By General Strategy To Prepare The Hierarchical Metal-organic Frameworks And Its Catalytic Performance

Metal-organic frameworks are famous for their highly adjustable pore structure,ultra-high surface area,and highly dispersive metal center sites.Such materials have been widely used in various types of catalytic reactions,such as heterogeneous catalysis,electrocatalysis and photocatalysis.However,some problems trouble metal-organic framework,such as the large diffusion resistance caused by the microporous structure,and the poor stability in water because the frameworks' structure formed by coordination,which have greatly restricted the applications of the metal-organic frameworks.This thesis uses two different methods of assembling the hierarchical metal-organic frameworks,which is modified from the “top-down” and “bottom-up”ideas,so that they can have wonderful performance in the catalytic reaction,and under some harsh conditions,such as water,acid,alkali can exist stably.The main contents are as follows:(1)Based on the theory of plasma,a "top-down" method has been developed to prepare hierarchical metal-organic frameworks.This strategy is simple and easy to implement.By etching the micron particles of metal-organic frameworks by argon plasma,a hierarchical metal-organic framework with a core-shell structure can be obtained(the large-pore MOF is the shell and the small-pore MOF is the core).The relative ratio of macropores and micropores can be highly controlled by the plasma irradiation time and intensity.This method can be applied to different types of metalorganic frameworks,such as ZIF-67,ZIF-8,HKUST-1,etc.This method provides a new idea for the controllable formation of hierarchical MOFs.(2)Develop a "bottom-up" method based on the self-assembly/polymerization of non-aqueous interfaces to prepare hierarchical metal-organic frameworks.This method is relatively easy to implement.By first dispersing MOF nanoparticles into formamide solution to form a "hydrophilic phase",and then mixing with the oil phase through high-speed shearing to form a nanoparticle-stable emulsion,which be polymerized at 65 ? to form a firm hierarchical structure.The hierarchical metal-organic frameworks formed by this method is coated with hydrophobic polydivinylbenzene,so that the MOF nanoparticles can be prevented from directly contacting water,acid,and alkali,thereby stabilizing the metal-organic frameworks.This method can also be applied to different kinds of MOFs,such as HKUST-1,UIO-67(N),Al-MIL-53-NH2 and other MOFs which are unstable in water,as well as ZIF-8 which is unstable in acid condition and NH2-MIL-125(Ti)which is unstable in alkali condition,etc.Catalytic performance studies have shown that under water condition,HKUST-1 composite material still maintains high catalytic activity even after 5 cycles of using;while the structure of pure HKUST-1 has long been destroyed and leaching has occurred,which heavily influence the catalytic performance.This work provides a general strategy for simultaneously achieving hierarchical,machinability,and stable MOF.