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

Abstract

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/Zn₃In₂S₆ nanoflower composites were prepared for the comprehensive treatment of low-concentration tetracycline (Tc) hydrochloride in wastewater based on the adsorption/photocatalysis of Zn₃In₂S₆ 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 Zn₃In₂S₆ 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 Zn₃In₂S₆ was slightly reduced after being combined with PPy, its photocatalytic efficiency was substantially enhanced. Specifically, 0.5%PPy/Zn₃In₂S₆ 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/Zn₃In₂S₆ ten times. The photocatalytic degradation mechanism analysis revealed that the enrichment of Tc on 0.5%PPy/Zn₃In₂S₆ negatively impacts the photocatalytic efficiency, while •O₂^- and •OH radicals were the main oxidative species that played an important role in the photoregeneration process.

Keywords: Adsorption enrichment; Photocatalytic degradation; Polypyrrole; Tetracycline hydrochloride; Zn(3)In(2)S(6).