Photocatalytic decolorization of crystal violet in aqueous nano-ZnO suspension under visible light irradiation

Nanosized ZnO was prepared through hydrothermal process and characterized by scanning electron microscopy, X-ray diffraction and laser-induced breakdown spectra measurement techniques. The as-prepared nanosized ZnO was used to investigate the decolorization/degradation of crystal violet, a cationic dye which is extensively used in dyeing/textile industries, under visible light through adsorption studies of the dye solution with ZnO in the dark. The results show that the adsorption of CV on ZnO takes about 200 min to reach equilibrium, and the equilibrium time at a certain concentration of the dye seems to be independent of temperatures that are used for the preparation of ZnO samples. The adsorption data follow the pseudo-first-order kinetic model (Lagergren), and the adsorption pattern follows the Langmuir model. Prepared ZnO (300°C) was found to be a more efficient photocatalyst among others including pristine ZnO, to decolorize/degrade the dye. The decolorization rate is increased with the decreasing of the initial dye concentration and reached at a limiting value. The catalyst loading also influences the decolorization/degradation of the dye, and decolorization rate is increased with increasing the catalyst loading and reached at a limiting value. ZnO was found to be stable under visible light irradiation at solution pH = 6. The photocatalytic degradation of the dye followed zero-order kinetics, and the Langmuir-Hinshelwood mechanism was found to be valid.