Comparative studies of operational parameters of degradation of azo dyes in visible light by highly efficient WOx/TiO2 photocatalyst

The multidimensional aspects of the photocatalytic activity were investigated in a systematic way by employing the dyes Acid Orange 7 (AO7) and Methyl Orange (MO) as substrates in terms of their degradation or conversion rates. 4.0% WOx/TiO2 nanocomposite demonstrated the best reactivity under visible light, allowing more efficient usage of solar light. The reduced form of W decreased the band gap and inhibited electron hole recombination efficiently. This composite was characterized by X-ray diffraction spectroscopy (XRD), UV-vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). A series of experiments were conducted to investigate the operational parameters under visible light irradiation such as optimization of nanocomposites wt%, change of pH, reuse of catalyst and initial dye concentration. The kinetics of the dyes degradation was found to follow the Langmuir-Hinshelwood model. Decomposition or mineralization was investigated with the changes of absorption spectra, pH, degradation efficiency and TOC removal in visible irradiation systems. FT-IR spectroscopy of these adsorbed dyes on WOx/TiO2 powder provided an insight to the mode of its adsorption on WOx/TiO2. It was found that the dye adsorbed on WOx/TiO2 underwent a series of oxidation steps which lead to decolorization and formation of a number of intermediates mainly aromatic and aliphatic acids. These intermediates were quantified by GC/GC-MS. (C) 2010 Elsevier B.V. All rights reserved.