Magnetically recyclable spherical Cu2O@Fe3O4 S-scheme heterojunction for efficient tetracycline removal via visible light-activated peroxydisulfate

Abstract

The overuse of antibiotics in treating bacterial infections is a significant threat to the environment and human health. The utilization of visible-light-assisted peroxydisulfate (PDS) activation for eliminating organic pollutants is a promising approach. This study uses a straightforward hydrothermal method to prepare magnetically recyclable spherical Cu₂O@Fe₃O₄. The efficacy of this material in removing antibiotic pollutants was assessed using simulated wastewater containing tetracycline (TC). TC removal was achieved by activating PDS with Cu₂O@Fe₃O₄ as the visible light photocatalyst. Experimental findings revealed that under specific conditions—a pH of 9, a Cu₂O@Fe₃O₄ concentration of 60 mg L⁻¹, and a PDS concentration of 25 mg L⁻¹—the removal rate of TC reached 97.67% after 30 min of irradiation. Moreover, Cu₂O@Fe₃O₄ exhibited excellent recyclability, maintaining a removal rate of 93.33% after five recycling rounds. X-ray diffraction characterization of the Cu₂O@Fe₃O₄ composite before and after cycling confirmed its robust stability and reusability. In situ X-ray photoelectron spectroscopy analysis showed that electrons migrated from Fe₃O₄ to Cu₂O during the photocatalytic reaction, indicating the formation of an S-type heterojunction in Cu₂O@Fe₃O₄. Free radical trapping experiments demonstrated the active involvement of ·OH, ·O₂⁻, SO₄˙⁻ and h⁺ radicals in TC removal.