Papers by Keyword: Microwave Irradiation

Abstract: Monoglycerides (MAG) and Diglycerides (DAG) have wide applications in the food, pharmaceutical and cosmetic industries. Despite the economic competitiveness of producing this type of emulsifier from vegetable oils, the increasing demand for products with high nutritional value makes certain types of healthy oils such as rice bran oil (RBO) a potential raw material for high quality fats to serve this growing market. However, the high free fatty acids (FFA) and RBO content which is insoluble in acetone make it difficult to process and is categorized as a low-quality oil, causing RBO to be only used as biodiesel feedstock. Enzymatic catalytic route for glycerolysis of vegetable oil offers milder operating conditions and higher product selectivity (MAG) but it has high production costs and long processing time. In this study, biodegradable catalysts were used, namely deep eutectic solvents (DES) based on phosponium and choline chloride for glycerolysis of dewaxed/degummed RBO (DDRBO) assisted with microwave irradiation. Effects of different types of DES catalysts (phosphonium and choline chloride based DES) on DES-catalyzed glycerolysis of low quality oil will be evaluated using 5%wt of DES, 300 W(150°C) for about 15 minutes. Out of the four DESs used, DES [TBAB][PTSAM] and DES [ChCl][AcAd] both showed outstanding catalytic performance. Especially [ChCl][AcAd] as a reaction catalyst for DDRBO glycerolysis showed the best catalytic activity, and high selectivity for the formation of monoglycerides (MG). Meanwhile [TBAB][PTSAM] showed high selectivity (92.57%) for diglyceride (DG) formation.

Abstract: Physical and chemical approaches for synthesizing ZnO have disadvantages, such as requiring high temperatures, expensive equipment, and dangerous substances. Preparation of ZnO nanoparticles has shifted its focus to the biosynthesis technique involving plant extracts in order to support ecologically friendly activities. In this study, biosynthetic ZnO nanoparticles were produced using Sentul (Sandoricum koetjape) peel extract under two distinct microwave irradiation powers (i.e., 360 W and 720 W) for three minutes. The effects of microwave irradiation power on the morphology and optical properties of ZnO were investigated. Prior to microwave irradiation, Sentul (Sandoricum koetjape) peel extract (20g/l) and zinc nitrate hexahydrate (0.2M) as a precursor were mixed homogeneously. Morphological, structural, and optical absorption of the samples were characterized using field effect scanning electron microscopy (FESEM), X-ray diffractometer (XRD), and UV-Vis spectroscopy, respectively. Surprisingly, the surface morphology of ZnO displays geometric forms resembling flowers. Higher irradiation power resulted in uniformly smaller ZnO nano-flowers. The crystal structure of both ZnO samples is wurtzite with a hexagonal structure. Maximum light absorption occurs at 349 nm and 358 nm, respectively, for ZnO samples subjected to 360 W and 720 W of microwave radiation. However, the bandgap energies are 3.29 and 3.28 eV, which is significantly less than the bandgap energy of bulk ZnO. (3.37 eV). According to the results, it is possible to control the form and size of ZnO nanoparticles using microwave heating.

Abstract: Alternative synthesis methods are need of the hour to provide easy protocol for synthesizing biologically active heterocyclic compounds. In this connection, this paper describes the development of a concise, convergent protocol for diversely substituted Suzuki–Miyaura cross-coupling reactions of heteroaryl bromides and boronic acids under microwave irradiation using Sodium aluminate (NaAlO₂) as a solid support as well as base. According to my knowledge, this is the first report of the strategy that involves the use of zinc as a catalyst on fused tricyclic di-halo quinolones in a solvent-free condition using simple microwave irradiation. Earlier research from the same laboratory established a solid support assisted Suzuki–Miyaura cross-coupling reaction for forming C–C bonds under the influence of microwave irradiation. Therefore, sodium aluminate (NaAlO₂) was attempted as a base and solid support instead of traditional mineral bases. Moreover, zinc was used as a catalyst replacing palladium. The new method is unique and effective due to its energy economy, procedural simplicity, and general applicability. Moreover, the use of Sodium aluminate (NaAlO₂) is expected to extend this green-protocol and atom-friendly chemistry for the synthesis of varied heterocyclic compounds of interest.

Abstract: This study deals with the synthesis of cubic shape platinum nanoparticles (Pt NPs) by adjusting the oleylamine (OAm):polyvinylpyrrolidone (PVP) ratio in the solution media. The mass ratios between the OAm:PVP were respectively set to the 1:2, 1:1, 2:1 values. Platinum acetylacetonate (Pt(acac)₂) was used as Pt precursor and the reduction of this salt to the metallic Pt was provided by microwave irradiation technique. It is seen that increasing amount of OAm triggers the formation of cubic shape Pt NPs. The average sizes of the Pt NPs fall in the range of 6-8 nm. The unsupported Pt NPs were directly used as a catalyst for the oxygen reduction reaction (ORR). According to the hydrodynamic ORR voltammograms of the catalysts, the Pt NPs prepared with 1:2 (OAm:PVP) exhibit the highest current density at all stirring rates of rotating disc electrode (RDE). Besides, Pt NPs prepared with 2:1 (OAm:PVP) have the minimum charge transfer resistance based on electrochemical impedance spectroscopy (EIS) analysis conducted at 0.9 V. After all these analyses, Pt NPs were synthesized using extra five different ratios (1.5:1, 1:1.5, 2.5:1, 3:1, 1:3) of (OAm:PVP) for thoroughly examining the optimum value for the ORR catalytic activity. As a result, the Pt NPs prepared with a 2.5:1 (OAm:PVP) ratio provided the best performance among all the catalysts.

Abstract: The objectives of this study are to investigate the influence of concentration variation of potassium hydroxide (KOH) and to remove a heavy metal in liquid waste of the activated carbon. The raw material of activated carbon was obtained from pineapple crown waste. Pineapple crowns pre-carbonized at 180 ^oC for 1 hour. Chemical activation was carried out using KOH with concentration 2M, 3M, and 4M for 20 hours at 30 ^oC and temperature 60 ^oC for 2 hours. Microwave irradiation was conducted at 630 Watt of output power for 15 minutes. The physical properties of activated carbon were characterized using scanning electron microscopy to determine surface morphology of activated carbon, X-ray diffraction to calculated microstructure (i.e. interlayer spacing and microcrystalline dimension) using Bragg’s and Scherer’s equations, specific surface area was calculated from N₂ adsorption-desorption isotherm using BET equation, Fourier-transform infrared (FTIR) identify the functional groups of activated carbon, and heavy metals absorption was tested using atomic adsorption spectrophotometric. The highest surface area of activated carbon is 300,901 m²/g for activated carbon with concentration 2M corresponding to the highest stack height (L_c) of activated carbon of 10,470 nm. The carbon chain structure shows the functional groups C-H, C≡C, O-H, C-OH, and CH₂ at wavenumbers of 2889,49 cm^-1, 2360,97 cm^-1, 2339,97 cm^-1, and 998,21 cm^-1, respectively.

Abstract: One-dimensional nanostructures have been the focus of recent research interests because they possess high aspect ratio. In this study, bismuth sulphide nanorods have been synthesized via a simple microwave irradiation of bismuth dithiocarbamate complex in ethylene glycol (EG) and N,N-dimethyl formamide (DMF) solvents. The optical properties of the nanorods was studied by UV-vis spectroscopy, and the structural characterization was carried out using powder X-ray diffraction (p-XRD) analysis, transmission electron microscopy (TEM, HRTEM), scanning electron microscopy (SEM), and selected area electron diffraction (SAED). The XRD patterns indicated cubic phase, and the TEM analysis confirmed rod-like morphology with mean diameter of about 60 nm and irregular lengths. The role of the solvents on the nanostructures was discussed, and the band gap energies were estimated from Tauc plot. The synthesized bismuth sulphide nanorods exhibited quantum confinement effect. The synthesis approach via microwave irradiation of single source precursor is facile and efficient, thus promotes the production of large scale Bi₂S₃ nanorods by an environmentally friendly approach.

Abstract: The aim of this article is to develop a method in order to investigate the surface modifications of degraded polyacrylonitrile powders under microwave treatment in air. Microwave treatment of polyacrylonitrile powders in air recorded two stages of degradation firstly an exothermic reaction that started in the range of (86-117)°C. Secondly the Thermal runway here the weight loss reached a peak value between 80-90 percent with the small quantity of 0.25g polyacrylonitrile and in the ashes with a bigger quantity 1g of polyacrylonitrile. Scanning electron microscopy analysis technique revealed the morphological characteristics and the porosity of the carbon compound that may play an important role in the construction of high porosity area and so in electrochemical supercapacitor devices with high performances.

Abstract: An investigation of the effect of the addition of char from agricultural residues on the torrefaction of moist municipal solid waste (MSW) pellets (40 wt.% moisture) was carried out in a microwave oven (500-800 W for 4-12 minutes). Char from agricultural residues, including corncob, palm shell, straw, and bagasse, was used as the microwave absorbers to enhance the absorption of microwave irradiation. It was found that the addition of char from bagasse yielded the lowest remaining mass (or mass yield) and volatile matter (VM) content, but the highest temperature and heating value, of the torrefied MSW pellet. Moisture in the MSW pellet with or without the addition of microwave absorber was completely removed after being torrefied for 8-12 minutes. The VM contents remained in the MSW pellets with the addition of microwave absorbers were lower than that in the MSW pellet without the addition of microwave absorber. The addition of microwave absorbers led to an increase in carbon (C) content but a decrease in oxygen (O) content of the torrefied MSW pellets, compared to those of the raw MSW pellet. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were equivalent to that of sub-bituminous coal, enhanced from that of the raw MSW pellet, which was lower than that of lignite.

Abstract: Activated carbon from biomass namely coconut shell (CS-AC), rubber seed pericarp(RSP-AC) and their mixed blend (50:50 w/w) coconut shell-rubber seed pericarp activated carbon(CSRSP-AC) were successfully produced by using ZnCl2 as chemical activating agent viamicrowave irradiation heating system. Activation process was performed in commercial microwaveoven at power of 600W for 20 min by using 30%, 40% and 50% of ZnCl2 concentrations. Theactivated carbon was characterized according to BET surface morphology, iodine number andpercentage of MB removal. The results showed that the mixed CSRSP-AC produced the highestsurface area of 584.68 mg2/g with comparison to single CS-AC and RSP-AC at 445.9 mg2/g and462.5 mg2/g respectively. Although CSRSP-AC has the highest surface area and pore volumedevelopment, RSP-AC was found to have the highest iodine number, with the opposite trend beingobserved with MB removal indicating that RSP-AC has the highest adsorptive capacity among thethree activated carbons. The iodine number value and percentages of MB removal increased as theZnCl2 concentration increase from 30% to 50%. These findings revealed that activated carbonproduced from mixed blend of coconut shell and rubber seed pericarp has almost similarcharacteristics to their respective activated carbon derived from single individual biomass.

Abstract: A microwave irradiation involved process was applied to fabrication of graphene/polyaniline nanocomposite via in-situ polymerization of aniline monomers on graphene sheets. Structure and morphology of composites were characterized through scanning electron microscopy, Raman spectra, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectra. Electrochemical performances for energy storage applications were examined by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge/discharge measurements. Owing to the homogeneous coating of polyanilline on the large surface of graphene, graphene/polyaniline composite-based electrode exhibits remarkably enhanced capacitive behavior with a specific capacitance of 429 F/g at 0.2 A g^-1, a good cyclic stability and an excellent conducting behavior, which are much superior to those of individual components of composites. The improved electrochemical behavior of the composite resulting from the irradiation of microwave suggests the promising potentials for supercapacitors.