Efficiency And Mechanism Of Fenton-like Advanced Oxidation System For The Removal Of Typical Micropollutants In Water

With the rapid development of the global economy,the problem of water pollution has become increasingly severe,and ensuring water quality has become an important issue closely related to human production and life safety.Conventional water treatment processes have limited capabilities in removing typical micropollutants in water that are difficult to remove effectively,such as heavy metals and endocrine disruptors.Hence,there is an urgent need to introduce advanced treatment technologies.Advanced oxidation processes,such as Fenton-like processes,have prominent advantages such as high reaction efficiency,simple operation,and low risk of secondary pollution,and have been widely used in the treatment of typical micropollutants in water.Therefore,this article focuses on the removal of typical micropollutants in water,and constructs three efficient Fenton-like advanced oxidation systems:single-metal-based,bimetallic-based,and graphene-enhanced bimetallic-based systems.The targeted removal of typical metalloids,electron-rich micropollutants and weak electron-withdrawing micropollutants in water was systematically investigated in these Fenton-like systems.This study aims to provide theoretical guidance for the high-efficient and sustainable removal of typical micropollutants in water.First,targeting the removal of typical metalloids,a monometallic Fenton-like（MnO₂-H₂O₂）system,based on environmentally friendly,inexpensive and abundant MnO₂,was constructed,and its one-step"oxidation-adsorption"arsenic removal performance and mechanism were investigated.Compared with MnO₂ alone,the MnO₂-H₂O₂ system has a high arsenic removal efficiency,with a maximum saturation adsorption capacity of more than 33.6 mg·g^-1,which is twice the maximum adsorption capacity of the MnO₂ system.Model fitting of adsorption kinetics and adsorption thermodynamics confirmed that the adsorption kinetics of As（III）by the MnO₂-H₂O₂ system was in accordance with the quasi-secondary kinetic model,which was dominated by chemisorption,and the adsorption thermodynamics was in accordance with the Freundlich adsorption model,which was dominated by multilayer adsorption.Through reaction kinetic tests and ESR characterization,it was found that the MnO₂-H₂O₂ system can enhance the oxidation efficiency of the system by mediating the generation of highly active species such as·OH and O₂^·-;in addition,the turbulent hydraulic state caused by the in-situ generation of a large amount of O₂ can optimize mass transfer;in-situ free radical oxidation and the hydraulic conditions of enhanced mass transfer synergistically enhanced the oxidation efficiency of As（III）and improved the adsorption and removal efficiency.The MnO₂ adsorbent micro-interfaces were characterized by FTIR,XPS and Raman spectroscopy,and it was demonstrated that both As（III）and As（V）could be adsorbed on the MnO₂ surface.The adsorption state As was dominated by As（V）,and the adsorption force was the internal ligand binding interaction formed by As and MnO₂surface hydroxyl groups.The MnO₂-H₂O₂ system can adapt to complex water quality conditions,namely,it is less influenced by temperature and has excellent results in the applicable p H range（p H 6.0-p H 8.0）of the actual water environment,and it can maintain the efficient As removal level under the actual surface water and groundwater water quality conditions,which has good application prospects.Targeting the removal of electron-rich micropollutants,a bimetallic catalyst,LaCoO₃（LCO）,and S-doped LaCoO₃(S_x%-LCO)were prepared by sol-gel method and sulfurization heat treatment.An S_x%-LCO/PAA catalytic oxidation system was constructed to remove bisphenol A（BPA）from water.S_x%-LCO exhibited superior catalytic performance compared to undoped LCO.Specifically,s-doping significantly promoted the BPA degradation of PAA catalyzed by LCO.Under optimized conditions,including a solution p H of 7,0.2 mmol/L PAA,and0.1 g/L S_7.2%-LCO,the degradation rate of BPA reached 99%within 20 min at room temperature,and the decomposition rate of PAA was 52%.In addition,its wide p H adaptability（p H=3.0-11.0）,good resistance to ionic strength and actual water quality background interference made it as a promising environmentally friendly catalyst.Free radical quenching experiments,ESR tests,and electrochemical analysis demonstrated that organic free radicals（R-O·）were the dominant oxidation mechanism of S_x%-LCO catalyzed PAA degradation of BPA,and direct electron transfer was a minor oxidation mechanism.The enhanced PAA catalytic activity of S_x%-LCO could be attributed to S doping,which induced the reduction of high-valent Co（III）to Co（II）in the catalyst and generated more oxygen vacancies on the catalyst surface,thereby improving the reducibility and electron transfer ability of S_x%-LCO and promoting the effective decomposition of PAA.In addition,the redox reaction between≡Co（III）/≡Co（II）and PAA ensured the continuous generation of R-O·and higher degradation efficiency.Further,for the more challenged removal of the weakly electron-withdrawing micro-pollutants,a Fenton-like advanced oxidation system of a highly active and stable graphene oxide-supported cobalt ferrite（GO-CoFe₂O₄）/permonosulfate（PMS）was constructed.Through the analysis of the structural characteristics and catalytic properties of GO-CoFe₂O₄,it was found that the introduction of GO obviously boosted the catalytic performance of GO-CoFe₂O₄ for PMS on removing di-n-butyl phthalate(DBP,R_DBP=90%,R_TOC=37%),which indicated by the first-order kinetic constant(k DBP=0.060min^-1)being roughly 4 times than pure CoFe₂O₄(k DBP=0.015 min^-1).The fabrication of GO-CoFe₂O₄ brought the favorable stability and repeatability up to six cycles.Moreover,the method of batch dosing catalyst was creatively proposed to improve the PMS utilization efficiency.The coupling of GO enhanced the dispersion of CoFe₂O₄particles to expose sufficient active sites,additionally,the plentiful C=O groups and free-flowing electrons on GO promoted GO-CoFe₂O₄ to coordinate a redox process during PMS activation.Theoretical calculations indicated that the GO-CoFe₂O₄ was revealed to exhibit a strong affinity toward PMS adsorption,where PMS spontaneously dissociated into sulfate radical(SO₄^·-),hydroxyl radical（·OH）and singlet oxygen（¹O₂）,acting as the reactive oxygen species（ROSs）.Electrons cycling between Co,Fe and O species ensured excellent catalytic performance and continuous ROSs generation.In summary,this study provides a green,economic,and efficient Fenton-like advanced oxidation technologies for the removal of typical micropollutants in water,and clarifies the mechanism of the oxidation process and important means of regulation and optimization,which enriches the theoretical basis of Fenton-like advanced oxidation technology,and provides important technical guidance for the development of efficient and advanced water treatment technology.