Carbon–Oxygen and Carbon–Hydrogen Surface Complexes

Smith, R. Nelson; Duffield, Jack.; Pierotti, Robert A.; Mool, John

doi:10.1021/j150538a025

Cited by 22 publications

(5 citation statements)

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“…Few data on chemisorption kinetics are extant, and their meaning is obscured by lack of knowledge (338) of the physical and chemical properties of the adsorbent and by the frequent occurrence of surface interactions other than simple chemisorption. Some recent work indicates that charcoals contain significant amounts of hydrogen, that the surface is acid (126, 251), and that it contains free radicals (8,67,147) and surface complexes (5,6,251,252,285,334). An electron resonance study (147) suggests the existence of two types of oxygen interactions with the surface.…”

Section: Carbon Adsorbentsmentioning

confidence: 99%

Kinetics of Chemisorption of Gases on Solids.

Low¹

1960

Chem. Rev.

796

309

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Section: Carbon Adsorbentsmentioning

confidence: 99%

Kinetics of Chemisorption of Gases on Solids.

Low¹

1960

Chem. Rev.

796

309

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“…The strong sites could also be due to chemical heterogeneities, particularly functional groups. , Although it is commonly believed that functional groups are removed in highly graphitized thermal carbon black at very high graphitization temperatures, recent experimental evidence suggests that a small concentration of functional groups can still be found even after graphitization at extremely high temperature (∼3000 K). − These groups are likely to be present at the unsaturated valencies at edge sites at the same locations as the ultrafine crevices (defects), and they will carry partial charges that can undergo strong electrostatic interactions with molecules having high multipole moments, such as water and ammonia. The synergistic effect of crevices plus functional groups could enhance the initial interaction of associating adsorbates on a carbon surface.…”

Section: Introductionmentioning

confidence: 99%

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

Zeng

Nicholson

2015

Langmuir

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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.

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“…Other evidence also points to the existence of residual functional groups on the surface of graphitized carbon black, for example: Campanella et al (1982), Bruner et al (1976), Zettlemoyer (1968), Smith et al (1956) and Healey et al (1955).…”

Section: Methodsmentioning

confidence: 99%

“…However, the very large number of edge sites per particle is likely to ensure that residual electrostatic charge and breaks in the basal planes will be present at the edges. Although there are reports stating that highly graphitized carbon blacks have no oxygen-containing groups on the surface, because they are decomposed at high temperatures, evidence suggests that a small quantity of these groups remains even after graphitization at high temperature (Campanella et al, 1982;Bruner et al, 1976;Zettlemoyer, 1968;Healy et al, 1955;Smith et al, 1956;Young et al, 1954).…”

Section: Introductionmentioning

confidence: 99%

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

Tan

Zeng

et al. 2015

Journal of Colloid and Interface Science

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We analyse in detail our experimental data, our simulation results and data from the literature, for the adsorption of argon, nitrogen, carbon dioxide, methanol, ammonia and water on graphitized carbon black (GTCB), and show that there are two mechanisms of adsorption at play, and that their interplay governs how different gases adsorb on the surface by either: (1) molecular layering on the basal plane or (2) clustering around very strong sites on the adsorbate whose affinity is much greater than that of the basal plane or the functional groups. Depending on the concentration of the very strong sites or the functional groups, the temperature and the relative strength of the three interactions, (a) fluid-strong sites (fine crevices and functional group) (F-SS), (b) fluid-basal plane (FB) and (c) fluid-fluid (FF), the uptake of adsorbate tends to be dominated by one mechanism. However, there are conditions (temperature and adsorbate) where two mechanisms can both govern the uptake. For simple gases, like argon, nitrogen and carbon dioxide, adsorption proceeds by molecular layering on the basal plane of graphene, but for water which represents an extreme case of a polar molecule, clustering around the strong sites or the functional groups at the edges of the graphene layers is the major mechanism of adsorption and there is little or no adsorption on the basal planes because the F-SS and FF interactions are far stronger than the FB interaction. For adsorptives with lower polarity, exemplified by methanol or ammonia, the adsorption mechanism switches from clustering to layering in the order: ammonia, methanol; and we suggest that the bridging between these two mechanisms is a molecular spill-over phenomenon, which has not been previously proposed in the literature in the context of physical adsorption.

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Carbon–Oxygen and Carbon–Hydrogen Surface Complexes

Cited by 22 publications

References 0 publications

Kinetics of Chemisorption of Gases on Solids.

Kinetics of Chemisorption of Gases on Solids.

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

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

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