Hydrogen Adsorption and Diffusion in p‐tert‐Butylcalix[4]arene: An Experimental and Molecular Simulation Study |
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| Authors: | Dr. Saman Alavi Prof. Tom K. Woo Andrew Sirjoosingh Dr. Stephen Lang Dr. Igor Moudrakovski Prof. John A. Ripmeester |
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| Affiliation: | 1. Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa, Ottawa, Ontario K1A 6N5 (Canada), Fax: (+1)?613‐562‐5179;2. Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Dr., Ottawa, Ontario K1A 0R6 (Canada), Fax: (+1)?613‐998‐7833 |
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| Abstract: | Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H2 gas uptake in the low‐density p‐tert‐butylcalix[4]arene (tBC) phase. 1H NMR peak intensity measurements for pressures up to 175 bar were used to determine the H2 adsorption isotherm. Weak surface adsorption (up to ≈2 mass % H2) and stronger adsorption (not exceeding 0.25 mass % or one H2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H2 molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H2 gas to ≈60 bar are also presented, and show a maximum H2 adsorption of 0.4 H2 per calixarene bowl. Adsorption isotherms of H2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ≈1 H2 per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H2 in the solid with different loadings. |
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| Keywords: | calixarenes computational chemistry hydrogen storage molecular dynamics NMR spectroscopy |
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