A molecular simulation study of adsorption and desorption in closed end slit pores: Is there a hysteresis loop?

Fan, Chunyan; Zeng, Yonghong; Do, D.D.; Nicholson, D.

doi:10.1016/j.ces.2014.08.018

Cited by 14 publications

(5 citation statements)

References 22 publications

(15 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The latter rule is rationalized by considering, that if only one single bond is unfilled, no nucleation of a liquid bridge has to occur as the liquid vapor interface can propagate along the junction into the last remaining pore. In our consideration, the latter rule ("z-1 out of z") is best suited, as the phenomenon at hand is represented as realistic as possible using macroscopic combination rules, also being in accordance with simulation studies on dead end pores 81 . We have to stress, that even this better suited combination rule is most likely not able to describe the complete mechanistic picture of the mechanism at the nanoscale.…”

Section: Interface Propagation Rules At Junctions In Interconnected P...mentioning

confidence: 59%

Development and application of an advanced percolation model for pore network characterization by physical adsorption

Söllner,

Neimark,

Thommes

2024

Preprint

View full text Add to dashboard Cite

Physical adsorption is one of the most widely used techniques to characterize porous materials because of being reliable and able to assess micro- and mesopores within one approach. However, challenges and open questions persist in characterizing disordered and hierarchically structured porous materials. This study introduces a pore network model aiming to enhance the textural characterization of nanoporous materials. Our model, based on percolation theory on a Bethe lattice, includes all mechanisms known to contribute to adsorption hysteresis in mesoporous pore networks during capillary condensation and evaporation. The model accounts for delayed and initiated condensation during adsorption as well as equilibrium evaporation, pore blocking and cavitation during desorption. Coupled with dedicated non-local-density functional theory (NLDFT) kernels, the proposed method provides a unified framework for modeling the entire experimental adsorption-desorption isotherm, including desorption hysteresis scans. Hence, this model unveils key pore network characteristics like the effective connectivity, but also has the potential to determine pore size distributions of mesoporous materials by taking quantitatively pore network effects into account. The applicability of the method is demonstrated on a selected set of nanoporous silica materials exhibiting distinct types of hysteresis loops (types H1, H2a, H1/H2a and H5), including ordered mesoporous silica networks, i.e, KIT-6 silica, hybrid SBA-15/MCM-41 silica with plugged pores, but also two disordered silica pore networks, i.e., a hierarchical meso-macroporous monolith and porous Vycor glass. For all materials, good correlation is found between calculated and experimental primary adsorption and desorption isotherms as well as desorption scans allowing for a determination of key pore network characteristics such as pore connectivity and pore size distributions as well as a parameter correlated with the impact of pore network disorder and corresponding effects on the adsorption behavior. The versatility and enriched textural insights provided by the proposed novel network model allows for a comprehensive characterization previously inaccessible, and hence will contribute to a further advancement in the textural characterization of novel nanoporous materials. It has the potential to provide important guidance for the design and selection of porous materials for optimising various applications, including separation processes (such as chromatography), heterogeneous catalysis, gas-and energy storage.

show abstract

Section: Interface Propagation Rules At Junctions In Interconnected P...mentioning

confidence: 59%

Development and application of an advanced percolation model for pore network characterization by physical adsorption

Söllner,

Neimark,

Thommes

2024

Preprint

View full text Add to dashboard Cite

show abstract

“…The latter rule is rationalized by considering, that if only one single bond is unfilled, no nucleation of a liquid bridge has to occur as the liquid vapor interface can propagate along the junction into the last remaining pore. In our consideration, the latter rule ("z-1 out of z") is best suited, as the phenomenon at hand is represented as realistic as possible using macroscopic combination rules, also being in accordance with simulation studies on dead end pores 80 . We have to stress, that even this better suited combination rule is most likely not able to describe the complete mechanistic picture of the mechanism at the nanoscale.…”

Section: Interface Propagation Rules At Junctions In Interconnected P...mentioning

confidence: 59%

Development and application of a novel model based on percolation theory for advanced pore network characterization by physical adsorption

Söllner,

Neimark,

Thommes

2024

Preprint

View full text Add to dashboard Cite

Physical adsorption is one of the most widely used techniques to characterize porous materials because of being reliable and able to assess micro- and mesopores within one approach. However, challenges persist in characterizing disordered and hierarchically structured porous materials. This study introduces a pore network model aiming to enhance the textural characterization of nanoporous materials. Our model, based on percolation theory on a Bethe lattice, includes all mechanisms known to contribute to adsorption hysteresis in mesoporous pore networks during capillary condensation and evaporation. The model accounts for delayed and initiated condensation during adsorption as well as equilibrium evaporation, pore blocking and cavitation during desorption. Coupled with dedicated non-local-density functional (NLDFT) kernels, the proposed method provides a unified framework for modeling the entire experimental adsorption-desorption isotherm, including desorption hysteresis scans. Hence, our model unveils key pore network characteristics like the effective connectivity, but also has the potential to determine pore size distributions of mesoporous materials by taking quantitatively pore network effects into account. The applicability of the method is demonstrated on a selected set of nanoporous silica materials exhibiting distinct types of hysteresis loops (types H1, H2a, H1/H2a and H5) including ordered mesoporous silica networks, i.e, KIT-6 silica, hybrid SBA-15/MCM-41 silica with plugged pores, but also two disordered silica pore networks, i.e., a hierarchical meso-macroporous monolith and porous Vycor glass. For all materials, good correlation is found between simulated and experimental primary adsorption and desorption isotherms as well as desorption scans allowing for a determination of key pore network characteristics such as pore connectivity and pore size distributions.The versatility and enriched textural insights provided by the proposed novel network model allows for a comprehensive characterization previously inaccessible, and hence will contribute to a further advancement in the textural characterization of novel nanoporous materials for optimizing important applications such as catalysis, separation processes, gas-and energy storage.

show abstract

“…Parry and co-workers [46] have argued that there is no hysteresis because adsorption and desorption progresses through the same interface and that the Cohan form of equation in which the adsorbate resembles the bulk liquid-like is applicable. However, evidence from our simulations [37, 38,47] suggests that the packing of the condensate in the presence of an external adsorbent field is not the same as in the bulk liquid and differs along the desorption and adsorption branches. The adsorbate at saturation therefore has a lower energy (is more cohesive) than at the condensation pressure and is not disrupted until a lower pressure has been reached on desorption.…”

Section: Adsorption In the Closed End Pore (C-pore)mentioning

confidence: 80%

On the microscopic origin of the hysteresis loop in closed end pores – Adsorbate restructuring

Phadungbut

Nicholson

2016

Chemical Engineering Journal

Self Cite

View full text Add to dashboard Cite

We present here compelling evidence for adsorbate restructuring as the microscopic origin of hysteresis in closed end pores. Our argument is based on molecular simulations in the grand canonical (GCE) and mesocanonical (MCE) ensembles, for argon adsorbed at 87K in slit mesopores of different topologies (open end, closed end and closed pores). The MCE isotherms have sigmoidal van der Waals type loops, while the GCE isotherms exhibit hysteresis loops, which are confined between the gas-like and liquid-like spinodal points. One interesting feature, not previously recognized, is that the condensation in the MCE isotherms for pores of different topologies is identical, and it occurs at the same chemical potential, which is the coexistence chemical potential of two phases in equilibrium: the liquid-like condensate and the gas-like phase. At the onset of the condensation, the liquid-like condensate is a thin liquid bridge formed by taking molecules from the metastable adsorbed film, resulting in a thinner and stable adsorbed film. As more molecules are added into the pore, the liquid bridge thickens along the axial direction and both menisci advance towards the pore mouth. As the menisci approach the pore mouth, the liquid condensate is progressively restructured to become more cohesive.When the pressure is reduced in the grand canonical ensemble (open system), a lower pressure is required to disrupt this cohesive structure, resulting in hysteresis in the closed end pores. The classical theories, which conclude that isotherms for closed end pores must be reversible, are in error because they assume that the interfacial energy parameter (the product of the surface tension and the liquid molar volume) has the same value as in a bulk liquid.

show abstract

A molecular simulation study of adsorption and desorption in closed end slit pores: Is there a hysteresis loop?

Cited by 14 publications

References 22 publications

Development and application of an advanced percolation model for pore network characterization by physical adsorption

Development and application of an advanced percolation model for pore network characterization by physical adsorption

Development and application of a novel model based on percolation theory for advanced pore network characterization by physical adsorption

On the microscopic origin of the hysteresis loop in closed end pores – Adsorbate restructuring

Contact Info

Product

Resources

About