Preparation Of Porous Transition Metal Oxide By Oxalate Method And Its Catalytic Property For Degradation Of Methylene Blue Solution

With the rapid development of economy and society,more and more attention has been paid to the shortage of fresh water resources and water environmental pollution.Dye wastewater is a typical refractory industrial wastewater,which has the characteristics of high chroma,poor biodegradability,strong toxicity and large discharge.It has great potential harm to the surface water environment and human health.How to treat dye wastewater efficiently to meet the discharge standard has become a major issue to be solved.Advanced oxidation technology is widely used in the field of water treatment because of its good treatment effect and fast degradation rate of organic pollutants.In this study,porous transition metal oxides with hierarchical micro-nano structure were synthesized by the oxalate method and their performances for catalytic degradation of methylene blue was investigated.The effect of microstructure,such as morphology,composition and pore structure,on the catalytic activity of the material was investigated.The purpose of this study is to provide a theoretical reference for the treatment of printing and dyeing wastewater.（1）Two different morphological ZnO materials with hierarchical micro/nano structures were fabricated through solvothermal method and oxalate method,respectively.Their photocatalytic performances were evaluated by using the degradation of methylene blue（MB）solution as model reaction.The results show that the product via solvothermal method exhibits a flower-like micro-spherical appearance assembled by many nano-flakes,while its counterpart derived from oxalate strategy shows a micro-rod like morphology constructed by many nanoparticles.ZnO fabricated by oxalate method has a much better photocatalytic activity towards MB degradation.The identification results for active radicals verify that·OH and·O₂^–are both formed in the two samples when they are irradiated under ultraviolet light.However,due to their diverse band structures,there is a difference in number of active radicals produced in the reaction system,which can further lead to different photocatalytic efficiency for MB degradation.As for oxalate-derived ZnO,greater number of·OH and·O₂^–can be formed under the irradiation of ultraviolet light.Meanwhile,·OH with strong oxidation capacity plays a dominant role in the photocatalytic reaction system.As a result,it possesses more excellent property in degradation of MB than that of ZnO originated from solvothermal method.（2）Porousα-Mn₂O₃with irregular granular morphology stacked from microplates was synthesized through thermal decomposition of oxalate,and its performance as a catalyst to activate peroxymonosulfate（PMS）for degradation of methylene blue（MB）solution was explored.The results show that the product obtained at 450℃exhibits the most excellent catalytic ability due to its highest specific surface area among the samples.The results show that the degradation rate of MB solution increases with the increase of the amount of PMS and catalyst in the reaction system,and gradually comes to a standstill.In addition,it is found that the presence of anions has a negative effect on MB degradation.The order of their inhibitory effect is C₂O₄^2->PO₄^3->Cl^-.Furthermore,the active species identification results confirms that there are·OH,SO₄^·-,·O₂^-and ¹O₂ in the reaction system,and singlet oxygen（¹O₂）is the most important active intermediate involved in the direct oxidation degradation of MB.（3）Bimetallic rod-like compounds with different Fe:Coratios were synthesized by thermal decomposition of oxalate,and their performances as catalysts to activate peroxymonosulfate（PMS）for degradation of methylene blue（MB）solution were explored.The results show that CoFe₂O₄ with Fe:Co=2:1 exhibits higher performance towards PMS activation due to its largest specific surface area among the samples.A series of single-factor experiments were carried out to investigate the effects of parameters,including dosage of PMS,addition amount of catalyst,and co-existed anions,on the degradation efficiency of MB.Furthermore,the mechanism of MB degradation by PMS/CoFe₂O₄ was analyzed and ¹O₂ was regard as the primary reactive oxygen specie in the system.More importantly,CoFe₂O₄can be easily separated from the solution under external magnetic field after the catalytic reaction owing to its excellent magnetic property.