Dependence of superoxide radical generation on peroxymonosulfate under visible light: Enrofloxacin degradation and mechanism insight

Compared with the pure photocatalytic degradation system, although the sulfate radicals (SO4·-) generated in the peroxymonosulfate-assisted photocatalytic (PMS-photo) system redound to improve degradation activity. However, the degradation mechanism of the PMS-photo system still needs to be improved. For example, the relationship between superoxide radical (O2−) generation and PMS has been overlooked. Herein, the BiVO4/BiOBr photocatalyst was prepared via anion exchange method. Subsequently, the in-situ growth of BiVO4 on the surface of BiOBr nanosheet was confirmed though various characterization techniques. The degradation performance of the PMS-photo system was investigated, in which the 10 wt% BiVO4/BiOBr (BVB) composite exhibited the highest efficiency in degrading enrofloxacin (ENR, 95 %, 90 min) and tetracycline (TC, 94 %, 20 min) under visible light. Moreover, the structure of the intermediate product and the corresponding toxicity were determined by liquid chromatography-mass spectrometry (LC-MS) and Toxicity Estimation Software (T.E.S.T). Photoelectrochemical and fluorescence detection were employed to reveal that 10 wt% BVB has the fastest photogenerated carrier generation, separation and transmission efficiency. In addition, results from radicals quenching experiments, electron paramagnetic resonance (EPR), energy band structure analysis and DFT calculation were combined to substantiate the formation of II-type heterojunction between BiVO4 and BiOBr. More importantly, based on the above results, it was confirmed that the active species in the pure photocatalytic system were holes (h+) and electrons (e−). Due to the introduction of PMS, O2− and singlet oxygen (1O2) were generated, thereby achieving efficient degradation of pollutants. This result revealed the effect of peroxymonosulfate on the generation of O2−, presented a new perspective on the synergy of PMS with photocatalysis and offered a novel avenue for enhancing the performance of underperforming photocatalysts.