Photocatalytic treatment of Crystal Violet in aqueous solution: Box-Behnken optimization and degradation mechanism

A photocatalytic degradation of Crystal Violet (CV) in aqueous solution was investigated in batch reactor. Box-Behnken experimental design was using to establish a quadratic model showing the functional relationship between degradation rate and four operational parameters: pollutant concentration, irradiation time, zinc oxide (ZnO) dose, and stirring speed, at free pH (similar to 7), lamp irradiance (45 W m(-2)) and ambient temperature (similar to 25 degrees C). The results show that the most influential factor on the process was the CV concentration, with an effect of 48.27%, followed by the ZnO dose with an effect of 15.16%, at the third position comes the irradiation time with an effect of 11.81%, and the forth influencing parameter was the stirring speed with an effect of 1.04%. A total CV degradation (100%) was reached for ultraviolet (UV) irradiation time equal to 90 min, ZnO dose of 0.7 g L-1, and stirring speed of 558 rpm for CV initial concentration of 55 mgL(-1). For CV concentration equal to 100 mg L(-1)solar irradiation seems to be better up to 96% of degradation against 62% for UV lamp after 120 min of irradiation time. The O-2(center dot-) radicals were the main active species responsible for the degradation of CV. The degradation kinetic was well described by the pseudo first-order model.