| Peroxone process which relies on the reaction between O3 and H2O2 to generate highly reactive hydroxyl radical(·OH)is a typical advanced oxidation processes(AOPs)for wastewater treatment.However,this technology suffers from various problems,including the waste of O2 resource,the risk arising from the transportation and storage of H2O2,and the inefficient degradation efficiency in acidic solution,which seriously restricts its application.Via combining with electrochemical technology,heterogeneous catalyst or non-thermal plasma technology,it provides new solutions for the development of efficient peroxone technology.Although electro-peroxone process realizes the in-situ generation of H2O2,the deficiency of detailed reaction mechanism and low-utilization of O3 need to be explored.It is convinced that heterogeneous catalyst is the key method to resolve the inefficiency of peroxone process in acidic solution,but this study is still in the blank stage due to the complexity of the system.Dielectric barrier discharge non-thermal plasma technology possesses the advantage that it produces O3 and H2O2 simultaneously,but the defect of device confines the peroxone process.Aiming at solving the problems existing in various improvement measures,we achieve main conclusions as follows:(1)A three-electrode system equipped the rotating ring disk electrodes is established,and the synergy in electro-peroxone process is revealed.The in-situ generated O2 by O3 electrochemical reduction and O2 in bulk solution are reduced to form H2O2.Meanwhile,the increased OH' concentration near cathode,due to the electrochemical reaction on the electrode surface,accelerates the transformation of O3 to H2O2.These two pathways contribute to the higher amount of H2O2,thus promotes the peroxone process to generate ·OH.It combining with ·OH generated by O3 electrochemical reaction synergistically degrades the organic pollutants.In addition,the yield of · OH in carious pH solution are semi-quantitative analyzed by electrochemical method,alkaline solution>neutral solution>acidic solution.(2)Compared with bulk-g-C3N4 and porous-g-C3N4,the material comprised of nanosheet-g-C3N4 and MWCNTs exhibits optimal specific surface,N element content and electronic conductivity.Besides transforming O2 to H2O2 via electrochemical reaction,this material possesses strong catalytic ozonation activity.Applied in the electro-peroxone process,it can obviously enhanced the degradation efficiency of oxalic acid.The result confirms that catalytic ozonation process is an important means to enhance the degradation efficiency in the electro-peroxone process.(3)C3N4-Mn/CNT heterogeneous catalyst significantly increases the degradation efficiency of oxalic acid by 57.1 times in electro-peroxone process.Comparison tests confirm that the catalyst possesses catalytic peroxone reaction activity.In order to explore the catalytic mechanism,the C3N4-Mn catalyst is used as the research model.By the characterization of HAADF-STEM and XAFS,it is found that this catalyst is single atom Mn catalyst existing in the form of Mn-N4 configuration.Both free radical capture experiment and DFT calculation reveal the catalytic mechanism of Mn-N4 site.Firstly,H2O2 is adsorbed on the Mn-N4 site to form HOO-Mn-N4 bond.Secondly,O3 promotes the cleavage of HOO-Mn-N4 bond to generate HO2· and O3·-.Finally,·OH is formed by chain reactions of free radicals.Mn-N4 catalyst overcomes the defect of peroxone process which must be initiated by HO2-,and further expands the application scope of this technology.(4)In dielectric barrier discharge non-thermal plasma device,adding carbon electrode can efficiently increase the yield of O3 and H2O2,and gas-liquid mixing column can provide the reaction space for O3 and H2O2,which change the treatment area of organic pollutants from discharge zone to mixing column.These improvements significantly enhance the reaction efficiency between O3 and H2O2,thus increase the efficiency of wastewater treatment. |
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