| As an emerging class of highly ordered crystalline porous materials,metal–organic frameworks(MOFs)with flexible and variable ligands and metal nodes,high specific surface areas,tunable pores,as well as intriguing functionalities have exhibited promising potentials in gas storage,separation,catalysis,and energy technology applications.After nearly two decades of development,the synthesis of MOF materials has gradually evolved from exploration and trial to precise-design,including functional-oriented microstructure design and optimization,pore size tailoring,and secondary building unit modification.The unique pore environments of MOF materials enable their unique advantages in gas adsorption and separation applications.Furthermore,MOF-based adsorbents and separation membranes exhibit superior separation performance in many industrial gas purification processes.In this thesis,a series of function-oriented MOFs are synthesized through optimization of microstructure design,pore size tailoring,secondary building unit modification,and post-synthesis modification.Their gas adsorption and separation performances are improved through pore environment and size optimization.In addition,based on the MOF-based adsorbents and separation membranes,an energy-intensive,environmentally-friendly alternative separation route is explored to achieve efficient separation of hydrogen,carbon dioxide,natural gas,and petroleum-based compounds.The main achievements of the thesis are as follows:(1)The presence of multiple channels in the MOF frameworks increases the affinity of the MOF frameworks to light hydrocarbon gas molecules.Based on this theory,we have further optimized by taking advantage of the MOF structure design,and chose a metal-organic framework material(iso-MOF-1)with three channels of quadrilateral,pentagonal,and hexagonal as the template.Through performing-F,-Cl,-NH2,-CH3,and-OCH3 on its organic ligand[1,1':3',1'-terphenyl]-4,4'',5'-tricarboxylic acid(H3TTCA)and modifying different numbers of functional groups such as-CH3 and-Cl at different positions of pyrazine(pyz),a series of microporous Cu-MOF with controlled pore environment were synthesized based on iso-MOF-1 framework,realizing efficient storage and separation of light hydrocarbons.Gas adsorption test results indicated that-F and-CH3 modified iso-MOF-4showed ultra-high C3H6 storage capacity.Grand Canonical Monte Carlo(GCMC)simulation and Density Functional Theory(DFT)calculation results reveal that the iso-MOF-4 framework preferentially adsorbs C3H6 under low pressure.Single crystal X-ray diffraction analysis and molecular simulation were employed to accurately determine the adsorption site of C3H6 in the iso-MOF-4 framework.Breakthrough experiments showed that iso-MOF-4 exhibits excellent separation performance for C3H6/C2H4.In summary,these experimental results suggest that the optimal framework of iso-MOF-4 obtained by pore environment regulation achieves selective separation of light hydrocarbon gases,which provides a new idea for improving the gas adsorption and separation capabilities of MOFs.(2)By functional modification of the ligand(H3TTCA)and modification of the[Ni3(?3-O)(COO)6]node with pyridine-N ligands(dimethylamine,pyridine,p-aminopyridine,and isonicotinic acid),a series of microporous nickel metal–organic frameworks with controlled pore environments based on UPC-105 were synthesized to realize the regulation of C2H2/CO2storage and separation performances.UPC-106 constructed with H3TTCA-F ligand has the highest C2H2 and CO2 storage performances.The aminopyridine and dimethylamine modified UPC-110 has the smallest open pore size and porosity,but the C2H2/CO2 separation selectivity(IAST)is the highest,supported by GCMC simulation and penetration experiments.UPC-110has a high C2H2 storage and C2H2/CO2 separation selectivity due to the pore size effect and the Lewis acid-base effect increasing the interaction between the MOF framework and the C2H2gas molecules.Our work provides a synergistic strategy to improve the storage and separation performances of gases by simultaneously modifying organic ligands and metal nodes to design metal–organic framework materials with controlled pore environments.(3)By functional modification of the ligand(H3TTCA)and modification of the[Fe3(?3-O)(COO)6]node with imidazole-N ligand(imidazole,4-methylimidazole and benzimidazole),and pyridine-N ligand(pyridine,2-methylpyrazine,4-aminopyridine and isonicotinic acid),a series of isomorphic metal–organic framework membrane materials were designed and synthesized.As the size of the modifying group increases,the opening size of the large cage and the small cage decreases from 8.2?to 3.5?,which is exactly between the dynamic diameters of H2(2.9?)and N2(3.6?).We then prepared MOF polycrystalline membranes by in-situ growth method and focused on their membrane separation performances of H2/N2.Due to molecular sieve effect and molecular diffusion effect,the UPC-120 polycrystalline membrane synthesized by H3TTCA-F and benzimidazole ligands exhibits the highest H2/N2separation selectivity(123.7)with the H2 permeability of 2.97×10-7 mol·m-2·s-1·Pa-1 and excellent long-term test stability.Using the concept of isoticular chemistry,through optimizing the pore environment and size of MOF,it suggests the new possibilities for the synthesis of promising gas separation membrane materials.(4)In view of the problem that the industrial H2/CO2 separation process is usually carried out under high temperature and water vapor conditions,a defect-free polycrystalline film of metal–organic framework(UPC-31)with an octahedral cage structure was successfully prepared on a silica substrate,coated with a layer of hydrophobic polydimethylsiloxane(PDMS)by thermally deposition,and this obtained UPC-31@PDMS polycrystalline composite membrane exhibits high vapor stability.The membrane effectively shields against moisture attack and significantly improves the hydrothermal stability of the polycrystalline membrane.The hydrophobic UPC-31@PDMS polycrystalline composite membrane exhibits high H2/CO2separation performance of 24.3 and H2 permeance of 3.0×10-7 mol·m-2·s-1·Pa-1(884 GPU)under high temperature and water vapor conditions(200?,0.1 MPa,H2/CO2 mixed gas mixture containing?4 mol%H2O water vapor),which is the first case to achieve the target H2/CO2separation performance under high temperature and steam conditions(H2 permeance>200GPU,Selective>20)of MOF polycrystalline membrane.This work greatly expands the application of MOF polycrystalline membrane in industrial H2/CO2 separation processes. |
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