Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Han, Kuk Nam; Bernardi, Stefano; Wang, Luyao; Searles, Debra J.

doi:10.1016/j.memsci.2015.08.033

Cited by 20 publications

(41 citation statements)

References 66 publications

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“…As found in our previous work (Han et al, 2015), clustering of water has a significant impact on the self and collective diffusion coefficients. Therefore, we examine how the cluster size and stability affect water diffusivity in 1-D pore zeolites and zeolites with channels in three directions (referred to as '3-D pore zeolites') that could potentially offer faster diffusion rates than the most commonly considered 3-D channel zeolites (i.e.…”

Section: Introductionsupporting

confidence: 80%

“…Water clusters were expected to form in the hydrophobic inner-pores of the zeolites with small to moderate loading as found in our previous work (Han et al, 2015) and experimentally proved by in situ SAXS and in situ XRD . In simulations, this phenomenon can be observed through direct visualisation of the water molecules within the framework, and quantitatively characterised by calculating the radial distribution function g(r)…”

Section: Characterisation Of Transport and Structure Of Water In Zeolsupporting

confidence: 70%

“…Measurements of the diffusion coefficients were also made for MFI13 (13 water molecules in a simulation cell consisting of 1×1×2 unit cells) and MFI80 (80 water molecules in the simulation cell) which has a similar loading to MFI13, but is extended six-fold (2×2×3 unit cells). As summarised in Table 5-3, these two cases share the same water loading (0.39 g cm −3 ), however the larger system has slightly lower diffusion coefficients due to the possibility for formation of larger water clusters (Han et al, 2015). The fact that the diffusion coefficient only changes by a very small amount indicates that the system size is sufficient.…”

Section: Validation Work On Water Diffusion Within Mfimentioning

confidence: 95%

“…In most cases water molecules were added to the pores of the zeolites to give a densities of 0.39 g cm 3 in the accessible pore volume, which corresponds to the loading density of VET zeolite that was considered in our previous study (Han et al, 2015). For the MFI zeolite, this density is obtained with MFI13 (13 water molecules in 2 unit cells) and MFI80 (80 molecules in 12 unit cells).…”

Section: Simulation Proceduresmentioning

confidence: 99%

“…In addition, it was shown that the penetration of Cl − into the framework was energetically unfavourable. In our previous work (Han et al, 2015), two different 1-D pore zeolites (i.e. VET-and TON-type) were examined, and self-diffusion coefficients were found to be around 5 times higher than that in commercial aromatic polyamide membranes (Ding et al, 2014a) with water densities of 0.39 and 0.52 g cm 3 .…”

Section: Introductionmentioning

confidence: 97%

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A computational approach to evaluation of nanoporous zeolitic membranes for reverse osmosis desalination

Han¹

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Water scarcity has become one of the major global concerns. Research has shown that more than one-third of the population throughout the world resides in water-stressed regions now.Reverse osmosis (RO) desalination has recently been highlighted as a clean technology that is less energy intensive using membranes rather than directly consuming fossil fuels.Advances in nanomaterials have opened new possibilities for RO membrane materials. Zeolites are one of the candidate materials due to their crystalline structures and durability. However, the performance of zeolite membranes has not been successful for practical use due to poor water flux.Thus, we used molecular dynamics simulations to investigate, at the molecular level, a series of potential zeolite types which have been rarely studied for application in desalination. We determine diffusion coefficients and the structure of water when it passes through pores of these zeolites. In addition, we examine the potential of mean force for water or ions as they move into and through a zeolite membrane in order to evaluate how favourable the passage of the molecule of interest through each membrane is. This provided us with some criteria (i.e. water permeability and ion selectivity) to judge if the membrane is likely to have suitable desalination performance. Without this molecular-level understanding, selection of zeolite materials for desalination membranes is difficult.Some widely-studied types and potential types of zeolites were selected for our study. The common types have all 3-dimensional (3-D) pore structures, while the potential zeolites have 1-dimensional (1-D) cylindrical pores. To investigate the water dynamics and structure in these different pores, we employed molecular (MD) dynamics simulations. The MD results showed the water self-diffusivity, which indicates a molecular mobility, in the 1-D pores is up to 18-time higher than that of the 3-D pores. As it was found that water molecules formed clusters, water droplets, and moved collectively at low water density in the zeolite pores, the water collective diffusivity, which is directly related to water flux, was also measured for the all the case of zeolites. This collective diffusivity through the 1-D pore zeolites was around one order of magnitude higher than that of the 3-D pore zeolites, suggesting our 1-D zeolites selected are promising as high flux membranes.To evaluate the thermodynamic stability for water or ion of interest when they pass across the zeolite membranes, the potential of mean force calculations were carried out using MD simulations.We selected one of the 3-D pore zeolites (LTA) and another of the 1-D pore zeolites (VET) for the membrane. In general, these membranes had a moderate energy barrier to water transport, but a very high barrier to sodium or chloride ion transport except the VET membrane. The chloride ion ii had a minimum in the potential of mean force at the pore entrance and a preference for the chloride ion to enter the pore than to enter the bulk solution for the...

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Section: Introductionsupporting

confidence: 80%

Section: Characterisation Of Transport and Structure Of Water In Zeolsupporting

confidence: 70%

Section: Validation Work On Water Diffusion Within Mfimentioning

confidence: 95%

Section: Simulation Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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A computational approach to evaluation of nanoporous zeolitic membranes for reverse osmosis desalination

Han¹

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Anisotropic diffusion of water molecules in hydroxyapatite nanopores

et al. 2017

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New insights into the dynamical properties of water in hydroxyapatite (HAP) nanopores, a model system for the fluid flow within nanosize spaces inside the collagen-apatite structure of bone, were obtained from molecular dynamics simulations of liquid water confined between two parallel HAP surfaces of different sizes (20 Å ≤ H ≤ 240 Å). Calculations were conducted using a coreshell interatomic potential for HAP together with the extended simple point charge model for water. This force field gives an activation energy for water diffusion within HAP nanopores that is in excellent agreement with available experimental data. The dynamical properties of water within the HAP nanopores were quantified in terms of the second-order water diffusion tensor. Results indicate that water diffuses anisotropically within the HAP nanopores, with the solvent molecules moving parallel to the surface twice as fast as the perpendicular direction. This unusual dynamic behaviour is linked to the strong polarizing effect of calcium ions, and the synergic interactions between the water molecules in the first hydration layer of HAP with the calcium, hydroxyl, and phosphate ions, which facilitates the flow of water molecules in the directions parallel to the HAP surface.

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Fast transport diffusion of bound water in cellulose fiber network

et al. 2023

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A remarkable property of cellulose-based materials is that they can absorb huge amounts of water (25% of the dry mass) from ambient vapor, in the form of bound water confined at a nanoscale in the amorphous regions of the cellulose structure. The control of the dynamics of sorption and desorption of bound water is a major stake for the reduction of energy consumption and material or structure damages, but in the absence of direct observations this process is still poorly known. Here we present measurements of bound water transport thanks to Nuclear Magnetic Resonance relaxometry and Magnetic Resonance Imaging measurements. We show that the bound water is transported along the fibers and throughout the network of fibers in contact. For each material a single transport diffusion coefficient value allows to represent the processes over the whole range of saturation. The dependence of the transport diffusion coefficient on the fiber density and orientation is then analyzed to deduce the (elementary) transport diffusion coefficient of bound water along a cellulose fiber axis. This constitutes fundamental physical data which may be compared with molecular simulations, and opens the way to the prediction and control of sorption dynamics of all cellulosic materials or other hygroscopic materials.

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Water diffusion in zeolite membranes: Molecular dynamics studies on effects of water loading and thermostat

Cited by 20 publications

References 66 publications

A computational approach to evaluation of nanoporous zeolitic membranes for reverse osmosis desalination

A computational approach to evaluation of nanoporous zeolitic membranes for reverse osmosis desalination

Anisotropic diffusion of water molecules in hydroxyapatite nanopores

Fast transport diffusion of bound water in cellulose fiber network

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