Showing papers by "Sounak Roy published in 2017"

Structure sensitive photocatalytic reduction of nitroarenes over TiO 2 .

Abstract: It is a subject of exploration whether the phase pure anatase or rutile TiO2 or the band alignment due to the heterojunctions in the two polymorphs of TiO2 plays the determining role in efficacy of a photocatalytic reaction. In this work, the phase pure anatase and rutile TiO2 have been explored for photocatalytic nitroarenes reduction to understand the role of surface structures and band alignment towards the reduction mechanism. The conduction band of synthesized anatase TiO2 has been found to be more populated with electrons of higher energy than that of synthesized rutile. This has given the anatase an edge towards photocatalytic reduction of nitroarenes over rutile TiO2. The other factors like adsorption of the reactants and the proton generation did not play any decisive role in catalytic efficacy.

All that Glitters Is Not Gold: A Probe into Photocatalytic Nitrate Reduction Mechanism over Noble Metal Doped and Undoped TiO2

Abstract: Photocatalytic reduction of aqueous nitrate has been thoroughly studied over noble metals doped and pristine TiO2 synthesized by a customized single step microwave assisted hydrothermal method. The synthesized catalysts are systematically characterized using XRD, Raman spectroscopy, FE-SEM, HR-TEM, XPS, diffuse reflectance spectroscopy, and PL measurements. The characterization reveals the successful synthesis of highly crystalline doped and undoped nano-TiO2. The photocatalytic rate of aqueous nitrate reduction over undoped TiO2 is found to be higher than that of noble metal doped TiO2. Mechanistic studies of the photocatalytic reduction are carried out with the help of different hole (oxalic acid, and methanol) and electron (sodium persulfate) scavengers, which reveal that the photogenerated electrons are the primary agents toward efficient nitrate photoreduction. Detailed studies have revealed that the noble metal doping in TiO2 helps in efficient photogeneration of H2 compared to the undoped analogue,...

The role of fuel to oxidizer ratio in solution combustion synthesis of TiO2 and its influence on photocatalysis

Abstract: Recently, solution combustion synthetic approach has emerged as a potential route to synthesize a wide range of catalytic oxides. Nano TiO2 was synthesized by solution combustion methods using glycine, urea, and oxalyldihydrazide as fuels. X-ray diffraction and field emission scanning electron microscopy analyses revealed the structural and morphological differences of TiO2 synthesized with different fuels. The oxidizer to fuel ratio from lean to rich conditions also played a crucial role in determining the polymorphic percentage concentration in the synthesized TiO2 powders. However, diffuse reflectance spectroscopy and photoluminescence spectroscopy studies did not show any significant differences in the electronic properties of the synthesized TiO2. As the polymorphic composite phases synergistically influence the catalytic performances, photodegradation of methylene blue (MB) and photo hydrogen production were studied with the synthesized catalysts. The synergistic role crucially depended on the specific reaction. The presence of different TiO2 polymorphs due to difference in fuels during combustion controlled the photocatalytic efficiency of the catalysts toward MB degradation and hydrogen production.

TiO2 synthesized by various routes and its role on environmental remediation and alternate energy production

Abstract: Researchers debate on if it is only the crystalline properties of TiO 2 or also the surface morphology and even optical properties of different types of TiO 2 are the instrumental parameters on photocatalysis. It is a subject of exploration whether the phase pure anatase TiO 2 or the heterojunctions and band alignment in the two polymorphs of TiO 2 (anatase and rutile) plays the determining role in efficacy of a photocatalytic reaction. Three different synthetic routes such as polymerizable sol–gel, solution combustion and customized microwave assisted hydrothermal method have been employed to synthesize TiO 2 . The materials are characterized systematically using XRD, FE-SEM, HR-TEM, diffuse reflectance, photoluminescence, BET surface area and Raman spectroscopy. It is found that TiO 2 synthesized by polymerizable sol–gel approach yields a mixed phase of anatase and rutile, while the other two approaches yield phase pure anatase. The band gap obtained from diffuse reflectance measurements are compared with the direct and indirect band gaps derived from Kubelka–Munk plots. Among the three synthetic routes, TiO 2 synthesized by customized microwave assisted hydrothermal method exhibits the highest surface area, pore volume and diameter, and lowest recombination, which in turn play a crucial role in high rate of photocatalytic degradation of methylene blue. On the other hand, the phase pure anatase made out of solution combustion route with moderate surface area, pore volume and diameter outperformed the rest two catalysts in photocatalytic hydrogen production. The different reaction specific photocatalytic efficacies of these two materials are discussed with respect to the combinatorial role of nano-crystallinity, surface properties, and optical properties.

Unusual photoluminescence of Cu–ZnO and its correlation with photocatalytic reduction of Cr(VI)

Abstract: Cu–ZnO was synthesized by sol–gel route with a varied copper concentration of 1, 2 and 3 mol%. The synthesized materials were structurally characterized with powder X-ray diffraction and Raman spectroscopy, morphologically using a field emission scanning electron microscope, and electronic properties were studied with UV–visible spectroscopy and photoluminescence spectroscopy. Variation in Cu doping showed enhancement/quenching in photoluminescence of ZnO. This special characteristic is reflected in photocatalytic reduction of Cr(VI).