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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Water-polyamide chemical interplay in desalination membranes explored by ambient pressure X-ray photoelectron spectroscopy

Reverse osmosis using aromatic polyamide membranes is currently the most important technology for seawater desalination. The performance of reverse osmosis membranes is highly dependent on the interplay of their surface chemical groups with water and water contaminants. In order to better understand the underlying mechanisms of these membranes, we study ultrathin polyamide films that chemically resemble reverse osmosis membranes, using ambient pressure X-ray photoelectron spectroscopy. This technique can identify the functional groups at the membrane–water interface and allows monitoring of small shifts in the electron binding energy that indicate interaction with water. We observe deprotonation of free acid groups and formation of a ‘water complex’ with nitrogen groups in the polymer upon exposure of the membrane to water vapour. The chemical changes are reversed when water is removed from the membrane. While the correlation between functional groups and water uptake is an established one, this experiment serves to understand the nature of their chemical interaction, and opens up possibilities for tailoring future materials to specific requirements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Molecular mechanisms of thickness-dependent water desalination in polyamide reverse-osmosis membranes

Here, using non-equilibrium molecular simulations, we systematically elaborate the relationships among synthesis (membrane's thickness and morphology), atomic-scale transport mechanism, and separation performance (permeability and selectivity) for 3D-printed polyamide (PA) membranes. Results indicated that water diffusion, swelling ratio, water flux, and water permeance proportionally decrease with increasing membrane thickness (4.0–32.5 nm). PA membranes with different thicknesses can achieve almost 100% salt rejection over the simulation time. Importantly, water permeability exponentially decreases with increasing thickness, and 15 nm is identified as the critical membrane thickness for efficient water transport. The discontinuous water-available space spreads all over PA membranes with thicknesses greater than 5 nm, allowing water molecules to jump by way of the temporary open-and-close pores. However, the connected water-useable space exists in PA membranes with thicknesses below 5 nm, offering the continuous channels to dominate water transport. More significantly, pore distribution is more homogeneous as the thickness increases. The applied high pressures can lead to membrane compaction during reverse osmosis and the thicker membranes show a lower compression ratio. In short, these investigations provide molecular insights for effectively designing and manufacturing PA membranes for water desalination and treatment at the molecular level.

42 ENGINEERING↗
DOE OSTI2023

Carbon-doped metal oxide interfacial nanofilms for ultrafast and precise separation of molecules

Membranes with molecular-sized, high-density nanopores, which are stable under industrially relevant conditions, are needed to decrease energy consumption for separations. Interfacial polymerization has demonstrated its potential for large-scale production of organic membranes, such as polyamide desalination membranes. We report an analogous ultrafast interfacial process to generate inorganic, nanoporous carbon-doped metal oxide (CDTO) nanofilms for precise molecular separation. For a given pore size, these nanofilms have 2 to 10 times higher pore density (assuming the same tortuosity) than reported and commercial organic solvent nanofiltration membranes, yielding ultra-high solvent permeance, even if they are thicker. Owing to exceptional mechanical, chemical, and thermal stabilities, CDTO nanofilms with designable, rigid nanopores exhibited long-term stable and efficient organic separation under harsh conditions.

Science & Technology - Other Topics↗
DOE OSTI2022

Effect of different manufacturing methods on polyamide reverse-osmosis membranes for desalination: Insights from molecular dynamics simulations

Membranes are a key technology platform for a broad application of energy-efficient separations. To best serve the separation demands of industry, the manufacturing processes for these membranes are garnering increasing attention. In particular, for water desalination, the industry leading polyamide (PA) reverse osmosis (RO) membranes can be manufactured via molecular layer-by-layer (mLBL) deposition, interfacial polymerization (IP), and 3D-printing technique. However, the influence of different manufacturing methods on PA membrane’s properties is far from understood. Here, in this study, we present the high-pressure transport behavior of water and salt ions for PA membranes formed with IP, mLBL, and 3D-printing through non-equilibrium molecular dynamics simulations. Studies show that membranes fabricated with 3D-printing have similar performances to those manufactured using mLBL, quantified by water permeability, rejection of salt ions, structural integrity, and porosity features. However, the membranes formed with IP exhibit faster water transport, lower rejection, worse structural integrity, and more inhomogeneous network pores than those constructed using mLBL and 3D-printing. The unconnected water-accessible space governs water transport for PA membranes formed with mLBL and 3D-printing, which offers the impermanent open-closed pores that enable water to jump through PA membranes. In contrast, the permeated water-enterable space plays a prominent role in water movement across the PA membrane formed with IP, providing a continuous transport channel at high pressure. Importantly, we observe the more significant compaction features at high pressure for PA membranes formed with IP than mLBL and 3D printing. In short, these findings provide a comprehensive understanding of existing membrane preparation technologies. It also provides a guide for developing the new membrane preparation process at the molecular level.

3D-printing↗
DOE OSTI2022

Molecular insights into the structure-property relationships of 3D printed polyamide reverse-osmosis membrane for desalination

3D-printing is an emerging method for manufacturing polyamide (PA) reserve osmosis (RO) membranes for water treatment and desalination, which can precisely control membrane structural properties, such as thickness, roughness, and resolution. However, the synthesis-structure (i.e., degree of cross-linking (DC), m-phenylenediamine/trimesoyl chloride (MPD/TMC) ratio, and membrane thickness) to property (permeability and water-salt selectivity) relationships for these membranes has not been well understood. At the same time, a microscopic understanding of the physical mechanism of water and salt transport is needed to guide the design of high-performance 3D-printed membranes and improve the printing efficiency. Furthermore, the atomic-scale transport features and energetics of water and salt ions are studied at high pressure for the 3D-printed PA RO membranes with the different DCs and MPD/TMC ratios through non-equilibrium molecular dynamics (NEMD) simulations. Factoring in membrane structure properties, rejection ratio of salt ions and pressure-dependent water flux, 3D-printed PA membranes having an MPD/TMC ratio of 3.0:2.0 and a DC between 80%~90% attains ideal performance: high water flux, high rejection of salt ions, and excellent structural integrity. Mechanistically, water permeability for highly cross-linked PA RO membranes depends on the temporary on-and-off channels that allow water molecules to jump from one cavity to another at high pressure. In addition, higher pressures cause rapid compaction of PA membranes’ free volume and membrane thickness. Membrane failure at high pressure is determined by the DC and MPD/TMC ratios-dependent compressive yield strength. In short, these findings provide physical insights for optimizing existing PA membranes and designing next-generation desalination membranes at the molecular level.

3D-printed PA RO membrane↗
DOE OSTI2024

Polyamide-Based Ion Exchange Membranes: Cation-Selective Transport through Water Purification Membranes

Ion-selective membranes are necessary components of many electrochemical systems including fuel cells, electrolyzers, redox flow batteries, and electrodialyzers. Perfluorinated sulfonated membranes (PFSMs) dominate these applications due to their excellent combination of fast ion transport, stability, and processability. However, perfluorinated cation exchange membranes (CEMs) are expensive, and their production process involves chemistry that generates toxic perfluorinated chemicals. The development of affordable, nonfluorinated membranes with a competitive combination of high ion selectivity, transport, and stability could help enable the widespread use of the technologies listed above while hastening the development of emerging electrochemical systems, including aqueous alkaline CO 2 sorbent regeneration. To this end, we pursue the use of thin-film composite polyamide (PA-TFCs) membranes–those that typically find application in reverse osmosis and nanofiltration desalination–as cation-selective exchange membranes. Given their negative surface charge under neutral-to-alkaline conditions, PA-TFCs can serve as effective CEMs in these pH regimes. We prepared a series of PA-TFCs from traditional monomers (trimesoyl chloride and piperazine) and compared their thicknesses, charge densities, water transport properties, ion transport properties, and long-term stability in a high pH environment to traditional CEMs (Nafion and FKE) and commercial nanofiltration and reverse osmosis membranes. We find that some of the best-performing PA-TFC membranes have similar resistances and Na + transference numbers compared to Nafion 117 in Na 2 SO 4 and NaHCO 3 -containing solutions. This proof-of-principle study suggests that further optimization of PA-TFCs could enable cost-effective ion exchange membrane alternatives to PFSMs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Synthesis and Performance of Aromatic Polyamide Ionenes as Gas Separation Membranes

Here, we report the synthesis and thermophysical properties of seven primarily aromatic, imidazolium-based polyamide ionenes. The effects of varied para-, meta-, and ortho-connectivity, and spacing of ionic and amide functional groups, on structural and thermophysical properties were analyzed. Suitable, robust derivatives were cast into thin films, neat, or with stoichiometric equivalents of the ionic liquid (IL) 1-benzy-3-methylimidazolium bistriflimide ([Bnmim][Tf 2 N]), and the gas transport properties of these membranes were measured. Pure gas permeabilities and permselectivities for N 2 , CH 4 , and CO 2 are reported. Consistent para-connectivity in the backbone was shown to yield the highest CO 2 permeability and suitability for casting as a very thin, flexible film. Derivatives containing terephthalamide segments exhibited the highest CO 2 /CH 4 and CO 2 /N 2 selectivities, yet CO 2 permeability decreased with further deviation from consistent para-linkages.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Grazing Incidence Wide-Angle X-ray Scattering of Water Adsorption in Polyamide Barrier Layers of Reverse Osmosis Membranes

To understand the relationship between the intermolecular structure of aromatic polyamide (PA) scaffold and the water molecules in the barrier layers of reverse osmosis (RO) membranes, a grazing incidence wide-angle X-ray scattering (GIWAXS) study was carried out on freestanding PA thin films at varying relative humidity (RH) conditions. The scattering results were analyzed by an interference scattering model, containing a phase factor between a PA chain and an adsorbed water molecule. This model yielded good fits to the GIWAXS profiles where the water adsorption was found to vary linearly with RH. Atomistic molecular dynamics (MD) simulations were also performed to complement the experimental study. Furthermore, the simulations revealed that a rapid condensation layer initially formed on the PA film surface, followed by the slow water molecule diffusion inside the PA membrane. Sparse adsorbed water, isolated in subnanopores of the PA film adjacent to the polar atoms, even in very low quantities, modifies the X-ray scattering. Atomistic simulations at the microscopic scale provide partial support for several X-ray scattering findings.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Engineering surface charges of nanofiltration membranes to maximize Li + /Mg 2+ separation properties

Polyamide-based nanofiltration (NF) membranes are attractive for Li + /Mg 2+ separation for lithium recovery from salt brine (containing mainly Mg 2+ ). However, Li + and Mg 2+ have similar hydration radii, resulting in a low separation factor (SF Li/Mg ). Herein, we demonstrate that SF Li/Mg can be significantly enhanced by optimizing the membrane surface positive charges. This results in an unexpected maximum SF Li/Mg at a solution pH slightly below its isoelectric point (IEP). Specifically, NF270 membrane was surface-grafted with 2-(methacryloyloxy)ethyltrimethylammonium chloride (META) or polyethylenimine (PEI) using bio-adhesive dopamine, forming a thin, stable, charged layer (20–40 nm) on the surface. The effects of solution pH and surface modification on the surface zeta potential (ZP) and single- and mixed-salt Li + /Mg 2+ separation properties are thoroughly investigated. For example, the META grafting increases the ZP from 9.2 to 16 mV and SF Li/Mg by 130 % from 35 to 80 at pH 4, superior to the state-of-the-art commercial NF membranes. Furthermore, this surface modification occurs at ≈22 °C in aqueous solutions and can be utilized to enhance commercial modules for practical applications.

Li+/Mg2+ separation↗
DOE OSTI2021

Unraveling the mysteries of the thin film composite reverse osmosis membrane

A recent article in Science by Culp, Kumar, Gomez, and colleagues introduces a new approach to characterizing reverse osmosis thin film composite membranes to provide critical insights into understanding how polymer membrane microstructure affects water permeability. Such approaches offer a degree of microstructure characterization that has up until now been unavailable to the membrane science community. Here, combined with modeling of water diffusion coefficient in the polymer membrane itself, this effort has begun to answer decades-old questions about how polyamide reverse osmosis membranes function.

McCutcheon, Jeffrey R.↗
DOE OSTI2024

Rejection of malathion by nanofiltration and reverse osmosis membranes exposed to foulant and two clean-in-place procedures

This research tested the treatment efficacy of an Energy Savings Nanofiltration 1 Low Fouling (ESNA 1-LF) nanofiltration (NF) and an Energy Saving Polyamide 2 (ESPA2) reverse osmosis (RO) membrane for removing malathion from water. Both membranes are of composite polyamide construction. The study included measuring malathion rejection using both pristine membranes and membranes exposed to a simulated secondary wastewater effluent foulant before and after two types of clean-in-place procedures. Across all conditions studied, malathion rejection ranged from 84 to 95% for the ESNA1-LF NF membrane and 77 to 94% for the ESPA2 RO membrane. Contact angle measurements were also collected for each membrane exposure condition. While the contact angle measurements indicated changes to the hydrophobicity of the selective layer of the membranes, they did not correlate to changes in the performance of malathion rejection. As expected, it was observed that malathion rejection improved with the introduction of foulant. Also, the clean-in-place procedures helped restore flux while maintaining malathion rejection.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Nanofiltration Membranes for Li + /Mg 2+ Separation: Materials and Mechanisms

Nanofiltration (NF) membranes have garnered significant interest for Li + /Mg 2+ separation, a crucial step in lithium extraction from brines. The state-of-the-art commercial LiNE-XD membrane exhibits a Li + /Mg 2+ separation factor (SF Li/Mg ) of 42 at pH 3.3, due to the positive charges on the membrane surface and its strong size-sieving ability. Membranes with higher separation factors at a broad pH range are being pursued to improve separation efficiency. This work aims to provide a timely and comprehensive assessment of advanced NF membranes with superior Li + /Mg 2+ separation properties, as well as their structure and property relationships for designing next-generation membranes. We describe transport mechanisms for ions in NF membranes and discuss governing parameters and models employed to quantify the Li + /Mg 2+ separation. High-performance membrane materials are exhaustively introduced, including commercial and modified polyamides, two-dimensional materials, metal–organic frameworks, crown ethers, and their blends. Finally, we critically compare these membranes in an upper bound plot and highlight the opportunities and challenges of NF membranes for practical Li + /Mg 2+ separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ultrathin-film composite (uTFC) membranes based on amorphous perfluoropolymers for liquid separations

Thin-film composite membranes based on ~100nm cross-linked polyamides (PAs) are state-of-the-art membranes for liquid separations such as desalination. However, the PA layer shows poor antifouling properties and instability in chlorine solutions. Herein, we show for the first time that glassy amorphous perfluoropolymers (PFPs, such as Teflon AF and Hyflon AD) can be fabricated into ultrathin film composite (uTFC) membranes with a selective layer of <20nm for desalination. Increasing the polymer concentration in the coating solutions from 0.05 mass% to 0.3 mass% increases the selective layer thickness from 9 to 25nm. When Teflon AF2400 was fabricated into 16-nm selective layers on various porous supports, the water permeance decreases from 0.37 LMH/bar for PES10k to 0.07 LMH/bar for PES1k, and the Na 2 SO 4 rejection increases from 86.6% to 95.2%. While the water permeance is lower than the commercial PA-based NF membranes, the rejection in these PFP-based membranes is comparable. Furthr, the effect of the porous support on the water permeance can be ascribed to the geometric restriction and satisfactorily described using an empirical model. Interestingly, the membranes also exhibit good Na + /Li + separation performance and stable performance for organic solvent nanofiltration, showcasing the versatility of the PFP-based uTFC membranes for various liquid separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Ultrahigh pressure compaction-resistant thin film crosslinked composite reverse osmosis membranes

In this study, we present a class of thin-film crosslinked (TFX) composite reverse osmosis (RO) membranes that resist physical compaction at ultrahigh pressures (up to 200 bar). Since RO membranes experience compaction at virtually all pressure ranges, the ability to resist compaction has widespread implications for RO membrane technology. The process described herein involves crosslinking a phase inverted porous polyimide (PI) support membrane followed by interfacial polymerization of a polyamide layer, thereby forming a fully thermoset composite membrane structure. We explore a range of phase inversion membrane formation parameters such as PI concentration, solvent-cosolvent ratios, coagulation bath composition, and crosslinking methods in addition to interfacial polymerization reaction chemistry and conditions. Overall, TFX membranes exhibit significantly less compaction compared to hand-cast and commercial high-pressure RO membranes, experiencing less than 10% decline in water permeance and maintaining salt rejection over 99% for NaCl solutions up to 180,000 mg/L with 200 bar applied pressure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Resilient high-temperature reverse osmosis desalination membranes

Conventional thin-film composite (TFC) reverse osmosis (RO) membranes experience irreversible performance loss at high temperatures, restricting their use in industries with high-temperature streams, including oil and gas, pharmaceuticals, electronics, power generation, food production, and hybrid desalination plants. However, the mechanisms driving the performance decline of TFC membranes at high temperatures remain poorly understood. Herein, we combine controlled experiments, molecular dynamics simulations, and micromechanical modeling to elucidate TFC failure mechanisms and to evaluate thermally resilient thin-film cross-linked (TFX) composite membrane. Upon exposure to elevated temperatures (>60°C), salt rejection of TFC dropped from ~99 to <90%, with irreversible structural damage in the polysulfone layer, confirmed by scanning electron microscopy. In contrast, the TFX membrane maintained ~99% salt rejection and showed no signs of physical degradation up to 80°C. Our combined analyses revealed that TFC membrane failure arises from irreversible pore expansion in the thermoplastic polysulfone support, leading to polyamide film rupture and delamination. TFX membranes resist thermal deformation, enabling ultrahigh-temperature RO desalination and water reuse.

Wu, Jishan [Rice Univ., Houston, TX (United States↗