Study On The Influencing Factors And Mechanism Of MnO₂ Decomposing Hydrogen Peroxide And Peroxymonocarbonate

Water pollution has become a problem that cannot be ignored.Manganese dioxide（MnO₂）-hydrogen peroxide（H₂O₂）system has been initially applied to the removal of pollutants,and it is popular in the fields of advanced oxidation processes and in-situ chemical oxidation technology.MnO₂ is abundant in natural and H₂O₂ is ubiquitous in the natural environment,therefore,their interaction is also crucial to the migration and transformation of pollutants in the environment.However,due to the lack of studies on the influence of background environmental factors on the effectiveness of MnO₂-H₂O₂system,the degradation of pollutants in MnO₂-H₂O₂ system cannot be accurately predicted,which limits its practical application.Hence,this paper mainly studied the effects of typical environmental factors(pH value,NaCl,phosphate,HCO₃^-,Br^-,Ca²⁺,Mn²⁺,DOM,SiO₂)on MnO₂-H₂O₂ system,and carried out kinetic fittings of the relevant data.Meanwhile,during the above experimental processes,it was found that high concentration of HCO₃^-could significantly promote H₂O₂ degradation,therefore,the MnO₂-H₂O₂-HCO₃^-system was subsequently proposed in this study,and its mechanism and potential in pollutants removal were studied.In this study,commercial MnO₂ and MnO₂ synthesized by hydrothermal method were used.XRD analysis indicated that the main component of the former isε-MnO₂,while the latter is well-crystallizedβ-MnO₂.The experimental of influencing factors showed that H₂O₂ degradation increased with the increase of pH.Low pH value,phosphate and high concentration of Na⁺significantly inhibited the degradation of H₂O₂,2-100 mg·L^-1 of DOM inhibited the reaction slightly,50 m M of HCO₃^-,SiO₂ only has a slight inhibitory effect onε-MnO₂-H₂O₂ system,and the influence of Br^-,Cl^-,Ca²⁺,Mn²⁺on the system is negligible.The kinetic fitting results showed that in the presence of HCO₃^-,H₂O₂ degradation by the two kinds of MnO₂ conformed to the pseudo first-order kinetic model,and the reaction betweenβ-MnO₂ and H₂O₂ at pH=8 and 9 were better fitted to the pseudo-first-order kinetic model,other than that,reactions of other groups were in line with the pseudo-second-order kinetic model.The influencing factor experiments can provide certain data support and theoretical reference for the practical application of the MnO₂-H₂O₂ system.Secondly,the MnO₂-H₂O₂-HCO₃^-system was studied.XPS analysis illustrated that there were lattice oxygen,chemically adsorbed oxygen and physically adsorbed oxygen in MnO₂ structure,Mn（Ⅳ）and Mn（Ⅲ）coexisted in MnO₂.After the reaction of MnO₂-H₂O₂-HCO₃^-,the contents of lattice oxygen and Mn（Ⅳ）decreased,while the contents of physically adsorbed oxygen,chemically adsorbed oxygen and Mn（Ⅲ）increased.EPR analysis results and radical verification experiment results proved that MnO₂ could activate HCO₄^-（the reaction product of HCO₃^-and H₂O₂）to generate active species such as CO₃·^-,¹O₂ and O₂·^-.The MnO₂-H₂O₂-HCO₃^-system can completely degrade 2,4,6-Trimethylbenzene（TMP）and Sulfamethoxazole（SMX）within 5 minutes.CO₃·^-proved to be the only species that degraded SMX.0.01,0.1,1m M of phosphate had no significant effect on SMX degradation by this system,100mg·L^-1 of DOM inhibited the degradation of SMX to a large extent,and the MnO₂-H₂O₂-HCO₃^-system could still degrade SMX well in the effluent of the secondary sedimentation tank.In brief,coupling MnO₂ with H₂O₂-HCO₃^-will help to develop more efficient and economical water treatment technology.