Unveiling the interaction of epigallocatechin-3-gallate with peroxymonosulfate for degradation of bisphenol S: Two-stage kinetics and identification of reactive species

Abstract Epigallocatechin-3-gallate/peroxymonosulfate (EGCG/PMS) process was investigated as a process and evaluated for its performance to degrade emerging contaminants such as bisphenol S (BPS). Results showed that BPS degradation followed a two-stage kinetics process (i.e., a fast stage followed by a slow stage), and both stages obeyed the pseudo-first order kinetic model. The two-stage process was because both EGCG and EGCG quinones can activate PMS, and EGCG was completely transformed to quinones in the slow stage. The impacts of EGCG concentration, dissolved oxygen, pH, alkalinity, and natural organic matter on the performance of EGCG/PMS process were investigated in detail. The presence of EGCG significantly accelerated BPS degradation by PMS at pH 3.0–7.0, but at pH 8.0–10.0, EGCG began to inhibit BPS degradation by PMS. This inhibition was attributed to the base activation of PMS as the main mechanisms at pH 8.0–10.0. Further, EPR experiments indicated that sulfate radical, hydroxyl radical, and singlet oxygen were generated and responsible for BPS degradation in EGCG/PMS process. Various kinds of reactions including hydroxylation, electron transfer, and C-O radical coupling occurred in EGCG/PMS process. The acute toxicity of the treated solution was reduced after the EGCG/PMS process. Overall, EGCG/PMS process shows promising performance to remove emerging contaminants at acidic conditions, and our study shed light on a novel PMS-based process.