Comparative study on bisphenols oxidation via TiO2 photocatalytic activation of peroxymonosulfate: Effectiveness, mechanism and pathways

In this work, degradation of bisphenol F (BPF), bisphenol AF (BPAF) and bisphenol S (BPS) by peroxymonosulfate (PMS) with TiO2 nano-tubes arrays (TiO2NTAs) under simulated sunlight irradiation was investigated and compared for the first time. All three bisphenols exhibited appreciable degradation following the order of BPS < BPAF < BPF, and acidic conditions were more conducive to their degradation. The SO4•-, ·OH, h+ and •O2- were all identified in three bisphenols degradation processes. Among these, SO4•- and •O2- were proven to play a dominant role in BPF oxidation process, but SO4•- and h+ were confirmed as the main reactive species for BPAF and BPS removal. Owing to the different reactive species worked in different bisphenols degradation processes, the influences of inorganic anions on three bisphenols degradation were also different. By analyzing the oxidation intermediates of the three bisphenols, it was found that there were some common degradation pathways including bond-cleavage and hydroxylation of the benzene ring shared by three bisphenols. Besides, some specific degradation pathways were also identified, for example, the self-coupling was found in BPF and BPS degradation process, while the benzene ring splitting was occurred only in BPAF transformation process.