The degradation of diazo Direct Yellow 12 dye (Chrysophenine G) was studied by using photocatalytic oxidation (UV/semiconductor). The influence of various parameters, including the type of catalyst. the presence of H2O2, initial pH of the solution and the catalyst loading on the degradation process were investigated. The photocatalysts were TiO2, ZnO, Fe2O3 and 5nO(2). In addition, the effects of several cations (Cu2+, Al3+, Cr3+, and Sn4+) and anions (BiO3-, SO42-, and CN-) were examined in UV/TiO2 system. The results obtained showed that acidic pH is proper for the photocatalytic removal of Direct Yellow 12. In optimum pH, the degradation of dye was completely performed in UV/TiO2 system but other catalysts did not show any significant photodegradation of the dye. However, the addition of H2O2 to the heterogeneous system activated these catalysts. After 90 min of reaction, the order of photocatalytic activity of various photocatalysts was: UV/H2O2/TiO2>UV/H2O2/Fe2O3>UV/H2O2/ZnO>UV/H2O2/SnO2. (C) 2009 Elsevier B.V. All rights reserved.