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Here, we report an X-ray radiation-induced modification of the structure and gas permeation behavior of ZIF-8 membranes. With 300 min irradiation time, CO 2 permeance decreases by only 9 %, while N 2 and CH 4 permeances reduce by 75 and 65 %, respectively, leading to 3.7- and 2.6-fold enhancements in ideal selectivity for CO 2 /N 2 and CO 2 /CH 4 .
ABSTRACT Syntrophic cocultures (hitherto assumed to be commensalistic) of Clostridium acetobutylicum and Clostridium ljungdahlii , whereby CO 2 and H 2 produced by the former feed the latter, result in interspecies cell fusion involving large-scale exchange of protein, RNA, and DNA between the two organisms. Although mammalian cell fusion is mechanistically dissected, the mechanism for such microbial-cell fusions is unknown. To start exploring this mechanism, we used RNA sequencing to identify genes differentially expressed in this coculture using two types of comparisons. One type compared coculture to the two monocultures, capturing the combined impact of interactions through soluble signals in the medium and through direct cell-to-cell interactions. The second type compared membrane-separated versus -unseparated cocultures, isolating the impact of interspecies physical contact. While we could not firmly identify specific genes that might drive cell fusion, consistent with our hypothesized model for this interspecies microbial cell fusion, we observed differential regulation of genes involved in C. ljungdahlii’s autotrophic Wood-Ljungdahl pathway metabolism and genes of the motility machinery. Unexpectedly, we also identified differential regulation of biosynthetic genes of several amino acids, and notably of arginine and histidine. We verified that they are produced by C. acetobutylicum and are metabolized by C. ljungdahlii to its growth advantage. These and other findings, and notably upregulation of C. acetobutylicum ribosomal-protein genes, paint a more complex syntrophic picture and suggest a mutualistic relationship, whereby beyond CO 2 and H 2 , C. acetobutylicum feeds C. ljungdahlii with growth-boosting amino acids, while benefiting from the H 2 utilization by C. ljungdahlii . IMPORTANCE The construction and study of synthetic microbial cocultures is a growing research area due to the untapped potential of defined multi-species industrial bioprocesses and the utility of defined cocultures for generating insight into complex, undefined, natural microbial consortia. Our previous work showed that coculturing C. acetobutylicum and C. ljungdahlii leads to a unique metabolic phenotype (production of isopropanol) and heterologous cell fusion events. Here, we used RNAseq to explore genes involved in and impacted by these fusions. First, we compared gene expression in coculture to each monoculture. Second, we utilized a transwell system to compare gene expression in mixed cocultures to cocultures with both species physically separated by a permeable membrane, isolating the impact of interspecies “touching” on the transcriptome. This study deepens our mechanistic understanding of the C. acetobutylicum-C. ljungdahlii coculture phenotype, laying the groundwork for reverse genetic studies of heterologous cell fusion in Clostridium cocultures.
Direct lithium extraction via membrane separations has been fundamentally limited by lack of monovalent ion selectivity exhibited by conventional polymeric membranes, particularly between sodium and lithium ions. Recently, a 12- Crown-4-functionalized polynorbornene membrane was shown to have the largest lithium/sodium permeability selectivity observed in a fully aqueous system to date. Using atomistic molecular dynamics simulations, we reveal that this selectivity is due to strong interactions between sodium ions and 12-Crown-4 moieties, which reduce sodium ion diffusivity while leaving lithium ion mobility relatively unaffected. Furthermore, the ion diffusivities in the membrane, when scaled by their respective solution diffusivities and free ion fractions, can be collapsed to an almost universal relationship depending on solvent volume fraction.
The goal of achieving energy-efficient, precise molecular separations has motivated interest in developing and employing porous crystalline frameworks as membrane materials. Covalent organic frameworks (COFs) are ordered crystalline matrices composed of covalently bonded organic monomers and are synthesized via reversible reticular chemistry. COFs possess high porosity, structural tunability, and chemical and thermal stability, making them ideally suited for emerging, high-value membrane separation processes, such as ion separations, organic solvent nanofiltration, and gas separations. Although a range of COF membranes have been fabricated and tested in the past decade, these membranes are primarily polycrystalline, weakly crystalline, and/or discontinuous, resulting in suboptimal performance. In this review, we identify the properties that make COFs well-suited as membrane materials, while critically outlining the shortcomings of existing disordered COF membranes. We then highlight the recent emergence of highly crystalline, continuous, oriented two-dimensional COF membranes as a promising path forward for highly selective molecular separations. These continuous, oriented COF membranes exhibit tunable one-dimensional nanochannels, allowing for ultrafast molecular transport and precise species selectivity, thereby expanding the set of separations that can be practically achieved with membrane systems. We discuss synthesis and modification techniques that result in continuous, oriented COF membranes and evaluate the performance of such membranes for a variety of molecular separations. We conclude by identifying ongoing challenges in the development of COF membranes and outlining the future of their applications in molecular separations, which will necessarily rely on advancements in the synthesis of continuous, oriented membranes.
Many functional polymeric materials are inherently fragile at ambient conditions. Consequently, making them elastic and flexible is a challenging task, and such achievement is especially meaningful in a wide range of applications including separation membranes and stretchable devices. Poly(ionic liquids) (PILs), such as vinyl-imidazolium-based polymers, are known to be “brittle” functional polymers due to their “glassy” nature at ambient temperature. We herein developed a viable approach to enable glassy PILs with high flexibility and good elasticity via a rational molecular design of chemical composition and polymer architectures. The reversible addition/fragmentation chain transfer agents (RAFT-CTAs) were attached to the flexible poly(dimethylsiloxane) (PDMS) backbones. The polymerization of functional ionic liquid monomers from RAFT-CTAs provided grafted copolymers with the functional side chains, which were further cross-linked by di-functional PDMS. Poly(ethylene glycol) methacrylate is copolymerized with ionic liquid monomers to reduce the glass transition temperature (Tg), providing higher chain mobility and elasticity at ambient temperature. The synthesized elastic PIL-based membranes (E-PILs) have dramatically improved stretchability, reaching 122–422%. In addition to significantly improved extensibility, the synthesized E-PILs also exhibit higher ionic conductivity, critical for potential applications in solid-state batteries. Moreover, in comparison to glassy solid PIL membranes, the E-PILs also exhibited enhanced flexibility and excellent gas-separation performance.
In this work, we explore the use of CO2-selective flat sheet membranes for capturing CO2 from point sources. We employ Computational Fluid Dynamics (CFD) models to design high-flux plate-and-frame membrane modules to achieve uniform flow distribution among membrane elements, minimize dead-end zones, and ease the common concentration polarization issue for gas separation membranes. The goal is to drive membrane technology improvements by providing better module designs for given membrane properties and operating conditions.
In this work, we explore the use of CO2-selective flat sheet membranes for capturing CO2 from point sources. We employ Computational Fluid Dynamics (CFD) models to design high-flux plate-and-frame membrane modules to achieve uniform flow distribution among membrane elements, minimize dead-end zones, and ease the common concentration polarization issue for gas separation membranes. The goal is to drive membrane technology improvements by providing better module designs for given membrane properties and operating conditions.
In this work, we explore the use of CO2-selective flat sheet membranes for capturing CO2 from point sources. We employ Computational Fluid Dynamics (CFD) models to design high-flux plate-and-frame membrane modules to achieve uniform flow distribution among membrane elements, minimize dead-end zones, and ease the common concentration polarization issue for gas separation membranes. The goal is to drive membrane technology improvements by providing better module designs for given membrane properties and operating conditions.
An ultrathin high permselectivity carbon molecular sieve membrane (CMSM) for industrial gas separations is provided. The CMSM includes porous metal or ceramic supports to provide superior stability at high temperatures, pressures and chemical environments. The CMSM also offers the potential for cost-effective gas processing while overcoming disadvantages found in alternative media that are fragile and susceptible to shock due to thermal cycling and prone to end-sealing problems under industrial conditions.
The application of field ionization mass spectrometry (FIMS) to the detection of air pollutants was investigated. Current methods are reviewed for measuring contaminants of fixed gases, sulfur compounds, nitrogen oxides, hydrocarbons, and particulates. Two enriching devices: the dimethyl silicone rubber membrane separator, and the selective adsorber of polyethylene foam were studied along with FIMS. It is concluded that the membrane enricher system is not a suitable method for removing air pollutants. However, the FIMS shows promise as a useable system for air pollution detection.
A solar membrane distillation apparatus includes a housing comprising a light transmitting wall. A solar distillation membrane is positioned in the housing to receive solar radiation transmitted through the light transmitting wall. The solar distillation membrane includes a porous graphitic foam and a coating of a hydrophobic composition on the surface and pores of the graphitic foam. A water chamber within the housing is provided for retaining water adjacent to the solar distillation membrane. A vapor chamber is provided for collecting water vapor distilling through the solar distillation membrane. A condenser is provided for condensing distilled water vapor from the vapor chamber into liquid water. A separation membrane and a method of solar distillation are also disclosed.
The recognition of membrane separations as a vital technology platform for enhancing the efficiency of separation processes has been steadily increasing. Concurrently, 3D printing has emerged as an innovative approach to fabricating reverse osmosis membranes for water desalination and treatment purposes. This method provides a high degree of control over membrane chemistry and structural properties. In particular, when compared to traditional manufacturing techniques, 3D printing holds the potential to expedite customization, a feat that is typically achieved through conventional manufacturing methods but often involves numerous processes and significant costs. This review aims to present the current advancements in membrane manufacturing technology specifically tailored for water desalination purposes, with a particular focus on the development of 3D-printed membranes. A comprehensive analysis of recent progress in 3D-printed membranes is provided. However, conducting experimental work to investigate various influential factors while ensuring consistent results poses a significant challenge. To address this, we explore how membrane manufacturing processes and performance can be effectively pre-designed and guided through the use of molecular dynamics simulations. Finally, this review outlines the challenges faced and presents future perspectives to shed light on research directions for optimizing membrane manufacturing processes and achieving optimal membrane performance.
Ammonia is a promising carbon-free fuel, but current methods to produce ammonia are energy intensive. New methods are thereby needed, with one promising method being electrochemical nitrogen reduction cells. Efficient cell operation requires robust catalysts but also efficient membrane separators that permit the selective transport of ions while minimizing the transport of the products across the cell. Commercial membranes have an unknown morphology which makes designing improved cells challenging. To address this problem, we synthesized a series of membranes with controlled crosslinking density and chemical composition to understand their impact on ammonium transport. Higher crosslinking density led to lower ammonium permeability. At the highest crosslinking density, similar ammonium permeability was observed independent of the water volume fraction and hydrophobicity of the monomers. These results suggest new directions to develop membranes with reduced ammonium crossover to improve the efficiency of these electrochemical cells.
Produced water is a by-product of industrial operations, such as hydraulic fracturing for increased oil recovery, that causes environmental issues since it includes different metal ions (e.g., Li+, K+, Ni2+, Mg2+, etc.) that need to be extracted or collected before disposal. To remove these substances using either selective transport behavior or absorption-swing processes employing membrane-bound ligands, membrane separation procedures are promising unit operations. This study investigates the transport of a series of salts in crosslinked polymer membranes synthesized using a hydrophobic monomer (phenyl acrylate, PA), a zwitterionic hydrophilic monomer (sulfobetaine methacrylate, SBMA), and a crosslinker (methylenebisacrylamide, MBAA). Membranes are characterized according to their thermomechanical properties, where an increased SBMA content leads to decreased water uptake due to structural differences within the films and to more ionic interactions between the ammonium and sulfonate moieties, resulting in a decreased water volume fraction, and Young’s modulus increases with increasing MBAA or PA content. Permeabilities, solubilities, and diffusivities of membranes to LiCl, NaCl, KCl, CaCl2, MgCl2, and NiCl2 are determined by diffusion cell experiments, sorption-desorption experiments, and the solution-diffusion relationship, respectively. Permeability to these metal ions generally decreases with an increasing SBMA content or MBAA content due to the corresponding decreasing water volume fraction, and the permeabilities are in the order of K+ > Na+ > Li+ > Ni2+ > Ca2+ > Mg2+ presumably due to the differences in the hydration diameter.
The CELSS (controlled ecological life support system) resource recovery system, which is a waste processing system, uses aerobic and anaerobic bioreactors to recover plants nutrients and secondary foods from the inedible biomass. The anaerobic degradation of the inedible biomass by means of culture of rumen bacteria,generates organic compounds such as volatile fatty acids (acetic, propionic, butyric, VFA) and ammonia. The presence of VFA in the bioreactor medium at fairly low concentrations decreases the microbial population's metabolic reactions due to end-product inhibition. Technologies to remove VFA continuously from the bioreactor are of high interest. Several candidate technologies were analyzed, such as organic solvent liquid-liquid extraction, adsorption and/or ion exchange, dialysis, electrodialysis, and pressure driven membrane separation processes. The proposed technique for the on-line removal of VFA from the anaerobic bioreactor was a nanofiltration membrane recycle bioreactor. In order to establish the nanofiltration process performance variables before coupling it to the bioreactor, a series of experiments were carried out using a 10,000 MWCO tubular ceramic membrane module. The variables studied were the bioreactor slurry permeation characteristics, such as, the permeate flux, VFA and the nutrient removal rates as a function of applied transmembrane pressure, fluid recirculation velocity, suspended matter concentration, and process operating time. Results indicate that the permeate flux, VFA and nutrients removal rates are directly proportional to the fluid recirculation velocity in the range between 0.6 to 1.0 m/s, applied pressure when these are low than 1.5 bar, and inversely proportional to the total suspended solids concentration in the range between 23,466 to 34,880. At applied pressure higher than 1.5 bar the flux is not more linearly dependent due to concentration polarization and fouling effects over the membrange surface. It was also found that the permeate flux declines rapidly during the first 5 to 8 hours, and then levels off with a diminishing rate of flux decay.
In this work, we use computational modeling to examine the viability of adsorption-based pore-flow membranes for separating gases when a purely size-based separation strategy is ineffective. Using molecular dynamics simulations of O 2 and N 2 , we model permeation through a nanoporous graphene membrane. Permeation is assumed to follow a five-step adsorption-based pathway, with desorption being the rate-limiting step. Using this model, we observe increased selectivity between O 2 and N 2 , resulting from increased adsorption energy differences. We explore the limits of this strategy, providing an initial set of constraints that need to be satisfied to allow for selectivity. Finally, we provide a preliminary exploration of some transition metal oxides that appear to satisfy those conditions. Using density functional theory calculations, we confirm that these oxides possess adsorption energies needed to operate as adsorption-based pore-flow membranes. These adsorption energies provide a suitable motivation to examine adsorption-based pore-flow membranes as a viable option for air separation.
The upper part of the figure depicts an aperture-coupled L-band antenna comprising patterned metal conductor films supported on two thin polyimide membranes separated by an air gap. In this antenna, power is coupled from a microstrip line on the lower surface of the lower membrane, through a slot in a metal ground plane on the upper surface of the lower membrane, to a radiating metal patch on the upper surface of the upper membrane. The two-membrane configuration of this antenna stands in contrast to a three-membrane configuration heretofore considered as the basis for developing arrays of dual-polarization, wideband microwave antennas that could be thin and could be, variously, incorporated into, or supported on, thin structures, including inflatable structures. By reducing the number of membranes from three to two, the present design simplifies the problems of designing and fabricating such antennas or arrays of such antennas, including the problems of integrating such antennas or arrays with thin-membrane-mounted transmit/ receive modules. In addition, the use of aperture (slot) coupling eliminates the need for rigid coaxial feed pins and associated solder connections on thin membranes, making this antenna more mechanically reliable, relative to antennas that include coaxial feed pins. This antenna is designed for a nominal frequency of 1.26 GHz. The polyimide membranes are 0.05 mm thick and have a relative permittivity of 3.4. The radiating patch is square, 8.89 cm on each side. This radiating patch lies 1.27 cm above the ground plane. The feeding microstrip line is 0.12 mm wide and has a characteristic impedance of 50 . The aperture-coupling slot, etched in the ground plane, is 0.48 mm wide and 79.5 mm long. In order to maximize coupling, the microstrip line is extended beyond the middle of the slot by a length of 36 mm, which corresponds to a transmission- line electrical length of about a quarter wavelength. The other end of the microstrip line is transformed to a 50-Ohm coplanar waveguide line, which is used for connection to a transmit/receive module. Some plated-through vias are added to the outer conductors of the coplanar waveguide to suppress parallel-plate modes. The measured and calculated 10-dB-return-loss bandwidth of the antenna is 100 MHz. By eliminating the radiating patch and the upper membrane that supports it, and performing two other simple modifications, one can convert the two-membrane antenna described above to a paper-thin single-membrane antenna, shown in the lower part of the figure. One modification is to increase the slot length to 104.95 mm; the other is to extend the microstrip to 36.68 mm past the middle of the slot. With these modifications, the slot now becomes a half-wavelength radiator with a nearly omnidirectional radiation pattern. In one potential use, such a paper-thin antenna could be pasted on an automobile window to enable omnidirectional communication.
A program was successfully completed to evaluate an electrochemical nitrogen/hydrogen (N2/H2) separator for use in a spacecraft nitrogen (N2) generator. Based on the technical data obtained a N2/H2 separator subsystem consisting of an organic polymer gas permeator first stage and an electrochemical second and third stage was estimated to have the lowest total spared equivalent weight, 257 kg (566 lb), for a 15 lb/day N2 generation rate. A pre-design analysis of the electrochemical N2/H2 separator revealed that its use as a first stage resulted in too high a power requirement to be competitive with the organic polymer membrane and the palladium-silver membrane separation methods. As a result, program emphasis was placed on evaluating the electrochemical. A parametric test program characterized cell performance and established second- and third-stage electrochemical N2/H2 separator operating conditions. A design verification test was completed on the second and third stages. The second stage was then successfully endurance tested for 200 hours.