The Study Of Intermediate Active Species Production Mechanism And Organic Pollutants Degradation In Mxene-Mediated PMS Oxidation System

The removal effect of refractory organic pollutants such as antibiotics,pesticides and chemicals in traditional water treatment processes is inefficient.Their strong biological enrichment effect in animals,plants and human bodies leads to the potential damage risks towards environment and human beings.Persulfate-based advanced oxidation processes exhibit the characteristics of high redox potential and long life of free radicals,which have been widely concerned in the field of degrading refractory organic pollutants.Transition metal ions-activated peroxymonosulfate（PMS）process requires no external energy supply and is economical,which is considered to be one of the feasible and effective methods.However,transition metal ions-activated PMS process has some problems of low p H applicability,large consumption and slow regeneration efficiency of transition metal ions.MXene is a kind of two-dimensional transition metal carbon/nitrogen compounds with high reductivity and negative surface charge,which can accelerate the regeneration of low-valent transition metal ions and stabilize low-valent transition metal ions.Therefore,it has a good application prospect in the field of reducing transition metal ions and activating persulfate technology.In this dissertation,MXene/transition metal irons/PMS process was developed to solve the problems of large consumption of transition metal ions and slow regeneration efficiency.This technology can strengthen refractory organic pollutants degradation efficiency,broaden p H applicability and improve the understanding of intermediate active species production and organic pollutant degradation mechanism in MXene-mediated PMS oxidation process.This dissertation provides the reliable theoretical guidance and technical support for the practical engineering application of MXene-mediated PMS oxidation process.The main research contents are as follows:（1）Ti₃C₂T_x MXene was prepared by etching Ti₃Al C₂ MAX ceramic.Then,MXene/Cu（Ⅱ）/PMS oxidation process was constructed using atrazine as the target pollutant.The degradation kinetic of atrazine（ATZ）in MXene/Cu（Ⅱ）/PMS system under different p H conditions was studied.Under acidic condition,the degradation effect of ATZ in MXene/Cu（Ⅱ）/PMS process(k=0.12 min^-1)was better than that in Cu（Ⅱ）/PMS system(k=0.001 min^-1),and the increase of MXene,PMS and Cu（Ⅱ）concentrations significantly improved ATZ degradation efficiency.MXene inhibited ATZ degradation efficiency under alkaline condition,increasing of PMS and Cu（Ⅱ）concentrations could improve ATZ degradation efficiency.This was because MXene reduced Cu（Ⅱ）to Cu（Ⅰ）under acidic condition,which activated PMS to generate HO^·,SO₄^·-and ¹O₂.The inhibitory effect of MXene on ATZ degradation under alkaline condition was attributed to that Cu（Ⅰ）was not converted to Cu（Ⅲ）.The strong metal-support interaction shifted the intermediate product from Cu（Ⅲ）（two-electron transfer pathway）to free radicals（one-electron pathway）.The MXene-mediated Cu（Ⅱ）/PMS oxidation system could solve the problems of small p H range,large loss of metal ions and slow regeneration efficiency of low-valent metal ions,and proposed a novel MXene-mediated electron transfer mechanism.（2）Different from Fe,Co,Cu and other transition metal ions,Mn has abundant valence states and complicated electron transfer mechanism in advanced oxidation system.In order to further study the electron transfer pathway of Mn species and degradation of refractory organic pollutant in MXene-mediated PMS oxidation process,we constructed MXene/Mn（Ⅱ）/PMS system in this dissertation.The degradation kinetic of ibuprofen（IBP）in MXene/Mn（Ⅱ）/PMS system under different p H conditions was studied,IBP degradation efficiency in MXene/Mn（Ⅱ）/PMS system was significantly better than that of Mn（Ⅱ）/PMS and MXene/PMS system under acidic condition.The reaction concentration of MXene,Mn（Ⅱ）and PMS exhibited the optimal stoichiometric ratio.MXene/Mn（Ⅱ）/PMS system generated HO^·,SO₄^·-,¹O₂ and Mn（Ⅲ）.However,there existed significant differences between MXene/Mn（Ⅱ）/PMS system and KMn O₄/Na HSO₃ system in the formation of intermediate Mn species（Mn（Ⅲ）and Mn（Ⅴ））.MXene might reduce Mn（Ⅱ）to Mn（Ⅰ）,which triggered the activation mechanism of PMS.At the same time,Mn（Ⅰ）continued to transform into Mn（Ⅲ）,which generated synergistic effect coupled with free radicals to improve IBP degradation efficiency.In addition,the electron transfer pathway of Mn species in MXene-mediated Mn（Ⅱ）/PMS system was different from KMn O₄/Na HSO₃ system,which could accelerate the electron transfer rate of Mn species and enhance organic pollutants degradation efficiency.In this dissertation,MXene-mediated Mn（Ⅱ）/PMS reaction mechanism with intermediate Mn species as the dominant oxidation species was proposed,improved the understanding of electron transfer pathway of Mn intermediate species in PMS oxidation system.