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Atrazine is one of the most extensively used herbicides. Being non-biodegradable in nature, it has a long half-life in water and hence it is prone to contaminate the water bodies and even seeps into the ground to pollute underground water. In this study, we developed a photocatalytic method for the degradation of Atrazine in water samples. Highly ordered mesoporous Ag-WO3/SBA-15 composites were tested as photocatalysts for the degradation of atrazine in water. It was found that 40% WO3 loading rendered an optimum surface area and material content in the SBA-15 template and hence favored the enhanced photocatalytic degradation of atrazine in water. The further addition of Ag onto the WO3/SBA-15 composite not only made this catalyst very effective in the most sought visible region due to solar energy harvesting, but also significantly reduced the electron hole recombination as evidenced by photoluminescence studies to enhance the degradation efficiency. As a result, the Ag-WO3/SBA-15 composite the photo-catalytic degradation of atrazine in water under visible radiation was significantly enhanced.

The well-dispersed nanoparticles of Au-Ag alloys on graphitic carbon nitride (g-C 3 N 4 ), with varying ratios of Au, were synthesized by a facile route. The diffuse reflectance spectroscopy (DRS) verified the upsurge in the intensity of characteristic surface plasmonic resonance (SPR) absorption bands with the increasing Au contents. The photoluminescence (PL) spectroscopy estimated the role of surface dispersed Au-Ag alloy NPs on the luminescence properties of g-C 3 N 4 and the suppression the probable recombination of photo-generated excitons. The structural characterization by XRD and morphological assessment by SEM revealed the uniform dispersion of Au-Ag alloy nanoparticles on the surface of g-C 3 N 4 whereas XPS analysis endorsed the presence of Au and Ag in metallic form. The HRTEM analysis confirmed the homogeneous distribution of Au and Ag contents in the alloys. The photocatalytic activity of the Au-Ag/g-C 3 N 4 was evaluated in the exposure of natural sunlight and artificial visible light for the degradation of dye substrate and compared with that of g-C 3 N 4 , Ag/g-C 3 N 4 and Au/g-C 3 N 4 . The Au-Ag alloy modified g-C 3 N 4 photocatalysts exhibited significantly higher activity for the decolorization of Rhodamine B in the visible light as compared to pure, Ag and Au loaded g-C 3 N 4 that signified the contributing role of SPR in the degradation process. The individual role of SPR in the photocatalytic process was also verified by using monochromatic (532 nm) visible laser light. The mineralization ability of the synthesized alloy catalysts was estimated by TOC removal efficiency. The kinetics of the degradation/mineralization processes under various experimental conditions was also evaluated.

Bi 2 WO 6 nano-rods and g-C 3 N 4 -Bi 2 WO 6 heterojunction and their corresponding silver loaded nanocatalysts were synthesized and characterized using XRD, FE-SEM, HR-TEM, XPS, photoluminescence (PL), and diffuse reflectance spectroscopy (DRS). FE-SEM micrographs indicates that g-C 3 N 4 nano-sheets are agglomerated with WO 3 particles and Bi 2 WO 6 nanorods in g-C 3 N 4 -WO 3 and g-C 3 N 4 -Bi 2 WO 6 catalysts respectively whereas, HR-TEM images confirmed the presence of interface between g-C 3 N 4 sheets and Bi 2 WO 6 nano-rods, and dispersion of less than 10 nm Ag particles over the heterojunction. A significant reduction in PL signal due to reduced electron hole recombination and consequent enhancement of catalytic activity were observed with the Ag/g-C 3 N 4 -Bi 2 WO 6 catalyst. On bare Bi 2 WO 6 nano-rods, N -deethylation was found to be the prominent degradation pathway and with 1% silver nanoparticles (Ag NPs), this is fully quenched and ring closure pathway accounts for the dye degradation. In addition, performance of our catalyst was benchmarked with commercially available visible light driven photo-catalysts. The appropriate band positions for reduction and oxidation reactions, with the reduced charge recombination make this heterojunction suitable for applications like water splitting and other environmental applications.

Owing to its high toxicity, chromium(VI) is considered as top priority pollutant for many countries in the world and removal of this pollutant from waste water is highly desirable. The present investigation addresses the synthesis of NiO nanoparticles using sol–gel method and their application in heterogeneous photocatalytic reduction of Cr(VI) using a 355 nm laser radiation generated from Nd:YAG laser. The study showed that ∼90% Cr(VI) was removed within short laser exposure time (75 min) in presence of nanostructured NiO without the use of any additive as reported in other studies. Effect of critical parameters, such as calcination temperature, calcination time, laser energy, catalyst amount, chromium concentration, and added electron donor and acceptor on the photocatalytic reduction process was investigated. The photocatalytic reduction of metal was found to be strongly dependant on the above mentioned parameters.

Photocatalytic oxidation of phenol was studied using nickel oxide (NiO) nanoparticles synthesized by sol–gel method. The morphology of synthesized catalyst was studied by using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The average particle size was 6.5 nm as estimated by Scherrer formula and was confirmed by HRTEM and FESEM analysis. The photocatalytic activity of NiO was evaluated by degradation of phenol under irradiation of unique source like UV laser. The influence of various key parameters such as amount of photocatalyst, initial solution pH and the initial concentration of phenol was investigated. The operational parameters show the expected influence regarding the efficiency of the photocatalytic degradation process. The photocatalytic degradation efficiency of NiO was found to decrease with the increase in the initial solution pH. The degradation of the phenol followed a pseudo first-order rate kinetics with k = 5.7 × 10 −2 min −1 .

Nano-tungsten trioxide (n-WO3) was synthesized by dehydrating tungstic acid (H2WO4) at 300 °C. Nano-palladium (n-Pd) was then loaded as 10 wt% on this n-WO3 by impregnation for the synthesis of the desired n-Pd/n-WO3 photocatalyst. This loading process enhanced the photocatalytic activity of n-WO3 for the removal of Escherichia coli microorganism from water when applying 355-nm UV laser radiation. The absorption and photoluminescence spectra revealed a blue-shift for the band gap energy (Eg) from 2.71 eV for the undoped n-WO3 to 3.5 eV for the doped one. This shift in Eg caused a near resonance condition, which accounts for the significant improvement of the photocatalytic activity upon doping n-WO3.

An innovative approach based on laser-induced photocatalytic approach, a H-rich mixture was produced by using p-type NiO, for the reforming of methanol at ambient temperature has been developed. A hydrogen-rich mixture of hydrogen (>70%) and carbon monoxide (

The pH changes during the course of photocatalytic splitting of water significantly affect the band edges of the semiconductor and enhance or retard the rate of the splitting process. The effect of pH on photocatalytic activity in splitting of water over WO3, TiO2 (rutile) and NiO by using a monochromatic light source such as laser at 355 nm wavelength was studied for the first time. The mechanism of action of oxygen and metal ions (Fe3+ and Ag+) as electron capture agents was investigated on the basis of pH changes under illumination. It was observed that the pH changes measured during the course of reaction provides a deep insight of different processes occurring simultaneously in photocatalytic systems.

A laser based method for photocatalytic reforming of methanol at ambient temperature using n-type WO3 semiconductor catalyst has been investigated for the first time. A non-explosive mixture of gases containing hydrogen, carbon monoxide and methane with high concentration of hydrogen was observed. The amount of catalyst and laser energy was optimized for maximum yield of hydrogen. The effect of aging of the catalyst proved that there was no deactivation of catalyst; instead, an increase in the activity of the catalyst was observed. The effect of addition of water to methanol in various proportions as feedstock on the hydrogen yield during this laser induced photocatalytic process was also studied.

A comparative study of photocatalytic splitting of water into hydrogen and oxygen over NiO and TiO 2 was carried out using 355 nm laser radiations as a light source. The effect of dissolved metal ions on photocatalytic splitting of water over these catalysts was also studied by using Fe 3+ , Ag + and Li + ions to enhance the efficiency of the process by suppressing the non-productive electron–hole recombination. The dependence of products yield on incident laser energy, amount of catalyst (particle density), stirring rate and laser beam diameter was also investigated for activity comparison of these catalysts. It was demonstrated for the first time that by using a high photon flux source such as laser, the problems of longer exposure time and low photonic efficiencies could be resolved which is common problem with conventional UV lamp based photocatalysis.