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

Do, D.D.; Tan, Shiliang; Zeng, Yonghong; Fan, Chunyan; Nguyen, Van Thuong; Horikawa, Toshihide; Nicholson, D.

doi:10.1016/j.jcis.2015.01.028

Cited by 28 publications

(25 citation statements)

References 107 publications

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“…In the Henry's law region, the adsorbate is sufficiently rarefied that interactions between adsorbate molecules are entirely negligible in comparison to interactions between the adsorbate molecules and the adsorbent; and the relationship between the amount adsorbed, which is measured as an excess density, and the pressure is linear. We have previously used Monte Carlo integration to determine the Henry constant and isosteric heat at zero loading [1,2], and drawn attention to the fact that the choice of the reference volume, which has been a subject of debate in the literature [3], is crucial in the calculation of these two variables.…”

Section: Introductionmentioning

confidence: 99%

A coherent definition of Henry constant and isosteric heat at zero loading for adsorption in solids – An absolute accessible volume

Prasetyo

Nicholson

2018

Chemical Engineering Journal

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We present a new analysis of the Henry's law constant and isosteric heat at zero coverage for gas adsorption on solid surfaces, which removes the ambiguities inherent in earlier definitions [1]. A new definition of accessible volume ensures physical self-consistency between these two properties. We show that an earlier definition of accessible volume, as the volume within which the adsorbate-adsorbent potential energy is non-positive, is too restrictive because it neglects the penetration of molecules with large kinetic energies into the highly repulsive (positive) regions of the potential, which occurs more frequently at higher temperatures. The new definition has been tested for a number of adsorbents, and for a wide range of adsorbates commonly used in the characterization of porous solids. In particular, we have highlighted the differences between the old and new definitions of the Henry constant and the isosteric heat at zero loading. Our analysis also reveals that, contrary to a common assumption made in the adsorption literature, the van't Hoff plot is non-linear, and linearity is only satisfied over a narrow range of temperature.

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Section: Introductionmentioning

confidence: 99%

A coherent definition of Henry constant and isosteric heat at zero loading for adsorption in solids – An absolute accessible volume

Prasetyo

Nicholson

2018

Chemical Engineering Journal

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“…These activated samples are called ACF-HP1, ACF-HP2, ACF-HP3, and ACF-HP4, according to the molar concentrations (1, 2, 3, and, 4 M, respectively) of the H 3 PO 4 solutions. Since the micropores of porous carbon materials play an important role in gas adsorption [10,11], the micropore fraction of prepared samples was calculated using the DFT (density functional theory) equation. The obtained micropore fractions of the pore volume and surface area are presented in Table 1.…”

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confidence: 99%

Pore structure control of activated carbon fiber for CO gas sensor electrode

Bai¹,

배태성²

2016

Carbon letters

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Materials with porous structures developed in previous research have been used extensively in industrial purification and chemical recovery operations due to their large specific surface areas and pore volumes. Among a wide range of activation methods, chemical activation is an effective and simple method to prepare activated carbons with a high specific surface area. Depending on the chemical agents used, chemical activation can lead to unique pore structures [1][2][3].CO gas detection has recently become a critical issue because CO is one of the most common air pollutants. Pollutant CO gas is produced by incomplete hydrocarbon burning and accompanies almost all combustion processes. CO is especially dangerous because it possesses no odor or color and is therefore undetectable by humans. CO gas also becomes explosive at concentrations above 12% and has a threshold limit value of 25 ppm. Vehicle exhaust is a major source of environmental CO emissions and contributes to smog formation. Thus, the development of highly selective and stable CO sensors is an important goal and will assist in the study of environmental impacts. Motivated by the increasingly strict laws for different pollutant sources, recently there has been rapid progress in the fabrication of sensors to detect and monitor the environment, and several types of gas sensors have been reported in the literature [4][5][6][7][8][9].In this study, carbon based materials were used to fabricate a gas sensor matrix by electrospinning and heat treatment. To improve the sensitivity of the sensor by enhancing the gas adsorption, a porous structure was developed using chemical activation. The gas sensing mechanism was discussed based on the carbon pore structure.A polymer solution was prepared by dissolving polyacrylonitrile (PAN; d = 1.184, 181315 Aldrich, USA) in N,N-dimethyl formamide (DMF; d = 133, 766137 Fisher, USA). Electrospun fibers were obtained from the polymer solution using the electrospinning method. The electrospinning process was carried out under the following conditions: 0.8 mL/h polymer solution feed rate, 13 kV supplied voltage, 12 cm tip to collector distance, and 120 rpm collector rotation. The electrospun materials were stabilized by heating up to 523 K in air at a heating rate of 3 K min -1 , followed by treatment of the samples at 523 K for 3 h. Carbonization of the stabilized electrospun materials was carried out under an argon atmosphere with the following conditions: 15 K/min heating rate, 1273 K reaction temperature, 1 h holding time, and a 50 mL/h argon feed rate. The prepared sample was named CF.H 3 PO 4 solutions (1, 2, 3, and 4 M) were prepared as chemical activation agents. The CF was placed in an alumina boat in a steel pipe at a ratio of 20 mL/g (H 3 PO 4 solution/CF) to carry out the chemical activation. Activation was conducted at 1023 K for 2 h in an argon atmosphere. The heating rate was 5 K/min and the feed rate of the argon gas was 30 mL/min. Following the chemical activation, the obtained samples were washed several time...

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“…Following Deitz 35 , we use a dual Langmuir equation to describe adsorption in ultrafine pores and at sub-monolayer coverage on the graphene surface. The implicit assumption in using the dual Langmuir equation is that there is no interaction between adsorbate molecules, and therefore none between molecules on the two types of adsorption sit e. Although this is a reasonable first approximation, it should be kept in mind that the interaction between molecules on different patches can lead to interesting behaviour, such as the spill over phenomenon, recently proposed by our group, as a possible mechanism for physical adsorption in some systems and not previously recognized 119 .…”

Section: Adsorption On Two Patches Of Adsorption Sitesmentioning

confidence: 99%

“…In simulation, the intrinsic Henry constant can be defined as the ratio of the excess amount to the bulk gas density, which is given by [117][118][119] :…”

Section: Henry Constantmentioning

confidence: 99%

“…Therefore adsorption occurs initially around the functional groups, which act as nucleation sites for ammonia molecules to form clusters which then grow as pressure is increased until ammonia molecules spill-over onto the graphite basal planes because the interaction between ammonia molecules (primarily electrostatic interactions), and the interaction of ammonia with the graphite surface are of comparable magnitude 119 . For the same reason, the second Henry law region, corresponding to the molecular layering on the basal plane, and seen with the electrostatically weaker adsorbates, is absent.…”

Section: Adsorption Of Other Adsorbates On Gtcbmentioning

confidence: 99%

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Fundamental study of adsorption and desorption process in porous materials with functional groups

Zeng¹

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Adsorption is used in industries for gas separation and purification because of its less energy intensive than other traditional separation processes, such as distillation and gas absorption.However, its effective application depends on the theoretical understanding of the underlying phenomena of adsorption of molecules in porous solid adsorbents. With the advances in molecular simulation techniques, investigation into the microscopic mechanisms of adsorption phenomena can be realized and this will lead to a development of an unambiguo us approach for the characterization of porous solids. This is the aim of this project to understand adsorption and desorption mechanisms in porous materials, especially porous carbons with functional groups because they are not fully studied in the literature.One of the significant points of this thesis is the development of a novel molecular model for porous carbon. Graphitized thermal carbon black (GTCB) was used as model adsorbent modelled as a composite of basal plane of graphene layers with crevices (ultrafine micropores) and oxygen functional groups attached at the edges of the graphene layers. This model was used in adsorption of various gases, and was validated with high resolution experimental data and theoretically analysed with simulation results obtained with a grand canonical Monte Carlo simulation.Excellent agreement between the experimental data and the simulation results has led us to derive the structural properties of GTCB and the nature of the functional group. Furthermore, the experimental Henry constant and the isosteric heat at zero loading (in the region of very low loadings) are described correctly with the Monte Carlo integration of the Boltzmann factor of the pairwise interaction between an adsorbate molecule and the porous carbon. It was found that adsorbate dominantly adsorbs in the fine crevices at very low loadings because of the enhancement of the solid-fluid potential energy, followed by adsorption on the basal plane of graphene layers. This is the case for non-polar fluids, such as argon and nitrogen. On the other hand, polar fluids, such as ammonia and water, the dominance of the functional group in adsorption is manifested, especially water.This novel model for carbon can be extended to describe practical porous carbons containing both micropores (for adsorptive capacity) and mesopores (for transport). Adsorption in mesopores is associated with capillary condensation and evaporation, and the se are commonly used in the literature to derive the mesopore size distribution. For this determination to be realized, the fundamental understanding of condensation and evaporation must be understood, and this is the second objective of this thesis. We chose graphitic slit pores to model the mesopore, and investigated the effects of various parameters on the capillary condensation and evaporation. Grand ii canonical Monte Carlo technique is used to obtain the isotherm and the isosteric heat, and we particularly investigate the mechanisms of adsorpti...

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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

Cited by 28 publications

References 107 publications

A coherent definition of Henry constant and isosteric heat at zero loading for adsorption in solids – An absolute accessible volume

A coherent definition of Henry constant and isosteric heat at zero loading for adsorption in solids – An absolute accessible volume

Pore structure control of activated carbon fiber for CO gas sensor electrode

Fundamental study of adsorption and desorption process in porous materials with functional groups

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