Visible-light-excited humic acid for peroxymonosulfate activation to degrade bisphenol A

In this study, a novel peroxymonosulfate (PMS) activation method by visible light (VL) excited humic acid (HA) was developed and applied to degradation of bisphenol A (BPA). Results showed that, in HA (2 mg/L)/PMS (1 mM)/VL system, the degradation rate of BPA could reach 95.4% within 30 min, which was much higher than that of HA/VL system (9.4%) and PMS/VL system (15.5%). Meanwhile, the concentration of HA was also decreased in this process and the original structure of HA was obviously destroyed. Reaction mechanism accounting for the effect of HA on BPA degradation in the PMS/HA/VL system was explicated by the quenching experiments, electron paramagnetic resonance (EPR) detection and HA fractionation experiments. Results showed that singlet oxygen (1O2), hydroxyl radical (OH) and sulfate radical (SO4−) were all involved in the system, and 1O2 was the primary reactive species responsible for BPA degradation. The aromatic constituents of HA made the dominant contribution to the generation of reactive species, in which the phenolic groups played the role of electron-donor, and the quinone moieties acted as the electron shuttles could accelerate the electron-transfer between HA and PMS, which thus activated PMS to form the reactive species for BPA degradation. As HA is ubiquitous in nature, this study may provide a new insight into the in situ water treatment with the assistance of PMS.