Study On The Design Of Highly Efficient CoMn₂O₄ Catalysts And Their Catalytic Degradation Properties By Activating Peroxymonosulfate Salts

It is always a fascinating research field to find and develop wastewater treatment technologies for efficient degradation of toxic and harmful pollutants in water.This paper takes CoMn₂O₄ as the research object,makes full use of the advantages of CoMn₂O₄,overcomes its shortcomings to the greatest extent,and achieves the goal of improving its catalytic degradation performance.Based on the above thinking and literature research,three kinds of Fenton-like catalysts were designed and carried out the following three aspects of research works.In the second chapter,sulfur-functionalized CoMn₂O₄（S-CoMn₂O₄）was prepared as a Fenton-like catalyst by the sol-gel process,followed by calcination and sulfurization,and ued to active peroxymonosulfate（PMS）ions to degrade rhodamine B（Rh B）.The catalytic activity of CoMn₂O₄ was significantly increased by the incorporation of sulfur.The S-CoMn₂O₄（5.00%）catalyst modified with 5.00%sulfur in atomic percentage exhibited the best catalytic performance,and the reaction rate constant is 1.72 times higher than that of CoMn₂O₄.The presence of coordinated sulfate groups and a large number of oxygen vacancies on the surface of CoMn₂O₄ effectively promoted the generation of active species.The synergistic effect of Co and Mn ions in CoMn₂O₄ and the higher electron transfer efficiency are also the reasons for the improved catalytic degradation performance of S-CoMn₂O₄（5.00%）.The excellent stability of S-CoMn₂O₄（5.00%）catalyst has been confirmed by cyclic tests.The results of the trapping agent experiment and EPR test showed that singlet oxygen（¹O₂）and sulfate radical(SO₄^·–)were the main active species,and the possible degradation mechanism of Fenton-like reaction was proposed.In the third chapter,oxygen vacancies-enriched CoMn₂O₄（V_O-CoMn₂O₄）was prepared by mixing CoMn₂O₄and urea and calcination at high temperature,which was used as a Fenton-like catalyst to activate PMS to degrade Rh B.The results showed that the catalytic activities of V_O-CoMn₂O₄ catalysts were better than that of CoMn₂O₄,and Vo-CoMn₂O₄-1.5 showed the best catalytic degradation performance among them.EPR characterization confirmed that the oxygen vacancy content of V_O-CoMn₂O₄-1.5 was higher than that of CoMn₂O₄.The presence of a large number of oxygen vacancies in the catalyst contributes to the formation of singlet oxygen,and promotes the redox cycles of Co²⁺/Co³⁺,Mn²⁺/Mn³⁺,and Mn³⁺/Mn⁴⁺.Moreover,oxygen vacancies can be used as active defect sites to directly participate in the reaction to generate active species,so the introduction of more oxygen vacancies in CoMn₂O₄ significantly enhanced the catalytic activity.In addition,V_O-CoMn₂O₄-1.5 has better electrochemical performance and larger specific surface area,which also contributes to the improvement of CoMn₂O₄ catalytic performance.V_O-CoMn₂O₄-1.5 has high stability and excellent catalytic degradation performance in a wide p H range（p H=3–11）.The quenching experiments showed that ¹O₂ and SO₄^·–played dominant roles in the Fenton-like degradation of Rh B in the V_O-CoMn₂O₄-1.5/PMS system.In addition,it was found that V_O-CoMn₂O₄-1.5 could achieve efficient oxidative degradation of different dyes under strong acid conditions without oxidant（PMS）and light.In the fourth chapter,CoMn₂O₄/K-CN composite catalysts with different mass fractions of CoMn₂O₄ were prepared by combining CoMn₂O₄ with graphitic carbon nitride which electronic structure was adjusted by a small amount of potassium（K-CN）.The results showed that the catalytic activities of CoMn₂O₄/K-CN composite were higher than that of a single component,and 60%CoMn₂O₄/K-CN had the best catalytic activity.The successful recombination of CoMn₂O₄ and K-CN was proved by various characterization methods.In the process of photo-assisted Fenton-like reaction catalytic degradation,the efficient separation of photogenerated electrons and holes was realized,and the mutual conversion of high-valence metal ions and low-valence metal ions was also promoted.So that both photocatalytic reaction and Fenton-like reaction are improved.The excellent stability of the composite catalyst was confirmed by cyclic experiments.The trapping agent experiment showed that ¹O₂ and SO₄^·–were the main active species in the process of Rh B degradation,and the possible degradation mechanism of 60%CoMn₂O₄/K-CN/Vis/PMS system was proposed by investigating the literatures.In this thesis,three new Fenton-like catalysts were prepared by different optimization methods,such as the functionalization of sulfur on the surface,the introduction of rich oxygen vacancies,and the composite with K-CN material,to improve the catalytic performance of CoMn2O4.These catalysts showed excellent catalytic degradation performance in the activation of PMS to degrade organic pollutants,and all of them had high stability.This study provides a feasible solution to improve cobalt-manganese oxide as a more effective and long-lasting Fenton-like catalyst for the degradation of organic pollutants,which made them have great potential application value in practical wastewater treatment.