A noncatenated, crystalline 3D metal-organic framework (MOF) with post assembly tunable internal cavity volume modification that can accommodate a range of gas adsorption. Abstract ADVANTAGES A flexible noncatenated MOF system where separation capacity can be modified as needed by post assembly ligand introduction. SUMMARY Crystalline metal-organic frameworks (MOFs) comprise a growing class of permanently microporous materials, with low densities, high internal surface areas and uniformly sized pores and channels. MOF syntheses typically produce catenated structures with reduced cavity size, increased density, reduced surface area and diminished vapor-uptake capacity. Thus, unambiguous synthesis of non-catenated MOFs is desired for optimal application performance. An alternative design strategy employing robust precursor MOFs, which can be internally and/or externally modified, has been used to generate MOFs with tunable desired properties. A new MOF framework employing a novel tetracarboxylic acid (TCA) species that resists catenated MOF formation was created. Solvothermal reaction of this material with Zn(NO3)2 in DMF affords a non-planar, 3D framework possessing large cavities. This noncatenated structure, confirmed by X-ray diffraction, is thermally stable to 425°C. CO2 adsorption (273°K) measurements established promising empty cavity surface area (1370 m²/g) and pore volume (0.404 cm3/g) values. The unsolvated MOF exhibits 2.2% hydrogen uptake at 77 K°/1 atm (Figure 1). The framework Zn2 nodes reversibly bind solvates which alter MOF internal volume. The degree of gas uptake could be controlled by ligand incorporation. MOF cavity volume adjustments, by coordinating pyridine analogs of varying size, provides selective control of hydrogen (Figure 1) and carbon dioxide (Figure 2) uptake, demonstrating system flexibility for post-assembly modification of sorption properties for gases and mixtures. This noncatenated, crystalline 3D MOF with post assembly tunable internal cavity volume modification can accommodate a range of gas adsorption. These properties offer significant chemical separation and catalytic application potential.
|State||Published - Mar 14 2013|