S-scheme BiVO4/CQDs/β-FeOOH photocatalyst for efficient degradation of ofloxacin: Reactive oxygen species transformation mechanism insight

Photocatalysis technology exhibited promising application for advanced treatment of wastewater. Nevertheless, the design of efficient photocatalyst and the mechanism of free radicals in pollutant degradation still remained to be further investigated. Herein, BiVO4/CQDs/beta-FeOOH photocatalyst was fabricated by electrostatic self-assembly method, which exhibited the excellent photocatalytic performance. Under visible-light irradiation, the removal rate of ofloxacin by BiVO4/CQDs/beta-FeOOH (0.25 min(-1)) was 1.93 times than pristine BiVO4, and the removal efficiency in 15 min reached 99.21%. The perfect reusability of BiVO4/CQDs/beta-FeOOH was ascribed to the persistent catalytic active centers provided by the renewable surface oxygen vacancies on the beta-FeOOH. As electron transfer channels, CQDs facilitated the transfer of BiVO4 photogeneration electrons. The matched band structure allowed the construction of S-scheme heterojunctions, and the higher conduction band position was retained while the carrier separation was promoted. More importantly, this work firstly reported the phenom-enon that the main reactive groups in the photocatalysis process would be directionally transformed with the change of pH conditions. Based on the analysis of capture and electron paramagnetic resonance experiments, center dot O-2(-) was the main free radicals to photodegrade OFL in neutral and alkaline conditions. However, when the solution pH turned into acidic, the photodegradation of OFL was dominated by O-1(2). This innovative phenomenon was due to that acidic condition accelerated the reaction kinetics of spontaneous transformation of center dot O-2(-) to O-1(2) and inhibited the direct oxidation of pollutants by center dot O-2(-) . Accordingly, this research could inspire theoretical study of free radical reaction and the design of S-scheme heterojunction photocatalysts.

Automated summary

This study successfully prepared a highly efficient BiVO4/CQDs/beta-FeOOH photocatalyst and revealed its mechanism. The photocatalyst showed significantly improved removal efficiency of ofloxacin under visible-light irradiation and exhibited good reusability. Additionally, the study also reported for the first time the phenomenon of directional transformation of reactive groups in the photocatalysis process under different pH conditions.