Synergistic adsorption and Z-Scheme charge transfer in MnO2/BiOBr heterojunctions for enhanced photocatalytic removal of antibiotics

The removal of antibiotics from water remains a challenge, where adsorption as a pre-concentration step is crucial for subsequent photocatalytic degradation. Herein, we propose a synergistic strategy by constructing a heterojunction between the strong adsorbent MnO 2 and the photocatalyst BiOBr. A series of MnO 2 /BiOBr composites were synthesized via an in-situ redox method under an ice bath. The optimal 1% MnO 2 /BiOBr composite exhibited remarkably enhanced simultaneous adsorption and photocatalytic degradation efficiency towards ciprofloxacin (CIP), norfloxacin (NOR), and tetracycline (TC) under simulated sunlight, significantly outperforming pristine BiOBr and MnO 2 . Comprehensive characterizations confirmed the successful formation of an intimate heterojunction. Mechanistic studies, including active trapping species and electron spin resonance (ESR) analysis, revealed that the superoxide radical (•O 2 - ) and hydroxyl radical (•OH) were the dominant reactive species. The band structure alignment and charge transfer analysis supported a direct Z-scheme mechanism, which effectively promotes the separation of photogenerated carriers while preserving high redox potentials. Furthermore, the effects of operational parameters (catalyst dosage, initial concentration, pH), inorganic anions, and natural organic matter (NOM) on CIP removal were systematically investigated, demonstrating good practicality. The degradation pathways of CIP were elucidated via LC-MS analysis, and toxicity assessment using T.E.S.T. software indicated a general reduction in the ecotoxicity of the intermediates. This work highlights MnO 2 as a multifunctional modifier and provides a feasible approach for designing efficient adsorbent-photocatalyst hybrids for antibiotic wastewater remediation.