Construction Of Transition Metal Oxide/Carbon Composites For Enhanced Photocatalytic Performance

Energy crisis and environmental pollution are two major problems that restrict the sustainable development of human beings.Photocatalysis technology is the application of solar energy to decompose aquatic hydrogen,pollutant degradation,synthesis of organic matter and other fields through photocatalyst,which is considered as one of the ideal ways to solve the current problems.Transition metal oxide composites are widely used in fine chemical industry and environmental catalysis because of their good stability and high catalytic activity.However,the traditional preparation method is complicated,which has many influencing factors and poor repeatability.In order to solve this problem,a simple and easy hydrothermal synthesis method is adopted in this paper.Which is combined with high temperature firing to synthesize high efficient transition metal oxide and carbon composite catalyst,and its photocatalytic performance is studied.Specific research contents are as follows:(1)First,MIL-101(Cr)@TiO2 composite structure was formed by a simple secondary hydrothermal method,and then the Cr2O3/C@TiO2 composite material was formed at 500? under nitrogen protection.MIL-101(Cr)is not only the substrate for TiO2 shell growth,but also the source of Cr element in Cr2O3.Perfect energy efficiency structure was formed by regulating the content of TiO2 reactants and reaction temperature.A small amount of Cr3+ in MIL-101(Cr)doped into TiO2 resulted in the decrease of band gap value of TiO2 which widened the visible light response region.The presence of carbon in the composites also accelerates the transfer of electrons and holes,and the unique nanostructure and appropriate combination of elements give the Cr2O3/C@TiO2 composites excellent photocatalytic performance.Under the irradiation of 300 W xenon lamp,the photocurrent density reached 2.1 mA/cm2 at 0.4 V(vs.Ag/AgCl),which was about 3.5 times of that of pure TiO2.The photodissociation rate of aquatic hydrogen was 446 mol h-1 g-1,which was about 4 times that of pure TiO2.(2)In this paper,MIL-101(Fe)was synthesized by a one-step hydrothermal method,and then the sample was characterized by simple morphology and XRD analysis.It was found that the morphology of MIL-101(Fe)was octahedron,the particle size was and the crystallinity was high.The sample was dried and stored in an open beaker,which was gradually converted to MIL-101(Cr)@Fe2O3 composite at room temperature,and then heated at 500? under nitrogen protection to form Fe3O4/C/Fe2O3 composite.The composition of Fe3O4 and Fe2O3 can form a good complement,while the formation of Fe3O4/Fe2O3 composite interface with carbon material can significantly improve the charge transfer of Fe3O4/Fe2O3 catalyst and further improve its photocatalytic activity.Under the irradiation of 300 W xenon lamp,the photocurrent density of the composite material reaches 3.7 mA/cm2 at 0.4V(vs.Ag/AgCl),which is about 2 times of pure Fe2O3.The results showed that the degradation efficiency of Fe3O4/Fe2O3 was about 4 times that of a single Fe2O3 nanoparticle.In addition,Fe3O4/Fe2O3 has good recyclability under the action of appropriate magnetic field,which can effectively avoid the pollution caused by the catalyst itself and save the cost.