Photolytic reaction mechanism and impacts of coexisting substances on photodegradation of bisphenol A by Bi2WO6 in water

Bi2WO6 displayed great photolytic degradation efficiency to bisphenol A (BPA) under simulated solar light irradiation but its reaction mechanism and the impacts of coexisting substances on the degradation remain unclear. In present study, the reaction mechanism was investigated using DMPO spin-trapping ESR spectra and experiments with scavengers of hydroxyl radicals (OH) and holes. The results supported that hole oxidation mainly governed the photodegradation process. As a common humic substance in natural water, humic acid accelerated the degradation of BPA when its concentration was 1 mg/L, while the photodegradation was impeded with the increase of humic acid concentration in the range of 5–20 mg/L. Almost all anions, including NO3−, HCO3−, Cl−, SO42− inhibited the degradation of BPA by Bi2WO6 and their inhibition effects followed the order of SO42− > Cl− > HCO3− > NO3−. Cations of Na+, K+, Ca2+ and Mg2+ displayed slight suppressing effect on BPA degradation mainly due to the impact of Cl− coexisting in the solution. However, Cu2+ hindered the BPA photodegradation heavily. Fe3+ and H2O2 affected the photodegradation in a complicated way: they suppressed or promoted the photodegradation depending on their concentrations. This could be the result of competition between photolyitc hole generated by Bi2WO6 and OH produced by Fe3+ or H2O2.

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► Direct hole oxidation dominated the photodegradation of BPA by Bi2WO6.
► Humic acid accelerated BPA degradation at low concentration but inhibited it at higher concentration.
► Almost all inorganic ions inhibited BPA degradation by Bi2WO6.
► Cu2+ suppressed the BPA photodegradation greatly.
► Fe3+ and H2O2 affected BPA degradation and mechanism depending on their concentrations.