Preparation And Modification Of Amorphous Manganese Dioxide And Its Properties Of Activating Peroxymonosulfate

Advanced oxidation technologies（AOPs）based on persulfate have been successfully applied to the degradation of organic pollutants in wastewater treatment.Compared with most radical oxidation processes,the non-radical oxidation process is less affected by the water matrix,and can selectively degrade the target pollutants,avoiding the generation of toxic by-products.Therefore,it has become the focus of scientific researchers to explore the way to degrade pollutants by non-radicals.Manganese oxide has the advantages of high natural abundance,low toxicity and low cost,and is often used in AOPs.Research shows that amorphous MnO₂ catalyzes the activation of peroxymonosulfate（PMS）to degrade pollutants in a non-radical way.However,due to many disputes about its mechanism,improving its efficiency is still a challenge.Therefore,the mechanism of amorphous MnO₂ catalytic activation of PMS was first studied in this paper.Then the catalyst with rich oxygen vacancies on the surface is obtained by reduction of nanometer carbon powder,which further improves the performance of catalytic activation of PMS.Finally,MnO₂ was modified and its activity was improved by adding Fe.（1）Amorphous MnO₂ was synthesized by hydrothermal reaction between KMnO₄ and manganese sulfate.The structure,specific surface area and surface chemical state of the catalyst were characterized.The results show that the surface of the sample（AM4）prepared at the hydrothermal temperature of 180℃has a high content of Mn⁴⁺.Using phenol as the target pollutant,the performance of MnO₂prepared at different temperatures for catalytic activation of PMS was evaluated.The experimental results show that AM4 sample has the best activity.This is related to the higher content of Mn⁴⁺on its surface.The main active species of AM4-PMS system is determined to be ¹O₂ through the capture agent experiment and EPR test analysis,and the evolution process of ¹O₂ is described.The effects of different initial p H,PMS dosage,catalyst dosage and coexisting substances in water on the degradation of phenol by activated PMS were studied for AM4 catalyst.The reusability and stability of AM4 catalyst were tested by cycle experiments and degradation of various pollutants.（2）Amorphous MnO_X was synthesized through the hydrothermal reaction between KMnO₄ and carbon nanopowder.The characterization results indicated that the hydrothermal temperature had little effect on the structure of the products but affected their surface composition.The sample prepared at 180°C（MnO_X-180）had rich oxygen vacancies and exhibited high activity for sulfamethoxazole（SMX）degradation with PMS.More than 97%of SMX was removed within 30 min by 0.5g L^-1 of MnO_X-180 and 1 mmol L^-1 of PMS at p H₀=6.5.Activated PMS adsorbed on catalyst surface and singlet oxygen（¹O₂）produced from the non-radical pathway were the active species.Surface Mn⁴⁺and oxygen vacancies were found to be responsible for the generation of activated PMS and ¹O₂,respectively.The degradation efficiency of SMX by MnO_X-180 increased with decreasing solution p H,which can be attributed to the enhanced production of activated PMS under acidic conditions.The water matrix had little effect on the performance of MnO_X-180 due to the non-radical activation mechanism.（3）A series of Fe Mn composite oxides were prepared and used to activate peroxymonosulfate（PMS）for removing phenol in water.The correlation between the surface properties and catalytic performance of the catalysts was studied,and the possible mechanisms for PMS activation and pollutants degradation were discussed.The characterization results showed that the composite oxides were composed of Fe₂O₃ and amorphous MnO₂.Amorphous MnO₂ should be the active component for PMS activation,while the incorporated Fe changed the surface charge property of MnO₂.The incorporation of an appropriate amount of Fe was conducive to the adsorption and further surface activation of PMS,but the excessive amount of Fe covered the active sites of MnO₂.The sample with the Mn:Fe ratio of 5:3（AMF2）exhibited the highest activity for the degradation and mineralization of phenol,and its performance was barely affected by water matrix due to the non-radical mechanism.Singlet oxygen（¹O₂）was the dominant active species for pollutants removal,which was produced from by superoxide anion(O₂^·-).