Removal of hazardous textile dyes from water using Ni impregnated ZnO through sonophotocatalytic degradation

The visible-light-induced semiconductor photocatalyst nickel (Ni) impregnated ZnO was prepared by the wet impregnation method. Impregnation of Ni on ZnO shifts the bandgap from UV to the visible region. The present study involves the sonophotocatalytic degradation of textile dyes Acid Violet 49 (AV-49) and Acid Blue 45 (AB-45) in the presence of Ni-ZnO photocatalyst under the irradiation of visible light. The degradation efficiency of sonophotocatalysis was higher than sonolysis, sonocatalysis, photolysis and photocatalysis. The photocatalyst was characterized by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction. Effect of different operational parameters such as pH, catalyst dosage, oxidizing agents (enhancers), initial dye concentration, scavengers, catalyst re-usability, catalyst settling time and catalyst poisoning were studied. Maximum degradation (100%) of AV-49 and AB-45 was found at pH 10 in 20 min. The re-usability of the photocatalyst test showed an increase in time of degradation from 20 to 60 min with a 10%-20% decrease in degradation efficiency. The degradation of AV-49 and AB-45 follows the pseudo-first-order kinetic model. The results of sonophotocatalytic degradation of textile dyes were attributed to the efficient absorption of visible light, separation of charge carriers and good surface area. The method of sonophotocatalytic degradation assisted with the oxidizing agents has also advantages like safety, high efficiency and economy if applied to the textile dye wastewater treatment.