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Hydrogen Adsorption and Diffusion in p ‐ tert ‐Butylcalix[4]arene: An Experimental and Molecular Simulation Study
Author(s) -
Alavi Saman,
Woo Tom K.,
Sirjoosingh Andrew,
Lang Stephen,
Moudrakovski Igor,
Ripmeester John A.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000589
Subject(s) - calixarene , adsorption , chemistry , desorption , pulsed field gradient , molecular dynamics , diffusion , hydrogen bond , molecule , force field (fiction) , hydrogen , analytical chemistry (journal) , saturation (graph theory) , phase (matter) , bar (unit) , thermodynamics , organic chemistry , computational chemistry , physics , mathematics , combinatorics , artificial intelligence , computer science , meteorology
Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H 2 gas uptake in the low‐density p ‐ tert ‐butylcalix[4]arene (tBC) phase. 1 H NMR peak intensity measurements for pressures up to 175 bar were used to determine the H 2 adsorption isotherm. Weak surface adsorption (up to ≈2 mass % H 2 ) and stronger adsorption (not exceeding 0.25 mass % or one H 2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H 2 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 H 2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H 2 gas to ≈60 bar are also presented, and show a maximum H 2 adsorption of 0.4 H 2 per calixarene bowl. Adsorption isotherms of H 2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ≈1 H 2 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 H 2 in the solid with different loadings.