Design And Synthesis Of MOF-Based Photocatalytic Materials And Their Applications In The Conversion Of Small Molecules

With the rapid development of the economy,the problems related to the environment and energy have become a major challenge for all mankind,and seeking renewable energy is an effective way to solve the energy crisis and environmental problems.Solar energy is a kind of abundant and renewable energy and converting solar energy into hydrocarbon fuels through artificial photosynthesis is one of the most effective ways to solve the above problems.The use of semiconducting photocatalysts to realize photocatalytic water splitting and carbon dioxide reduction reactions to prepare solar fuels has obvious advantages.However,the existing photocatalysts cannot meet the need of human production and life due to their relatively low catalytic efficiency and complex catalytic systems.As a new type of porous materials,metal-organic frameworks（MOFs）have both organic molecules and metal sites and have the properties of inorganic semiconductors,so they show great potential in the field of photocatalysis.Therefore,from the perspective of the development and further modification of new materials,a series of MOF materials have been successfully prepared in this thesis,and the structure-activity relationship of such materials in photocatalytic water splitting and CO₂ reduction has been deeply explored.This provides an idea for the preparation of efficient photocatalytic solar fuel conversion catalysts.The main results are as follows:（1）From the perspective of amino functional modification,heterostructure construction and catalytic site construction of MOF,amino functionalized MIL-125（Ti）was combined with Cu₂O to form an II-type heterojunction,followed by a series of stable Ti³⁺-rich MOF composite catalysts for photocatalytic water splitting for hydrogen production were prepared under different cold plasma treatment conditions.The II-type heterojunction can effectively separate the photogenerated carriers.At the same time,the cold plasma reduces Cu⁺to Cu⁰ in Cu₂O,Ti⁴⁺in Ti-MOF is reduced to Ti³⁺,and the localized Surface Plasmon Resonance（LSPR）effect generated by Cu⁰ is similar to the ligand-to-metal charge transfer of MOF.The effect further transfers a number of electrons to Ti³⁺with high catalytic activity,and it can be retained in the environment for a long time,thus providing a large number of reaction sites for subsequent photocatalytic reactions.The composite catalyst obtained by cold plasma treatment at a power of 350 W for 15 minutes has the best activity up to 1138μmol·g^-1·h^-1,which is 9 times the activity of pristine NH₂-MIL-125（Ti）.（2）From the perspective of metal doping of MOF,preparation of MOF derivatives by pyrolysis and control of catalyst morphology,Cu and Co bimetallic hollow MOF materials were first prepared by soft stencil method and co-precipitation method.A series of nitrogen-doped carbon hollow sphere catalysts loaded with Cu and Co nanoparticles were obtained by pyrolysis at different temperatures in an Ar gas environment.The results show that the construction of the hollow sphere structure can effectively improve the mass transfer rate during the catalytic reaction,the larger specific surface area of the catalyst increases the absorption and utilization of light by the catalyst,and the carbon in the outer layer can effectively avoid the serious damage of metal nanoparticles.At the same time,Co,Cu nanoparticles are encapsulated in the carbon layer,so that Lewis acid sites（such as metal sites）and Lewis base sites（such as pyridine N）are incorporated into the porous carbon,thereby synergistically catalyzing CO₂ molecules and applying them to the photocatalytic CO₂ reduction to CO.When the Cu:Co ratio is 2:4 and the pyrolysis temperature is750°C,the obtained catalyst has the best activity,and the CO production rate can reach 47.626 mmol·g^-1·h^-1.