Anatomy of Adsorption in Open-End and Closed-End Slit Mesopores: Adsorption, Desorption, and Equilibrium Branches of Hysteresis Loop

Zeng, Yonghong; Phadungbut, Poomiwat; D., D.; Nicholson, D.

doi:10.1021/jp507600s

Cited by 21 publications

(16 citation statements)

References 31 publications

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“…The origin of this hysteresis is usually attributed to the different mechanisms of adsorption and desorption [21][22][23][24][25][26][27][28]. Experimentally observed hysteresis loops are classified into six types [29].…”

Section: Introductionmentioning

confidence: 99%

On the adsorbate restructuring induced hysteresis of simple gas adsorption in slit micropores

Diao

Fan

et al. 2016

Chemical Engineering Journal

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Simulations of adsorption isotherms for simple gases in homogeneous slit pores with two open ends often show hysteresis, between condensation and evaporation branches. The hysteresis may result either, from the difference in the curvature of the interface separating the adsorbed and gas phases, or from molecular restructuring when the adsorbate is densely packed. The order-disorder transition that occurs in the second case, has also been observed experimentally for adsorption on a graphite surface, and is supported by molecular simulation [1,2]. In this paper we report a comprehensive set of GCMC simulations designed to explore the effects of pore size and temperature on the hysteresis loop induced by adsorbate restructuring. We report isotherms, isosteric heats, and microscopic analyses of the local density distribution, and the 2D and 3D radial density distributions. Local compressibilities reinforce the supposition that adsorbate restructuring is the origin of the ordering hysteresis.

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Section: Introductionmentioning

confidence: 99%

On the adsorbate restructuring induced hysteresis of simple gas adsorption in slit micropores

Diao

Fan

et al. 2016

Chemical Engineering Journal

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“…33 Simulations suggest that even in closed pores hysteresis may occur when the diameter is smaller. 34 To understand adsorption on pore constrictions better, tailored duplex layers formed by straight, cylindrical, noninterconnected pores of different diameter have been prepared. The two resulting geometries are "ink-bottle", 35 where a narrow pore (constriction) constricts a wider pore (cavity), and "funnel", with the cavity above the constriction.…”

Section: ■ Introductionmentioning

confidence: 99%

Adsorption on Ordered and Disordered Duplex Layers of Porous Anodic Alumina

et al. 2015

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We have carried out systematic experiments and numerical simulations of the adsorption on porous anodic aluminum oxide (AAO) duplex layers presenting either an ordered or a disordered interconnecting interface between the large (cavity) and small (constriction) sections of the structured pores. Selective blocking of the pore openings resulted in three different pore topologies: open structured pores, funnel pores, and ink-bottle pores. In the case of the structured pores having an ordered interface, the adsorption isotherms present a rich phenomenology characterized by the presence of two steps in the condensation branch and the opening of one (two) hysteresis loops during evaporation for the ink-bottle (open and funnel) pores. The isotherms can be obtained by summing the isotherms measured on uniform pores having the dimensions of the constrictions or of the cavities. The numerical analysis of the three different pore topologies indicates that the shape of the junction between the two pore sections is only important for the adsorption branch. In particular, a conic junction which resembles that of the AAO pores represents the experimental isotherms for the open and funnel pores better, but the shape of the junction in the ink bottle pores does not matter. The isotherms for the duplex layers with a disordered interface display the same general features found for the ordered duplex layers. In both cases, the adsorption branches coincide and have two steps which are shifted to lower relative pressures compared to those for the ordered duplex. Furthermore, the desorption branches comprise hysteresis loops much wider than those of the ordered duplex layers. Overall, this study highlights the important role played by morphologies where there are interconnections between large and small pores.

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“…pores. The hysteresis was attributed to the restructuring of the adsorbate as the meniscus reaches the pore mouth 145,146 However, when the number of cycles was increased to 2 million (2 10 9 configurations) in using conventional GCMC, we find that the isotherms are reversible (red curves). The general mechanisms of adsorption and desorption can be described as follows: During adsorption, molecular layering occurs on the two opposite pore walls as well as at the closed end.…”

Section: Pore Filling At Temperatures Greater Than the Critical Hystementioning

confidence: 85%

“…In uniform pores, as the pore size is increased, the condensation and evaporation pressures shift to a higher pressure, and the extent of this increase is greater for condensation than for evaporation, giving a larger hysteresis loop. The adsorption and desorption mechanisms have been discussed elsewhere 146 .…”

Section: Simulation Modelmentioning

confidence: 99%

“…The mechanism for condensation in a parallel-sided slit pore has recently been elucidated in detail; simulation studies show that adsorbed layers on opposite surfaces each with an undulating interface between the dense adsorbate phase and the contingent rarefied phase eventually contact to form bridges bounded by cylindrical surfaces at which stage condensation is nucleated 71,146 . A simple thermodynamic argument for condensation at a cylindrical surface, originally proposed by Cohan 68 , leads to the equation:…”

Section: Introductionmentioning

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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Anatomy of Adsorption in Open-End and Closed-End Slit Mesopores: Adsorption, Desorption, and Equilibrium Branches of Hysteresis Loop

Cited by 21 publications

References 31 publications

On the adsorbate restructuring induced hysteresis of simple gas adsorption in slit micropores

On the adsorbate restructuring induced hysteresis of simple gas adsorption in slit micropores

Adsorption on Ordered and Disordered Duplex Layers of Porous Anodic Alumina

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

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