Hysteresis Loop and Scanning Curves of Argon Adsorption in Closed-End Wedge Pores

Klomkliang, Nikom; D., D.; Nicholson, D.

doi:10.1021/la5035992

Cited by 19 publications

(16 citation statements)

References 25 publications

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“…26 The mechanisms for hysteresis and scanning are the same as those discussed for 70 K in the last section. The only difference between the two temperatures is that there are three steps instead of two at 77 K; these steps correspond to condensation in Z 1 and Z 2 (Points C 1 C 2 ), Z 3 , and Z 4 , respectively.…”

Section: Resultsmentioning

confidence: 98%

“…26 We start at the point A 00 2 where the Junction J 3,4 is partially filled. When the pressure is decreased, the scanning curve traces this segment until Junction J 3,4 is emptied, and then spans across the hysteresis loop by exactly the same mechanism as desorption from an open end wedge pore via two distinct processes: (1) gradual decrease from the zone and (2) sharp evaporation from the junction, that is, a. gradual decrease in density in Zone 3, followed by b. sharp evaporation from the Junction J 2,3 , and c. gradual decrease in Zone 2, and d. sharp evaporation from the Junction J 1,2 .…”

Section: Resultsmentioning

confidence: 99%

“…However, experimental scanning curves do not necessarily follow this simple behavior and can be classified into three broad categories: (1) crossing directly between the boundary curves of the hysteresis loop, (2) converging to the closure point, and (3) returning back to the same boundary [17][18][19]21,22,24,25 and further insight is needed into the origin of these three types of scanning curve. In our recent study, 26 we studied the scanning curves in a wedge pore with either its narrow end or its wide end closed, to understand the way in which such a simple connectivity (in the form of a linear change in pore size in the axial direction) affects the scanning curve.…”

Section: Introductionmentioning

confidence: 99%

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Scanning curves in wedge pore with the wide end closed: Effects of temperature

2015

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The desorption scanning curves within the hysteresis loop of argon adsorbed in a wedge-shaped pore with its wide end closed have been studied in the temperature range between 60 and 87 K, using grand canonical Monte Carlo simulation. The distinct features are: (1) adsorbate packing follows a sequence of commensurate regions (zones) and incommensurate regions (junctions); (2) the mechanism for evaporation switches from cavitation-like pore blocking to cavitation when the temperature is increased; as typically observed for ink-bottle pores. When cavitation is the operating mechanism, the descending scanning curve spans across the loop in two stages: a gradual decrease in density in a zone followed by a sharp evaporation from a junction, and then terminates at the lowest point on the vertical cavitation boundary. The adsorption scanning curve proceeds across the loop in two stages complementary to the desorption scanning-curve: a gradual change in density at a junction followed by a sharp change through a zone. Conversely, when cavitation-like pore blocking is operating, the descending curve leaves the adsorption boundary, spans across the hysteresis loop and returns to a different point on the same boundary, rather than to the desorption boundary or to the lower closure point. This feature does not seem to have been recognized in earlier literature and should be considered in the classification of scanning curves.

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Scanning curves in wedge pore with the wide end closed: Effects of temperature

2015

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“…The descending scanning curve is associated with stretching of the condensate in Region I, followed by evaporation, and the ascending scanning curve is associated with further layering of molecules on the pore walls in Region II, followed by condensation [15][16][17] .…”

Section: Introductionmentioning

confidence: 99%

Hysteresis and scanning curves in linear arrays of mesopores with two cavities and three necks

Zeng

Tan

et al. 2016

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Adsorption of argon at 87K in a linear array of slit mesopores composed of two cavities and three necks has been investigated using Grand Canonical Monte Carlo simulation. Hysteresis and scanning was found to depend on the relative size of the necks and cavities and on whether the necks are wider or narrower than the critical width that demarcates cavitation from pore blocking. There are 26 possible combinations for the linear array. By considering the behaviour of hysteresis scanning curves, we are able to identify four distinct groups: (i) Group 1: The descending scanning spans the boundary curve of the hysteresis loop due to stretching of the condensate in the small cavity.(ii) Group 2: The descending curve partially spans the loop and returns to the adsorption boundary. This occurs either because the condensate stretches in the small cavity, followed by evaporation via a pore blocking mechanism; or because the condensate evaporates as the meniscus recedes in the large neck that joins the two cavities.(iii) Group 3: The descending curve spans the loop as in Group 1 but there is a small sub-loop associated with emptying and filling of the large neck connecting the large cavity to the surrounding gas.

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“…The compressibility shows peaks and troughs, corresponding to ordered and disordered domains along the pore. These structures are associated with the commensurate and incommensurate packing 159 The snapshot at Point A shows that the pore can be divided into four domains, each of which contains a different number of adsorbate layers. In the junction between two adjacent domains, the packing of the adsorbate is incommensurate and therefore the compressibility is higher.…”

Section: The Effect Of the Adsorbent Field On Desorptionmentioning

confidence: 99%

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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Hysteresis Loop and Scanning Curves of Argon Adsorption in Closed-End Wedge Pores

Cited by 19 publications

References 25 publications

Scanning curves in wedge pore with the wide end closed: Effects of temperature

Scanning curves in wedge pore with the wide end closed: Effects of temperature

Hysteresis and scanning curves in linear arrays of mesopores with two cavities and three necks

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

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