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Published October 14, 2010 | Supplemental Material
Journal Article Open

Adsorption Mechanism and Uptake of Methane in Covalent Organic Frameworks: Theory and Experiment

Abstract

We determined the methane (CH_4) uptake (at 298 K and 1 to 100 bar pressure) for a variety of covalent organic frameworks (COFs), including both two-dimensional (COF-1, COF-5, COF-6, COF-8, and COF-10) and three-dimensional (COF-102, COF-103, COF-105, and COF-108) systems. For all COFs, the CH_4 uptake was predicted from grand canonical Monte Carlo (GCMC) simulations based on force fields (FF) developed to fit accurate quantum mechanics (QM) [second order Møller−Plesset (MP2) perturbation theory using doubly polarized quadruple-ζ (QZVPP) basis sets]. This FF was validated by comparison with the equation of state for CH_4 and by comparison with the experimental uptake isotherms at 298 K (reported here for COF-5 and COF-8), which agrees well (within 2% for 1−100 bar) with the GCMC simulations. From our simulations we have been able to observe, for the first time, multilayer formation coexisting with a pore filling mechanism. The best COF in terms of total volume of CH_4 per unit volume COF absorbent is COF-1, which can store 195 v/v at 298 K and 30 bar, exceeding the U.S. Department of Energy target for CH_4 storage of 180 v/v at 298 K and 35 bar. The best COFs on a delivery amount basis (volume adsorbed from 5 to 100 bar) are COF-102 and COF-103 with values of 230 and 234 v(STP: 298 K, 1.01 bar)/v, respectively, making these promising materials for practical methane storage.

Additional Information

© 2010 American Chemical Society. Received: May 14, 2010; Revised Manuscript Received: August 4, 2010. Article ASAP September 16, 2010. Published In Issue October 14, 2010 Partial support was provided by DOE (DE-FG01-04ER0420 to W.A.G., DE-FG02-06ER15813 to O.M.Y.). The computer facilities of the Materials and Process Simulation Center were supported by ONR-DURIP and ARO-DURIP. J.L.M.-C. acknowledges support through a Graduate Fellowship from the California Institute of Technology. Supporting Information: The volumetric uptake for all COFs against density, pore volume, surface area, and isosteric heat of adsorption are described. Experimental and theoretical methane uptake for MOF-177 is included. The QM energies and BSSE corrections are included. The data plotted in Figure 3 are tabulated. This material is available free of charge via the Internet at http://pubs.acs.org.

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August 19, 2023
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