Key parameters for enhancing visible-light-driven photocatalytic activity of ZnS nanoparticle

The use of pharmaceuticals is increasing rapidly as the industrialization of the pharmaceutical industry progresses. Accordingly, antibiotics discharged into wastewater are attracting attention as emerging pollutants that aggravate water pollution. The spread of antibiotic-resistant bacteria that cause clinically infectious diseases is also a global challenge. In this study, ZnS nanoparticles were synthesized using a simple hydrothermal process and applied to the photocatalytic degradation of antibiotic tetracycline and the photocatalytic inactivation of high-strength multidrug-resistant bacteria (Klebsiella pneumonia and Staphylococcus aureus) and total coliforms under visible light irradiation. The prepared nanomaterial was characterized using a range of analytical techniques to confirm the properties of the ZnS nanoparticles. The photocatalytic activities of nanoparticles were investigated with various parameters, such as catalyst dose, type and intensity of light, antibiotic concentration, and pH. Among them, the type of light (white light) and pH were the most important factors affecting the photocatalytic activity of ZnS nanoparticles. The basic pH condition (pH 10) improved the photocatalytic reaction activity (k = 0.0318 min−1, R2 = 0.9653), approximately 30 times more than acidic conditions (pH 3) and approximately 3.3 times more than neutral conditions (pH 7). The total coliforms in wastewater effluent were completely inactivated within 30 min of reaction time using white light irradiation (80 mW/cm2). The scavenger experiment revealed that the reactive oxygen species appeared in the order of O2·− > ·OH > h+. The reusability studies showed that the ZnS nanoparticles were very stable and retained more than 94% of their catalytic capacity after five cycles.