Gas adsorption properties of highly porous metal–organic frameworks containing functionalized naphthalene dicarboxylate linkers

Abstract

Three functionalized metal–organic frameworks (MOFs), MOF-205-NH₂, MOF-205-NO₂, and MOF-205-OBn, formulated as Zn₄O(BTB)_4/3(L), where BTB is benzene-1,3,5-tribenzoate and L is 1-aminonaphthalene-3,7-dicarboxylate (NDC-NH₂), 1-nitronaphthalene-3,7-dicarboxylate (NDC-NO₂) or 1,5-dibenzyloxy-2,6-naphthalenedicarboxylate (NDC-(OBn)₂), were synthesized and their gas (H₂, CO₂, or CH₄) adsorption properties were compared to those of the un-functionalized, parent MOF-205. Ordered structural models for MOF-205 and its derivatives were built based on the crystal structures and were subsequently used for predicting porosity properties. Although the Brunauer–Emmett–Teller (BET) surface areas of the three MOF-205 derivatives were reduced (MOF-205, 4460; MOF-205-NH₂, 4330; MOF-205-NO₂, 3980; MOF-205-OBn, 3470 m² g⁻¹), all three derivatives were shown to have enhanced H₂ adsorption capacities at 77 K and CO₂ uptakes at 253, 273, and 298 K respectively at 1 bar in comparison with MOF-205. The results indicate the following trend in H₂ adsorption: MOF-205 < MOF-205-NO₂ < MOF-205-NH₂ < MOF-205-OBn. MOF-205-OBn showed good ideal adsorbed solution theory (IAST) selectivity values of 6.5 for CO₂/N₂ (15/85 in v/v) and 2.7 for CO₂/CH₄ (50/50 in v/v) at 298 K. Despite the large reduction (−22%) in the surface area, MOF-205-OBn displayed comparable total volumetric CO₂ (at 48 bar) and CH₄ (at 35 bar) storage capacities with those of MOF-205 at 298 K: MOF-205-OBn, 305 (CO₂) and 112 (CH₄) cm³ cm⁻³, and for MOF-205, 307 (CO₂) and 120 (CH₄) cm³ cm⁻³, respectively.