Study On Synthesis And Application Of Layered Double Hydroxide Based Catalysts For The Degradation Of Typical PPCPs Via Peroxymonosulfate

Pharmaceutical and personal care products（PPCPs） are a kind of organics with high chemical stability,strong biological activity and potential toxicity.Environmental persistence and biological accumulation make PPCPs continuously enrich in organisms through ecological cycle,which could lead to organ lesions even malignant tumors.Therefore,exploration of effective removal of PPCPs from aqueous phase is of great significance to the protection of ecological environment.Advanced oxidation process（AOPs） has been demonstrated as a novel technology for the degradation of organic pollutants.Further,functional materials based on layered double hydroxide（LDH） and its derivatives become research hotspots in heterogeneous advanced oxidation recently,for their easy synthesis,regulatability and relatively high catalytic activity.However,weak resistance to environmental impacts and poor stability limit their further application in AOPs.In order to overcome the defects of LDH,four LDH based catalysts with unique advantages were synthesized,and used to catalyze peroxymonosulfate（PMS） degrading typical PPCPs in water.Degradation efficiency and ecotoxicity inhibition ability of catalytic systems were evaluated.Catalytic mechanisms,including formation and transformation of reactive species were studied as focused topics.Firstly,CoAl hydroxide@hydroxysulfide（CoAl-LDH@CoS_x）was synthesized to catalyze PMS degrading sulfamethoxazole（SMX）in aqueous solution.Catalytic experiments showed that CoAl-LDH@CoS_x exhibited higher catalytic activity than pure LDH,and 98.5%SMX could be removed in CoAl-LDH@Co S_x/PMS system within 4 min.According to quenching experiments and ESR analysis,the main reactive species in the system was identified as ¹O₂,while SO₄^·-,O₂^·- and surface-bound^·OH played a secondary role in the degradation of SMX.Analysis of catalytic mechanism exhibited that two redox cycles,Co（Ⅱ）/Co（Ⅲ） and S₂^2-/(S^2-,SO_x),were conducive to the electron transfer between catalyst and PMS.Secondly,for the degradation of SMX via PMS,trace of boron doping Co OOH（B-CoOOH）was prepared using CoAl-LDH as the template.Catalytic experiments indicated that doping of trace boron greatly enhanced the catalytic activity and stability of CoOOH,not only 99.4%SMX could be degraded in B-CoOOH/PMS system within 6 min,but satisfactory removal ability in a wide pH range（3.0-9.0）was also obtained.Quenching experiments and ESR characterization showed that surface-bound^·OH,SO₄^·-,O₂^·-and ¹O₂ were all involved in the degradation of SMX,and ¹O₂ dominated the degradation process.Analysis of catalytic mechanism exhibited that oxygen vacancies on catalyst surface were the main electron donators during catalytic reaction.In the early stage reaction,O₂ was an essential precursor of O₂^·-,while PMS controlled the reaction after O₂ consumed in the later stage.Third,CoAl-LDH@CoFe-PBA was composed of CoAl-LDH and Co Fe-PBA,and used to catalyze PMS degrading SMX in solution.Effect of p H on the degradation of SMX,and formation and transformation of reactive species were thoroughly investigated.Quenching experiments and ESR characterization indicated that ^·OH,SO₄^·-,O₂^·-and ¹O₂ were all involved in the degradation of SMX at different initial pH values.¹O₂ was mainly produced from O₂^·-at acidic condition,while O₂^·-and SO₄^·- co-contributed to ¹O₂ generation at alkaline condition.Analysis of catalytic mechanism showed that surface-bound^·OH and ¹O₂ were the dominated reaction species in acidic pH,while SO₄^·-and ¹O₂ controlled the degradation reaction at alkaline condition.Finally,PBA@LDH was formed with Prussian blue analogue（PBA） synthesized in the interlayer of LDH using MgAl-LDH as the supporter.Applying PBA@LDH to catalyze PMS for the degradation of CBZ showed that catalytic activity of PBA@LDH was much higher than that of pure PBA,nearly 100%CBZ could be degraded in PBA@LDH/PMS system within 15 min,while only 31.8%CBZ could be removed in PBA/PMS system at the same condition.Quenching experiments and ESR characterization indicated that the main reactive species in the system was SO₄^·-,and a small amount of^·OH was also involved.Analysis of catalytic mechanism showed that the redox cycle of Co（Ⅱ）-CN-Fe（Ⅲ）/Co（Ⅲ）-CN-Fe（Ⅱ）in PBA played an important role in the activation of PMS.Two USEPA’s ecotoxicity assessment softwares,ECOSAR and T.E.S.T.,were employed to evaluate the ecotoxicity potential of targeted pollutants and their degradation products in the four catalytic systems.It was found that although the four catalytic systems could effectively reduce the ecological toxicity of targeted pollutants,accumulation of toxicity of organic intermediates still need attention.Extending the degradation reaction time or connecting with depth treatment technology could further inhibit the ecotoxicity potential of targeted pollutants.