Papers by Keyword: Hydrothermal Process

Abstract: Zeolites being used as builders in detergents are synthesized from expensive chemicals with a cumbersome production process. In this study, zeolite was synthesized from cheaper and readily available kaolin for possible use in detergent production. Kaolin from two sources namely Ajebo, Ogun State and Darazo, Bauchi State, Nigeria was used as starting materials while wet beneficiation followed by acid leaching was used to purify the kaolin and hydrothermal process was used to synthesize the zeolite. The chemical analysis confirms the presence of silica and alumina which are the precursors materials for zeolite synthesis. An increase in the amounts of the desired silica and alumina for both kaolin accompanied by a reduction in the amounts of the undesired oxides present in the kaolin as impurities are clear indications that the acid leaching was successful. The zeolites synthesized from both kaolin shows better water adsorption capacity and ion exchange capacity compared to those reported for zeolite synthesized from pure chemicals, this ability makes zeolite more suitable for the production of detergent. These results are indications that zeolites synthesized from kaolin can serve as a possible replacement for the more expensive zeolite synthesized from chemicals used as builders in detergent production.

Abstract: Lead-free ferroelectric materials of sodium-potassium bismuth titanate, (1-x)NBT-xKBT systems were synthesized by a hydrothermal process. In this way, the appropriate conditions for the hydrothermal synthesis of NBT and KBT (i.e., concentrations of synthetic precursors, solution pH and temperature) are given graphically. Ceramics of (1-x)NBT-xKBT with (x(mol.%) = 0; 12; 16; 20; 30 and 100) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The rhombohedral-tetragonal morphotropic phase boundary (MPB) was confirmed to be in the region of 0.12 ≤ x ≤ 0.20 for (1-x)NBT-xKBT at ambient temperature. Scherrer's formula and the Williamson-Hall (W-H) analysis were used to examine the average crystallite size and lattice strain. Raman spectroscopy was effectively applied to study the structural evolution of the (1-x)NBT-xKBT phase. The ceramics exhibited a high temperature of maximum dielectric permittivity at (Tmax = 343 °C at 100 kHz) along with electromechanical coupling factors (kp = 0.34, d33 = 147 pC/N). Based on the composition of all specimens, the results indicate a diffuse phase transition, probably of second order, between ferroelectric and paraelectric phases.

Abstract: The present study investigates the effect of different reaction times on the crystallinity, surface morphology and size of iron oxide nanoparticles. In this synthetic system, aqueous iron (III) nitrate (Fe (NO₃)₃·9H₂O) nonahydrate, provided the iron source and triethylamine was the precipitant and alkaline agent. The as-synthesised iron oxide nanoparticles were characterised by X-ray diffraction (XRD), Rietveld analysis, Scanning Electron Microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Prolonged reaction times indicated the change on nanoparticle shape from elongated nanorods to finally distorted nanocubes. Analysis on the crystallinity of the iron oxide nanoparticles suggest that the samples mainly consist of two phases, which are Goethite (α-FeOOH) and Hematite (α-Fe₂O₃) respectively.

Abstract: A hydrothermal process was proposed to prepare BiVO₄/ diatomite composite photocatalysts, where BiVO₄ was grown from a precursor solution containing diatomite, and EDTA used as a chelating agent to prevent the precipitation of precursor solution compositions on diatomite before hydrothermal treatment. The effect of some processing parameters like diatomite percentage and Ag-loaded amount on their photocatalytic performance were also investigated in detail by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET, and UV‐Vis spectroscopy. The results show that BiVO₄/ diatomite composite photocatalysts can be successfully prepared at 160 °C for the duration of 3h by the hydrothermal process. The diatomite has two significant impacts on their photocatalytic performance: (1) enhancing the dispersion of BiVO₄ crystallites due to its high porosity and specific surface area to favor their photocatalytic performance, and (2) having a light screening effect to incident visible light to decrease their photocatalytic activity. Appropriately incorporating diatomite could improve their photocatalytic performance, but the overuse of diatomite would reduce that. Similarly, depositing Ag could effectively improve their photocatalytic activity because of its good light absorption and photosensitive characteristics, but excessive addition would result in their decrease since the overuse of Ag would also promote the electron-hole recombination.

Abstract: Nickel cobaltite has become a popular energy storage material in recent years for high performance energy storage devices because of its low lost, high electronic conductivity, high electrochemical activity and environmental benignity. Nickel cobaltite (NCO)/porous graphene nanosheets network (PG) composites were synthesized via the two-steps hydrothermal method to enhance electrochemical properties in this study. The NCO/PG composite electrode demonstrated high specific capacitance of 3965 F g^-1 at the current density of 1 A g^-1 compared with the value of NCO that capacitance is 644 F g^-1, and it maintained the 72% of the original capacitance after 3,000 charge-discharge cycles. It showed the maximum energy density of 46.3 Wh kg^-1 and maximum power density of 1450 W kg^-1. The NCO/GO composite has high potential as a psudocapacitance material for energy storage devices.

Abstract: Hydrogarnet Ba₃In₂(OH)₁₂ was synthesized by hydrothermal method from raw materials Ba(NO₃)₂ and In(OH)₃. The obtained sample was characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS) and N₂ adsorption-desorption isotherms (BET). Photocatalyitc activity was tested via rhodamine B(RhB) degradation as the modle pollutant. The influence of hydrothermal reaction temperature (T), hydrothermal reaction time (t), Ba/In molar ratio(Ba/In), and NaOH concentration(C_g) on the photocatalytic activity of Ba₃In₂(OH)₁₂ were investigated. The results showed that the synthetic Ba₃In₂(OH)₁₂ exhibited highest photocatalytic activity under the optimum hydrothermal reaction conditions of T=200°C, t=14 h, Ba/In=2:1 and C_g=7 mol/L. RhB can be completely mineralized by Ba₃In₂(OH)₁₂ under 125 W mercury light irradiation for 3 hours. There are many scholars and experts engaged in the research of various types of photocatalytic materials and applied in the degradation of environmental pollutants in the last 40 years. Such as, the oxide of In₂O₃[1], ZnO, TiO₂ et al. The ternary oxide of indium, molybdate, tungstate and vanadate et al. New type quaternary metal oxide. In the past 20 years, indium-based semiconductor material were got rapid development in the field of display, laser, microwave devices, light-emitting diodes and photocatalyst because of which had good gas sensitivity, heat sensitivity, photosensitivity and other characteristics. CaIn₂O₄ was synthesized using self-propagating high-temperature sysnthesis method[2]. RhB can be absolutely mineralized under solar irradiation for 2 hours. The g-C₃N₄/CaIn₂O₄ composite was synthesized using facile solvothermal method[3]. The g-C₃N₄/CaIn₂O₄ composite reached a high H₂ evolution rate of 62.5 μmol/h from CH₃OH/ H₂O solution when the content of grapheme was 1wt%. Furthermore, the 1wt% g-C₃N₄/CaIn₂O₄ composite did not show deactivation for H₂ evolution for longer than 32 h. The core-shell like composite In₂O₃@Ba₂In₂O₅ was synthesized via chemical impregnation method with sample calcination[4]. It degraded 100% of the MB in 30 min compared with P-25, which degraded 100% of the MB in 120 min. C-CdIn₂O₄ nanoparticle was synthesized by sol-gel templating method[5]. Natural sunlight illumination experiments showed the H₂ evolution rate of C-CdIn₂O₄ was 17 μmol/h as compared to 2.1 μmol/h for the Pt:TiO₂. Hydrogarnet Ba₃In₂(OH)₁₂ was first described by Kwestroo et al in 1977, who used the prolonged refluxing of BaCl₂ and In₂O₃ in 12 mol/L NaOH at 110°C[6]. The pure Ba₃In₂(OH)₁₂ was prepared by first preparing pure Ba₃In₂O₆ by prolonged reaction of stoichiometric amounts of BaCO₃ and In₂O₃ at 1300 °C. Then, the pure Ba₃In₂O₆ was reacted with 12 mol/L NaOH at 85 °C for 12 hours under a pure nitrogen atmosphere[7]. Hydrogarnet Ba₃In₂(OH)₁₂ was synthesized by hydrothermal method, using In(OH)₃, Ba(NO₃)₂ and NaOH. With RhB as a model degradation pollutant, the influence of hydrothermal reaction temperature, hydrothermal reaction time, Ba/In molar ratio and NaOH concentration on the photocatalytic activity of Ba₃In₂(OH)₁₂ were investigated and the photocatalytic degradation mechanism of RhB were investigated. The results can provide references for the research and application of this material system in the future.

Abstract: F-doped ZnO nanorod structures were synthesized via hydrothermal process with variation of doping content starting from zinc nitrate solution and zinc oxide thin film used as seeding layer. The zinc oxide seeding film was fabricated by spin coating on glass substrate using zinc acetate precursor and annealed at 500 °C for 2 h. Relevant properties of ZnO:F nanorod structures were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and UV-VIS spectrophotometer. Corresponding results indicated that ZnO:F nanorod array, grown in (002) plane, has the characteristics of good crystallinity. In addition, this study showed that ZnO:F nanorod with exceptional structure can be obtained by hydrothermal process, operated at proper treatment time, temperature and F-doping content.

Abstract: Titanate nanowires were synthesised by hydrothermal process in 10M NaOH aqueous solution at 200oC for 24h. The samples were washed repeatedly in HCl aq. solution and deionized water until pH ~7. Subsequently, the samples were heat-treated at 400-850°C in air for 2h. The X-ray diffraction (XRD) analysis of the sample heat-treated at 800°C showed the crystalline structure of sodium titanate (Na₂Ti₆O₁₃ ), while the presence of anatase phase was detected from the sample heat-treated at 850°C. Wire-like morphology of the synthesized sample was observed using FE-SEM. The photocatalytic activity of the samples heat-treated at 600,800, 850°C and 900°C was investigated by measuring the degradation of methylene blue (MB) in aqueous solution under UV-light irradiation and more than 90% of the dye was efficiently degraded by the sample heat-treated at 850°C within 45 minutes irradiation time as compared to other tested samples.

Abstract: We present the synthesis of ZnO nanostructures grown by the hydrothermal method using the rapid microwave heating process. First, 10 mM solutions of zinc acetate dihydrate and 1-propanol were three cycles spin coated on glass substrates at 2000 rpm by 70 s, 90 s and 90 s, respectively. Second, nanostructures were then grown by dipping the substrates in a solution of zinc nitrate hexahydrate, polyethyleneimine (PEI), hexamethylenetetramine and ammonia. The hydrothermal process were carried out with a commercial microwave at 300, and 600 W power settings during 20 min. The structural and morphological properties were investigated using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The influence of the ammonium concentration in the morphology of the nanostructures was analyzed.Keywords: ZnO, nanostructures, XRD, SEM, spin coating, ammonium, hydrothermal process.

Abstract: Titania (TiO₂) nanotube gaining predominance as a bioceramic due to its excellent features such as high specific surface area and exhibiting appropriate cellular response. At present, we showed a conversion from titania nanoparticle to nanotube by hydrothermal treatment with 10M soduim hydroxide and 1M HCl solutions at 150°C over 48h. Then the sample annealed at various temperatures. Results indicate the reaction temperature is a main factor in determining the aspect ratio of the tubes. FESEM image conformed the synthesis of nanotube. In vitro study by using 150 °C-synthesized nanotube calcined at different temperatures are also presented establishing the potential of nanotubes in biomedical applications