Activation PMS By Iron Cobalt Copper Spinel Anchored On Palygorskite And Its Efficiency And Mechanism For The Degradation Of Bisphenol S

Bisphenol S（BPS）is a trace organic pollutant in water and is difficult to be biodegraded,which is labeled as a“safe”substitute for BPA and has been widely used in industrial production.In recent years,BPS has been frequently detected in many environmtal samples,especially in water samples.The conventional water treatment process has difficulty in completely removing BPS from water.Peroxymonosulfate（PMS）is considered potential oxidant and easily activated to produce SO4^·-to quickly degrade organic pollutants in water.PMS can be effectively activated by metal oxides,such as iron cobalt spinel（CoFe₂O₄）.However,CoFe₂O₄ nanoparticles are easy to agglomerate,which makes them expose less active sites.In addition,a large number of metal ions leached from CoFe₂O₄ may cause secondary water pollution.Therefore,it is necessary to use a good carrier to disperse CoFe₂O₄ nanoparticles.Palygorskite（PAL）is a green natural material with high resource utilization value,which has unique advantages.To solve the above problems,in this work,PAL was used to load iron cobalt binary spinel to prepare the PMS catalyst for BPS degradation.The optimal catalytic performance was obtained when the loading amount of CoFe₂O₄ on PAL was 16%,and the optimal catalyst was named as CoFe₂O₄@PAL（CFO@PAL）.The unique property of PAL made CFO@PAL have large the specific surface area(172 m²·g^-1)and pore capacity(0.61 m³·g^-1),which larger than the specific surface area(75 m²·g^-1)and pore capacity(0.28 m³·g^-1)of CoFe₂O₄.In CFO@PAL catalyst,CoFe₂O₄ nanoparticles are uniformly loaded on the PAL surface,which helps expose more available specific surface area and active sites.CoFe₂O₄ nanoparticles were firmly anchored on the surface of PAL by the Al-O-Fe bond,greatly reducing the content of metal ions leached and improving the stability of CFO@PAL catalyst.The degradation and mineralization performance of BPS by PMS alone are not good.However,BPS removal rate was 99.1%in CFO@PA/PMS system,increasing 73.03 percentage points compared with PMS alone,meanwhile the mineralization rate of BPS increased 18.7%after degradation for 30 min.In CFO@PAL/PMS system,the optimal catalytic performance was obtained when the concentration of CFO@PAL and PMS was 50 mg·L^-1 and 0.16 mmol·L^-1,respectively.In CFO@PAL/PMS system,the low concentration of Cl^-inhibited the removal of BPS,while the high concentration promoted.The result shows that amount of HClO was generated when the high concentration of Cl^-was presented in CFO@PAL/PMS system,which promoted BPS degradation by electrophilic bombarding.BPS was finally degraded by the combined action of HClO,SO₄^·-,·OH and ¹O₂.Furthermore,under the premise that the metal oxide loading amount was 16%,iron cobalt copper ternary spinel was constructed on the surface of PAL by copper doping to prepare CoCu_0.4Fe_1.6O₄@PAL（CCFO@PAL）catalyst with abundant oxygen vacancies（VO）to improve the catalytic performance for PMS.When the Cu/Fe ratio is 0.4/1.6,the crystal structure remained and the optimal catalytic performance was obtained.CoCu_0.4Fe_1.6O₄ nanoparticles were still mono-dispersed on the surface of nano-rod of PAL,and Al-O-Fe（Al-O-Cu）and Al-O-Cobonds were formed between the nanoparticles and PAL.This distribution state allowed CoCu_0.4Fe_1.6O₄ nanoparticles to expose more metal sites as well as VO and improved the catalytic stability of the CCFO@PAL.Copper doping improved the catalytic capacity from three aspects.Firstly,copper doping makes more Cu sites exposed to the CCFO@PAL surface,which can cooperate with Coand Fe to activate PMS.Secondly,copper participated in the creation of VO in CFFO@PAL,which provided another pathway for PMS activation.Thirdly,the formation of Al-O-Cu bond between CoCu_0.4Fe_1.6O₄ and PAL reduces the release of metal ions from the catalyst.The formation of VO greatly improved the reducibility and electron transfer ability of the catalyst.The number of Bader charges transferred to the PMS from CCFO@PAL is 0.690 e,which increased by 0.017 e compared with that before copper doping.In CCFO@PAL/PMS system,the destruction rate of BPS was 99.3%after reaction for25 min,kobs was 0.185 min^-1,and the leaching concentration of metal ions was low.After performing 5 consecutive tests,CCFO@PAL still has good PMS catalytic performance,showing good recycling performance.Besides BPS,CCFO@PAL/PMS system showed good degradation ability for nitrophenol,parachlorophenol,sulfamethoxazole,BPA,2,4-dichlorophenoxyacetic acid,and atrazine.In CCFO@PAL/PMS oxidation system,the optimal degradation performance of BPS has achieved under the optimal dosage of catalyst and PMS was 50 mg·L^-1 and 0.16mmol·L^-1,respectively.In addition,the lower the concentration of BPS in water bodies,the higher the degradation efficiency.The degradation efficiency of BPS increased with the increase in solution temperature.And the activation energy of the system was 35.58 k J·mol^-1.The water matrix of humic acid,NO^3-,and H2PO4^-can decrease the degradation ability of CCFO@PAL/PMS system.The Cl^-at low concentration inhibited the removal of BPS,while promoted at the high concentration.The mechanism is similar to CFO@PAL/PMS system above.During the process of PMS activation by CFO@PAL and CCFO@PAL,SO4^·-,hydroxyl radical（·OH）,and singlet oxygen（¹O2）were produced,among which SO4^·-was the main active species for BPS degradation.For the CFO@PAL catalyst,PMS was activated mainly through the redox process of Co（Ⅱ）to Co（Ⅲ）and Fe（Ⅱ）to Fe（Ⅲ）.As for CCFO@PAL,PMS was activated at the exposed metal sites（i.e.,Co,Fe,Cu）through the synergistic action of Co（Ⅱ）/Co（Ⅲ）,Fe（Ⅱ）/Fe（Ⅲ）,and Cu（I）/Cu（Ⅱ）.Besides metal sites,VO was also an activation center for PMS,which mainly captured the OI atom in[H-OI-OⅡ-SO3]^-,and then donated an electron to OI,cleaving OI-OⅡ bond and thus promoting SO4^·-generation.Compared with the catalyst before copper doping,the decomposition rate of PMS by CCFO@PAL was enhanced 19.7%through this dual-path activation mechanism.BPS degradation products were detected by the UPLC-QTOF/MS instrument.The main degradation mechanisms of BPS in the CCFO@PAL/PMS oxidation system included·OH substitution,dehydro-oxidation,and coupling reactions of free radical.The formation mechanisms of these products were further analyzed by the Fukui index of each ato m of products.Based on this,the possible degradation pathways of BPS were proposed.the eco-toxicity of most of the intermediates was lower than that of BPS.The results of overall toxicity indicated that BPS affects embryonic development and hormone levels of 17β-estradiol,testosterone,and vitellogenin in adult male zebrafish,and was also toxic to testes,liver,and intestinest issues of zebrafish.The overall toxicity of BPS-contaminated water was reduced by treatment with CFO@PAL/PMS process and CCFO@PAL/PMS process.And the detoxification efficiency of the CCFO@PAL/PMS system was better than that of the CFO@PAL/PMS system.In this study,iron cobalt copper spinel nanoparticles were anchored on the surface of natural clay of PAL in the form of monodispersed nanoparticel to construct a composite catalyst for the activation of PMS to degrade BPS in water.This paper provides a new idea for the preparation of highly efficient heterogeneous PMS catalyst,and provides a reference for the construction of an efficient PMS-based water treatment process,which is of significance in science and environment.