Study On Bisphenol Contaminants Degradation By EGCG And Its Cu(Ⅱ) Complex Catalyzing PMS

Bisphenol compounds（BPA,BPAF,BPS,etc.）have been widely applied in industrial manufacturing of daily necessities as they are synthetic chemical raw materials.In recent years,they have been frequently detected in aqueous environment.Because of their estrogenic activities,they have potential risk to human health as endocrine interferon.Bisphenol contaminants are difficult to biodegrade,therefore conventional water treatment processes have limited ability to remove them,which has received widespread attention.Because sulfate radicals based advanced oxidation processes show superior degradation performance for refractory contaminants,in this study,reducing agent EGCG and transition metal ion Cu（II）were adopted to activate PMS to degrade bisphenol contaminants.The degradation performance,influencing factors,kinetic analysis and mechanism were systematically investigated.First,an eco-friendly reducing reagent epigallocatechin-3-gallate（EGCG）was applied to activate PMS in this study.Results showed that EGCG can effectively activate PMS to degrade bisphenol S（BPS）at acidic conditions.The removal rate of BPS in EGCG/PMS process can reach 57%within 24 h,while only 8%BPS was removed in only PMS process.In addition,the impacts of EGCG dosage,PMS dosage,dissolved oxygen,initial solution p H and co-existing water matrix components on BPS degradation were explored.Results showed that the optimal reaction condition s in the experiment were 7.5μmol/L EGCG and 1.0 mmol/L PMS.The kinetic analysis results showed that BPS degradation in EGCG/PMS process followed a two-stage kinetics process（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 transformed to quinones in the slow stage.The presence of EGCG significantly accelerated BPS degradation by PMS at p H 3.0–7.0,but at p H 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 p H 8.0–10.0.Further,quenching experiment and electron paramagnetic resonance（EPR）experiments indicated that sulfate radical,hydroxyl radical,and singlet oxygen were generated in EGCG/PMS process.According to the eight intermediate products determined by HPLC/MS,various kinds of reactions including hydroxylation,electron transfer,direct oxidation,and C-O radical coupling occurred in EGCG/PMS process.Adding transition metal copper ion to EGCG/PMS process,the presence of EGCG can significantly improve the degradation performance of Cu（II）/PMS process.Due to the strong reducing and chelating ability of EGCG,Cu（II）was transformed to Cu（I）then Cu（I）was chelated by EGCG forming Cu（I）-EGCG complex.Thus,the Cu（I）concentration in the solution can be maintained at a stable level,continuously activating PMS to generate reactive radicals.The removal rate of BPA in Cu（II）/EGCG/PMS process can reach 80%within 15 min.The degradation efficiency of Cu（II）/EGCG/PMS process is quite higher than EGCG/PMS process.The impacts of Cu（II）,EGCG and PMS concentration and co-existing components including natural organic matters,alkalinity,and chloride ion were investigated.The kinetic analysis results showed that BPA degradation in Cu（II）/EGCG/PMS process followed the pseudo-first order kinetic model.The impacts of solution p H and dissolved oxygen on BPA degradation were also evaluated to interpret the roles of Cu（I）and superoxide radical in Cu（II）/EGCG/PMS process.The concentration of Cu（I）was detected by UV-visible spectrophotometry,and the possible production pathway of Cu（III）was proposed.By quenching experiment and EPR analysis,SO₄^·-and HO^·in Cu（II）/EGCG/PMS process were confirmed to be main contributors for BPA degradation.Furthermore,six transformation products of BPA were identified by HPLC/MS and their respective eco-toxicities were calculated by ECOSAR.In this study,a green tea extract EGCG and EGCG-Cu（II）complex are selected to catalyze PMS.The degradation performance and mechanism of bisphenol contaminants in EGCG/PMS process and Cu（II）/EGCG/PMS were comprehensively investigated.It provides a theoretical basis for the eco-friendly reducing reagent EGCG catalyzing PMS to purify source water polluted by bisphenol contaminants,and it has a promising future in practical applications.