Preparation Of Fe₂M-MOFs-based Artificial Photosynthetic Catalyst For Studying Their Performance

The excessive consumption of fossil energy has led to the continuous increase of carbon dioxide（CO₂）content in the atmosphere.Converting CO₂ into energy or high value-added chemicals by artificial photosynthetic technology is an effective mean to achieve the goal of carbon neutrality.Among them,the researches and exploitations of high-efficiency photocatalysts are the key to the development of artificial photosynthesis technology.Metal organic frameworks（MOFs）have become emerging materials in the field of photocatalysis due to the outstanding specific surface area,porous and adjustable structure.However,the influence of the electronic effect of the organic ligands and the electronic structure of the metal center for the performance of artificial photosynthesis in MOFs catalysts is still unclear,and the strategies are relatively limited for regulating and promoting the performance.In response to the above problems,we use Fe₂M-MOFs as a model framework to regulate the substituents of organic ligands and metal clusters to construct photocatalyst with dual-active-site synergistic catalytic effect,which improves the photocatalytic activity of MOFs.Furthermore,loading ionic liquids（ILs）with the strong CO₂ enrichment in the channels of MOFs to construct a host-guest synergistic catalytic system,and further enhance the photocatalytic activity of MOFs.The specific research contents are as follows:For the first time,the effect of the substituents of the organic ligands and metal clusters in Fe₂M-MOFs with the same framework structure on the artificial photosynthesis CO₂ reduction performance was systematically studied.We used terephthalic acid with hydroxyl,nitro,and amino substituted terephthalic acid with Fe₂Co clusters to prepare PCN-242-Fe₂Co-X with different substituents（X=-H,-NO₂,-OH,-NH₂）,and then use 2-aminoterephthalic acid with Fe₂M（M=Fe,Co,Ni,Cu,Zn,Mn）to prepare a PCN-242-Fe₂M-NH₂ photocatalyst by solvothermal method.X-ray powder diffraction（PXRD）and infrared spectroscopy（FT-IR）characterization confirm that these MOFs have the same framework,and the morphology was characterized by scanning electron microscop y（SEM）.The artificial photosynthetic CO₂ reduction performance show that the electron-donating substituents of the ligand are beneficial to improve the artificial photosynthetic performance.Therefore,the catalytic activity of different Fe ₂M clusters varies greatly.Among them,PCN-242-Fe₂Co-NH₂ has the highest rate of HCOOH of 205.9μmol g^-1 h^-1,which is the best CO₂ reduction performance for MOFs-based photocatalyst in photosynthesis so far.The photoelectrochemical and in-situ-FT-IR results suggest that the NH₂-organic ligand can not only improve the light absorption of MOFs,but also promote the charge transfer by the synergistic effect of the organic ligand and Fe₂Co cluster,so that the photocatalyst shows excellent artificial photosynthetic CO₂ reduction performance.The ILs@MOFs host-guest synergistic catalytic system was firstly constructed by loading ILs into Fe₂M-MOFs channels,and improve the artificial photosynthetic performance.The stable ILs@PCN-250-Fe₂Co composite material was synthesized by solvothermal and stirring method.The FT-IR,N₂ adsorption and desorption show that ILs are successfully loaded in the pores of PCN-250-Fe₂Co;the CO₂ adsorption proves that ILs can effectively enhance the CO₂adsorption capacity of ILs@PCN-250-Fe₂Co composites;the energy band test suggests that ILs@PCN-250-Fe₂Co meets the thermodynamic requirements of photocatalytic CO₂ to CO.The artificial photosynthetic CO₂ reduction performance tests show that ILs（39.3 wt%）@PCN-250-Fe₂Co has the best CO production of 545.23μmol cm^-2 h^-1.The photoelectrochemical tests show that ILs@PCN-250-Fe₂Co has excellent ability to separate and transport photogenerated electrons and holes.It shows that the decoration of guest ILs can not only enhance the CO₂adsorption capacity of host MOFs,but also promote the separation of photo-generated charges through the synergistic effect of host-guest,thereby effectively enhance the photocatalytic activity of the composite material.