Ultraviolet to visible-light range photocatalytic activity of ZnO films prepared using sol-gel method: The influence of solvent

The textile industry is characterized by high consumption of water, fuel, and chemicals. The wastewater treatment and recycling possibilities in the textile industry are environmentally of the highest importance. The most common chemical pollutants present in textile industry wastewater are the azo-dyes. The solution based sol-gel method was used to synthesize ZnO thin films using different solvents to evaluate the morphology-dependent photocatalytic activity toward the degradation of two azo dyes including sodium [3-[(4,5-dihydro- 3-methyl-5-oxo-1-phenyl-1H-pyrazol-4-yl)azo]-2-hydroxy-5-nitrobenzenesulp-honato (3-)] hydroxychromate (1-) and sodium (5-((4'-((2,6-dihydroxy-3-((2-hydroxy-5-sulfophenyl)azo)phenyl)azo)-4-biphenylylazo) salicylato (4-)) cuprate (2-) in water. 2-Propanol, methanol, ethanol, and 1,4-butanediol were used as solvents. The photocatalytic degradation rates depend on the dye structure and concentration, solvent-dependent ZnO film morphologies, pH of the medium and excitation light source. The observed rate constants of ZnO film prepared using 2-propanol and of ZnO film prepared using methanol were enhanced approximately by a factor of 3 under UV light and under visible light, respectively. The obtained results were discussed according to the structure and morphology of ZnO films as key parameters in photocatalytic activity. (C) 2012 Elsevier B. V. All rights reserved.