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

Abstract

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.

Molecular Insights into the Effect of Temperature and Functional Groups on the Nonwetting, Prewetting, Partial Wetting, and Complete Wetting Transitions of Ethanol on Graphite

“…Since the OH group in this work was grafted on a basal plane, which is a connected hexagon-C, the OH group of the benzene ring model was appropriate. Moreover, these parameters are used widely with varied adsorbates, and it is possible to study the adsorption behavior of polar fluids. ,, This functional group model is simple and useful to easily study the effect of functional groups. No matter how the functional groups of real graphite are, their adsorption process follows the same manner.…”

Competitive and Synergistic Adsorption of Mixtures of Polar and Nonpolar Gases in Carbonaceous Nanopores

“…Henry’s law constant, K , which represents the strength of adsorption of the adsorbate on the adsorbent, is defined as the ratio of the number of molecules ( N ) to the bulk gas density (ρ G ). This was quantified by integrating the Boltzmann factor over the volume of the system ( V ) and orientation space of the adsorbate molecule , and further nondimensionalized with the accessible volume in the pore ( V acc )­ where φ is the potential energy between a molecule and the adsorbent and k B is the Boltzmann constant.…”

Fundamental study of adsorption of non-polar and polar fluids on hydrophobic ordered solids

“…The behaviour of water adsorption in carbon materials is different from that for simple gases, such as nitrogen or argon, which adsorb strongly on graphite at low temperatures via a molecular layering process. At ambient temperatures, water interacts very weakly with graphite, but strongly with strong sites, such as functional groups via electrostatic forces 56,201 . Initially water adsorption occurs around these strong sites, and subsequently hydrogen bonding between water molecules gives rise to clusters 81,202,203 .…”

“…It has been widely recognized that functional groups (FGs) are the main source of strong sites that facilitate water adsorption in carbonaceous materials 13,200,201,[216][217][218][219][220] . Yet there is evidence both from simulation 204,[221][222][223] and experimental studies 222,223 that water adsorption can occur on adsorbents that do not possess functional groups.…”