Simulation Study of Water Adsorption on Carbon Black:  The Effect of Graphite Water Interaction Strength

Abstract

The adsorption of water on carbon black has been calculated on several model graphitized carbon blacks using Monte Carlo simulation. The surface is modeled using different interaction strengths for a Steele type potential and the placement of various functional groups on the surface. The results for the various surface configurations are compared with the few experimental results available in the literature. Traditionally used parameters for the Steele potential provide isotherms with no similarity to those seen in experiment. Increased interaction well depths with the surface lead to more realistic isotherms but still require strongly attractive functional groups for qualitative agreement. The well depth used to achieve this falls within the realm of interaction strengths proposed in the literature by various methods. Full agreement with experiment isotherms is not achieved apparently because of a lack of large clusters formed in the simulations.

Tunable sieving of ions using graphene oxide membranes

“…Therefore to clarify the role of oxidized regions on the permeation mechanism we have carried out free energy calculations with a deprotonated OH group (the parameters for the oxygen atom, q = -0.6400 C, = 0.307 nm,  = 0.65 kJ/mol were taken from Ref. 22) attached to the carbon atom at the center of the nanochannel with an interlayer spacing of 8 Å. The resulting free energy barrier for K + ions turns out to be ~15 kJ/mol similar to that of the pristine channel (17.4 kJ/mol), confirming the dominant importance of the interlayer spacing rather than the chemical functionality for the proposed dehydration mechanism.…”

“…However, it is difficult to achieve the high density and uniformity of such pores, which is required for industrial applications, because of the stochastic nature of the involved processes. In contrast, graphene oxide (GO), a chemical derivative of graphene with oxygen functionalities 17 , has attracted wide-spread interest due to its exceptional water permeation and molecular sieving properties [18][19][20] as well as realistic prospects for industrial scale production 21,22 . Molecular permeation through GO membranes is believed to occur along a network of pristine graphene channels that develop between functionalized areas of GO sheets 18 (typically, an area of 40-60% remains free from functionalization 23,24 ), and their sieving properties are defined by the interlayer spacing, d, which depends on the humidity of the surroundings 18,19 .…”

Water as a potential molecular probe for functional groups on carbon surfaces

“…Structural heterogeneity could result, for example, from defects in the graphene layers or from the overlap of adsorbent forces in spaces very close to a molecular width. Even this strong enhancement of the adsorption potential energy is not sufficient to explain the experimental observations [29]. The only possible enhancement that can reconcile simulation results and experimental data is an increase in adsorption energy from electrostatic interactions between water molecules and partial charges, most probably due to residual polar groups attached to the edge sites of carbon adsorbents, and usually described as functional groups [30][31][32][33][34].…”

“…One implication of this is that this cluster growth does not conform to the conventional thermodynamics of adsorption, in which the amount adsorbed decreases with an increase in temperature. The significance of functional groups in water adsorption in porous carbons has been investigated in a number of computer simulations [11,15,17,21,22,29,[35][36][37][38]. Several oxygencontaining groups (e.g.…”

The interplay between molecular layering and clustering in adsorption of gases on graphitized thermal carbon black – Spill-over phenomenon and the important role of strong sites

“…Chemical heterogeneities (Jorge et al, 2002), often as functional groups attached to the graphene surface, (Birkett and Do, 2007;McCallum et al, 1998;Liu and Monson, 2006;Lodewyckx andVansant, 1999, Muller et al, 1996) have been invoked as an explanation for the experimental observations of water (and other associating fluids) adsorption on carbon material. However, theoretical considerations suggest that attachment to the surface of the basal plane is improbable, and that the dangling bonds at edge sites, leading to localised charge density are a more probable location for functional groups Miura, 1985-1991), or indeed it is possible that the edge charges alone are sufficient to nucleate water adsorption (Nakada et al, 1996;Segara and Glandt, 1994;Ohba and Kanoh, 2012).…”