Hamed Rashidi

Recent Advances in Application of Polyoxometalates for the Synthesis of Nanoparticles

Recent developments in the synthesis of nanoparticles using polyoxometalates (POMs) are reviewed. This review demonstrates the importance and various roles of POMs in developing of nanotechnology. Special attention has been paid to the synthesis of silver, gold, selenium, cadmium sulfide, palladium, and calcium carbonate nanoparticles using POMs.

Photocatalytic Synthesis of Gold Nanoparticles Using Preyssler Acid and Their Photocatalytic Activity

Abstract Preyssler acid H 14 [NaP 5 W 30 O 110 ] was used as reducing agent and stabilizer for the synthesis of gold nanoparticles by photolysis of Au(III)/Preyssler acid/propan-2-ol solution. Preyssler acid plays both the role of transferring electrons from propan-2-ol to Au(III) and stabilizing the nanoparticles. Propan-2-ol was used as sacrificial reagent for the photoformation of reduced Preyssler acid. Gold nanoparticles (Au NPs) were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), and particle size distribution (PSD) measurements. The synthesized Au NPs had a uniform hexagonal morphology and their size was about 17 nm. The catalytic performance of these NPs for photodegradation of methyl orange (MeO) was investigated in aqueous solution. UV-Vis studies showed that Au NPs can catalyze photodegradation of this azo dye. The pseudo-first-order rate constants were also calculated for this reaction.

Improving methane storage on wet activated carbons at various amounts of water

Abstract Different mesoporous activated carbons were prepared by both chemical and physical activation processes and were examined for methane uptake in the presence of water. Methane isotherms were obtained at wet condition by wetting samples with water at mass ratio of water/carbon (R) close to 1.0. To compare, the amount of methane storage were also measured at dry situation. The maximum amount of methane stored was attained as 237 V/V at R=1.0 by hydrate formation at the methane critical pressure. In the next step, mass ratios of water/carbon were changed to investigate various amount of water for methane storage enhancement. Two other values of mass ratio of water/carbon (R=0.8 and 1.4) were selected and methane isotherms were obtained at the same conditions. Maximum values of 210 and 248 V/V were reached for methane storage, respectively. It was also observed that, in the pressure range lower than hydrate pressure, by increasing water ratio the hydrate formation pressure was decreased and methane uptake was much less than that of dry condition due to pore filling by water.

OPTIMIZATION OF THE EXPERIMENTAL CONDITIONS IN SYNTHESIS OF Au NPs USING PREYSSLER HETEROPOLYACID BASED ON THE TAGUCHI ROBUST DESIGN

Preparation of gold nanoparticles by chemical reduction method using Preyssler heteropolyacid was investigated. The experimental conditions have been optimized using Taguchi robust design method with L9 orthogonal array. Particle size of the gold nanoparticles was considered as the property in the optimization. Amounts of Preyssler heteropolyacid, pH and irradiation time were selected as the main parameters. The result of Taguchi analysis has shown that in this process, the preyssler acid amount is the most influencing parameter on the size of gold nanoparticle. Also, the effects of different parameters are in order to: Preyssler acid amount > pH > irradiation time (negligible). This method showed that decreasing Preyssler amount and increasing pH of solution lead to formation of smaller nanoparticles. Finally, the prepared nanoparticles at optimum condition with a size of about 6.42 were characterized by using Dynamic Light Scattering (DLS) method, transmission electron microscopy (TEM), and UV-Vis spectroscopy.

Controllable one-step synthesis of ZnO nanostructures using molybdophosphoric acid

ZnO nanostructures were synthesised in a hydrothermal reaction of zinc acetate in the presence of molybdophosphoric acid (H3[PMo12O40]) as well as its vanadium-substituted acid (H4[PMo11VO40]) at various times, temperatures, and concentrations. The ZnO nanostructures were characterised by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The results demonstrated that the synthesised products are crystalline with a zincite hexagonal phase. Various ZnO nanostructures, such as nanoparticles, microrods, and nanosheets, were produced by changing the experimental conditions. The photocatalytic degradation of methyl orange was also investigated using the ZnO nanoparticles thus prepared. These particles exhibited high performance in the photocatalytic degradation of MO and almost 100 % decolourisation occurred within only 20 min.

Application of Artificial Intelligent Modeling for Predicting Activated Carbons Properties Used for Methane Storage

Performance characterization and optimization of activated carbons are extensively studied using artificial intelligence modeling. In this study, the effect of several parameters on the preparation of activated carbon by chemical activation is investigated. Various preliminary parameters have been considered. The study has resulted in finding four parameters, which are of higher importance compared to the others. These parameters include chemical agent type, chemical agent to precursor ratio, activation temperature, and activation time. In our previous study, 36 activated carbon (AC) samples were prepared using the aforementioned parameters at various levels. In the present investigation, these experimental results have been used for the modeling. As a novel approach, an adaptive neuro-fuzzy inference system (ANFIS) is also applied to the experimental data presented in this study. ANFIS is established by combining artificial neural network (ANN) with fuzzy inference system. After determining the model parameters, some additional data points are used to validate the models. Finally, the outcomes are compared with the experimental results. The normalized mean square error (NMSE) has been obtained as 0.00327, which is very satisfactory for the model validation. These attempts to simulate the preparation stage of activated carbons would provide a simple and flexible route with various AC preparations. Such an effort is essential to develop the adsorbed natural gas (ANG) technology.

Comparing the Performance of KOH with NaOH-Activated Anthracites in terms of Methane Storage

Anthracite activated carbons are proper adsorbents for methane storage. In this study, Iranian local anthracite was activated using two commonly used chemicals (sodium hydroxide and potassium hydroxide) at similar conditions and their products are compared with regard to various properties in order to find the optimal operating parameters such as temperature, chemical ratio and pyrolysis time for producing ACs with high surface area. Three activation temperatures (670, 730 and 790 °C), three chemical-to-coal ratios (2, 2.5 and 3) and two pyrolysis times (1 and 2 hours) were studied in each carbon series (NaOH and KOH). Accordingly, the pore structures of Activated carbon (ACs) were investigated accurately based on adsorption isotherms of nitrogen as well as density functional theory. In addition, their methane storage capacities were also measured and discussed. Specific volumes (microporosity and mesoporosity) of products were also calculated. The KOH ACs had higher micropore volumes, whereas NaOH ACs had relatively higher densities. The highest methane storage was obtained by a KOH AC sample with 3:1 chemical-to-coal ratio (R), activated at 730 °C for 1 hour (AK37301). The stored and delivered methane for this sample were 176 and 158 vol/vol, respectively.

Enhancement of methane storage on activated carbons in the presence of water

ABSTRACT Methane storage was studied on the wet activated carbons by hydrate formation in the mesopore structures. Coconut shell was used as a raw material for preparation of the activated carbon samples. These highly mesoporous samples were prepared by the combination of both physical and chemical activation processes. After wetting the adsorbents with a constant water/carbon weight ratio (R) close to 1, the isotherms were obtained at 2°C up to the pressure of 80 bars. Wetted carbons exhibited stepwise isotherms at the critical pressure in the pressure range of 25–50 bars depending on the activated carbon samples. At this critical pressure, hydrate formation took place slowly. The amounts of methane uptake at 80 bars were obtained ranging from 14.9 to 24.8 mmol.g–1 based on the dry adsorbent for different samples. By considering the density of activated carbon samples, the amounts of methane storage varied in the range of 185–237 V/V.