| Recently,heterogeneous catalytic ozonation is widely used to remove harmful pollutants because of its strong oxidation ability.Catalysts are important active components in catalyzing ozone oxidation,so it is very important to select efficient and harmless catalysts.Graphitic carbon nitride（g-C3N4）,as a typical of polymeric layered metal-free carbonaceous material,has become a research hotpot.However,the original G-C3N4 is rarely used in catalytic ozonation due to lack of active sites.Therefore,in this paper,hetero-atom doped g-C3N4 was used to improve catalytic ozone activity.The main research contents and results are as follows:（1）A series of S doping g-C3N4 composites labeled as SCN were synthesized by one-step pyrocondensation method using thiourea as a sulfur source.The composites were systematically characterized and used as efficient catalysts for the catalytic ozonation of iopamidol（IPM）.The morphology and structure of the SCN composites were comprehensively characterized by various techniques such as BET,XRD,FTIR,SEM,and XPS.Results demonstrated that S was successfully doping in the skeleton of g-C3N4 with strong interactions by S-C.The doping of S could modulate surface chemical properties of g-C3N4.The presence of SCN composites significantly enhanced the degradation of IPM compared to sole ozonation.The degradation efficiency of IPM was 89.1%within 15 min.Meanwhile,the composite showed equivalent catalytic activity after five recycling experiment.In addition,the addition of SCN could improve the utilization rate of ozone by measuring the concentration of ozone in the solution,which was beneficial to catalytic ozonation.The catalytic mechanism for IPM degradation was also elucidated by radical scavenging experiment.Moreover,this study provided an efficient and harmless catalyst for the catalytic ozonation and possessed promising prospect in practical water treatment for environmental applications.（2）Boric acid was used as dopant to introduce B and O atoms to modify g-C3N4（denoted as BOCN）.The BOCN was as ozone catalyst to evaluate catalytic ozonation activity for IPM degradation.The addition of BOCN could significantly improve the degradation efficiency of IPM,which could be completely removed within 7 min.In addition,the effects of different influencing factors on the IPM degradation efficiency were studied.The optimal operation parameters were determined.By a series of characterization,O atoms were doped g-C3N4 in the form of oxygen-containing functional groups（C-O and C=O）,and B atoms were doped with B-N bonds.The structure-activity relationship between the structure and catalytic performance was further studied.It was found that the content of oxygen-containing functional groups and B-N had a positive linear correlation with the catalytic degradation rate of IPM.The main active species produced in catalytic ozonation were hydroxyl radical,superoxide radical and singlet oxygen（·OH,·O2-and ~1O2）through inhibition experiment and ESR analysis.Moreover,the intermediates of IPM in the reaction process were detected and the degradation path was proposed.The structure of BOCN and the active site of ozone adsorption were determined by DFT calculation,which provided theoretical support for exploring the mechanism of catalytic ozonation. |
