Dual regulation of hydroxyapatite for BiOBr towards significantly enhanced photocatalytic degradation of ciprofloxacin

The photocatalytic degradation of refractory antibiotics still suffers from severe charge carrier recombination and thermodynamically limited oxygen activation. Herein, a hydroxyapatite/bismuth oxybromide (HAp/BiOBr) photocatalyst with a tight hetero-interface was designed for the degradation of ciprofloxacin (CIP), where a dual microenvironment regulation mechanism endowed by HAp was revealed to be responsible for the boosted catalytic activity of HAp/BiOBr. On the one hand, the spontaneous polarization of PO 4 3− groups in HAp generates a robust local built-in electric field (LEF) at the interface, which promotes the highly efficient spatial dissociation of photogenerated charges within BiOBr. On the other hand, unsaturated-coordinated Ca 2+ on HAp functions as Lewis acid active sites to in situ activate the interfacial dissolved oxygen (O 2 ), which effectively overcomes the thermodynamic limitation caused by the relatively positive conduction band of BiOBr for massive superoxide radical (·O 2 − ) generation. As a result, the optimized HAp/BiOBr achieves a 99.3% degradation efficiency of CIP in 60 min under visible light irradiation, with an apparent reaction rate constant 2.7 times higher than that of pure BiOBr. In addition, CIP degradation pathway and multidimensional ecotoxicity were analyzed. The results in this work not only provide a novel strategy utilizing polar dielectric materials to design highly efficient catalysts, but also supply a theoretical support for the removal of CIP contamination from water environments.