Photo-enzymatic synergistic degradation of ciprofloxacin hydrochloride by CeO2(100)/Bi2Fe4O9 S-scheme heterojunction induced by crystal phase effect

S-scheme heterojunction has a broad application prospect in the field of water purification, but its construction faces a big challenge. We synthesized rod-like, cubic, and spherical cerium oxide (CeO2) loaded bismuth ferrite (Bi2Fe4O9) heterojunctions. The peroxidase-like (POD-like) activity of the heterojunction and the degradation performances of ciprofloxacin (CIP) were investigated using the crystal phase effect, thus achieving the effect of 'killing two birds with one stone'. Not only that, different crystal phases correspond to different band gaps and work function, which can control the energy band structure. Density functional theory (DFT) calculations show that the (100) crystal face of CeO2 has the maximum adsorption energy for hydrogen peroxide (H2O2) which can accelerate the cleavage of O-H bond and reduce the energy barrier of the reaction. The superiority of the transfer paths and charge transfer capability of S-scheme heterojunctions was confirmed by X-ray photoelectron spectroscopy (XPS), work function and charge differential distribution. The presence of multiple synergistic effects (combination of photocatalysis and enzyme catalysis, built-in electric field (BIEF), oxygen vacancies) accelerates carrier segregation of CBFO-C S-scheme heterojunctions and promotes redox cycling of Fe and Ce. Due to the increasing active free radicals, S-scheme heterojunctions (CBFO-C) exhibited the best POD-like activity and degraded 92.6% of CIP compared to type I heterojunctions (CBFO-R, CBFO-S).This study provides a new perspective for using crystal phase effect to activate H2O2 to construct S-scheme heterojunctions applied in environmental remediation.