Ali Ayati

A review on catalytic applications of Au/TiO2 nanoparticles in the removal of water pollutant.

Nanomaterials are showing great potential for the improvement of water treatment technologies. In recent years, catalysis and photocatalysis processes using gold nanoparticles (Au-NPs) have received great attention due to their effectiveness in degrading and mineralizing organic compounds. This paper aims to review and summarize the recently published works and R & D progress in the field of photocatalytic oxidation of various water pollutants such as toxic organic compounds (i.e. azo dyes and phenols) by Au-NPs/TiO2 under solar, visible and UV irradiation. Extensive research which has focused on the enhancement of photocatalysis by modification of TiO2 employing Au-NPs is also reviewed. Moreover, the effects of various operating parameters on the photocatalytic activity of these catalysts, such as size and loading amount of Au-NPs, pH and calcination, are discussed. The support type, loading amount and particle size of deposited Au-NPs are the most important parameters for Au/TiO2 catalytic activity. Our study showed in particular that the modification of TiO2, including semiconductor coupling, can increase the photoactivity of Au/TiO2. In contrast, doping large gold NPs can mask or block the TiO2 active sites, reducing photocatalytic activity. The optimized loading amount of Au-NP varied for each experimental condition. Finally, research trends and prospects for the future are briefly discussed.

Emerging adsorptive removal of azo dye by metal–organic frameworks

Adsorptive removal of toxic compounds using advanced porous materials is one of the most attractive approaches. In recent years, the metal-organic frameworks (MOFs), a subset of advanced porous nano-structured materials, due to their unique characteristics are showing great promise for better adsorption/separation of various water contaminants. Given the importance of azo dye removal, as an important class of pollutants, this paper aims to review and summarize the recently published research on the effectiveness of various MOFs adsorbents under different physico-chemical process parameters in dyes adsorption. The effect of pH, the adsorption mechanism and the applicability of various adsorption kinetic and thermodynamic models are briefly discussed. Most of the results observed showed that the adsorption kinetic and isotherm of azo dyes onto the MOFs mostly followed the pseudo-second order and Langmuir models respectively. Also, the optimum pH value for the removal of majority of azo dyes by MOFs was observed to be in the range of ∼5-7.

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.

Rate redox-controlled green photosynthesis of gold nanoparticles using H3 + x PMo12 − x V x O40

Stabilized and size-controlled gold nanoparticles were synthesized using molybdophosphoric acid (H3[PMo12O40], HPMo) and its vanadium-substituted mixed addenda (H3 + x[PMo12 − xVxO40], (x = 0–3); and HPMoVx) under UV irradiation by a simple green method. In the process, HPMo and HPMoVx play the role of photocatalyst, reducing agent and efficient stabilizer. Control of gold nanoparticles size was achieved by variation of initial gold ions concentration and molar ratio of HPMo to gold ions. The synthesis rate of Au nanoparticles was found to be parallel to an increasing x value in the order of: HPMoV3 > HPMoV2 > HPMoV > HPMo, which leads to smaller and more uniform particles. Also, by substitution of vanadium instead of molybdenum in the HPMo formula, the morphology of nanoparticles was gradually changed from spherical-shaped nanoparticles in the presence of HPMo to nanorods in the case of HPMoV3.

H3PMo12O40 immobilized chitosan/Fe3O4 as a novel efficient, green and recyclable nanocatalyst in the synthesis of pyrano-pyrazole derivatives

A novel nanomagnetic composite heteropolyacid immobilized chitosan/Fe3O4 was prepared via a facile one-pot synthetic approach. This magnetically recoverable nanocatalyst, H3PMo12O40/chitosan/Fe3O4 (PMo/chit/Fe3O4), was fully characterized by XRD, FTIR, SEM and EDX analysis methods. A rapid, efficient and the chemoselective synthesis of different pyrano-pyrazole derivatives was achieved in excellent yields via a one-pot four-component reaction in the presence of catalytic amount of PMo/Chit/Fe3O4.

A Green and Simple Route for the Controlled-Size Synthesis of Gold Nanoparticles Using Preyssler Heteropolyacid

The authors describe a facile procedure for size-controlled synthesis of gold nanoparticles based on the reduction of Au3+ (HAuCl4) using Preyssler heteropolyacid (H14[NaP5W30O110]) under UV irradiation. Preyssler plays the role of green reducing agent and also efficient stabilizer. This method allows the synthesis of uniform hexagonal nanoparticles with an average size that is tunable between 1.35 and 86.7 nm by varying the gold ion concentration, molar ratio of gold ion to Preyssler, and Propan-2-ol amount. The authors found that there is a critical ratio for [Au3+]/[Preyssler] in which two opposing trends in the size of nanoparticles would happened.

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.

Partially carboxymethylated and partially cross-linked surface of chitosan versus the adsorptive removal of dyes and divalent metal ions

Industrial wastes and their effluents containing dyes and heavy metals are a tremendous threat to the environment, and to treat these toxic waste streams, effective and environmentally benign methods are needed. In this study, NaCS-GL was used as an effective adsorbent, for the removal of dyes and metal ions from their aqueous solution. The presence of carboxylate groups on the NaCS-GL surface has altered the protonation of amino groups. The adsorption kinetics of dyes on NaCS-GL was initially controlled by the film diffusion or chemical reaction after which the intra-particle or pore diffusion started to govern the rate. Leaching of sodium ion confirmed the crosslinking of two carboxylate groups of NaCS-GL with the metal ions. Modeling of the adsorption isotherms revealed that the different active surface sites of NaCS-GL were involved in the adsorption of dyes and metals, suggesting the simultaneous removal of these components from the wastewater.

Acidic cesium salt of Preyssler nanoparticles: a new, green and recyclable nanocatalyst for the synthesis of 6-aryl-1H-pyrazolo[3,4-d]pyrimidin-4[5H]-ones

The synthesis of 6-aryl-1H-pyrazolo[3,4-d]pyrimidin-4[5H]-ones, (3) has been achieved via the reaction of 5-amino-1-phenyl-1H-pyrazolo-4-carboxamide 1 with aromatic aldehyde in the presence of acidic cesium salt of Preyssler as a green and reusable nanocatalyst.