Diffusive Skin Effect in Zeolites

Rao, Wei; Yuan, Jiamin; Tang, Xiaomin; Lin, Kaifeng; Xu, Xianzhu; Xia, Hongqiang; Jiang, Yanqiu; Zheng, Anmin; Liu, Zhiqiang

doi:10.1021/acs.jpclett.2c00285

Cited by 7 publications

(3 citation statements)

References 46 publications

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“…3l ), which was in accordance with the van der Waals analysis (Supplementary Fig. 1 ) of the ideal model 38 . This was further confirmed by ab initio MD simulations (Supplementary Fig.…”

Section: Resultssupporting

confidence: 88%

Hyperloop-like diffusion of long-chain molecules under confinement

et al. 2023

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The ultrafast transport of adsorbates in confined spaces is a goal pursued by scientists. However, diffusion will be generally slower in nano-channels, as confined spaces inhibit motion. Here we show that the movement of long-chain molecules increase with a decrease in pore size, indicating that confined spaces promote transport. Inspired by a hyperloop running on a railway, we established a superfast pathway for molecules in zeolites with nano-channels. Rapid diffusion is achieved when the long-chain molecules keep moving linearly, as well as when they run along the center of the channel, while this phenomenon do not exist for short-chain molecules. This hyperloop-like diffusion is unique for long-chain molecules in a confined space and is further verified by diffusion experiments. These results offer special insights into molecule diffusion under confinement, providing a reference for the selection of efficient catalysts with rapid transport in the industrial field.

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“…3l ), which was in accordance with the van der Waals analysis (Supplementary Fig. 1 ) of the ideal model 38 . This was further confirmed by ab initio MD simulations (Supplementary Fig.…”

Section: Resultssupporting

confidence: 88%

Hyperloop-like diffusion of long-chain molecules under confinement

et al. 2023

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“…In the procedure studied by Zhao et al, 22 the gas molecules are deleted after passing the DPR, which could mask velocity correlation effects and how a backscattered molecule will influence the entrance of a new molecule coming from the bulk region. This effect could be minimal for rough zeolites such as LTA, SAS, where a higher number of wall collisions is expected, 99 but highly important in soft-pore networks such as PON, TON, or AFI. Three-dimensional zeolites like MFI have a complex interplay of interactions because one molecule traveling through straight-channel pore could interact with molecules going through a sinusoidal-channel pore.…”

Section: Effects Attributable To the System Size And Entrymentioning

confidence: 99%

Influence of Host-Framework Flexibility on Gas Transport Properties of Nanosheets and Finite-Size Nanomaterials

Zuluaga-Bedoya

Bhatia

2023

J. Phys. Chem. C

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Nanoscale systems such as hierarchical nanoporous materials, nanosheets, and ultrathin membranes are rapidly finding increasing interest as a means of reducing transport resistance. However, the analysis of such finite-size systems is generally based on transport coefficients in bulk systems when assessing the separation performance of membrane systems, without reconciling end effects; these attenuate transport and can be governing at nanoscales. Furthermore, framework flexibility has been an open topic of discussion, especially its effect on the gas transport properties and separation factors in kinetically driven separations, but its effect in finite-size systems is largely unexplored and the underlying mechanisms still unclear. Here, we assess the gas transport limitations in finite zeolite/MOF nanosheets for flexible and rigid-averaged frameworks, using equilibrium molecular dynamics simulations to investigate the internal interfacial resistance. Three coexisting effects trigger the flexibility effect: vibrating window, thermal effect, and finite-size (entry length) effects. The last one is a function of the confinement, pore texture, and momentum accommodation on wall collision and is related to an entry region of developing flow. We find the thermal effect in the bulk system to be negligible, but in the finite system, it depends on the guest− host thermalization, with diffusion coefficients up to three times higher for CH 4 in TON zeolite and over an order of magnitude higher for CO 2 in ZIF-8. We observe that the entry length effect is present in both the flexible and rigid systems but lowered for the flexible framework. Diffusivity profiles indicate that flexibility leads to reduction in the entry length for the CH 4 /TON system and enhanced diffusivity for C 2 H 6 in TON zeolite. Our results demonstrate that the extent of flexibility effects is specific to the host− guest interactions and momentum accommodation, which are influenced by the level of confinement, pore network topology and connectivity, and generalizations require extreme caution. We find that a flexible framework allows higher diffusion coefficients and reduced transport resistances, which promote an improvement in the separation performance, and its consideration is important for realistic nanomembrane design.

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“…Experimentally, interfacial resistance to fluid transport in nanomaterials, as determined by fitting of diffusion models with finite surface permeability to transient uptake data, is believed to arise from surface pore blockages and structural distortions. ,− On the contrary, it has also been observed that the low surface permeability is largely nonstructural in origin, and not entirely due to blockages and surface defects, and that it may be a surface diffusion process occurring in a finite region in the vicinity of the pore mouth or external surface. − In support, molecular dynamics (MD) simulations have suggested the existence of interfacial resistance even in ideal materials, albeit putatively. − In such simulations, the excess resistance of a finite nanoscale material over that expected based on the diffusivity under periodic boundary conditions (i.e., in the absence of boundaries) is attributed to interfacial resistance, but without direct evidence for its existence or of the underlying mechanisms. These simulations and thermodynamic theories assume the interfacial resistance to reside in a very narrow zone in the solid in the vicinity of the external surface, whose length may be of the order of a nanometer, which is the distance over which the density profile develops, essentially resembling a sharp interface.…”

Section: Introductionmentioning

confidence: 99%

On the Origin of Interfacial Resistance in Ideal Nanomaterials

Bhatia

Dutta

2023

J. Phys. Chem. C

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Interfacial resistance significantly hinders transport in nanomaterials and membranes, limiting efficiency improvement as system size is reduced. While slow transport of fluids in finitesized materials, found in experiment and simulation, has been imputed to interfacial resistance, the underlying mechanism is unclear, and no theory exists for its prediction. A kinetic theorybased approach for low-density transport in finite nanopores is developed here, which demonstrates interfacial resistance to arise from an entry region of developing flow, in which the transport coefficient is nonuniform. The origin of interfacial resistance is shown to lie in the enhanced influence of short molecular trajectories in the entry region, with increased frequency of wall collision, which reduces the local transport coefficient. It is shown that the relative interfacial resistance is a universal function of a parameter related to length and surface momentum accommodation factor for a given fluid−solid interaction potential. While interfacial resistance is system size-dependent, it approaches a limiting value in long nanopores that is readily determined. Application of the approach to H 2 transport in carbon nanotubes using molecular dynamics simulation results shows the apparent interfacial resistance to increase with decrease in nanotube diameter and with increase in fluid−solid interaction strength.

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Diffusive Skin Effect in Zeolites

Cited by 7 publications

References 46 publications

Hyperloop-like diffusion of long-chain molecules under confinement

Hyperloop-like diffusion of long-chain molecules under confinement

Influence of Host-Framework Flexibility on Gas Transport Properties of Nanosheets and Finite-Size Nanomaterials

On the Origin of Interfacial Resistance in Ideal Nanomaterials

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