Study On Catalytic Ozonation Performance And Mechanism Of A Core-shell Mn-c@Fe Nanocatalyst

The seriousness of water pollution problem in our country cannot be ignored due to the extreme shortage of per capita water resources.Water pollution in our country mainly comes from domestic sewage and industrial wastewater,and how to efficiently,economically and greenly treat these polluted water bodies has become a top priority.Traditional water treatment technologies need to be continuously improved and perfected,as well as be continuously explored and researched emerging water treatment technologies in order to meet the demand for healthy water under growing population.The refractory organics in polluted water are great danger that threatens human health,which have the characteristics of strong persistence and multiple pollution channels.Therefore,it is necessary to explore more advanced treatment technologies for the effective degradation of these substances.Heterogeneous catalytic ozonation technology has been intensively studied and applied at present.This technology has the advantages of significant effect,strong applicability,and green pollution-free in the removal of refractory organic matter,and as an alternative treatment of organic pollutants from water or wastewaters.Previous studies on the mechanism of catalytic ozonation systems focused on the pathway of hydroxyl radicals,because of its superior oxidizing ability,and less studies of non-radical pathways.However,hydroxyl radicals（·OH）are likely to be scavenged by carbonate and bicarbonate as their quenchers in real water background,which will weaken their oxidizing ability and even more adverse effects.In this paper,a core-shell Mn-C@Fe nanocatalyst was first synthesized by solvothermal and hydrothermal methods.The catalyst is magnetic due to its Fe₃O₄core which is easy to recycle,and the carbon shell outside the iron core supports Mn₃O₄on the surface for catalysis.Combine with the ozone oxidation technology which is a kind of advanced oxidation technology to establish a heterogeneous Mn-C@Fe/O₃catalytic system.At the same time,a series of experiments were designed to evaluate the catalytic activity of catalysts in the coordinated system of ozone to degrade a variety of organic substances in water.Further investigate the reactive substances in the catalytic system and proposed possible non-radical pathways in the catalytic process.The results are as follows:（1）FESEM,BET,HRTEM and XRD were used to observe Mn-C@Fe structural characteristics,surface morphology and phase composition of the catalyst,and Mn-C@Fe was characterized as a core-shell structure which core is Fe₃O₄,covered by a carbon layer,and surface is Mn₃O₄.The magnetism of the catalyst was tested by VSM,which proved that the Mn-C@Fe catalyst is a magnetic material,and is helpful for the recovery after use.（2）Oxalic acid（OA）is a typical small molecule compound that cannot easily removed by·OH catalyzed ozone oxidation.OA was selected as a model compound to investigate the effect of different processes on the removal of OA and the influence of various key factors in the reaction process.The results show that the Mn-C@Fe/O₃catalytic ozonation process can effectively degrade OA.The removal rate is up to 90.9%in 20 minutes,and the kinetic constant is 0.045 min^-1.The p H of solution has a greater impact Mn-C@Fe/O₃catalytic system,and the optimal p H range is 3～5.In addition,the regeneration and stability of the catalyst Mn-C@Fe were investigated.The reacted catalyst can be reused after being treated by the regeneration method.The degradation after 5 times reuse is almost the same the reaction rate as the first use.The manganese ion and the iron ion leaching concentration in reaction solution are lower than the upper limit of the concentration allowed by China’s health standards.（3）Through radicals probe experiments,EPR reactions and XPS tests,the results showed that the oxidation of hydroxyl radicals was ruled out.The possible pathway of the Mn-C@Fe/O₃system was studied intensively,and a non-radical catalytic oxidation technology using a high-valence manganese intermediate as the oxidant was proposed.Furthermore,selected two typical refractory organics:atrazine（ATZ）and ibuprofen（IBU）as model compounds to verify the wide applicability of the technology,which shows great feasibility of decontamination as an alternative ozone-based water treatment.