Study On Structure-activity Relationship Of Heterogeneous Metal Oxide Catalyst For Degradation Of Organic Pollutants

With the rapid industrialization in China,the composition of wastewater becomes increasingly complex bringing great challenges to the treatment of water environment.Fenton system,especially the heterogeneous Fenton system in which the organic contaminants can be mineralized thoroughly has great importance to national health,environmental protection,as well as the social economy.Therefore,the development of high-performance heterogeneous Fenton catalysts has become the key point of Fenton technology.However,the limitation of low degradation performance and H2O2 efficinecy has been the two major factors that hinder its practical application in industry.In this work,two heterogeneous Fenton catalysts,Fe based and Cu based,were designed and prepared via controllable preparation technology.Two reactions,the generation of OH from catalytic decomposition of H2O2 and the degradation of contaminants,were studied with different emphasis.For the reaction of H2O2 decomposition and OH generation,the structure-activity relationship of the catalytic system was established according to the ideas of enhancing the rate-controlling steps and inhibiting the side reactions.Combined with the related kinetic studies,the H2O2 efficiency was improved.For the reaction of contaminant degradation,guided by practical industrial application,refractory pollutants(such as nitrobenzene,quinoline,dyes,etc)from industries were selected as target pollutant molecules to investigate the influence of process conditions and explore the possibility of coupling with biodegradation technology.Firstly,the Fe-Cu bimetallic catalytic system with Fe as the main active phase was studied.Novel Fe-Cu bimetallic catalysts supported on Al2O3 were prepared and applied in nitrobenzene degradation.The highest degradation efficiency is achieved by 5Fe2.5Cu-Al2O3,and the degradation rate can reach 100%within 1 h.By analyzing the accumulation concentration of OH and the electronic structure of the catalyst,it can be found that the synergistic interaction between Fe and Cu enhances the generation of OH and the degradation of nitrobenzene.The kinetic studies of nitrobenzene degradation,H2O2 decomposition and OH production were also conducted.Combined with the qualitative analysis of intermediates,it was confirmed that the dominant degradation pathway was the direct oxidation of organics by OH.To further improve the degradation efficiency of nitrobenzene,the activity of the catalysts and the H2O2 utilization efficiency should be optimized.Hence,a regression equation was obtained through the Box-Behnken experimental design to evaluate the influence of initial H2O2 concentration,pH value,reaction temperature,and their interactions on H2O2 utilization efficiency,and the response surface methodology was used to further optimize the H2O2 utilization efficiency.Secondly,the Cu-based catalytic system was investigated.Since OH is generated from H2O2 activation over the catalyst surface,Cu@SiO2 catalysts with tunable Cu species were prepared by modified Stober method.Combining characterizations and density functional theory calculations,Cu+was proved to be the main active site for·OH production,revealing the mechanism of OH production from the H2O2 activation over heterogeneous Cu-based catalysts.On the basis of above-mentioned study,Sn was introduced as the second metal and the OH generation ability was improved with the increase in the electron-rich Cu species(OH yield is 10 times higher than that in the related literatures over Cu-based catalysts).In the meantime,the invalid decomposition of H2O2 is inhibited with the decrease in the electron-poor Cu species.As a result,the H2O2 utilization efficiency is significantly improved by more than two times.Meanwhile,the optimized reaction conditions were applied to mineralize other pollutants(such as dyes,phenols,pyrrole,pyridine,indole,aniline,etc)to verify the adaptability of the as-prepared catalysts,and satisfying degradation efficiency was obtained.It was also found that the biodegradability of the treated wastewater was improved.This benefits the deep degradation of industrial wastewater in practical applications by coupling with biochemical treatments.Combined with the recycle experiments of the catalyst,quantitative analysis of the heavy metal ions after the reaction was conducted to investigate the catalyst durability and the application prospect of the catalytic system.Finally,in order to solve the problem of heavy metal leaching thoroughly,some prospective studies on metal free catalysts were carried out,including the controllable preparation of C3N4 and the exploration of reactive oxygen species.Besides,the possibility of the coexistence of radical and nonradical degradation pathways was preliminarily investigated,which would inspire more ideas on the future research of this type of catalyst.