Gas Storage and Diffusion through Nanocages and Windows in Porous Metal–Organic Framework Cu2(2,3,5,6-tetramethylbenzene-1,4-diisophthalate)(H2O)2

Abstract

A novel nanoporous metal–organic framework NPC-4 with excellent thermal stability was assembled from 2,3,5,6-tetramethylbenzene-1,4-diisophthalate (TMBDI) and the paddle-wheel secondary building unit (Cu2(COO)4). The porous structure comprises a single type of nanoscale cage (16 A diameter) interconnected by windows (5.2 × 6.3 A), which give a high pore volume. CH4 (195–290 K), CO2 (198–303 K), N2 (77 K), and H2 (77 K) adsorption isotherms were studied for pressures up to 20 bar. NPC-4 exhibits excellent methane and carbon dioxide storage capacities on a volume basis with very high adsorbate densities, under ambient conditions. Isobars were investigated to establish the relationship for adsorption capacities over a range of storage temperatures. The isosteric enthalpies of adsorption for both CH4 and CO2 adsorption did not vary significantly with amount adsorbed and were ∼15 and ∼25 kJ mol–1, respectively. The adsorption/desorption kinetics for CH4 and CO2 were investigated and activation energies, enthal...