Papers by Keyword: Microwave Irradiation

Abstract: Unmodified gold nanoparticles (AuNPs) have been successfully synthesized by the chemical reduction of tetrachloride gold (III) ions ([AuCl₄]^-) in the presence of sodium citrate based on the rapid microwave−assisted approach. The diameter of the synthesized nanoparticles was found in the range of 16.50±2.75 nm. The AuNPs were characterized using UV−vis spectrophotometer, zeta potential analyzer and transmission electron microscope (TEM). The sodium citrate protected AuNPs were found to be selective and sensitive for the detection of dopamine. It was based on the aggregation change of the nanoparticles from random coil to hairpin structure upon the addition of dopamine concentration. The red shift of the plasmonic peak wavelength of AuNPs could be used for the detection of dopamine. The response to dopamine allows for a linear range from 10 to 125 mg⋅L^-1 (R² = 0.9804) with a limit of detection (LOD) at a signal to noise ratio of 3 of 12.85±1.38 mg⋅L^-1. The colorimetric sensor was evaluated with 98.0−99.9% recovery of added dopamine in urine sample. The proposed sensor was successfully applied to the determination of dopamine in biological samples.

Abstract: Novel simple route to prepare AlN nanoparticles was proposed in this study. Aluminum nitride powder was synthesized by microwave-assisted urea route. Aluminum chloride was dissolved in ethanol and urea was added to this solution considering molar concentration with Aluminum chloride. The solution was heated under microwave (MW) irradiation from 60°C to 80°C for 5-10 minutes. And then heat treatment was performed in N₂ atmosphere with various temperatures and time to obtain AlN particles. While microwave was irradiated to the mixed solution with Aluminum chloride, urea and ethanol, the solvent was eliminated and polymerization reaction was accelerated to formmetal-organic complex. AlN particles were successfully synthesized after heat treatment above 1600°C under N₂ or N₂-H₂ mixed gas atmosphere in the molar ratio (urea/Aluminum chloride) of 6.

Abstract: Conventional methods for the synthesis of silicon carbide were well studied and these methods included carbothermal reduction, mechanical milling, sol-gel process and others. However, conventional methods have limitations such as high energy consumption, presence of impurities and long reaction times. In this paper, microwave heating was applied for the first time for the synthesis of silicon carbide nanotube owing to the advantages of microwave heating such as shorter reaction time, uniform heat distribution and low cost. Mixture of silicon dioxide and carbon nanotube in the ratio of 1:3 as suggested by previous study were mixed in ultrasonic bath using ethanol as liquid medium for 2 hours and then dried on hot plate to evaporate ethanol. The mixture was then cold pressed into 3mm pellet and placed into an alumina crucible filled with silica sand acts as sand insulator and SiC susceptor. The pellet was heated to 1400°C with heating rate of 30°C/min for 40 minute. X-ray diffraction pattern verified the presence of single β-SiC phase in silicon carbide nanotubes. Meanwhile, scanning electron microscopy revealed that tubular structure of carbon nanotube was retained after microwave irradiation and energy dispersive x-ray spectroscopy shown the silicon carbide nanotube consist of only elemental C and Si and thus indicated that silicon carbide nanotubes were successfully synthesized through microwave irradiation.

Abstract: A simple one-pot amidation of carboxylic acids promoted by microwave irradiation is described. Reaction includes formation N-acylureas via interaction carboxylic acids and N,N-dicyclohexylcarbodiimide followed thermal decomposition N-acylureas in microwave reactor. This method allows carrying out the reaction in a short time with good yields.

Abstract: In this paper, we present an IR spectroscopy study of the molecular and supramolecular structure of the polypropylene fibre, used as a metal nanoparticle carrier, by the example of nanoparticles of tin dioxide. The aim of this work is to investigate the changes in the chemical structure of the polypropylene melt-blown web when modified with the tin dioxide nanoparticles. The paper shows that the metal-oxygen valence vibration bands appear in the IR spectra of modified polypropylene fibrous carriers. At the same time, the carrier material remains stereoregular and possess a helical structure.

Abstract: The use of waste materials for producing biodiesel via transesterification has been of recent interest. In this study, the pork bone was used as the raw materials for natural hydroxyapatite (NHAp) catalyst. The calcination of animal bone was conducted at 900 °C for 2 h. The raw material and the resulting heterogeneous catalyst were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method. The effects of reaction time, microwave power, methanol/oil molar ratio, catalyst loading and reusability of catalyst were systematically investigated. The optimum conditions, which yielded a conversion of oil of nearly 94%, were reaction time 5 min and microwave power 800 W. The results indicated that the NHAp catalysts derived from pork bone showed good reusability and had high potential to be used as biodiesel production catalysts under microwave-assisted transesterification of Jatropha Curcas oil with methanol.

Abstract: Calcium oxide (CaO) is one of the most promising heterogeneous alkali catalysts since it is cheap, abundantly available in nature, and some of the sources of this compound are renewable (waste material consisting of calcium carbonate (CaCO₃)). In this study, the waste enamel venus shell was used as the raw material for CaO catalyst. The calcination of bio-waste was conducted at 900 °C for 2 h. The raw material and the resulting CaO catalyst were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method. The effects of reaction variables such as reaction time, microwave power, methanol/oil molar ratio, and catalyst loading on the yield of biodiesel were investigated by gas chromatograph-mass spectrometry (GC-MS). From the experimental results, it was found that the CaO catalysts derived from waste material showed good catalytic activity (the conversion of oil of nearly 93%, a very similar catalytic activity with laboratory CaO) and had high potential to be used as biodiesel production catalysts in transesterification of Jatropha Curcas oil with methanol.

Abstract: The silica gel surface was alkylated by silane coupling agent KH-570 under the microwave assisted and orthogonal experiment was adopted to optimize the silica gel surface silanized experimental conditions with synthetic yield as index. With quercetin as the template molecule, 4 - vinyl pyridine as the functional monomer, ethylene glycol dimethyl acrylate as the cross linking agent, azodiisobutyronitrile as initiator, under the microwave assisted in silane silicone surface quercetin molecularly imprinted polymer was successfully synthesized. Take selected quercetin as index, another orthogonal experiment was implemented to optimize the quercetin-selective MIPs synthesis experiment on silica gel surface. What is more, the adsorptive property of quercetin-selective MIPs which was grafted on silica gel surface has been inspected. We have extracted of quercetin in the ethyl acetate from raspberry with quercetin-selective MIPs grafted on silica gel surface. Synthetic time have been shortened more than a dozen times, the efficiency of preparation of MIPs have been greatly improved.

Abstract: Poly (L-lactide) was grafted onto chitosan by ring-opening copolymerization under microwave irradiation in the presence of tin octoate (Sn (Oct)₂) as catalyst. The chemical structure and physical properties of the copolymers with different feeding ratios were discussed by FTIR, DTG and X-RD, taking pure chitosan as reference. The results showed that the application of microwave irradiation in the reaction could achieve the copolymer with high grafting percentage in a short time and low temperature. The thermal stability and crystallinity were decreased with the feeding ratio increasing, attributing to the increasing of grafting percentage.

Abstract: Potential agro wastes (i.e palm kernel shell and coconut shell) for producing low cost activated carbon (AC) was investigated. In this study, the activated carbon was produced by carbonization, chemical impregnation with KOH and microwave irradiation. The pyrolysis was carried out at 700 °C in an inert environment for 2 h. Microwave activation was carried out at 400W for 6 minutes. Characteristics of the material were investigated using Fourier transform infrared spectroscopy (FT-IR) analysis and scanning electrode microscopy (SEM). Methane adsorption equilibrium data on the activated carbons produced were obtained using static volumetric method. Microwave palm shell activated carbon (MPAC) and microwave coconut shell activated carbon (MCAC) recorded highest methane uptake of 2.489 and 1.929 mmol/g at 3 bar, 30°C. The adsorption data were correlated with Langmuir and Freundlich isotherms. The results shows that microwave activated carbon from palm shell and coconut shell have good methane adsorption characteristics.