Response Surface Methodology for Optimization of Solar Photo-Oxidation of Direct Violet 51 on TiO2 and ZnO

This work is a study of the optimization of the removal of a textile azo dye namely Direct Violet 51 (DV 51) by heterogeneous solar photocatalysis onto ZnO and TiO2. The Response Surface Methodology (RSM) was applied to design the experiments and to investigate the interactions between the physical parameters including the type of catalyst. Based on the results, a degradation efficiency of 100 % was obtained for the ZnO/Solar light system in the optimal conditions (catalyst dose = 0.1567 g/L, CO = 10 ppm, and reaction time = 120 min). Appropriate figures of merit were selected for evaluating the energy requirement for DV 51 removal. The estimation of collector area per order and electric energy per order confirmed that the ZnO photocatalytic system used the introduced light more efficiently both under artificial and solar light. According to the scavenging mechanism study, superoxide (O·2-) and electrons (e-) are the main species responsible for DV 51 degradation by ZnO.