Research On Design,preparation And Catalytic CO₂ Cycloaddition Of MOFs And MOF/POP Composites

Capturing and chemical fixation of carbon dioxide（CO₂）into cyclic carbonate is considered to be a promising way to alleviate the CO₂ problem and to use CO₂ to produce fine chemicals.Recently,developed porous heterogeneous catalysts with Lewis acid and nucleophilic sites can effectively facilitate this process,including metal-organic framework materials（MOFs）,covalent-organic frameworks（COFs）,nanoporous ionic organic networks（NIONs）,and porous organic polymers（POPs）.Among them,MOFs and POPs is widely used in cycloaddition of CO₂ and epoxide,because MOFs and POPs with large specific surface area and pore size can improve the ability of capturing CO₂ gas,can contribute to the effective diffusion of catalytic substrate and product,rich active sites can effectively activate the substrate and/or CO₂ molecules,good thermal stability and chemical stability ensures that they can be recycled.Therefore,based on the excellent catalytic activity of MOFs and POPs in CO₂ and epoxides cycloaddition,this paper designed and prepared several MOFs and MOF/POP composites.The synthesis and structure characteristics of these materials were summarized,and the application of those MOFs and MOF/POP composites in the cycloaddition reaction of CO₂ and epoxides was further explored.This paper is divided into five chapters:In the first chapter,the current research status of CO₂ utilization is summarized,and then the applications of MOFs and POPs in catalytic cycloaddition reactions of CO₂and epoxides are classified and introduced.In the second chapter,a bifunctional MOF@POP core-shell catalyst（NH₂-UiO-66（Hf）@Co TPy-CAP）was synthesized by amino functionalized MOF（NH₂-UiO-66（Hf））and Co-based porphyrin POP（Co TPy-CAP）.The MOF@POP core-shell structure not only increases the exposure of active sites in Co TPy-CAP,the Hf clusters in NH₂-UiO-66（Hf）also increase the concentration of active sites in the whole catalyst system.Meanwhile,bromine ions with nucleophilic effect were also introduced which made the catalyst system abundant in Lewis acid sites and nucleophilic centers,and could efficiently catalyze the fixation of CO₂ and epoxides without any homogeneous co-catalysts under mild conditions.Moreover,the catalytic activity of the catalyst did not decrease significantly after being recycled for five times,and it could still achieve efficient CO₂ conversion.In the third chapter,an amorphous layered POP material（ZnTImP-CP）was synthesized by using 5,10,15,20-tetra（4’-imidazolyl-phenyl）porphyrin zinc and1,4-dibromodimethylbenzene.ZnTImP-CP was exfoliated into nanosheets（nano ZnTImP-CP）by physical ultrasound method,and then nano ZnTImP-CP was added in the synthesis process of 2D layered MOFs（NUS-8（Hf））to form 2D/2D MOF/POP composite（NUS-8（Hf））/nano ZnTImP-CP),which served as catalyst for the cycloaddition reaction of CO₂ under mild conditions.The massive ZnTImP-CP was exfoliated into nanosheets to expose more catalytic active sites,which were conducive to the contact between the active sites and the substrate.The combination with NUS-8（Hf）is beneficial to increase the active sites and further enhance the reactivity.In the fourth chapter,we synthesized a series of hexanuclear cluster of MOFs （including UiO-66,UiO-67,UiO-67-Me,UiO-68,UiO-68-Me,PCN-56,PCN-57,UiO-68-NH₂）by using three linear carboxylic acid ligands with different lengths and different functional groups,transition metals（Zr and Hf）and rare earth metals（Y,Yb）.The structures and properties were analyzed and characterized by X-ray powder diffraction（PXRD）,Fourier transform infrared spectrum（FT-IR）,the static contact angle,N₂ adsorption,CO₂ adsorption and other methods.The influencing factors of MOFs as catalysts for CO₂ cycloaddition reaction under normal temperature and pressure were investigated and summarized.In the fifth chapter,the work of these MOFs and MOF/POP composites is summarized,and the advantages of these materials in the application of catalytic CO₂cycloaddition reaction are conclued.