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Adsorption and Diffusion of Light Gases in ZIF-68 and ZIF-70: A Simulation Study

2009; American Chemical Society; Volume: 113; Issue: 39 Linguagem: Inglês

10.1021/jp903735m

1932-7455

Rees B. Rankin, Jinchen Liu, Anant D. Kulkarni, J. Karl Johnson,

Membrane Separation and Gas Transport

We have computed the adsorption and diffusion of CO2, N2, CH4, and H2 in zeolitic imidazolate framework (ZIF) materials ZIF-68 and ZIF-70 from atomistic simulations. These simulations were performed using geometries obtained from density functional theory (DFT) optimization of the experimental crystal structure of ZIF-68 and on four structures of ZIF-70, one based on the experimental crystal structure and three having different imidazole/nitroimidazole substitution ratios. The framework charges for charge−quadrupole interaction (CQI) terms in our simulations were parametrized with charges obtained from Bader charge decomposition (periodic DFT calculations) and ChelpG charges (cluster DFT calculations). The adsorption and diffusion of the quadrupolar fluids can be dramatically different when using the Bader and ChelpG charges. Agreement between simulations and experiments for the N2 adsorption isotherms in ZIF-68 and 70 is very good when CQI terms are included. In contrast, simulations overpredict the amount of CO2 adsorbed at 298 K compared with experiments.