Synthesis And Photocatalytic Reduction CO₂ Property Of Iron-Based Metal-Organic Framework

Iron-based metal-organic frameworks（Fe-MOFs）have attracted much attention as photocatalysts due to their Fe-O clusters,which can be directly excited under visible light irradiation.However,the photocatalytic activity of most Fe-MOFs is often limited by the narrow light absorption range,severe photogenerated electrons-hole recombination and poor stability.In this thesis,based on the iron based MIL-88B material,through a series of different morphology,structure and other regulation,the catalytic activity and related catalytic mechanism of these catalysts for CO₂ reduction under visible light were studied.The specific research contents are as follows:1.A series of MIL-88B materials with {011}/{010} facets and different ratio of facets were prepared by changing the mole ratio of Fe salt and ligand terylene acid（H2BDC）.The morphology,structure and optical properties of these four materials were observed by conventional characterization methods,and these catalysts were applied in CO₂ reduction experiments to explore the influence of facets on catalytic activity.The results show that the products of CO₂ reduction catalyzed by all the samples are CO,CH₄ and C₂H₄.The samples with the largest proportion of exposed {011} facets have better selectivity for CO,while the catalysts with the largest proportion of exposed {010} facets have better selectivity for CH₄ and C₂H₄.2.We designed an N,S-codoped Fe-based MIL-88B catalyst with well-defined bipyramidal hexagonal prism morphology via a facile and effective process,which was synthesized by addition of appropriate 1,2-benzisothiazolin-3-one（BIT）and acetic acid to the reaction solution.Under simulated solar irradiation,the designed catalyst exhibits high C₂H₄ evolution yield of 17.7μmol/g·h,which has been rarely achieved in photocatalytic CO₂ reduction process.The synergistic effect of Fe-N coordinated sites and reasonable defects in the N,S-codoped photocatalyst can accelerate the migration of photogenerated carriers,resulting in high electron density,and this in turn helps to facilitate the formation and dimerization of C-C coupling intermediates for C₂H₄ effectively.3.Ag/MIL-88B composites were synthesized by immersion reduction method.With the advantages of silver nanoparticles and MIL-88B in photothermal effect and catalytic activity,the Ag/MIL-88B composites exhibited significant improvement in the activity of photocatalytic CO₂ reduction compared to the original MIL-88B,and the production of CH₄ and CO also increased.After cyclic testing,it was found that the catalytic activity was almost not lost during three consecutive runs,indicating its good stability.This work provides promising strategies for efficientively converting CO₂ into high value-added chemicals using solar energy under mild conditions.