Photocatalytic Degradation of Monoazo and Diazo Dyes in Wastewater on Nanometer-Sized TiO2

Advanced oxidation processes (AOPs) have proved very effective in treatment of the various hazardous organic pollutants in water. The photocatalytic degradation of two azo dyes, monoazo dye Acid Orange 10 (AO10) and diazo dye Acid Red114(AR114) present in wastewater were studied. Homogeneous photocatalytic degradation of the two azo dyes with UV/H2O2 process was investigated. The rates of disappearance of the two azo dyes were monitored spectrophotometrically at the visible maximum absorption wavelengths. It was found that the rate of decolorization rises by increasing the initial dosage of H2O2 up to a “critical” value at which it is maximum and beyond which it is inhibited. The rates of reactions follow pseudo-first-order kinetics. Also heterogeneous photocatalytic degradation of the two azo dyes with UV/TiO2 (titanium dioxide) interface was investigated. The photocatalytic degradation rate depends on dye structure, dye concentration, TiO2 concentration and pH of the medium. The mechanism of the photodegradation process under UV-visible light illumination involves an electron excitation into the conduction band of the TiO2 semiconductor leading to the generation of very active oxygenated species that attack the dye molecules leading to photodegradation. Photocatalytic activity of TiO2 was examined by focusing on its enhancement by electron scavengers in the photocatalytic decomposition of the two azo dyes. The electron scavengers employed was inorganic oxidant such as H2O2, adequate dose of H2O2 led to a faster degradation of the two azo dyes in the TiO2 photocatalytic system. The fast decolorization of monoazo dye (AO10) than diazo dye (AR114) is an indication that, the number of azo and sulphonate groups in the dye molecule may be a determining factor for increasing the degradation rates. [Researcher. 2010;2(9):52-71]. (ISSN: 1553-9865).