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In the present study, homogeneous and heterogeneous photocatalytic degradation of a hazardous and non-biodegradable compound, benzoic acid, in its aqueous solution by strong oxidizing agent, hydrogen peroxide, in the presence of ultraviolet (UV) radiation emitted from UV source is investigated. The different UV+Fe2++H2O2, UV+TiO2and UV+ZnO combinations generate hydroxyl radicals having very high oxidation potential, which helps in complete mineralization of the organic pollutants and are environmentally benign processes. Almost complete degradation of 97·6% and decolorization of the substrate is achieved within 90 min by UV+Fe2++H2O2system, while it takes 240 min with heterogeneous photocatalytic system. The experiments were carried out in a batch photoreactor using 8-W low-pressure mercury vapor lamp. Substrate concentration was determined by UV-visible spectrophotometry. The photocatalytic processes were strongly pH dependent and adhered to first-order kinetics.

The effluent from the textile, paper and food industries containing dye is strongly colored and reveals very harmful effects on living things. Heterogeneous photocatalysis is an effective treatment method for the removal of dyes from industrial wastewaters. In this work, the photocatalytic degradation of Eosin Y dyes is reported. The irradiation of aqueous solution of Eosin Y dyes in the presence of photocatalyst and UV light was carried out in a batch photoreactor. Titanium dioxide and zinc oxide were used as photocatalysts for the study. The rate of degradation was estimated from residual concentration spectro photometrically. The effects of operating conditions such as Eosin Y initial pH, H2O2/COD ratio and the amount of catalyst loading on the removal efficiency were evaluated. The results of experiments indicated that the removal of Eosin Y increased with increasing the catalyst loading. Results show that maximum degradation efficiency of 99·91% occurred in 60 min with 30 mg/750 ml of titanium dioxide catalyst dose.