Reinforced charge transfer on MnIn2S4/Co3O4 for the efficient treatment of chlortetracycline and real pharmaceutical wastewater: Z-scheme collaborating with S–O bridging bond

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Efficient carrier separation and photocatalytic reactions in heterojunctions are strongly dependent on the magnitude of interfacial resistance and the nature of charge transfer pathways. Herein, a novel MnIn 2 S 4 /Co 3 O 4 Z-scheme heterojunction photocatalyst with covalent S–O interfacial bonds was successfully fabricated via a calcination-hydrothermal method. The optimized MIS/CO-22 heterojunction exhibited exceptional performance, achieving a 96.9 % chlortetracycline degradation rate within 60 min and effectively treating real pharmaceutical wastewater by reducing its COD from 8115 mg/L to 1858 mg/L, substantially outperforming its single-component counterparts. Through systematic experimental characterization and theoretical calculations, this work proposes a cooperative Z-scheme photocatalytic degradation mechanism based on interfacial covalent bonds. Within this mechanism, the Z-scheme mode established a defined pathway for charge transmission, while the S–O covalent bonds effectively reduced interfacial charge transfer resistance and acted as charge transfer channels, thereby significantly enhancing the separation efficiency of photogenerated carriers. Besides, this study further combined mass spectrometry analysis with DFT calculation to analyze the possible degradation pathways of chlortetracycline, and evaluated the toxicity of the degradation intermediates through toxicological calculations. This work establishes a strategic design principle for reinforced charge separation toward advanced antibiotic degradation and environmental remediation.

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