Preparation Of Hierarchically Porous Metal-Organic Framework/Polymer Composites For Heterogeneous Catalysis

Metal organic frameworks because of their highly ordered pore structure,high internal surface areas,and chemical functionality,have been attracting strong research interest and can be widely used in various fields,such as catalysis,sensing and gas separation.However,due to the large diffusion resistance because of narrow microspore,poor processibility and water stability,the practical application is still subject to great resistance.Although each issue could be solved separately,it still remains a big challenge to develop a general strategy to simultaneously reduce the diffusion resistance of substrates and achieve the facile processibility for MOFs with different components and moisture-stability.In this paper,we started from MOFs nanoparticles to reduce the diffusion resistance and have demonstrated an interfacial nanoassembly/polymerization method to process MOFs/polymer composites into task-specific shapes with hierarchical porosity(micro-,meso-,and macropores)based on MOFs-stabilized emulsions and study its water stability and heterogeneous catalysis,the main research content is as follows:(1)We develop a general strategy to achieve simultaneously the formation of hierarchical porosity and easy processibility for MOFs composites through an interfacial nanoassembly/emulsion polymerization method.This method can be utilized in various MOFs nanoparticles with different components and stability including stable ZIF-8,UiO-66 and Cr-MIL-101 and moisture-sensitive HKUST-1.Taking ZIF-8 as an example,the size of macropore for the resulting hierarchically porous ZIF-8/polystyrene(ZIF-8/PS)composites can be facilely controlled from 6 μm to 28.5 μm through changing the amount of MOFs nanoparticles,which tunes the loading of MOFs within the composites at the same time.The fluidic nature of the emulsion before polymerization facilitates the easy processibility of MOFs composites into task-specific shapes,such as short,long,thin,or thick columns,spheres,and various irregular bodies.Additionally,the magnetic functionality can be facilely endowed to the MOFs composites through co-assembly of Fe3O4 and MOFs nanoparticles.The MOFs composites exhibit excellent mechanical stability even after pressing or long-term mechanical stirring.ZIF-8/PS shows high conversion rate and selectivity toward the Knoevenagel reaction of malononitrile with benzaldehyde,compared with ZIF-8 nanoparticles and microparticles.(2)Disperse the moisture-sensitive MOFs in the oil monomers by ultrasonic,simultaneously to achieve the formation of hierarchical porosity,water stability and easy processibility for MOFs composites through an interfacial nanoassembly/emulsion polymerization method.This method can be utilized in moisture-sensitive HKUST-1 and Fe-MIL-101.After dispersed of the metal organic frame nanoparticles in diethylbenzene for 12 h by ultrasonic,the high internal phase emulsion was prepared and then polymerization,the hydrophobic hierarchically porous MOF/polymer composite was obtained.Hydrophobic HKUST-1/PS and Fe-MIL-101/PS can be remained their structure and morphology after immersed in water for 15 d,compared with the structure was destroyed of HKUST-1 and Fe-MIL-101 nanoparticle.s only immerse in water for 1 h.and the integrity of.HKUST-1/PS shows high conversion rate and selectivity toward the Knoevenagel reaction of malononitrile with benzaldehyde,compared with HKUST-lmicroparticles,and only slightly lower than the HKUST-1 nanoparticles.