Theoretical and experimental insights into electrooxidation degradation of bisphenol A: Degradation pathways, toxicity evolution, comparison with phenol on molecular structure influence

Parent structures can greatly affect the free radicals attack, and the corresponding degradation efficiency and toxicity of organics, while the further influence mechanism of compounds' structure with similar parent structure still needs to be revealed. Herein, the electrochemical oxidation process (EOP) was applied to explore the effects of similar pollutants' (bisphenol-A(BPA)/phenol) structure on dominant radical and degradation mechanism, and comprehensively assessed the ecotoxicity of the BPA degradation intermediates/products. The removal efficiency of BPA achieved 84.2 %–98.3 % in all the experimental conditions. BPA degradation pathways, mainly including radical adduct formation, C–C bond cleavage and hydroxylation, were proposed based on density functional theory (DFT) calculation and intermediates detection. Toxicity assessment revealed the reducing trend of risk during BPA degradation, and the acute/chronic toxicity (toxic/very-toxic) of BPA were reduced to not-harmful/harmful. The slight increased toxicity in initial stage was due to the generated chlorinated products from the highest contribution of radical chlorine species (RCS). The comparison of BPA/phenol degradation demonstrated the influence of molecular structure on degradation even with similar parent structure. It seemed that the reaction time and rate constants between BPA/phenol and radicals were affected (achieved 5 orders of magnitude), which can further influence radical contributions (BPA: RCS (63.8 %) > OH (30.6 %) > direct oxidation (5.5 %), phenol: OH (78.78 %) > RCS (10.7 %) > direct oxidation (10.6 %)) and preferable attacking sites, and thus degradation mechanism and efficiencies. These results provided new insights into novel anodes/catalysts design during advanced oxidation process to improve their degradation performance and practical application safety.