Study On Preparation And Catalytic Properties Of Nano MnO₂/polymer Composite Membrane Materials

MnO₂ is abundant as natural oxidant,which has good adsorption,degradation and solidification effect on most environmental pollutants.However,most of the reported MnO₂ is in powder form,which is difficult to recycle and easy to form secondary pollution.In this paper,MnO₂/M was prepared by low temperature solvothermal method,and characterized by XRD,XPS and BET.The effects of p H,concentration,catalyst amount,temperature and isopropanol addition were investigated.The mechanisms of MB,phenol oxidation degradation and PAM viscosity reduction were proposed.The isotherm models were used to study the adsorption behavior and the change of adsorption energy,the kinetic model was used to study the controlling reaction pathways and mechanisms sorption reactions,and the thermodynamic parameters of adsorption reaction were calculated.The experimental results show that the pore volume of MnO₂/M prepared by preparation optimization is increased,and the operation stability and adsorption reactivity are enhanced.The loading MnO₂ is ofδtype.The average oxidation state is 3.71,and the lattice is activated by the introduction of valence heterocrystalline phase.According to Nernst equation,high concentration of H⁺in solution enhances MnO₂ activity,while alkaline condition can limit activity and stabilize crystal form.For MB decolorization,the selective oxidation degradation towards N atom was dominant at low p H,and electrostatic adsorption was dominant at high p H,while neutral and alkaline conditions are unfavorable.The degradation of phenol in acidic condition is based on the selectivity of manganese to hydroxyl O atoms of phenol,which leads to significant H⁺consumption.At the same time,MnO₂ is reductively dissolved,and the concentration of Mn（II）in liquid phase increases.The mechanism modeling shows that the electron transfer within the complex is the rate controlling step of phenol degradation.The viscosity reduction of PAM under acidic conditions is based on the interaction of self acidolysis and MnO₂ oxidation.Based on the selectivity of manganese sites for acylamine groups,the viscosity reduction of PAM involves overcoming both the intramolecular and external hydrogen bond energy barrier and remote structural destruction.The addition of isopropanol,exposure to roomlight or in the dark had no effect on the degradation,indicating the non photocatalytic mechanism.The model fitting showed that MB system conformed to Langmuir isotherm and phenol conformed to Freundlich model;PAM conforms to the Sips model.The pseudo 2nd order kinetic model had the highest fitting degree,indicating chemical adsorption was dominant.The controlling effect of external diffusion on adsorption rate could not be ignored.With the increase of the initial concentration of MB or phenol,the binding energy decreases,the adsorption capacity increases,the diffusion rate increases,the boundary layer expands,and the adsorption rate constant decreases;With the increase of PAM concentration,the binding energy increases,the adsorption capacity decreases,and the physical adsorption first increases and then decreases.With the increase of reaction temperature,the fitting degree of pseudo 1st order kinetic model decreased.The boundary layer expands and the diffusion increases.The calculation of activation energy accords with the typical activation range of manganese oxides.Thermodynamic calculation shows that MB decolorization,phenol degradation and PAM viscosity reduction are highly spontaneous,endothermic,with entropy increasing in the processes.