In this study, the photocatalytic activities were investigated for the treatment of Reactive Green 12 (RG 12) solution under UV and visible irradiation using Cu doped TiO2, and TiO2 impregnated on (1) cellulose and (2) UV-C activated polyester catalysts. The obtained results revealed that TiO2 impregnated on UV-C activated polyester showed promising performances compared to the other synthesized catalysts. Moreover, the dispersion of active sites on UV-C pretreated polyester was optimized and tested for RG 12 removal in the binary mixture, the presence of Direct Red 89 (DR 89) dye had an inhibiting effect on the rate of RG 12 discoloration process because of the competitive effect between dyes molecules toward the available active sites. The role and contribution of reactive oxidizing species (ROS): center dot OH, O-2 center dot(-) and h(+) was also examined with the two catalysts under different light sources; it was found that the superoxide radical anion played the key role in RG 12 photocatalytic degradation for both TiO2 supported catalysts. Nevertheless, the behavior of O-2 center dot(-) radicals was found to be changed from promoting effect to inhibitory effect when changing light from UV to Visible.