Exploring the synergism of sunlight and electrooxidation on persulfate activation for efficient degradation of bisphenol S: Performance, Pathway, and mechanism

Sulfate radical-based advanced oxidation processes had been widely applied in the water treatment. In this study, a novel solar-assisted electrooxidation process (SEOP) to activate peroxymonosulfate (PMS) or peroxydisulfate (PDS) was conducted for the degradation of bisphenol S (BPS). The SEOP with persulfate (PS) demonstrated its synergistic effect for BPS degradation, compared with the electrooxidation/PS and the solar process. The hydroxyl radical, sulfate radical (SO4·-), and singlet oxygen were regarded as primary active species in BPS degradation in SEOP with PS. The transition structure complex (persulfate*) on the anode promoted the efficiency of BPS degradation via the non-radical mechanism. The activation of PMS and PDS in SEOP was dominated through radical and non-radical mechanism, respectively. To effectively supplement experimental work with quantum chemical calculation, density function theory (DFT) showed that the active sites mainly focused on the phenol ring of BPS. The energy barrier calculation indicated that BPS was more susceptible to be attacked by SO4·- through electron transfer. BPS was mainly degraded by ring-opening, substitution, addition, C–C bond breaking, and decarboxylation reactions. Furthermore, the effective decrease in bio-toxicity of BPS intermediates in SEOP with PS was predicted. Experiments under various current densities, initial concentration of PS, electrolyte, and humic acid suggested the feasibility of SEOP with PS. BPS was degraded with lower energy consumption (0.18 kWh·m−3·order−1) in SEOP with PMS than that in SEOP with PDS (0.30 kWh·m−3·order−1) and without PS (0.38 kWh·m−3 order−1), respectively. The SEOP with PS poses the feasible, convenient, and economic potential for the degradation of refractory pollutants.