Preparation And Catalytic And Storage Properties Of Metallic Oxide/Graphene Composites

Metallic oxide such as TiO_2,Fe₃O_4,Mn₃O₄,etc.has unique electrical,optical,magnetic properties.However,the poor conductivity and ion transport performance of it severely limit its wide application in catalysts,solar cells,and energy storage,et.al.Graphene composed of sp2 hybrid carbon atoms arranged in a hexagonal honeycomb crystal lattice structure has excellent electrical conductivity,thermal conductivity and mechanical properties as well as ultra-high specific surface area.The combination of metallic oxide with graphene is expected to greatly enhance the conductivity and ion transport performance of metallic oxide effectively improving catalytic and energy storage properties.This paper focuses on the preparation of metallic oxide/graphene composites and their catalytic and energy storage properties.The specific research contents and results are as follows:（1）Nano-sheet self-assembled TiO₂ microspheres（TiO₂ HHMs）were successfully prepared by solvothermal treatment with cetyltrimethylammonium bromide（CTAB）as surfactant and HF as adjuvant.Graphene oxide（GO）was prepared by the modified Hummers method.The TiO₂HHMs/rGO composite photocatalyst was synthesized by a two-step hydrothermal method.Under simulated sunlight,the photocatalytic degradation efficiency of it for Rhodamine B（Rh B）is as high as 97.8%,which is significantly higher than that of pure Ti O2 HHMs（75.2%）and conventional TiO₂ P25（53.6%）.This is mainly attributed to the excellent conductivity after recombination with rGO,which can separate more effectively the electron-hole pairs.In addition,the large specific surface area of rGO can improve the adsorption performance of the composite.（2）Raspberry-like TiO₂ microspheres with uniform particle size were prepared by solvothermal method using sodium dodecyl benzene sulfonate（SDBS）as a surfactant.The layered MoS₂nanosheets were grown in situ on the surface of TiO₂microspheres by two-step hydrothermal reaction,and simultaneously combined with rGO to obtain MoS₂/TiO₂/rGO photocatalyst.The photocatalytic reduction efficiency of Cr（VI）on MoS₂/TiO₂/rGO composites is as high as 100%in the range of p H 2-5under simulated sunlight.After 7 cycles,the catalytic efficiency still reaches 66.7%,indicating the great potential in practical applications.（3）The Mn²⁺ ion doped Fe₃O₄ hollow microspheres were successfully synthesized for the first time by the solvothermal method.The monodisperse magnetic Mn-Fe₃O₄/rGO heterogeneous Fenton catalyst coated with rGO nanosheets was prepared by ultrasonic assisted mechanical stirring and Na BH₄ as reducing agent.Under simulated sunlight,the catalytic degradation efficiency of Rh B can reach 91%（p H=2）and 85%（p H=11）,and in the neutral solution（p H～6.5）,the catalytic degradation efficiency is as high as 96.5%.After 10 cycles,the catalytic degradation efficiency still reaches 90%,and the maintains high saturation magnetization Ms～33.23 emu g^-1.The excellent catalytic activity of it is mainly due to:Mn²⁺ion doping increases the defects concentration of Fe₃O₄ crystal and its catalytic active sites,rGO coated Mn-Fe₃O₄ hollow structure effectively increases the specific surface area of the composite significantly improving the adsorption performance for pollutants.（4）Magnetically easily recoverable MoS₂/Fe₃O₄/rGO composite heterogeneous Fenton catalyst was synthesized by one-step hydrothermal method.Under the simulated solar radiation,the degradation of it for Rh B,MO and MB three pollutants can reach 100%with the catalyst concentration of only 0.2 g L^-1 and H₂O₂concentration of 5.8 m M.After 10 cycles,the catalytic degradation efficiency can still reach 100%,and the saturation magnetization can maintain 67.1 emu g^-1.（5）The Zn²⁺ ion doped Fe₃O₄ hollow spheres were successfully prepared by solvothermal method and attached to the surface of rGO sheet to obtain Zn-Fe₃O₄HHMs/rGO-30 supercapacitor electrode materials.The specific capacitances are 707F g^-1 and 504 F g^-1 at current densities of 1 A g^-1 and 10 A g^-1,respectively.the specific capacitance still maintains 85.5%of the initial specific capacitance after 1500cycles of constant current charge and discharge cycles at a current density of 7.5 A g^-1.This excellent performance is attributed to the fact that the Zn²⁺ion doping increases the active site of the Fe₃O₄ crystal,the high specific surface area of the hollow structure Zn-Fe₃O₄,and the fast ion diffusion channel provided by the rGO nanosheet.（6）The flower-like Mn₃O₄ microspheres were prepared by solvothermal method with CTAB as surfactant,and then Mn₃O₄/rGO-20 supercapacitor electrode material was obtained by compounding with rGO.The specific capacitance are 947 F g^-1 and612 F g^-1 at current densities of 1 A g^-1 and 20 A g^-1,respectively.Moreover,the specific capacitance still maintains 88.1%of the initial specific capacitance after4,000 cycles of constant current charge and discharge cycles at a current density of 10A g^-1.These excellent properties are mainly attributed to the fact that the flower-like Mn₃O₄ structure provides more active sites for the redox reaction,as well as the fast ion diffusion channels provides by the rGO nanosheets which also provides more buffer space for the volume expansion of the electrode material.