| Metal-organic frameworks(MOFs),also known as porous coordination polymers(PCPs),represent an intriguing type of crystalline porous materials(CPMs)that can be readily self-assembled through the coordination of inorganic metal ions/clusters with organic bridging linkers,which is one of the most rapidly developed porous materials over past two decade.In recent years,owing to the structural visualization and tunability,high surface area and functional pore cage/channel,the bright potential of MOFs as emerging multifunctional materials is highlighted in many research areas,especially for gas storage and separation.The separation of light hydrocarbon mixtures represents one of the most important chemical processes in the petrochemical industry.In this dissertation,we aim to fabricate a series of cationic MOFs by rationally designing experimental schemes based on different azole ligands and metal salts.The effects of the template molecules,pore space partition ligands and counter anions on the robustness and stability of the host framework,and the selective adsorption separation performance of greenhouse gases and light hydrocarbon mixtures,were systematically investigated.Meanwhile,the relationship between structure and properties were further established.The research work of this dissertation provides theoretical basis and new research ideas for the application of MOF materials in greenhouse gases capture and petrochemical gases storage,separation or purification.At the same time,offers a novel avenue to construct and optimize MOF materials.We have synthesized three isostructural microporous cationic metal-organic frameworks(FJU-14)and firstly demonstrated that the robustness,stability and gas separation capacity of the MOFs could be tuned by alerting the weak interactions between the host and the counter anions.Among the three MOFs,FJU-14-BF4 containing BF4-anion in its tetrahedral cages can adsorb CO2 with high volume uptake(95.8 cm3 cm-3),but low enthalpy(18.8 kJ mol-1)at ambient conditions.The trapped CO2 density of 0.955 g cm-3 is the highest value among the reported MOFs.Dynamic fixed bed breakthrough experiments indicate that the separation of CO2/N2 mixture gases through a column packed with FJU-14-BF4-a solid can be efficiently achieved.The balanced multiple hydrogen-bonding interactions(MHBIs)between the BF4-counter anion and the cationic skeleton play crucial role in the stability of FJU-14-BF4-a.The high-density CO2 capture is mainly contributed from the multiple-point interactions between the adsorbate molecules and the framework as well as its counter anions.A pair of supramolecular isomers of Co(?)-based MOFs(FJU-88 and FJU-89)can be directionally fabricated by rationally tuning the template molecules.Although the isomers have the similar CO3 secondary building units(SBUs)and organic linkers,they adopt distinct nets with asc and snw topologies,respectively,which derive from the conformational flexibility of the organic ligands.It is noteworthy that the collapse of the porous structure of FJU-88 after removal of the solvent from the pores.But FJU-89a shows permanent porosity accompanied with unusual hierarchical micro-and mesoporous and superior gas selective adsorption performance.In addition,dynamic fixed bed breakthrough experiments indicate that the separation of C2H2/CO2 and C2H2/CH4 mixture gases through a column packed with FJU-89a solid can be efficiently achieved.We have successfully realized a microporous MOF(FJU-90)with dual functionalities for highly selective C2H2/CO2 separation through the pore space partition(PSP)strategy.The partition of the tripyridine ligands not only improves the framework stability,but also reduces the pore aperture sizes for the enhanced sieving effect for the gas separation.Notably,FJU-90a exhibits both moderately high C2H2 uptake capacity and adsorption selectivity,affording new benchmark C2H2 captured productivity toward C2H2/CO2(50%:50%)separation under ambient conditions.We have successfully synthesized two isostructural cationic microporous metal-organic frameworks(FJU-53)containing infinite zigzag copper-halogen chains and first demonstrated that the adsorption selectivity toward C2s/C1 mixtures in the charged MOFs can be improved by modulating the interactions between counterions and the trapping gas molecules.Crucially,FJU-53 shows the highest adsorption selectivity for C2H2/CH4 purification,and ultrahigh chemical stability in the aqueous solutions with pH ranging from 1 to 13.Meanwhile,FJU-53 also shows solvent-and halogen-dependent thermochromic behaviors owing to the thermally induced vibration of the(CuX)nn+chains.Its thermochromic mechanism obviously distinguishes from those for the pure inorganic copper halides. |
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