the rice straw adsorbent except that it appeared darker in color and had uniform particle size, as shown in Fig. 2B.

Fig. 1. Dried rice straw (A) and rice straw powder (B).

Fig. 1. Dried rice straw (A) and rice straw powder (B).

Fig. 2. Rice straw adsorbent (A) and the activated rice straw adsorbent (B).

Fig. 2. Rice straw adsorbent (A) and the activated rice straw adsorbent (B).

FTIR Characterization. The rice straw powder, rice straw carbon, -activated rice straw carbon before and after adsorption were characterized its functional groups using FT-IR. Table 1 provides information about the vibrational bands corresponding to the peaks in the spectra. The main peaks that appear indicate the presence of oxygen functional groups such as ether, ketone, phenolic, and alcohol groups. There are changes in the peaks in the spectra of the powder and adsorbent, specifically the disappearance of peaks at wavenumbers 1375 and . The absence of the peak at is due to dehydration and aromatization resulting from the decomposition and condensation of volatile compounds [25]. Meanwhile, no peak of methylene at is attributed to the decomposition of bonds during heating to form more stable aromatic bonds at high temperatures. Conversely, a new peak is formed in the adsorbent spectrum at wavenumber , indicating the oxidation of surface functional groups of the adsorbent. The increased intensity of the carboxylate peak in the spectrum of the -activated adsorbent is caused by the protonation of carboxylate groups by the acid activator [13].

Table 1. FT-IR vibration peak.

Wavenumber
(cm⁻¹)
Vibration
Peak

Rice straw powder
Rice straw activated carbon
H₃PO₄-activated rice straw adsorbent
H₃PO₄-activated rice straw adsorbent after adsorption

468
Si-O-Si stretch
✓
✓
✓
✓

800
C-H aromatic
✓
✓
✓
✓

1101
C-O/ C-O-C
✓
✓
✓
✓

1375
C-H aliphatic/ O-H phenolic
✓
✗
✗
✗

1639
C═C aromatic
✓
✓
✓
✓

1695
C═O
✗
✓
✓
✓

2060
Overtone aromatic
✓
✓
✓
✓

2920
C-H methylene
✓
✗
✗
✗

3420
O-H stretch
✓
✓
✓
✓

Calibration Curve. The calibration curve is depicted in Fig. 3. The calibration curve exhibits a linear equation, i.e. , with an value of 0.9968 . The value obtained is above 0.995 , which indicates that the calibration curve is acceptable and can be used to calculate the concentration of in the following tests.

Fig. 3. Calibration curve of the standard solution.

Fig. 3. Calibration curve of the standard solution.

Effect of pH. The testing of pH variations in the adsorbate was carried out to determine the optimum pH , using a range of pH values: , and 5 . The results of the removal percentage of can be found in Fig. 4. The removal percentage of increases with the acidity of the adsorbate solution, and the highest percentage is achieved at a pH of . This is followed by a decrease at pH 1 . This can be attributed to the fact that in an acidic environment, the surface of the activated carbon is surrounded by ions, which facilitate the binding of anionic, through electrostatic attraction. The more positive the surface of the activated carbon, the easier it is to bind ions [26]. In addition to electrostatic attraction, the removal mechanism of in the solution can be attributed to the reduction of ions to ions. In an acidic environment, ions exist in the form of and , which can be directly reduced to ions by electron-donating groups on the activated carbon [13], [27].

Fig. 4. Graph of the effect of varying pH on the removal percent of ions.

Fig. 4. Graph of the effect of varying pH on the removal percent of ions.

The reduction reaction of Cr (VI) ions can be seen in Fig. 5. Cr (III) ions, which carry a positive charge, can then be released back into the solution due to electrostatic repulsion from the surface of the activated carbon or adsorbed by the acidic active sites of the activated carbon through cation exchange [12], [15], [28]. At extremely acidic pH levels, the Cr (III) ions released back into the solution may have difficulty reabsorbing onto the surface of the activated carbon due to the excess ions present on both the carbon surface and in the solution. The results obtained align with the findings of Parlayici and Pehlivan [29], where a decrease in the removal percentage was observed at pH values below 2.

Fig. 5. Adsorption mechanism of ions in activated carbon surface.

Fig. 5. Adsorption mechanism of ions in activated carbon surface.

Effect of Contact Time. The effect of contact time was conducted by varying the duration of stirring between the adsorbent and adsorbate in the batch adsorption process. Various contact times of 5, 30, , and 720 minutes were used. The results of removal percentage by contact time variations is presented in Fig. 6. The graph indicates that the removal percentage of ions at a contact time of 5 minutes is , followed by a increasing the removal percentage at a contact time of 30 minutes. This is then followed by a gradual increase until equilibrium is reached at a contact time of 600 minutes, with an adsorption percentage of . A similar trend was observed in the research conducted by [17]. This phenomenon is attributed to the high availability of active sites on the -activated rice straw adsorbent at the beginning of the adsorption process, allowing VI to be readily bound to the adsorbent surface. One of the proposed mechanisms is the adsorption of by functional groups containing oxygen, either through ion exchange or complexation [17]. This mechanism may underlie the adsorption process in this study, as evidenced by the high presence of oxygen-containing functional groups in the FT-IR spectra obtained. The reduction of ions can be visually observed because ion solutions are yellow in color and will turn orange as the concentration of ions increases [30]. Fig. 7 illustrates the color change of the solution before and after the adsorption process.

Fig. 6. Graph of the effect of varying contact time on the removal percent of ions.

Fig. 6. Graph of the effect of varying contact time on the removal percent of ions.

Fig. 7. Comparison of working solution before (working solution) and after adsorption with contact time of 60 and 360 minutes.

Fig. 7. Comparison of working solution before (working solution) and after adsorption with contact time of 60 and 360 minutes.

Conclusions

The original version of this paper is available on https://www.scientific.net/EC.7.61.pdf

An adsorbent based on carbon derived from rice straw was successfully prepared, heated to for 2 hours, and activated with for the reduction of in aqueous solutions. The obtained results revealed an optimum pH at pH 2 and equilibrium at a contact time of 600 minutes, with a reduction percentage of 66.90%.

Acknowledgment

The original version of this paper is available on https://www.scientific.net/EC.7.61.pdf

The authors gratefully acknowledge financial support from the Institut Teknologi Sepuluh Nopember for this work, under project scheme of the Publication Writing and IPR Incentive Program (PPHKI) 2023.

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The original version of this paper is available on https://www.scientific.net/EC.7.61.pdf

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This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 71-78

doi: 10.4028/p-OI9QmD

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2023-12-06

Revised:
2023-12-31

Accepted:
2024-01-02

Online:
2024-06-26

Bilayer Solar Steam Generator by Co-Gelation Method

The original version of this paper is available on https://www.scientific.net/EC.7.71.pdf

Annisa Nur Fidyanti Pamuji , Juliananda , Widiyastuti , Tantular Nurtono , Heru Setyawan

¹Department of Chemical Engineering, Faculty of Industrial Technology, Sepuluh Nopember Institute of Technology, Kampus ITS, Sukolilo, Surabaya 60111, Indonesia

Department of Chemical Engineering, Faculty of Engineering, Brawijaya University, Jalan MT. Haryono 167, Klojen, Malang 65145, Indonesia

tantular@chem-eng.its.ac.id, sheru@chem-eng.its.ac.id

Keywords: Solar steam generator, cellulose aerogel, magnetite, co-gelation.

Abstract

The interfacial solar steam generator presents a viable and environmentally conscious solution for generating fresh water from seawater. The interfacial solar steam generator is accomplished through the integration of a photothermal material with a supporting material, resulting in a bilayer structure. In general, the efficiency of achieving a bilayer structure by the coating of a photothermal material on the surface of a substrate is limited. This is due to the potential for separation and variations in coating thickness, which can result in a drop in the rate of evaporation. In this study, a bilayer structure was successfully obtained through the implementation of a co-gelation technique utilizing a biomass-derived substrate, aerogel cellulose, and magnetite ( ) as photothermal materials. Additionally, we investigate the impact of magnetic fields on the evaporation rate of photothermal materials. The bilayer solar steam generator obtained demonstrates a notable evaporation rate of , which is sufficient to meet the daily water requirements of individuals.

Introduction

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The solar steam generator represents a practical and environmentally friendly solution to the global issue of water scarcity. Various technologies, such as technologies based on membrane and thermal energy has been employed for converting seawater into fresh water[1]. Nevertheless, it is important to note that these technologies consume a significant amount of energy, acquire high costs, and are prone to fouling, which ultimately diminishes their energy efficiency[2]. The utilisation of solar steam generators presents a potential solution to address the problem of water scarcity. By using solar radiation as a renewable energy source, these generators have the capacity to be constructed utilising biomass derived materials. This characteristic provides such a cost-effective and sustainable technology for mitigating water scarcity[3]. Solar radiation also have a wide range of application, for example there is research about substituting electricity with solar radiation for charging electrical vehicles in Bali, so the concept of independent powers producer can be achieved [22].
Solar radiation has wide range of applications, including large-scale power generation, desalination systems, etc., depend on the effective harvesting of solar energy for water evaporation or steam generation. However, those applications require high optical concentration of solar radiation and are prone from high optical loss, which are expensive and high maintenance[3]. Heat localization become one of solution to solve those problem without using high optical concentrator[4]. This method can minimize heat losses and simultaneously avoid unnecessary heating bulk water that only consumes energy. The system of heat localization works by using the ability of materials to efficiently absorb light and convert it into thermal energy, as well as their characteristics as thermal insulator, and wicking water towards surface (capillary action)[3].
Bilayer solar steam generator is consisted of photothermal conversion layer and water transport layer we called substrate, and is proved to have better ability to localizes solar radiation, reducing heat losses and enhancing efficiency[4]. The photothermal layer at the surface of the evaporator works as
converter of solar energy from solar radiation for steam generation. The water transfer layer or substrate below the photothermal layer continuously supplying water to surface and effectively reduces heat loss due to its characteristic as thermal insulator, maximizing the heat localization effect [5]. The water wicks to the surface, evaporates and forms vapour which leaves the structure [4].
In this study, we apply the co-gelation approach to build a bilayer solar steam generator with aerogel cellulose as the substrate and magnetite as the photothermal components. Aerogel cellulose has an appealing characteristic of low density and great porosity[6], enabling it to achieve buoyancy. Additionally, it possesses a low thermal conductivity and exhibits excellent capillarity, which are key attributes required for efficient heat localisation in solar steam generators[3]. Magnetite is used as a photothermal material due to its remarkable characteristics, including its high thermal conductivity and its capacity to efficiently absorb and transform solar radiation into thermal energy [7]. The cogelation method is used to prevent the separation of two components, which has the potential to reduce the evaporation rate of a solar steam generator. Magnet-assisted manufacturing was employed to reduce the amount of photothermal materials used and affecting the evaporation rate [8].

Materials and Methods

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Materials. Coir fibers were otabined from Tulungagung, Indonesia. Hydrochloric acid ( HCl ; ; reagent grade) and sodium hydroxide ( NaOH ; reagent grade) were supplied by Merck. Sodium hypochlorite ( NaOCl ; 5%) was supplied by Onemed. Ethanol ( ) was supplied from Sigma Aldrich. Urea was supplied by PT. Petrokimia Gresik, Indonesia. Demineralized water was used for all synthesis and treatment processes. All chemicals were used without purification.

Preparation of cellulose pulp. Various treatments were applied to coir fibers to eliminate the hemicellulose and lignin components. The coir fiberss undergoes a process of grinding and sieving using a 150 -mesh sieve. The 150 -mesh coir fibers were treated to two rounds of acid digestion, employing 1 M and 0.5 M hydrochloric acid solutions consecutively. The process of digestion is carried out at a temperature of for a duration of 30 minutes. The second treatment used 1 M sodium hydroxide alkali solution, which was repeated three times under identical conditions. The final step is the elimination of lignin, which is achieved through the bleaching using natrium hypochlorite solution on two separate processes[9]. The pulp obtained from the procedure is ready for utilization as aerogel cellulose.

Preparation of magnetite . The magnetite used throughout this study was generated by the electrochemical method, employing a formerly used iron plate and demineralized water as the electrolyte. The synthesis process was conducted under ambient conditions, specifically at room temperature, for a duration of three hours, employing a current of 3 volts[10]. The magnetite produced is filtered and subjected to a drying process at a temperature of for one hour, giving it suitable for using as a photothermal material.

Synthesis of bilayer solar steam generator. The pulp obtained from the previous procedure is mixed with a NaOH-Urea solution in an ice bath for a duration of 30 minutes. This solution serves as a crosslinking agent, facilitating the formation of aerogel cellulose. The NaOH-Urea solution used contains 1 gram of NaOH and 4 grams of urea dissolved in 10 mL of demineralized water. To further improve dispersion, the mixture was put through sonication for 10 minutes after the addition of magnetite as photothermal materials, constituting of the total weight. The mixture was kept to a temperature of for 24 hours that will encourage the process of co-gelation. In this stage, we introduced a magnetic field as an additional variable to investigate its impact on the evaporation rate. Once the gel had solidified, it was placed under ambient temperature to thaw and coagulated with ethanol ( ) as a coagulant, resulting in the formation of an alcohol-based gel. This gel was left undisturbed for a duration of 24 hours. Following coagulation, the gel formed was submerged in demineralized water to solvent exchange, and process was repeated until the solution's pH was neutral. Afterwards, the sample was kept to freezing at a temperature of for 24 hours in preparation for the following freeze-drying process. Freeze dry was done at , 15 bar for 8 hours.

The frozen sample underwent 8 hours of freeze drying. AM- 0 stands for bilayer aerogel magnetite without assisted by magnet, and AM-1 stands for magnet-assisted bilayer aerogel magnetite.

Characterization

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Density and Porosity Test. The density of cellulose aerogels was obtained from measured mass and bulk volume and porosity of cellulose aerogel was determined from its bulk density using the Eq. 1

where and , respectively, the bulk density of cellulose aerogel and the true density of cellulose ( ). The bulk density was determined from the measured mass and bulk volume of cellulose aerogel.
X-Ray Diffraction. The identification of XRD was using X-ray diffractometer (X'pert, Phillips). The light absorption of materials was determined using a light intensity meter (Apogee MQ-500), at 5-90 degrees.
Fourier Transform Infrared Spectroscopy. The identification of functional groups of the samples was analyzed using Fourier transform infrared spectroscopy (FTIR; IR Tracer-100, Shimadzu) with a scanning range of 400-4000 cm-1.

Conductivity Thermal Test.

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Fig. 1. Conductivity Thermal Test

Fig. 1. Conductivity Thermal Test

Conductivity thermal is conducted based on ASTM D5470. This test using peltier plate as heat source, aluminium plate as conductive plate and recording temperature using thermocouple in three points, as in Fig. Conductivity thermal can be calculated by:

Where is conductivity thermal of bilayer aerogel cellulose with magnetite, P is heat transferred from peltier plate to aluminium plate, h is height of sample, is conductivity thermal of aluminium plate, and T is temperature.

Evaporation Rate. A solar simulator (Toption) is used as light source. All solar steam generation experiments are conducted under room temperature, and the intensity of simulated sunlight controlled at (one sun). Surface temperature and bulk water temperature is monitored and recorded by thermocouple (PicoLog). The mass change of evaporation is determined by electronic balance (CHQ). The evaporation rate ( ) were calculated by Eq. 3, respectively:

Fig. 2. Evaporation Rate Tests

Fig. 2. Evaporation Rate Tests

Where is the mass water of evaporation in , A is the area of cross section of substrate , and t is the time of solar irradiation .

Results and Discussion.

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Fig. 3. FTIR Spectra of Bilayer Aerogel Cellulose, Aerogel Cellulose, and Pulp Cellulose

Fig. 3. FTIR Spectra of Bilayer Aerogel Cellulose, Aerogel Cellulose, and Pulp Cellulose

Figure 3 shows the FTIR spectra of three samples: a) pulp obtained after various treatment; b) aerogel cellulose; c) bilayer aerogel cellulose with magnetite. In all samples, it is possible to identify three prominent bands that correlate to cellulose. The band observed at a wavenumber of can be related to intramolecular hydrogen bonding, namely the stretching of bonds [11]. On the other hand, the band detected at related to the stretching of bonds in the CH and groups present in the cellulose molecule [12]. Next, the band at are related to carbonyl stretching of acetyl groups in hemicellulose that can be found in lignin compound [12]. However, the band in the samples after being aerogel is shifted to the right. These show that the mixture of NaOH , urea and demineralized water was added as crosslinker agent break up the intra- and intermolecular hydrogen bonding of cellulose and physically caused cellulose swelling in solution [13].
A new band at appears in the spectra of samples of aerogel cellulose and bilayer aerogel cellulose with magnetite, which is pulp that has been crosslinked by NaOH and urea. Cellulose is consisted of hydrophobic groups which are glucopyranose ring, and hydrophilic groups which are hydroxyl group. Addition of NaOH solution can disturb hydroxyl group in cellulose, making glucopyranose ring as hydrophobic groups able to form bonds with urea [13], [14]. The band seen in can be ascribed to the functional group known as [15]. There is no significant difference between FTIR spectra from aerogel cellulose and bilayer aerogel cellulose with magnetite
because magnetite added are low concentrations ( total weight), but can be explained in XRD peaks.

Fig. 4. XRD peaks for Bilayer Aerogel Cellulose, Aerogel Cellulose and Pulp Cellulose

Fig. 4. XRD peaks for Bilayer Aerogel Cellulose, Aerogel Cellulose and Pulp Cellulose

Figure 4 shows the XRD pattern of: a) pulp obtained after various treatment; b) aerogel cellulose; c) bilayer aerogel cellulose with magnetite. The XRD pattern for pulp cellulose have three peaks, ; which identical with patterns of cellulose I [13], [16], [17]. XRD pattern for aerogel cellulose and bilayer aerogel cellulose with magnetite have different peaks at which identical with patterns of cellulose II [13], [16], [17]. Dissolution of cellulose into crosslinker agent urea at followed by gelation results in the change of structure of cellulose I into cellulose II [17], [18]. There are differences between XRD pattern for bilayer aerogel with magnetite, with another peaked found in which is one of the peaks of standard magnetite by JCPDS No.19-0629. Peak at for bilayer aerogel cellulose is sharper, indicating magnetite that was added have a high crystallinity.

Fig. 5. Photo of AM-0 and AM-1 at different condition

Fig. 5. Photo of AM-0 and AM-1 at different condition

Figure 5 shows the physical appearance of AM-0 and AM-1. AM-0 stands for bilayer aerogel magnetite without assisted by magnet, and AM-1 stands for magnet-assisted bilayer aerogel magnetite. The density of both samples is very low, with AM-0 measuring and AM-1 measuring , fitting within the density range of cellulose aerogel, which is known for its lightweight properties, ranging from 0.047 to . The two samples obtained different
phenomena at coagulation. In contrast to sample AM-0, which has more scattered magnetite in the aerogel, sample AM-1 is made up of two layers that are clearly apparent. This suggests that the magnetic field applied during co-gelation can influence the position of the magnetite, because magnetite itself is ferrimagnetic [20].

Fig. 6. a) Thermal conductivity vs Porosity, b) Thermal conductivity vs Evaporation Rate, c) Time Dependent Surface Temperature

Fig. 6. a) Thermal conductivity vs Porosity, b) Thermal conductivity vs Evaporation Rate, c) Time Dependent Surface Temperature

Both samples have high porosity, each for AM-0 and. for AM-1 and are suitable with the characteristic of aerogel cellulose. The thermal conductivity values measured from both samples are 0.0275 and 0.0672 W.m. , falling within the range of insulating materials[21]. High porosity substrates have a lot of void spaces that is filled with air, which has a low thermal conductivity, and making them excellent heat insulating materials[3]. The evaporation rate is influenced by thermal conductivity, as a lower thermal conductivity allows for better heat confinement, hence reducing heat losses during evaporation. This is proved by evaporation rate of AM-0 which is is higher that AM-1 which is , which has lower thermal conductivity. Shown in Figure 6(c), surface temperature of AM-0 is constantly higher than AM-1. Because of the more dispersed magnetite at AM-0, sunlight is continuously reflected inside aerogel, raising surface temperature. The rate of evaporation in the solar steam generator will increase as the surface temperature rises.

Conclusion

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In conclusion, bilayer solar steam generator that is composed of magnetite ( ) as the photothermal material and cellulose aerogel from coir fibers as the substrate material is promising for SSG with high evaporation rate. It is characterized by low density, low thermal conductivity, and high porosity. As the porosity of aerogel cellulose increases, the thermal conductivity decreases, and the evaporation increases. In addition, deposition of magnetite ( ) is affected by magnetic field that was added at co-gelation. The highest evaporation rate was obtained by AM-0, bilayer aerogel cellulose magnetite without assisted by magnetic at .

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Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 79-88

doi: 10.4028/p-tHtN4C

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2023-12-02

Revised:
2023-12-29

Accepted:
2023-12-29

Online:
2024-06-26

Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

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Jauharatul Wardah , Sugeng Winardi , Suci Madhania , M. Irwan Fatkhur Rozi , and K. Kusdianto

Department of Chemical Engineering, Institut Teknologi Sepuluh Nopember, Kampus ITS Sukolilo, Surabaya 60111, Indonesia.

Keywords: Activated Carbon, AC/ZnO, Methylene Blue, Photocatalyst, Waste Paper

Abstract

Accumulation of untreated and unrecycled paper has a negative impact on the environment. Like liquid waste handling, paper waste handling is also still being developed. It is known that activated carbon (AC) is one of the promising adsorbents that can be used to solve the environmental issue. Activated carbon can be made from organic waste, such as waste paper. The objective of this study is to investigate the operation condition of the pyrolysis process to obtain the activated carbon. The furnace temperature was set at for 1 hour under stream with a flow rate of . To provide a synergistic effect in the adsorption process, ZnO was derived from as a chemical activator for making active carbon. While with different concentrations of 0.01 , 0.05 , and 0.1 M was grown into the pores of activated carbon. The photocatalytic activity of was identified in the degradation process of methylene blue as a model of organic pollutants. X-ray diffraction (XRD), scanning electron microscope (SEM), and fourier transform infrared (FTIR) were used to characterize the product. The morphology of ZnO was observed in the form of a flower-like and occupying the surface of activated carbon. The photocatalytic activity showed that the methylene blue was completely degraded.

Introduction

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Numerous scholars continue to be interested in environmental issues since they appear to have no end in sight. The link between garbage produced by cities and companies and environmental issues is not new [1]. Waste discharged into public rivers frequently has been found to contain various metals, colors, and even harmful microorganisms [2]. In addition to the persistent challenges of liquid waste management, the annual accumulation of millions of tons of untreated and unrecovered paper and its byproducts has emerged as a significant and pressing concern [3]. The majority of waste paper originates from wood or cotton pulp, primarily composed of cellulose fibers (constituting 90-99%), which are rich in carbon, possess a distinctive pore structure, and feature functional groups such as carboxylic and hydroxyl groups [4]. Addressing the mitigation of pollutants carried by effluents requires effective adsorbents like zeolites, activated carbon, activated alumina, silica gel, among others [5]. Activated carbon is particularly favored due to its commendable performance. Furthermore, given the abundant availability of waste paper, which inherently contains carbon-rich components, the synthesis of activated carbon from waste paper presents an appealing option, characterized by high efficiency and effectiveness [6].

The synthesis of activated carbon with high specifications, good structure and pore size is generally done through carbonization and activation processes [7]. Carbonization is part of the pyrolysis process, which involves the thermochemical decomposition of organic materials under controlled conditions, typically in a low-oxygen or oxygen-free environment [8]. During this process, organic matter found in the biomass substrate begins to break down, commencing at temperatures around and extending up to [8]. Pyrolysis has the capacity to transform lignocellulosic biomass, encompassing cellulose, hemicellulose, and lignin components, into a spectrum of solid, liquid, and gaseous products. The main products from pyrolysis are non-
condensable gas (e.g., , and ), light hydrocarbons (e.g., ), condensable gas (tar), solid residue (char), and mineral ash [9].

In the carbonization process, activated carbon is generated through activation, which can be achieved by either chemical or physical means. Physical activation entails the use of activation gases like steam, , or specific compounds. However, this method, despite being environmentally cleaner, is associated with prolonged activation times, lower production yields, and higher costs [10]. Conversely, chemical activation is typically favored due to its simpler process and more effective activation outcomes [9].

Aluminum chloride , potassium hydroxide , sodium hydroxide , phosphoric acid , and other activating agents are commonly employed in activated carbon production due to their benefits, such as low heating temperatures, short processing times, high carbon yields, precise pore control, and increased surface areas [11]. The most popular activating agent among them for the production of activated carbon is the alkali ZnCl 2 . When it comes to raw materials, ZnCl 2 is a more effective dehydrating agent than carbonized materials, which have lost water and volatiles during the carbonization process. [12].

The efficiency of activated carbon in eliminating contaminants from contaminated water has been recognized [13], but the absorption ability of activated carbon under UV light has not been widely studied. Velo-Gala et al. (2013) when exposed to UV light, activated carbon exhibits photoactive and semiconductor properties [14]. On the other hand, Cruz et al, (2017) mentioned that producing composite materials with combined or synergistic features like high surface area, mechanical strength, thermostability and insolubility, antibacterial capacity, and photocatalytic properties will be possible by growing semiconductors onto activated carbon [2].

The semiconductor that is often trusted to be used in various applications including water treatment is ZnO nanoparticles with the advantages of low price, wide band gap of 3.37 EV , high stability, environmentally friendly, and reusable [5]. However, due to the size and weak compatibility of ZnO causing aggregation and one of its lack is the low charge separation efficiency [15]. Many studies have described strategies to lower the rate of electron recombination in ZnO in order to boost its photocatalytic activity recently [16]. It has been claimed that the element C found in activated carbon lowers the band gap energy of semiconductors with large band gaps. ZnO will produce intermediate energy levels in its band gap when C is added, which will lower the material's absorption energy [17]. Thus, incorporating C on ZnO has the dual application of lowering the electron-hole recombination rate and restricting the band gap energy, which in turn causes ZnO's photo-response to shift from the UV to the visible area [18].

Materials and Procedure

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Material and Experimental Set Up

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In pretreatment for activated carbon synthesis, purity of ethanol as waste paper cleaner. The precursor solutions used were zinc chloride (E. Merc, D-7646 Darmstadt FR Germany), zinc acetate dihydrate (E. Merck, D-5970 Darmstadt, FR Germany) and the substance determined as the pollutant was methylene blue .

For the synthesis of activated carbon, chemical activation was taken as a single process where carbonization and activation were carried out at the same time. Waste paper that has been pre-treated using ethanol and water is impregnated using as a chemical activator at a ratio of and dehydrated in an oven at for 5 hours. The pyrolysis process starts by placing the material in a pyrolysis reactor (ceramic boat) which will be inserted into a tubular furnace as a place to burn at for 1 hour under an gas flow rate of . The use of is necessary to maintain an inert atmosphere during pyrolysis and help equalize the formation of activated carbon pores. The activated carbon that has been produced is washed using 0.1 M HCl and water until the pH is neutral, then drying for 24 hours at in an oven. In this study, the yield of activated carbon derived from waste paper was .

Fig. 1. Schematic representation of the synthesis of activated carbon using furnace pyrolysis method

Fig. 1. Schematic representation of the synthesis of activated carbon using furnace pyrolysis method

ZnO NPs were prepared from zinc acetate in 100 ml proportions of 0.01 ; 0.05 ; and 0.1 M , respectively. The solvent used to dilute the zinc acetate solid was distilled water while the solution chosen to adjust the pH to was sodium hydroxide grams of activated carbon were added to the solution and thoroughly mixed. The mixture was then homogenized for 2 hours while being vigorously stirred, and it was dried for eighteen hours at .

Methylene Blue Degradation Experiments

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The photocatalytic analysis was conducted under one predetermined condition, i.e. enclosed room and without light and only given ultraviolet (UV) light being used as an irradiation source. The UV lamp used was EVACO with specifications of T8 with a maximum intensity of 1190 lux. Before the photocatalytic treatment started, stirring was carried out at 250 rpm for 30 minutes to achieve adsorption-desorption equilibrium conditions. The conquest time of photocatalyst to methylene blue solution lasted at 15-75 minutes with constant stirring. A centrifuge (One Med ) at for 3 min was used to separate the supernatant from the solid at each analysis interval ( 15 min ). The absorbance was measured using a UV-Vis spectrophotometer at 665 nm [19] for methylene blue. Degradation methylen blue was estimated based on Eq. (1).

where and correspond to the initial concentration of MB and following radiation at a specific time ( t ), respectively. The dye concentration ( ) is represented by in the MB standard linear regression eq. (2), and the absorbance is represented by .

Material Characterization Methods

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Utilizing a scanning electron microscope (SEM) (FlexSEM1000, Hitachi High Technologies, Tokyo, Japan), the microstructure of activated carbon derived from waste paper was examined. Using energy dispersive spectroscopy (EDS)-equipped scanning electron microscopy, the composition of various elements on the surface of the adsorbent was determined. The Philip XPERT MPD, manufactured by Philips and located in Almelo, The Netherlands, uses X-ray diffraction to obtain information about the crystalline structure of the sample. Using the Scherrer equation on Eq. (3), the X-ray line broadening method was used to calculate the material's crystal size (D).

Where is the Scherrer constant which has the number is the X-Ray wavelength which has a value of is full width half maximum (FWHM) which is the maximum width of the peak at the total height of the peak and is the angle bragg.

Thermo Scientic Nicolet IS10 Fourier-transform infrared spectroscopy was utilized to identify the functional groups in waste paper-based activated carbon. Tests using infrared spectroscopy were conducted between 500 and .

Results and Discussion

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Activated Carbon (AC) and AC/ZnO Characterization

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Fig. 1 represent a micrograph of the activated carbon made from waste paper, demonstrating the high porosity of the material. The use of is responsible for the high abundance of pores that are produced [3]. It is believed that catalyzes the aromatization and rearrangement reactions that result in the formation of carbon and significant amounts of and , which is created when and react, further encourages the synthesis of carbon, , and . A large number of pores form on the carbon as a result of the material being cracked by at and the release of small molecular gases like and [11].

ZnO is produced during the pyrolysis process by the chemical activator [2]. It was discovered that the resultant ZnO resembled flowers. The zinc chloride solvent was found to be the chemical activator for this flower-like shape, and zinc acetate dissolved in distilled water was found to be the precursor of ZnO nanoparticles in the amounts of , and 0.1 M [20].

Fig. 2. SEM of activated carbon and doping ZnO (a.1, a.2) activated carbon (b.1, b2)

Fig. 2. SEM of activated carbon and doping ZnO (a.1, a.2) activated carbon (b.1, b2)

Fig. 3. SEM-EDS a) AC/ZnO 0.01 M , b) , and c)

Fig. 3. SEM-EDS a) AC/ZnO 0.01 M , b) , and c)

In Fig. 2, there is the element Cl in a low weight percent ranging from , indicating that Cl trapped in the carbon pores. Other elements such as Cr and Fe are among the elements found in ink or pen ink while the paper contains Si and Al . These elements have much weaker weight percent values or spectral peaks so as not to consider the presence of these elements in the activated carboncomposite examined [21]. Despite the fact that ink and other additives were eliminated from the waste paper prior to the carbonization stage, this may have happened because the ink layer's locally variable thickness is dependent on the pressure and speed used when writing or printing [21].

In each concentration of doping, it is known that contains the largest C of . Meanwhile, the concentrations of 0.05 M and 0.1 M have similar weight percentages of and . Comparably, the presence of zinc increased from to when the concentration of zinc acetate was raised from 0.01 M to 0.05 M . However, there was a minor drop in weight percent (48.08%) when the precursor concentration was increased by 0.1 M . If the impregnation process is carried out for two hours, with an estimated lack of maximum time given to occupy the pores of activated carbon, so that it is not perfectly impregnated, zinc loss as the precursor increases. The pH setting that is being used may also have other effects. The amount of or ions in the sol has a significant impact on the shape of metal oxide nanoparticles produced by sol-gel synthesis. During the ZnO growth process, these ions control the polymerization of metal-oxygen bonds [22].

In order to investigate the properties of AC and AC/ZnO further, XRD analysis revealed that the activated carbon obtained from waste paper was amorphous and had been effectively doped with ZnO nanoparticles. It is known that the activated carbon generated contains ZnO from the chemical activator used, namely , based on the XRD data in Fig. 4. A reaction occurs between and water resulting from thermal cutting of sellulose molecules which occurs at temperatures of . In a study conducted by Ma , et al. (2015), this reaction occurred at a temperature of which was indicated by the appearance of the compound identified by the sharp peak
of XRD at is and detected ZnO peak at between to followed up to , this indicates the decomposition of that can occur further when the temperature is increased to , where the evaporation of occurs with the following reaction taking place on eq. (4) and (5).

Fig. 4. Crystal phases on each variabel and JCPDS reference (036-1451)

Fig. 4. Crystal phases on each variabel and JCPDS reference (036-1451)

Table 1. Calculation results ZnO crystal diameter

Name | Crystal Diameter (nm)
Activated Carbon (AC) | 19.5711
AC/ZnO 0.01 M | 36.8390
AC/ZnO 0.05 M | 29.5939
AC/ZnO 0.1 M | 27.9779

The hexagonal wurtzite ( ) shape of the ZnO particles obtained is evident from the diffraction peak data of each variable on Fig. 4, and this is the most thermodynamically stable phase of ZnO [23]. And from Table 1, it is known that activated carbon has the smallest ZnO crystal diameter compared to activated carbon doped with ZnO from zinc acetate precursor. The small crystal size results in a wide diffraction peak in this method. The width of the diffraction peak is affected by microstrain (lattice strain), which is the effect of the displacement of a unit cell around its normal position which can be caused by several things such as: (1) Non-uniform lattice distortion, which can result from nanocrystal surface tension, crystal shape morphology, and interstitial impurities. (2) Dislocations, (3) Inter-phase domain boundaries formed during the preparation of material structures that are subjected to preparation transformation disturbances [24].

The functional groups of activated carbon were studied from the results of analysis using fourier transform infrared (FTIR). The O-H stretching vibrations of carboxylic acids correspond to the broad band at about . Due to the atmosphere used during the carbonization process, the peak near may be related to bending vibrations or bending vibrations. It also corresponds to the aromatic structure. The broad band at in the fingerprint area represents the stretching of cellulose and hemicellulose. The ester ether ring's symmetry vibration is represented by the peak at . The broad band at corresponds to a bend, while the peak at indicates and . This suggests that the waste paperbased adsorbent's surface has a large number of functional groups.

Fig. 5. FTIR of activated carbon based waste paper

Fig. 5. FTIR of activated carbon based waste paper

Photocatalytic Activity

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The synergistic effect, which combines an adsorbent and a photocatalyst, is a viable and effective method for eliminating pollutants from wastewater. When photonic energy radiation (hv) that is equal to or greater than the ZnO band gap is applied to the ZnO surface, the photocatalytic process starts [25]. Reactive species, like and , are produced when visible or UV light interacts with catalysis. These species can then interact with organic pollutants to initiate the degradation process [26]. In our earlier study, the mechanism of photocatalytic activity was thoroughly explained [23].

One of the most effective methods is MB photodegradation since MB can also act as a photocatalyst sensitizer. Irradiation time, light intensity source, and MB concentration are factors that can affect MB photodegradation [27]. Fig. 6(c), shows that perfectly degraded 15 of MB at 75 min . As for the adsorption-desorption, there was a very significant increase in the degradation rate within -30 min before irradiation. This indicates that ZnO formed from the pyrolysis and doping process plays a role in the MB degradation process in the absence of light. As the irradiation time increases, the rate of degradation will also increase. As the reaction time increases, the absorption peak progressively diminishes. The dye initially shifts from dark to bright, increases progressively with longer exposure times, and eventually becomes consistent.

The photocatalytic performance of 0.05 M and at was comparable to activated carbon. Further investigation is necessary to see the influence or differences between each particle, and the results indicate that performs better than the others, but AC catches up rather rapidly at 45 and 30 minutes with a degradation efficiency of and . This demonstrates that the surface area of activated carbon is greater than that of the combination. Its ability to adsorb MB will be impacted when the additional concentration of zno is raised because the carbon surface's active adsorption sites would decrease [2].

Fig. 6. AC and Methylene Blue Degradation Efficiency (MDE) with varying proportions (a) , (b) , and (c)

Fig. 6. AC and Methylene Blue Degradation Efficiency (MDE) with varying proportions (a) , (b) , and (c)

Summary

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Activated carbon was successfully made from waste paper in a single process that required an hour at a pyrolysis temperature. ZnO at concentrations of , and 0.1 M was synthesized from zinc acetate to conduct adsorption and photocatalytic tests. The resultant ZnO nanoparticles resembled flowers in shape. Various adsorbent loadings were used to test photocatalytic activity both with and without UV light irradiation. When methylene blue was used as a pollutant, the adsorbentcomposite's photocatalytic activity led to its complete degradation by , but for other particle mass concentration, it demonstrated how activated carbon can hinder ZnO 's ability to block UV light.

Acknowledgment

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With contract number 084/E5/PG.02.00.PT/2023, the writers would like to express their gratitude to DRPM Kementrian Pendidikan, Kebudayaan, Riset dan Teknologi Indonesia.

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The original version of this eBook is available on https://www.scientific.net/book/engineering-chemistry-vol-7/978-3-0364-1605-2

Engineering Chemistry, ISSN: 2813-6535, Vol. 7, pp 89-98

doi: 10.4028/p-GI7wfs

© 2024 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2023-12-02

Revised:
2023-12-25

Accepted:
2023-12-29

Online:
2024-06-26

Highly Porous Ni Electrode Decorated with for Oxygen Evolution Reaction (OER)

The original version of this paper is available on https://www.scientific.net/EC.7.89.pdf

Bayu Satriya Wardhana , Sheng-Wei Lee , Shian-Ching Jang

Department of Mechanical Engineering, Brawijaya University, Malang City, 65145, Indonesia

Institute of Material Science and Engineering, National Central University, Taoyuan City, 32001

Taiwan, ROC

Department of Chemical and Material Engineering, National Central University, Taoyuan City, 32001, Taiwan, ROC

4Department of Mechanical Engineering, National Central University, Taoyuan City, 32001

Taiwan, ROC

wardhanabayu@ub.ac.id, swlee@g.ncu.edu.tw, jscjang@ncu.edu.tw

Abstract

Hydrogen is an environmentally friendly energy source that can be extracted from water through electrolysis. However, the slow oxygen evolution reaction (OER) at the anode side is the main obstacle to the widespread use of water-splitting devices. This study used self-developed highly porous nickel structures(SMNF) and commercial nickel foam(CNF) as working electrodes in the electrolysis process. Iron(II, III) Oxide ( ) as a catalyst is coated with a dip coating technique on the Ni porous structure and then calcined using a laser process to produce a -based electrode. Electrochemical test results show that the presence of significantly impacts high reaction kinetics. The SMNF- demonstrated an overpotential of 217.3 mV at 1 M KOH electrolyte, at a current density of 10 mA , lower to SMNF electrode without with an overpotential of 361.4 mV under the same conditions. In addition, the difference in porosity less significantly affects the electrode's effectiveness due to the slight difference in mass loading, which is only . However, electro-impedance spectroscopy(EIS) testing shows better performance on SMNF-Fe with a smaller electrical series resistance (ESR), around , compared to , which is . Overall, observations by chronoamperometry test at an overpotential of 155 mV at 5 hrs show stable performance of SMNF- electrodes.

Introduction

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Hydrogen is a clean energy source that has become increasingly popular in recent years and is expected to be used as an alternative to fossil fuels [1]. Up to of all hydrogen produced is "grey hydrogen," which is produced by the cracking of non-renewable fossil fuels and high carbon emissions [2], [3]. On the other hand, "green hydrogen," or hydrogen produced with a low residual carbon by electrolysis, accounts for just around [3]. This fact occurs for efficiency reasons [4], [5], so increasing the efficiency of producing hydrogen through electrolysis is essential to raising the percentage of "green hydrogen" [6]. To raise green hydrogen production, electrodes with high electrocatalytic activity and economical price are essential in water-splitting. One of the main problems with water electrolysis is that the anode's oxygen evolution reaction (OER) is sluggish [7]. The OER consists of four steps, with one electron connected every step, whereas the hydrogen evolution reaction (HER) is more simply processed with a two-electron-transfer reaction. Consequently, the OER typically demonstrates slow kinetics and requires a bigger overpotential than the HER [8]. Therefore, one of the main goals in research in developing water-splitting devices is to develop and investigate electrodes with high-performance OER, which can increase efficiency.
According to the findings of several studies [8], the characteristics listed below must be possessed by an effective catalyst for the OER process: 1) low cost and earth abundance; 2) no environmental pollution; 3) excellent performance comparable to noble metal-based materials; 4) superior durability and long-term stability; 5) good conductivity; and 6) ease of shape-controlled synthesis. Nickel-based
electrocatalysts are a cheap and effective option for water electrolysis [9], [10]. They are stable and work well as electrocatalysts for HER and OER. [11]. Nickel exhibits favourable characteristics as an electrocatalyst due to its notable attributes, including elevated conductivity, thermal stability, and commendable electrical qualities [12]. Typically, nickel (Ni) exists as a divalent cation, although it can adopt various valences within the range of -1 to +4 [13]. This characteristic enables it to undergo a range of electronic transitions. In order to enhance the electrocatalytic performance of nickel materials, it is crucial to manipulate their chemical environment, structure, and morphology carefully [14], [15]. Several factors influence an electrocatalyst's effectiveness in water electrolysis, including its chemical composition, surface chemistry, crystalline structure, porosity, size distribution, and electrical conductivity [13]. As a result, a significant amount of research has been conducted on the development of electrocatalysts based on nickel for water electrolysis. Porous catalysts can be created using a high porous structure to improve active site exposure to electrolytes.
The presence of iron (II, III) oxide ( ) to form NiFe-based materials is one of the most promising OER catalysts due to their availability and high intrinsic activity [8], [16]. Koper and his colleagues conducted a comprehensive theoretical and experimental investigation to investigate the possible relationship between the activities of nickel-based double hydroxides toward oxygen evolution and the natures of the transition metals that were added to alkaline environments [17]. According to their findings, Mn and Fe have almost ideal binding energies, which lowers the predicted OER overpotential. Furthermore, Ni-Fe-based electrocatalysts have several advantages such as high activity and stability, tuning the electronic structure, cheap, and facilitating gas evolution [10]. Motivated by the previous achievements of -oxide electrocatalysts, which demonstrate stability and capability for water splitting process in an alkaline environment [18], we developed a highperformance and low-cost Ni porous structure with surface-decorated particle electrodes. Laser calcination with low power is used to deposit particles over the porous structure of Ni . The large porosity of the Ni structure is expected to maximize the loading of so that the area for electrochemical activity increases and improves the OER performance.

Experimental Section

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The research began by producing highly porous structures from nickel powder as described in schematic Fig.1. Self-manufactured nickel foam (SMNF) is produced by pressing Ni powder in the hydraulic cylinder with 6-ton force in 3 cm diameter dies. After this process, the green body was sintered in an environment at for 2 hrs to avoid oxidation, then cut the specimen into 2 cm x 1 cm large. This research also uses commercial Ni foam with a porosity of as a comparison to determine the tendency of porosity to electrochemical performance.
Fig. 2 shows the electrocatalyst fabrication process, which is started by immersing a 1 cm highly porous nickel area in solution for one hour. The solution was created by mixing deionized water with , maintained at and stirred at constant speed at 400 rpm for 30 minutes. The sample was dried in a vacuum oven at and ready for laser calcination. This research uses a low-power laser of 1 watts at an 18.5 cm distance and a 20 times/cycle scanning rate to keep the surface from overheating. The vacuum chamber is kept at 5.7 x bar to avoid contamination. Weighing is done on the sample before and after dip coating and after the laser calcination to get an overview of the mass loading of the oxide material over a nickel porous structure.

Fig. 1. Schematic picture of SMNF manufacturing

Fig. 1. Schematic picture of SMNF manufacturing

Fig. 2. Schematic picture of electrode manufacturing

Fig. 2. Schematic picture of electrode manufacturing

The phase analysis of NF- electrocatalyst was determined using an X-ray diffractometer (XRD, Bruker, D8A) with monochromatic radiation and a diffraction angle of to . In this research, we optimized the XRD result from our previous study, which uses the same method (laser calcination) to deposit active High Entropy Oxide (HEO) materials on nickel foam for supercapacitor applications[19]. To evaluate the application potential of electrodes in alkaline electrolyzers, a BioLogic Electrochemical Workstation SP-150 performed electrochemical tests with a sample in a high-concentration electrolyte at room temperature. The test was carried out with a three-electrode system with as the working electrode, while and Pt were used as reference and counter electrodes, respectively. A constant voltage (CV) test with a scan rate of and linear sweep voltammetry (LSV) with scanning rates of was employed to measure the complete polarisation curves of the oxygen evolution reaction (OER). The potential window for the CV test was between and , while for the LSV, it was between and vs , as used by several previous studies [8]. Tafel plots are then made based on the LSV test results to determine how sensitive the current response is to overpotential and provide information on the reaction mechanism and rate-limiting steps. The following equation (Eq. 1) calculates the electrochemical surface area (ECSA) based on double layer capacitance methods:

ECSA Double layer capacitance Specific capacitance

The double-layer capacitance (CdI) value is obtained from the anodic slope on the scan rate vs current density plot, while the specific capacitance ( ) is calculated via the CV curve through the Eq. (2):

A is the area under the I-V curve, k is the scan rate ( ), m is an active mass of oxide material , and is a potential window . In addition, for double-layer capacitance measurements, we set the potential window to a width of 0.1 mV , namely between and 0.477 , in order to obtain a CV response without a Faradaic reaction at the electrode-electrolyte, so that a more precise
measurement is obtained [12]. However, in actual observations, we had difficulty calculating the specific capacitance value precisely because the response of the measurements was inconsistent. McCrory et al. reported in their benchmarking publications that the values for different metal catalysts varied between 0.022 and in alkaline solutions [20]. This report uses most often the value of the about , as used by several research studies [20], [21].

Result and Discussion

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1. Characterization ofElectrocatalyst

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Fig. 3 shows the XRD results of laser calcination of the HEO element over the SMNF structure. We can find a sharp peak (shown with the star symbol) at about , and can be indexed as (220), (222), (400), and (551) planes. These diffraction peaks were identified as pure phases (JCPDS card no. 01-071-6336)[22]. The triangle symbol indicates the spinel structure of according to JCPDS card no. 10-0319. It belongs to a space group of Fd-3m with cell parameter . Other structures indicated by a dot symbol are identified as spinel structures of according to JCPDS card no. 75-0765[24]. The presence of Mn in the XRD results is understandable because, in our previous studies, MnO was one of the dominant elements in HEO . After all, it has good capacitive properties, making it suitable for supercapacitor applications.

Fig. 3. XRD result of electrode

Fig. 3. XRD result of electrode

Fig. 4 shows the observations on the porous nickel foam with an optical microscope at low magnifications. Visually, it can be seen that CNF has a rougher surface compared to SMNF, as seen in Fig. 4(a). Observation using optical microscopy shows striking differences in the pore sizes of the electrodes used in this study. The SMNF structure shows uniform porosity with a smaller pore size than the CNF structure. From measurements carried out, CNF has an average porosity of ca. (Fig. 4.b), while SMNF has an average porosity of ca. (Fig. 4.c). This difference in porosity shows that at the same area , the SMNF structure has a much larger active surface area, so it has an excellent opportunity to bind the particle as an active material.
Further investigation shows that the SMNF structure has many isolated/closed pores (Fig. 5). These pores allow the solution to have difficulty accessing the structure below the surface and during electrochemical tests, where it will be difficult for the electrolyte to reach parts below the surface. However, in Table 1, we can see that the increase of active material mass due to the differences in porosity is not too significant (less than 5 mg ). This fact shows that extensive access to the surface area does not guarantee that the oxide solution can stick optimally to the electrode surface. This incident was possible due to several factors apart from the porosity factor, including (1) the binder
not being used in the coated oxide solution, (2) an inappropriate molar solution, and (3) the electrode surface being hydrophobic. Overall, there is still an opportunity to prove the effect of porosity on performance by improving the pores' structure and manufacturing parameters.

Fig. 4. Optical Microscope of Ni porous structure

Fig. 4. Optical Microscope of Ni porous structure

Fig. 5. SEM image of SMNF structure
Table 1. Sample weight during manufacturing

Sample name
Before
Dip Coate
(mg)
After
Laser Calcination
(mg)
Mass
Loading
(mg)

CNF-Fe₃O₄
232.3
236.0
3.7

SMNF-Fe₃O₄
445.8
451.8
6.0

2. Electrochemical performance for

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Fig. 6(a) shows the CV curve of the SMNF and CNF electrodes, with and without . All CV curves have a quasi-rectangular shape, with very sharp edges, without redox peaks, and a shape that tends to be symmetrical and exhibits good electrochemical reversibility. The presence of the element makes the peak current density higher than electrodes without additional active material, as seen from the response curve, which shifts upwards at the tip. The curves on electrodes with additional active material are similar, meaning the electrodes have similar electrocatalytic properties. In addition, the interaction between Ni and Fe is essential to increase OER activity. According to Chai et al.[25], Fe doping encourages the chemisorption of oxygen-containing intermediates, which raises OER activity. While according to Boettcher et al.[26], Fe activates Ni centres by inducing a partial charge-transfer process.
Fig. 6(b) demonstrates the linear sweep voltammetry (LSV) test at the scan rate value of . From this figure, we can see that LSV curves show that the SMNF-Fe electrodes in the 1 M KOH electrolyte solution achieve an overpotential of about 271 mV at a current density of ,
lower than the SMNF electrode without catalyst overpotential with 361.4 mV , and become superior to the other electrode used in this research. However, the results are comparable to similar research that utilized alloy as an electrode in the water separation process [11], [18]. In addition, the influence of the material's porosity, which is expected to provide the maximum effect due to an enormous surface area, is less pronounced because the difference in mass loading is too small (less than 5 mg ). The low absorption of the SMNF structure towards metal oxide is possible because some of its structures tend to be closed pores/dead pores, as can be seen in the SEM test results in Fig. 5, which means that the metal oxide solution is less able to reach the inside of the structure [27].

Fig. 6. Electrochemical analysis of based electrode; (a) CV curve at the scan rate value of , (b) LSV curve at the scan rate value of , (c) Tafel plot of electrode SMNF- , (d) CdI graph of the SMNF- electrode, (e) EIS comparison of and electrode, (f) Chronopotentioamperometry of electrode.

Fig. 6. Electrochemical analysis of based electrode; (a) CV curve at the scan rate value of , (b) LSV curve at the scan rate value of , (c) Tafel plot of electrode SMNF- , (d) CdI graph of the SMNF- electrode, (e) EIS comparison of and electrode, (f) Chronopotentioamperometry of electrode.

Fig. 6(c) shows the Tafel plot results from LSV data processing. In line with the LSV results, the Tafel plot also shows that the influence of is more significant than the porosity itself. Without adding the metal oxide, CNF and SMNF show the overpotential of and , respectively, at the log current density of about 1 mA . The closeness of the curve positions on the CNF and SMNF electrodes shows that these two electrodes have similar chemical reactions. This close position also occurs in electrodes with the addition of active materials that have similar behaviour. Adding metal oxide as a catalyst shifted the overpotential to and for the CNF and SMNF, respectively. Changes in the reaction before and after adding are the main trigger for changes in reaction kinetics in redox reactions [8].
To analyze the effect of the active surface area in electrolysis (especially in the OER process), the theoretical active surface area (ECSA) is calculated using a double-layer capacitance (CdI) plot, as shown in Fig. 6(d). This calculation is only carried out on the electrode , which performs best. These results are then used to display the anodic and cathodic currents logarithmically and then to estimate the size of the area contributing to the reaction by comparing it with the specific capacitance. In this plot model, only anodic current was used in this study because only OER that occurred at the anode was calculated. As mentioned in the experimental section, this research accommodates the value of specific capacitance about , according to Connor's finding [21]. The results of measurements on the electrode show a slope of 0.076 mF with an ECSA value of approximately , slightly better than other research work on commercial nickel foam structures with an ECSA of . This small surface area shows that efforts to maximize the surface area still have an excellent opportunity to increase the efficiency of separating from .
To complete the study of the impact of differences in SMNF and CNF porosity along with the effect of active mass loading on electrode performance, electro-impedance spectroscopy(EIS) testing was carried out on both, as depicted in Fig. 6(e). In general, there is no significant difference in the results of the impedance spectroscopy test. The spectroscopy curve shows a minuscule semicircle shape with a 45-degree line, which indicates the cell type where polarization is due to a mix of kinetic and diffusion processes [29]. The three-electrode test was modelled as a Randle circuit with ( ) to measure the outcomes of the impedance spectroscopy measurement. The or solution resistance, or in some literature also known as electrical series resistance (ESR), represents the total internal resistance of the system/cell, the CdI represents the double-layer capacitance effect, the describes the value of charge transfer resistance between the electrodes and the solution interface, and the W represents the Warburg impedance, which represents the ion diffusion resistance. From this graph, we can see significant differences in impedance between the and electrodes. Graph measurements with the help of Z fit software show that in SMNF- is about , lower than at around . This fact shows that electrode with higher active surface area performs better in electrocatalyst application than commercial nickel foam.
Furthermore, the inserted picture in Fig. 6(e) shows the different values of in both porous structures, which is indicated by the diameter of curves in high frequency. electrode shows higher with than with . The charge transfer resistance value for both structures is small, which indicates that the structure has good electrical contact and conductivity, which is suitable for the water-splitting process[25]. For the last part, Fig. 6(f) shows the SMNF- electrode stability test results at an overpotential of 115 mV for 5 hours. The results are encouraging, as the current density response is stable at . Even though the voltage applied in the electrode stability test is still far below for commercial applications (usually ) [11], the electrode's good response shows that the laser calcination technique is quite good and reliable for calcining metal oxide on Ni porous structures. This good electrode response dismisses concerns because, in several previous reports [7], the coating technique could not provide stability when applying Fe oxide to the porous Ni structure. However, we can understand that the results are still not as good as when using the alloy technique, which chemically combines Ni and Fe elements. On the other hand, adding binder in the dip coating process must be considered to form a strong bond between the porous Ni substrate and the catalyst.

Conclusion

The original version of this paper is available on https://www.scientific.net/EC.7.89.pdf

Self-manufactured nickel foam has a larger electrochemical surface area than commercial nickel foam. This large surface area can directly increase the mass loading of active material, and the redox process runs more optimally. However, in this research, the structure does not have a significant effect due to minimum active mass loading differences ( ). This low effect is caused by closed pores in porous structures, which limit access for metal oxide catalyst to bind with Ni substrate and electrolyte access during performance tests.

By previous estimates, the presence of catalyst brings quite significant changes in the properties of the Ni electrode. Adding decreases the overpotential on the OER from 361.4 mV to 217.3 mV in 1 M KOH at a current density value of 10 mA . Observations by chronoamperometry test at an overpotential of 155 mV at 5 hours show the stable performance of electrodes, which shows that the laser calcination technique has promising opportunities for thin coating processes.

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The original version of this paper is available on https://www.scientific.net/EC.7.89.pdf

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Keywords Index

A

Ac/zno Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Activated Carbon Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Activated Charcoal Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

Adsorbent Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

Adsorption Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

B

Bioceramic Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

Biodegradability Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Biodiesel Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

Biomaterial Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

C

Carbonate Hydroxyapatite Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

Cellulose Aerogel Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material; Bilayer Solar Steam Generator by Co-Gelation Method

Co-gelation Bilayer Solar Steam Generator by Co-Gelation Method

Coir Fiber Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

I

Inhibitor Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

K

Ketapang Seed Outer Shell Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

L

Lasienthera Africanum Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Lead Metal Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

M

Magnetite Bilayer Solar Steam Generator by Co-Gelation Method

Methylene Blue Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Model Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

O

Optimization Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

P

Photocatalyst Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Phytochemicals Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

S

Solar Steam Generator Bilayer Solar Steam Generator by Co-Gelation Method

Solid Acid Catalyst Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

Synthesis Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

W

Waste Paper Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Authors Index

A

Adekanmi, D. Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

Ambarwati, R. Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

C

Chika, C. Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

F

Firyanto, R. Utilization of Ketapang Seed Shells in Reducing Metal Levels by Adsorption Process

G

Garcia, C. Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

H

Harmami, H. Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

J

Jang, J. Highly Porous Ni Electrode Decorated with for Oxygen Evolution Reaction (OER)

Juliananda, J. Bilayer Solar Steam Generator by Co-Gelation Method

K

Kusdianto, K. Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

L

Laksono, S. Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

Lee, S. Highly Porous Ni Electrode Decorated with for Oxygen Evolution Reaction (OER)

Lopez-Badillo, C. Carbonate Hydroxyapatite - A Multifunctional Bioceramics with Non-Medical Applications

M

Madhania, S. Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Madurani, K. Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

N

Nurtono, T. Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material; Bilayer Solar Steam Generator by Co-Gelation Method

Nwaeju, C. Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

O

Obaseki, M. Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Ofuyekpone, O. Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Ogagavwodia, E. Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

Okuma, S. Response Optimisation and Modelling of Experimental Data on the Performance of Lasienthera africanum Leaves Extract as a Corrosion Inhibitor on Mild Steel in Hydrochloric-Induced Environment

P

Pamuji, A. Bilayer Solar Steam Generator by Co-Gelation Method

R

Ramadhan, B. Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

Rozy, M. Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

S

Setyawan, H. Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material; Bilayer Solar Steam Generator by Co-Gelation Method

Suryandari, A. Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material

U

Ulfin, I. Utilization of Adsorbent Based on Rice Straw (Oryza Sativa) for Cr(VI) Ions Reduction in Aqueous Solutions

W

Wardah, J. Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications

Wardhana, B. Highly Porous Ni Electrode Decorated with for Oxygen Evolution Reaction (OER)

Widiyastuti, W. Effect of Sulfonating Agent on Esterification Reaction Using Aerogel Carbon Based Support Material; Bilayer Solar Steam Generator by Co-Gelation Method

Winardi, S. Effect of Doping ZnO on Activated Carbon Prepared from Waste Paper for Photocatalytic Applications