Existence of Ultrafine Crevices and Functional Groups along the Edge Surfaces of Graphitized Thermal Carbon Black

Abstract

Adsorption of different gases on graphitized thermal carbon black (GTCB) has been studied with a new molecular model to examine the consequences of micropore crevices and functional groups at the junctions between adjacent basal planes. Adsorption was simulated in the Grand Canonical Monte Carlo ensemble and the theoretical Henry constants were calculated by Monte Carlo volume integration over the Boltzmann factor of the solid-fluid potential. The simulation results are in good agreement with high-resolution experimental isotherms for argon on mineralogical graphite measured by Lopez-Gonzalez et al.1 From detailed inspection of the argon isotherms at extremely low coverages, we find two distinct Henry law regions, separated by a plateau (suggesting saturation of the stronger sites) that spans over a few decades of pressure. The first Henry law region is attributed to adsorption in the ultrafine crevices at the junctions between two adjacent basal planes, and the second region corresponds to adsorption on the basal plane, as confirmed by the theoretical Henry constant. The simulated isosteric heat and snapshots of molecular configurations show that argon adsorbs preferentially in the ultrafine crevices where there is a deep potential well due to overlap from the opposite pore walls. Similar behavior was found for other nonassociating fluids (Ar, N2, and CO2); however, for associating fluids (NH3 and H2O), the strong sites for adsorption and nucleation come from the combined effects of functional groups and ultrafine crevices, since the latter cannot alone account for the observed adsorption.

Adsorption of water and methanol on highly graphitized thermal carbon black: The effects of functional group and temperature on the isosteric heat at low loadings

“…We have shown in our recent work [30] that the dispersion energy at defects, in the form of grooves or crevices at the junctions of the adjacent graphene basal planes of GTCB, is not strong enough to enable this to happen. This implies that electrostatic interactions with functional groups are the only possible means by which nucleation of water clusters can be initiated.…”

“…These functional groups are grafted either at the edges of graphene layers or on the surface of the graphene layer, (probably at defects on the surface) [6,7,10,[30][31][32][33]. For most carbon blacks, the common functional groups are carboxylic, hydroxyl, and carbonyl [34].…”

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

“…To gain an idea of the contributions of various adsorbing entities on water adsorption at low loadings, we consider our previous work on water adsorption on Carbopack F as an example, where the concentration of carboxylic functional groups is around 1 × 10 –5 mmol/m 2 . The concentration of the crevices is around 0.1% of the monolayer coverage of argon, and the liquid molar volume of argon is 2.86 × 10 –5 m 3 /mol; therefore, the estimated volume of crevices is 3.5 × 10 –3 nm 3 /m 2 . The theoretical Henry constant for this model for Carbopack F and the contributions from each adsorbing entity, calculated from eq , are shown in Table .…”

“…For N 2 and CO 2 , the contribution from the functional groups to the Henry constant is negligible, and the contribution from the micropores is greater than that contributed by the basal plane by 3 orders of magnitude; therefore, their adsorption will occur initially in micropores and is characterized by a two-stage adsorption process identified in the adsorption isotherm. 29 For NH 3 and CH 3 OH, although the affinity of the functional groups (and micropores) is higher than the basal plane, it is compensated by the large surface area of the basal plane, and as a result, the contribution to the Henry constant from the functional groups is lower from the basal plane. H 2 O, represents a distinct case from the other adsorbates; although the concentration of the functional groups is very low, their contribution to the total Henry constant is 100 times greater than that from the basal plane; therefore, there is no doubt that initial adsorption of water proceeds by attachment to the functional groups.…”

Influence of initial assumptions on the kinetic models of CO2 gasification of chars and cokes in solid phase

“…According to the work [7], thermodynamic considerations can be omitted from the above-mentioned approaches to the analysis of the reaction/process (1), primarily because this reaction's ideal reversibility is observed only in the gas phase in very high temperature ([2700 K) [8], as shown in Fig. 1.…”