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Henry Constant of Water Adsorption on Functionalized Graphite: Importance of the Potential Models of Water and Functional Group

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journal contribution
posted on 27.09.2018, 00:00 by Yonghong Zeng, Hui Xu, Toshihide Horikawa, D. D. Do, D. Nicholson
We present a theoretical study of the Henry constant for water adsorbed on graphite decorated with functional groups at the edges of the graphene layers. A general expression for the Henry constant is developed to describe the initial adsorption on the basal plane, functional groups, and confinement in micropores. To shed further light on the role of functional groups, we have investigated the effects of partial charge, acidity and basicity, orientation, and separation between functional groups. Our main conclusions are (1) the strength of adsorption is sensitive to the accessibility of water to the functional groups, (2) a basic functional group can be as strong as an acidic functional group, (3) the affinity varies significantly with orientation and the separation between the functional groups, and (4) adsorption in microporous crevices may compete with functional group adsorption at very low loadings. While thermodynamics suggests that a Henry law region should always exist at low loading, this is not always observed in water/carbon systems because of the broad energy distribution of the possible adsorption sites (functional group, basal plane, and confinement) or because the Henry law region, corresponding to the strongest adsorbing sites, falls well below the measurable pressure range.