Oxygen vacancy boosted photocatalytic decomposition of ciprofloxacin over Bi₂MoO₆: Oxygen vacancy engineering, biotoxicity evaluation and mechanism study

Herein, efficient visible light driven photocatalytic degradation of ciprofloxacin was realized over Bi₂MoO₆ with oxygen vacancies (OVs) which can be tunably introduced through a facile solvothermal method via the modulation of tetramethylethylenediamine (TMEDA). The optimal Bi₂MoO₆ with OVs possessed the highest CIP degradation rate of 1.799 mg min^-1 m^-1, about 8.4 times than that of the pristine Bi₂MoO₆. And more than half of CIP was mineralized in only 2 h. The biotoxicity of ciprofloxacin and its byproducts to E. coli K-12 and saccharomyces cerevisiae was thoroughly eliminated after 6 h's photocatalytic treatment. Characterization methods revealed the rich oxygen vacancies in Bi₂MoO₆ not only endowed it with broader visible light absorption and faster transfer of photogenerated carriers, but also provided abundant absorption sites of surface oxygen for efficient molecular oxygen activation. Correspondingly, plentiful active species were produced and participated in the photocatalytic process, thereby efficiently promoting the ciprofloxacin degradation. Based on the HPLC-MS analysis, a possible decomposition pathway of CIP was finally proposed with the first decomposition step of pipetazine ring oxidation and breakage. This work might open up new avenues for superior visible light driven photocatalysts design to deal with pharmaceutical compounds contamination via tunable OVs Engineering.