Synthesis, Structure Characterization And Gas Sorption Performance Of Metal-Organic Frameworks Based On Aromatic Tetrcaboxylate

Metal-organic frameworks （MOFs）. also known as porous coordination polymers （PCPs）, are a rapidly expanding a class of porous crystalline materials constructed by self-assembly of metal-containing clusters （typically termed as secondary building units （SBUs）） and multitopic bridging organic linkers via metal coordination bonds. Due to their particular and favourable structural features such as high surface area, uniform but tunable pore size and chemically modifiable pore surface, MOFs have been actively investigated for their potential applications including gas storage/separation, heterogeneous catalysis, molecule sensing, drug delivery, etc.Among numerous MOFs. a fascinating NbO-type of MOFs constructed from square-planar dicopper paddlewheel SBUs and 4-connected diisophthalate linkers have gained extensive attention due to their unique structures featuring open metal sites and two different types of nanocages suitable for gas adsorption. More significantly, when different functional groups are grafted into diisophthalate organic linkers, the corresponding frameworks, in most cases, still adopt the same NbO-type structure, thus providing an ideal platform to investigate the effect of the functional groups on gas adsorption. Based on these considerations, the research contents are as follows1. Design and synthesize the novel metal-organic frameworks for methane storageTo improve methane adsorption by pore structure optimization, we have developed two new organic linkers, namely, 5,5’-（benzene-1,4-diyl-ethyne-1,2-diyl） diisophthalic aicd and 5,5’-（naphthalene-1,4-diyl-ethyne-1,2-diyl） diisophthalic acid, which reacted with copper ions under solvothermal conditions to form two isostructual metal-organic frameworks （ZJNU-50 and ZJNU-53）. These two compounds after activation exhibit the volumetric CH4 adsorption uptakes of 229 cm³ （STP） cm^-3and 241 cm³ （STP） cm^-3, respectively, at 298 K and 65 bar; when the pressures swing from 65 to 5 bar, the volumetric methane working capacities are 184 cm³ （STP） cm^-3 and 190 cm³ （STP） cm^-3, respectively, if the packing loss is not considered. The methane storage and working capacities are among the highest reported for MOF materials.2. Design and synthesize the metal-organic frameworks for CO₂ captureWe have developed three new organic linkers with different highly polarized heterocyclic moieties namely, oxadiazole, thiadiazole, and selenadiazole, respectively, which reacted with copper ions under solvothermal conditions to form two isostructual metal-organic frameworks （ZJNU-41, ZJNU-40, ZJNU-42）. After activation, the CO₂ adsorption capacities at 298 K and 1 atm reach 97.4,85.7, and 37.6 cm³ （STP） g-1, respectively. In particular, when the molecular dipole of the attached heterocyclic moieties increases, the CO₂ uptake also increases. This work demonstrates that the introduction of highly polarized heterocyclic functional groups into frameworks is a promising approach to target porous metal-organic framework materials with improved CO₂ adsorption performance.We have developed three new organic linkers with different number and orientation of Lewis basic nitrogen atoms, namely,5,5’-（quinoline-5,8-diyl）-diisophthalate,5,5’-（isoquinoline-5,8-diyl）-diisophthalate, and 5,5’-（quinoxaline-5,8-diyl）-diisophthalate, and used them to construct a family of isostructural copper-based metal-organic frameworks, ZJNU-43, ZJNU-44 and ZJNU-45. The three MOFs, after activation, exhibited almost the same porosities but distinctly different CO₂ adsorption properties. At room temperature and 1 atm, the adsorption capacities for CO₂ reached 103,116 and 107 cm³ （STP） g-1, respectively. Compared to ZJNU-43a and ZJNU-45a, ZJNU-44a adsorbs much more amounts of CO₂ （116 cm³ （STP） g-1）. The work demonstrates that the CO₂ adsorption properties of MOFs depend not only on the number of Lewis basic nitrogen sites but more importantly on their accessibility.3. Design and synthesize the metal-organic frameworks for acetylene storagewe have developed three new organic linkers with the nitrogen containing heterocyclic rings, namely,5,5’-（pyrazine-2,5-diyl） diisophthalate, 5,5’-（pyridazine-3,6-diyl）-diisophthalate, and 5,5’-（pyrimidine-2,5-diyl） diisophthalate, which were reacted with copper ions under solvothermal conditions to form three isostructual metal-organic frameworks （ZJNU-46, ZJNU-47 and ZJNU-48）. After activation, the gravimetric C₂H₂ adsorption uptakes reach 187,213 and 193 cm³ （STP） g-1 for these three compounds at 1 atm and 295 K. The gravimetric C₂H₂ adsorption amount of ZJNU-47a is the second highest reported for MOF materials. Notably, despite their same porosities, and densities of open metal sites and uncoordinated nitrogen sites, distinctly different C₂H₂ adsorption capacities were observed for these three compounds, which demonstrate that the rational arrangement of open nitrogen sites will favorably improve C₂H₂ uptakes.