Carbon dioxide adsorption over zeolite-like metal organic frameworks (ZMOFs) having a sod topology: Structure and ion-exchange effect

Zeolite-like metal organic framework (ZMOF) materials having rho and sod topologies were experimentally investigated as CO2 adsorbents for the first time. As-prepared ZMOF materials showed reasonably high CO2 adsorption capacities (ca. 51 and 53 mg/g(adsorbent) for rho-and sod-ZMOF, respectively) and high CO2/N-2 selectivity (> 20) at 298 K and 1 bar. The latter showed a higher heat of adsorption (27-45 kJ/mol). These ZMOFs exhibited better CO2 adsorption than ZIF-8, a commonly investigated zeolitic imidazolate framework (ZIF) material having the same sod topology but in a neutral framework. Partially ion-exchanged sod-ZMOFs by alkali-metals resulted in improved CO2 adsorption performance compared with the as-prepared ZMOF. The highest CO2 adsorption was obtained with K+-exchanged sod-ZMOF (61 mg/g(adsorbent)), representing a ca. 15% increase in adsorption capacity. Complete desorption of CO2 in the K+-sod-ZMOF was attained at mild conditions (40 degrees C, He purging), and reversible and sustainable CO2 adsorption performance was demonstrated in 5 sets of recycling runs. (C) 2011 Elsevier B.V. All rights reserved.