Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane

Gao, Weimin; She, Fenghua; Zhang, Juan; Dumée, Ludovic F.; He, Li; Hodgson, Peter; Kong, Lingxue

doi:10.1016/j.memsci.2015.03.052

Cited by 86 publications

(94 citation statements)

References 56 publications

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“…The densities of the dry and hydrated membranes are close to previous experimental and simulation values [11,14,16,24,25]. Like other recent studies [21,22], the simulated membranes under study are much thinner than actual polymeric membranes used commercially, which are typically about 0.2 µm thick [26]. Nevertheless, the water flux through the simulated membrane is in the range expected for commercial membranes [23].…”

Section: Methodssupporting

confidence: 83%

“…In this approach the actual operating conditions of the RO process are simulated by applying a pressure difference across the membrane. Progress has been achieved in understanding some aspects of water and ion transport, though two recent studies seem to consider the case of equal ion concentrations on both sides of the membrane [21,22], a situation that would not occur in practice. By contrast, we study the situation in which solutes are initially concentrated on the high-pressure feed side of the membrane with pure water on the low-pressure permeate side of the membrane, both in our recent work in which we considered the physical aspects of the transport including the impact of the percolated free volume and size of the solute [23] and the current study.…”

Section: Introductionmentioning

confidence: 99%

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Rejection mechanisms for contaminants in polyamide reverse osmosis membranes

Shen

Keten

Lueptow

2016

Journal of Membrane Science

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Despite the success of reverse osmosis (RO) for water purification, the molecular-level physicochemical processes of contaminant rejection are not well understood. Here we carry out non-equilibrium molecular dynamics (NEMD) simulations on a model RO membrane to understand the mechanisms of transport and rejection of both ionic and inorganic contaminants in water. While it is commonly presumed that the contaminant rejection rate is correlated with the dehydrated solute size, this approximation does not hold for the organic solutes and ions studied. In particular, the rejection of urea (2.4 Å radius) is higher than ethanol (2.6 Å radius), and the rejections for organic solutes (2.2-2.8 Å radius) are lower than Na + (1.4 Å radius) or Cl -(2.3 Å radius). We show that this can be explained in terms of the solute accessible free volume in the membrane and the solute-water pair interaction energy. If the smallest open spaces in the membrane's molecular structure are all larger than the solute size including its hydration shell, then the solute-water pair interaction energy does not matter. However, when the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule to pass through a portion of the membrane molecular structure, as occurs in RO membranes, the pair interaction energy governs solute rejection. The high pair interaction energy for water molecules in the solvation shell for ions makes the water molecules difficult to shed, thus enhancing the rejection of ions. On the other hand, the organic solute-water interaction energies are governed by the water molecules that are hydrogen bonded to the solute. While these hydrogen bonds have pair interaction energies that are much larger than that of the nonhydrogen bonded water molecules in the solute solvation shell, they are significantly less the ion-water pair interaction energy. Thus, organic solutes more easily shed water molecules than ions to pass through the RO membrane. Since urea molecules have more hydrogen-bonding sites than alcohol molecules, urea sheds 2 more hydrogen-bonded water molecules and forms more hydrogen bonds with the membrane leading to a higher rejection of urea than occurs for ethanol, a molecule of similar size but with fewer hydrogen bonding sites. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in the context of reverse osmosis, thus providing new insights into solute transport and rejection in RO membranes.

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Section: Methodssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Rejection mechanisms for contaminants in polyamide reverse osmosis membranes

Shen

Keten

Lueptow

2016

Journal of Membrane Science

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“…Overall, CC2 appears to be the best POC membrane for water desalination. The P w in CC2 is higher than in several 2D membranes such as graphene, 27 graphyne 31 and CTF-1, 32 and one order of magnitude higher than in a polyamide membrane, 33 commercial seawater RO, brackish RO and high-flux RO membranes. 34 It is also higher than the P w in ZIFs from our recent simulation studies.…”

Section: Water Flow and Salt Rejectionmentioning

confidence: 82%

“…This behavior is attributed to the relatively free water permeation through the straight large pores in CC2 and the porous network in CC17. Comparatively, water molecules , 27 graphyne, 31 CTFs, 32 polyamide, 33 commercial RO 34 and ZIFs [35][36][37] ). stay in CC3 and CC16 for a much longer period (30-40 ns) because of their tetrahedral network and small radius, which are not favorable for water permeation.…”

Section: Water Dynamics and Structure In Pocsmentioning

confidence: 99%

Porous organic cage membranes for water desalination: a simulation exploration

Kong

Jiang

2017

Phys. Chem. Chem. Phys.

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Porous organic cages (POCs) have emerged as a new class of porous materials and received considerable interest for their potential applications. Herein we report the first proof-of-concept simulation study on POC membranes for water desalination. Among the five POC membranes, CC2 is the best for water desalination with performance superior to other membranes reported in the literature. The membrane flexibility is revealed to have a weak effect on water permeation. To provide further microscopic understanding, the permeation duration, diffusion and hydrogen bonding of water in the POC membranes are quantitatively analyzed. From this simulation study, the key factors governing water permeation in the POC membranes are unraveled and CC2 is identified to be an interesting candidate for water desalination.

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“…1,2 In particular, membranes removing small ions, such as nanofiltration (NF) membranes and reverse osmosis (RO) membranes, are widely used in seawater and brackish water desalination. [1][2][3][4][5][6][7][8][9][10][11] Conventional membranes contain films of cross-linked polyamides or cellulose acetates as separation functional layers. However, these films contain a disordered structure and the nanopores or sub-nanopores formed in those membranes for the transportation of water molecules and ions are not uniform.…”

Section: Introductionmentioning

confidence: 99%

Transport mechanisms of water molecules and ions in sub-nano channels of nanostructured water treatment liquid-crystalline membranes: a molecular dynamics simulation study

Nada

Sakamoto

Henmi

et al. 2020

Environ. Sci.: Water Res. Technol.

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Membranes with sub-nano channels formed by self-organization of ionic liquid-crystalline (LC) compounds have great potential as water treatment membranes. In this study, the transport mechanisms of water molecules and ions in the sub-nano channels of the LC membranes are investigated by molecular dynamics simulations for NaCl and NaNO 3 solutions. The simulation results suggest that there are different transport mechanisms for water molecules and ions; the transport of water molecules occurs by Brownian diffusion, whereas that of ions occurs by jump diffusion between particular sites in the sub-nano channel. A free-energy landscape of an ion in the channel is analyzed using a metadynamics method, which indicates distinct local minima at particular sites and supports the jump diffusion mechanism. The effects of the LC compounds' structural flexibility and the electrostatic interaction with the wall of the sub-nano channels on the permeability of water molecules and ions are also investigated by molecular dynamics simulations. Simulation results suggest both the structural flexibility and the electrostatic interaction, which are characteristics of the LC membranes, are important factors in determining the water treatment performance. The structural flexibility affects the permeability of the membrane to water molecules and the electrostatic interaction reduces the permeability to ions. 604 | Environ. Sci.: Water Res. Technol., 2020, 6, 604-611This journal is † Electronic supplementary information (ESI) available: Details of the simulation method, MD simulations of the bulk solutions, an example of the jump diffusion mechanism for Na + observed during the simulation, and the mobility of water molecules in a nonequilibrium MD simulation. See Recently, we developed liquid crystalline (LC) membranes with sub-nano channels formed by self-organization of thermotropic ionic LC compounds. The LC membranes have great potential as excellent water treat membranes. In this work, we elucidated the transport mechanisms of water molecules and ions in the LC membranes by molecular dynamics simulations. We also elucidated the effects of the structural flexibility and the electrostatic interaction, which are characteristics of the LC membranes, on the water treatment performance. The knowledge obtained in this work has great potential to realize the development of future LC membranes of which the performances to water treatment are significantly improved.

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Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane

Cited by 86 publications

References 56 publications

Rejection mechanisms for contaminants in polyamide reverse osmosis membranes

Rejection mechanisms for contaminants in polyamide reverse osmosis membranes

Porous organic cage membranes for water desalination: a simulation exploration

Transport mechanisms of water molecules and ions in sub-nano channels of nanostructured water treatment liquid-crystalline membranes: a molecular dynamics simulation study

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