جستجوی مقالات مرتبط با کلیدواژه « امواج مایکروویو » در نشریات گروه « شیمی »

Domestic companies in metal and alloy production have faced many problems in providing the required energy. These companies often use traditional industrial furnaces, which consume a lot of energy, have a very negative impact on the environment. For this reason, the use of modern low-consumption processes for metal oxide reduction will be of great interest. In this research, the carbon bed of a new metal oxide reduction system operated under microwave heating is modeled. In this system, the carbon bed is responsible for the heating process and converts electromagnetic waves into heat. In this system, because the metal oxide granules are imbedded inside the carbon bed that converts almost all electromagnetic waves, the heating effects of metal oxides were ignored. Comparison of the modeling results with experimental data related to carbon bed temperature rising trend showed that the used model has good accuracy and the average error is less than 5%. Based on the modeling, it was found that the carbon bed temperature (excluding metal oxide granules) increased around 9% by increasing the microwave power from 1000 w to 1200 w. In addition, SiC had better performance compared to the carbon bed in terms of the rate of generated heat. It was determined that the maximum temperature decreased by increasing the carbon emissivity parameter and the final bed temperature increased by 9% after 15 minutes by changing the emissivity parameter from 0.95 to 0.65.

Metallic nanostructures have received a lot of attention. Rapid synthesis using microwaves is a suitable technology that has great potential for use in industrial fields due to the significant reduction in reaction time, increase in product yield, and the use of safe heating sources. The heating method with the help of microwaves has attracted a lot of attention as a suitable method for the synthesis of metal nanostructures in the solution phase. This method has been used to synthesize many nanostructures such as Ag, Au, Pt, Pd and Au-Pd. Not only spherical nanoparticles, but plate, rod, wire, tube and dendritic nanostructures are prepared in a few minutes. Generally, nanostructures with smaller size, narrower size distribution and higher degree of crystallinity are prepared method compared to conventional oil bath heating methods. On the other hand, room temperature ionic liquids (RTILs) have attracted much attention in recent years. ILs can absorb microwaves and increase the reaction speed and decrease the reaction time. The large cations with high polarizability in ILs make these materials suitable solvents for absorbing microwaves. Therefore, the use of microwaves as a heat source along with ILs as a catalyst, solvent, additive, co-solvent and template leads to the creation of a fast and environmentally friendly method (MAIL) for the synthesis of various nanostructures.

In this research nanocomposites of Pt-Co–Polyallylamine-Graphene Nanoplates (Pt-Co/PAA/GNPs) was developed to improve the oxygen reduction reaction activity and stability of commercial Pt/C electrocatalyst. For this purpose, first graphene oxide (GO) as a support material was synthesized according to hamer and affenman method. Then graphene oxide was functionalized with Polyallylamine through cross linking. After that Pt-Co as a catalyst was dispersed on the as prepared support by a novel process polyol synthesis method assisted by microwave. Raman spectroscopy measurements confirmed the graphitic structure of the produced reduced graphene oxide nanoplates. Fourier transform infrared spectroscopy results illustrate the presence of Polyallylamine in the composite. After investigation of the structure, morphology and composition of the prepared electrodes were characterized by X-ray diffraction, Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy. the catalytic activities of prepared electrodes for the oxygen reduction reaction were evaluated through cyclic voltammetry and linear sweep voltammetry measurements in the oxygen reduction reaction. X-ray diffraction results showed that Pt-Co particles were dispersed on the support with mean particle size of about 11. FESEM images showed that the nanosized Pt- Co were successfully dispersed on functionalized graphene oxide nanoplates. The nanoparticles in the film were observed to be uniform spherical objects and well distributed. According to the electrochemical measurements, active electrochemical surface area of 15.42 m2Pt/mgPt with 62% catalyst utilization and the specific and mass activity peak currents as high as of 26.3345 and 1.7078 mA/mgPt was found for Pt-Co/PAA/GNP which is comparable with respect to the Pt/PAA/GNP electrode and commercial one.

In this study, a new, cheap and green fluorescence sensor based on carbon quantum dots was used for Cr (VI) determination. Carbon quantum dots were synthesized from citric acid, polyvidon and boric acid by microwave assisted method. The size of carbon quantum dots estimated by high resolution transmission electron microscope (HRTEM) and was about 10 nm. Fourier transform infrared spectroscopy (FT-IR) was used for study of functional groups on the carbon dot surface. Synthesized carbon dots had excitation and emission peaks at 340 and 440 nm, respectively. Fluorescence quenching process was occurred after adding of Cr (VI) to synthesized carbon dots solution. At optimum condition (pH=3, t=1 min, excitation and emission slit widths = 10 nm, λ excitation =340 nm and λ emission =440 nm), linear dynamic range and detection limit of this sensor were 5-200 µM and 1.24 µM, respectively. Recovery percent was studied in different real samples such as tap water, river water, mineral water and canned fish.

In this paper, magnetic nanoparticles functionalized with sulfonic acid group as a heterogeneous and recyclable catalyst for the rapid synthesis of 1,5-benzodiazepine derivatives from condensation reaction of 2-phenylenediamine with various Chalcones under microwave irradiation and solvent-free conditions was used. The nano magnetic supported sulfonic acid provides high reactivity and, also it is separated easily from the reaction mixture by using an external magnet. The use of microwaves in solvent free condition compared to conventional heating methods, rapid, simple, safety, high yields and purity of the products of the remarkable advantages of this method is considered.