Activation Of Persulfate With Nano-Minerals Ecomaterials:Mechanistic Study Of ROS Generation

Advanced oxidation processes(AOPs)based on persulfate as oxidant to treat refractory organic pollutants has the characteristics of easy operation,strong oxidation ability and environment-friendly.This technology has been widely concerned in the field of wastewater and contaminated soil treatment.The development of transition metal catalysts with the advantages of environment-friendly,catalytic stability,low cost and easy availability is one of the research directions that researchers pay close attention to in recent years.Mineral materials exist widely in the natural environment,and have the characteristics of environmental coordination,environmental comfort,simple processing and preparation,low cost and so on.It is an important research topic in the field of contamination remediation.For mineral catalysts based on multivalent transition metals,realizing the effective cycle of M(n+1)+/Mn+ in heterogeneous system,improving the stability of the catalyst and reducing metal ions leaching;For mineral catalysts based on monovalent metals,the mechanism of activation of peroxymonosulfate(PMS)and the types of reactive oxygen species generated need to be further studied,which are the key problems to be solved.In this thesis,the objective is to develop the system of highly efficient degradation of organic pollution by peroxydisulfate(PDS)/stannite(Cu2FeSnS4).Novel heterogeneous AOPs systems based on the zincate(ZnO)catalyst and magnesite(MgO)catalysed activation of PMS.The contents of this thesis are divided into four chapters as follows:In Chapter ?,the development of advanced oxidation technology based on persulfate represented by iron-based catalysts are reviewed.The development of nano-minerals ecomaterials in the treatment of organic pollution is mainly introduced.Finally,scientific significance of this thesis is highlighted.In Chapter ?,stannite(Cu2FeSnS4,CFTS)nanomaterial was applied to the activation of PDS for the degradation of bisphenol A(BPA)in model industrial wastewater.The efficiency of PDS decomposition by CFTS,and the mechanism of contaminant degradation by SO4·-were investigated.The results revealed that CFTS catalyzes PDS decomposition more efficiently than the monometallic Cu/Fe/Sn sulfides and exhibits activity over a wide pH range.Electron spin resonance spectroscopy,X-ray photoelectron spectroscopy,and free radical quenching experiments revealed a tandem synergistic effect between Cu,Fe,and Sn in their quaternary chalcogenide systems upon PDS activation.The intrinsic electron transfer between Cu,Fe and Sn,especially the ?Fe(?)*species formed upon the complexation of Fe(?)by S on the surface of the CFTS,overcomes the inhibition of the M(n+1)/Mn+ redox cycle.GFTS shows promise as a catalyst for wastewater treatment.In Chapter ?,the multivalent transition metal oxide-mediated activation of PMS has been widely investigated for degradation of organic pollutants.Compared with that of valence electrons,the role of localized electrons of transition metal oxides in the activation of PMS has remained elusive.Zincate(ZnO),as a typical irreducible oxide,was used as an ideal model to determine the role of the localized electrons of oxygen vacancies(OVs)in the PMS heterolysis process.Combined experimental and theoretical analyses demonstrate that OVs,serving as the catalytically active sites,provide enough localized electron retransmission to the adsorbed HSOs-,via a one-electron transfer reaction resulting in the formation of OH-and SO4·-.In addition,OVs promote PMS dehydration to form metastable-SO4-O-O-O4S-that rapidly decompose into 02-,which is responsible for the 1O2 production.This work introduces a unique strategy for obtaining electronic-level insights into the role of catalyst defects in promoting efficient PMS activation.In Chapter ?,a novel PMS activator,periclase(MgO)was synthesized for efficient PMS degradation of organic contaminants in aqueous solution.It was found that MgO exerts an excellent and stable catalytic performance for PMS activation to degrade a wide range of pollutants including BPA,phenol,chlorophenol,and dye efficiently.Results from a combination of electron spin resonance(ESR),free radical quenching,chemical probe and isotope labeling investigations confirm that singlet oxygen(1O2)was the dominant reactive species generated in the MgO/PMS system and accounted for BPA degradation.Further evidence from X-ray photoelectron spectroscopy(XPS),Fourier-transform infrared(FTIR)spectroscopy,and density functional theory(DFT)suggested that 102 was generated by the self-decomposition of PMS induced by surface hydroxyl groups on MgO.In addition,the degradation of BPA was hardly affected by anions and humic acid(HA)that commonly existed in the environmental matrices.The naturally occurring periclase also has high catalytic ability for PMS activation and BPA degradation.Compared with other transition metals-based radical pathways and carbonaceous materials-based non-radical pathways of PMS activation,MgO exerts a comparable catalytic performance but less potential risk and cheaper.This study developed a novel environmentally friendly catalyst with low cost and high efficiency for the selective degradation of organic pollutants in wastewater treatment.