| In the past two decades,metal-organic frameworks?MOFs?have emerged as a unique type of inorganic-organic hybrid crystalline porous materials,which are usually composed of the corresponding organic ligands and metal ions/metal clusters in the form of coordination bonds or intermolecular forces.Therefore,reasonable selection of metal ions and organic ligands is of vital importance for the construction of MOFs with specific functions.Compared with traditional zeolites,carbon materials and mesoporous materials,MOFs not only possess a variety of novel topological structures,but also show good application prospects in the adsorption and separation of greenhouse gases,energy gases storage,fluorescent probes,drug delivery,heterogeneous catalysis,nonlinear optics and molecular magnetism,because they have larger specific surface area,higher porosity,high structural and functional designability.Considering the current research of MOFs materials for improved gas storage and selective separation,we designed and synthesized four copper-based and four zinc-based MOFs through pore size adjustment and functional group modification of organic ligands.The structures and properties of these materials have been studied using basic characterizations such as single-crystal X-ray diffraction,FTIR,PXRD,thermogravimetric analyses,and gas adsorption.1.To target a contracted version of the HKUST-1-like tbo-type tetraisophthate MOF MFM-181,a new tetraisophthalate ligand was designed and synthesized based on ligand contraction and conformation preorganization strategy.Compared to MFM-181,the resulting MOF ZJNU-10 features smaller cage sizes as well as higher density of open copper sites,thus endowing ZJNU-10 with the promising potential for C2H2/CH4 and CO2/CH4 separations associated with C2H2 purification and natural gas sweetening.At the atmospheric pressure and 298 K,the uptake capacities of C2H2and CO2 reach 151.5 and 108.3 cm3?STP?g-1,while the IAST?Ideal Adsorption Solution Theory?predicted adsorption selectivities of C2H2 and CO2 over CH4 are up to 29.9 and 7.6,respectively.2.We designed and synthesized four bent pentacarboxylic acid ligands bearing different organic functionalities?-H?-NH2?-CH3?-OCH3?at the central benzene ring,which were reacted with Zn?NO3?2·6H2O under suitable solvothermal conditions to afford four new three-dimensional zinc-based MOFs?Zn-MOF-1?Zn-MOF-2?Zn-MOF-3 and Zn-MOF-4?.Single-crystal X-ray diffraction analyses revealed that they all had dinuclear zinc-based secondary structural units,but showed different structural characteristics.In addition,the gas adsorption properties of one of them with respect to CO2,CH4,C2H2,C2H4 and C2H6 were also systematically studied,revealing its possible potential for natural gas purification.Although the adsorption and separation performance of the Zn-MOF-1 is not excellent compared with other reported MOFs,it has a flexible pore formed by a rigid organic ligand displaying selective gas adsorption.3.Inspired by the previous work,a pyridinecarboxylic acid ligand was obtained by replacing two isophthalic acids in pentacarboxylic acid organic ligands with two pyridine units.Three microporous copper-based MOFs derived from the N,O mixed-donor ligands were successfully synthesized under solvothermal conditions,in which the structure and performance of ZJNU-8 were mainly analyzed in detail.Single-crystal X-ray diffraction analyses showed that ZJNU-8 contains rich inorganic nitrate ions decorating the channel surface that can serve as C2H2 recognition sites.Its selective gas adsorption properties of C2H2 over CO2 and CH4 were evaluated by single-component equilibrium adsorption measurements and IAST?ideal adsorbed solution theory?calculations,establishing its promising potential for C2H2 separation and purification.At ambient conditions,the C2H2 uptake capacity reaches 92.2 cm3?STP?g-1,while the IAST-predicted adsorption selectivities are up to 30.5 and 4.5 for the equimolar C2H2-CH4 and C2H2-CO2 binary gas mixtures,respectively.Furthermore,DFT computation studies revealed that the inorganic nitrate ions play a very important role for preferential adsorption of C2H2 over CO2 and CH4. |
PDF Full Text Request