Photocatalytic degradation of reactive black 5 azo dye by zinc sulfide quantum dots prepared by a sonochemical method

Zinc sulfide (ZnS) nanoparticles (NPs) with an average particle size of 2 nm were successfully synthesized under ultrasonic irradiation without any surfactant and high temperature treatment. Prepared NPs were characterized by powder X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, dynamic light scattering analysis, and UV–vis absorption spectroscopy. The energy band gap of ZnS NPs was measured by UV–vis absorption spectroscopy. The photocatalytic activity of semiconducting sulfide quantum dots for degradation of an azo dye called reactive black 5 (RB5) was investigated. Results showed that the dye can be photocatalytically degraded with high rate by ZnS NPs under UV light irradiation. The kinetics of removal of RB5 in aqueous solutions was studied in a series of experiments which were varied in the amount of ZnS NPs, contact time, pH, dye concentration, and temperature. The experimental data were fitted very well in the pseudo-second order kinetic model. 95% of dye was successfully removed in 10 min using 0.2 g ZnS NPs in a neutral pH. A possible molecular mechanism for photocatalytic degradation of dye by ZnS NPs was also given.