Removal of low-concentration tetracycline from water by a two-step process of adsorption enrichment and photocatalytic regeneration.

Developing a high-performance method that can effectively control pollution caused by low concentrations of antibiotics is urgently needed. Herein, a novel three-dimensional PPy/ZnInS nanoflower composites were prepared for the comprehensive treatment of low-concentration tetracycline (Tc) hydrochloride in wastewater based on the adsorption/photocatalysis of ZnInS and the conductivity of PPy. In this preparation method, adsorption enrichment and photocatalytic regeneration were conducted in two steps, eliminating the dilution and dispersion effects of aqueous solvents on photocatalytic species and antibiotics. Results showed that ZnInS could effectively adsorb 87.85% of Tc at pH of 4.5 and photocatalytically degrade Tc at pH of 10.5. Although the adsorption capacity of ZnInS was slightly reduced after being combined with PPy, its photocatalytic efficiency was substantially enhanced. Specifically, 0.5%PPy/ZnInS could degrade 99.92% of the surface-enriched Tc in 1 h and induce the regeneration of the adsorption sites. Furthermore, the adsorption capacity remained above 85% even after recycling PPy/ZnInS ten times. The photocatalytic degradation mechanism analysis revealed that the enrichment of Tc on 0.5%PPy/ZnInS negatively impacts the photocatalytic efficiency, while •O and •OH radicals were the main oxidative species that played an important role in the photoregeneration process.