Peroxymonosulfate enhanced photocatalytic degradation of serial bisphenols by metal-free covalent organic frameworks under visible light irradiation: mechanisms, degradation pathway and DFT calculation

Visible light driven peroxymonosulfate (PMS) activation by metal-free photocatalysts has attracted great attention. In present study, covalent organic frameworks (COF-PRD, PRD refers to pyridine) were synthesized and utilized to activate PMS to degrade bisphenol A (BPA) with visible light (VL) irradiation. COF-PRD with PMS improved 3.5 times degradation kinetics for BPA degradation relative to that of COF-PRD without PMS with VL irradiation. ·O₂^–, h⁺ and ¹O₂ dominated the BPA degradation in COF-PRD with PMS with VL irradiation. Under anaerobic condition, BPA could still be effectively degraded due to the reaction of PMS with e^– to generate ·SO₄^–. In addition to BPA, bisphenol F (BPF), bisphenol B (BPB), bisphenol Z (BPZ) and bisphenol AP (BPAP) could also be effectively degraded by COF-PRD with PMS under VL irradiation conditions. Density functional theory (DFT) calculation together with intermediates determination showed that the main degradation pathway of bisphenols (BPs) included hydroxylation, electrophilic attack and ring-opening reaction. The bioaccumulation effects of BPs were greatly reduced during the degradation process. Moreover, COF-PRD exhibited excellent reusability in ten successive cycles. Clearly, COF-PRD could be employed as photocatalytic PMS activation to degrade bisphenols under both aerobic and anaerobic conditions.