Abstract:The photodegradation of azo-dye direct red 4BE (4BE) in aqueous solution by phosphatotungstic acid (PW12) as homogeneous catalyst was studied in a batch photoreactor. The parameters such as the concentration of 4BE and PW12were investigated, and the reaction mechanism involved was discussed. 4BE was decolorized effectively in the presence of phosphatotungstic acid under UV irradiation. When PW12 concentration was less than 600mg/L, the photocatalytic decolonization rate of 4BE increased along with the increase of PW12 concentration. The process of 4BE degradation followed a pseudo-first-order kinetics, and a maximum rate constant k of 0.1164min-1could be obtained at pH 2.0, PW12concentration of 600mg/L and 4BE initial concentration of 50mg/L. The photocatalytic degradation rate of 4BE decreased with the increase of dye concentration when 4BE concentration was in the range of 50 to 150mg/L. On the basis of the results of cyclic voltammogram and the UV-vis spectrum of 4BE, the mechanism for the photodegradation of 4BE by phosphatotungstic acid includes three pathways: oxidation by hydroxyl radicals, electron transfer within the complex of the excited phosphatotungstic acid and 4BE, and reduction of dye by the reduced phosphatotungstic acid, in which the oxidation of hydroxyl radicals palys a leading role.