Controllable Synthesis And Photocatalytic CO₂ Reduction Of Indium-based MOF And Its Derivatives

Energy shortage and environmental pollution have become the main existential crisis facing mankind.In recent years,the use of photocatalysis technology to convert CO₂ into valuable energy substances has become one of the effective ways to alleviate energy shortage and environmental pollution.MOFs have attracted much attention in the field of photocatalysis due to their advantages of large specific surface area,high porosity,adjustable pore size and abundant active sites.However,in terms of photocatalytic activity of catalysts,there are still some problems such as low photoelectron-hole separation efficiency,few photocarriers,small optical absorption range and wide band gap.Based on this,this paper selects In-based MOF photocatalyst and improves the catalyst through surface modification engineering and heterojunction engineering.Design and prepare Ni-doped In-based MOF,In-MOF derived Ni-doped In₂O₃ and In₂O₃@In-MOF compact heterojunction,and evaluate the photocatalytic reduction performance of CO₂ by three kinds of photocatalysts,respectively.XRD,TEM,FTIR,DRS,PL,XPS,Mott-Schottky and EIS are used to study the structure and properties of each photocatalyst.（1）The photocatalyst NH₂-MIL-68 doped with Ni is prepared by in situ one-pot solvothermal method for photocatalytic reduction of CO₂ by water vapor.The effect of Ni doping on the photocatalytic activity and properties of NH₂-MIL-68 is studied by the above characterization techniques.The results show that Ni doping can promote the separation of photogenerated electron-hole in NH₂-MIL-68,reduce the band gap energy of NH₂-MIL-68,and improve the CO formation rate and selectivity of NH₂-MIL-68 catalyst.NH₂-MIL-68-1%catalyst shows the best photocatalytic CO₂ reduction activity under visible light irradiation.The selectivity of NH₂-MIL-68-1%to CO is almost 100%,and the CO formation rate can reach 23.7μmol g^-1h^-1,which is about 2.5 times higher than that of NH₂-MIL-68 without Ni doping,and has good cyclic stability.（2）Ni-doped In₂O₃ derived from In-base MOF is prepared by a two-step method for photothermal catalytic reduction of CO₂.The characterization data shows that Ni doping can broaden the optical absorption range of MOF-derived In₂O₃,improve the separation efficiency of photo-generated electron-hole,generate more photo-generated carrier,and improve the efficiency of photothermal catalytic reduction of CO₂.In₂O₃-1 catalyst shows the best photocatalytic activity.Under 270°C and illumination conditions,the CO formation rate of In₂O₃-1 is 2080μmol g^-1 h^-1,which is 4 times highter than that of the undoped In₂O₃.The selectivity of CO is nearly 2 times higher than that of the undoped In₂O₃,and has good cyclic stability.（3）In₂O₃@In-MOF compact heterojunction is prepared by In-MOF in-situ partial pyrolysis for photocatalytic reduction of CO₂.In₂O₃@In-MOF compact heterojunction not only retains the original advantages of In-MOF precursors,enhances the adsorption and enrichment of CO₂and provides more active sites,but also generates close contact heterogeneous interfaces,significantly improving the separation and transfer efficiency of photogenerated electron-hole.The photocatalytic test results show that the best catalyst In₂O₃@In-MOF-1 has a CO formation rate of 19.6μmol g^-1 h^-1 and a CH₄ formation rate of 9.0μmol g^-1 h^-1,which is almost 6 times that of pure In-MOF or 2 times that of rh-In₂O₃.