Porous Polymer Substrates Research Articles

Zwitterionic covalent organic framework membranes for efficient liquid molecular separations

Covalent organic frameworks (COFs) featuring uniform topological structure and devisable functionality have emerged as promising membrane materials. The design and precise manipulation of COF membranes with advanced spatial structure to achieve efficient liquid molecular separations are of great necessity. Herein, zwitterionic COF membranes have been in-situ fabricated on porous polymeric substrates using an interfacial polymerization modification strategy. The continuous defect-free COF membranes with two-dimensional in-plane dominant growth can be achieved by optimizing the fabrication parameters including reaction time, monomer concentration, and catalyst concentration. Subsequent zwitterionic modification thereon not only favors the formation of hydrophilic surface but also improves the sieving capability by sheltering effect. Attributed to the synergistic contribution, the optimized zwitterionic COF membrane possesses a superior separation factor of 2839 with the water content in the permeate up to 99.7 wt%, while maintaining a comparable permeation flux of 3309 g m−2 h−1 during the ethanol dehydration process, outperforming most of other representative membranes. Furthermore, the excellent durability of the zwitterionic COF membrane in the ethanol dehydration process and its efficient separation performance towards other alcohol dehydration systems demonstrate its potential practical applications. The easy scalability of the fabrication and regulation method offers crucial guidance for the engineering of advanced COF membranes in efficient liquid molecular separations.

MIL-125 (Ti) and porous dielectric polymer substrate introducing composite gel polymer electrolyte with enhanced mechanical property, thermal stability and electrochemical property

Lithium metal batteries have potentially high energy density, but severe uncontrolled lithium dendrites and unstable side reactions prevent large-scale applications. Serial three-dimensional porous poly (vinylidene fluoride) and copolymer membrane-based composite gel electrolytes are designed by introducing MIL-125 (Ti) and ethylene carbonate. Abundant lithium-ion transportation channels and homogeneous ion transport microregion are provided the new type porous fluoropolymer substrate. We also find that crystalline phase and dielectric properties of serial polymer membrane have significant impact on electrochemical performance for composite gel electrolytes. The mechanical and dielectric property of composite electrolyte enhanced by incorporating uniform and well distribution MIL-125 (Ti), which improve the electrolyte/electrode interface charge distribution and promote uniform lithium deposition, leading to lithium dendrite suppression. MIL-125 (Ti)/P(VDF-TrFE-CTFE) composite membrane shows the enhanced maximum strain of 181 %, thermal stability (188 °C) and corresponding composite gel electrolyte reflects higher ionic conductivity of 1.7 × 10–3 S cm-1 and wider electrochemical window at room temperature than PVDF and PVDF-HFP composite electrolytes. Expectedly, quasi-solid state lithium metal battery of MIL-125 (Ti)/P(VDF-TrFE-CTFE) composite gel electrolyte exhibits higher discharge capacity (152.8 mAh g-1) at 240th cycle and 1 C, longer cycling life and better rate performance under large current density than PVDF and PVDF-HFP composite electrolytes.

High-Performance Flexible Hybrid Silica Membranes with an Ultrasonic Atomization-Assisted Spray-Coated Active Layer on Polymer for Isopropanol Dehydration.

Organic-inorganic hybrid silica materials, incorporating an organic group bridging two silicon atoms, have demonstrated great potential in creating membranes with excellent permselectivity. Yet, the large-scale production of polymer-supported flexible hybrid silica membranes has remained a significant challenge. In this study, we present an easy and scalable approach for fabricating these membranes. By employing a sol-gel ultrasonic spray process with a single-pass method, we deposited a thin and uniform hybrid active layer onto a porous polymer substrate. We first optimized the deposition conditions, including substrate temperature, the binary solvent ratio of the silica sol, and various ultrasonic spray parameters. The resulting flexible hybrid silica membranes exhibited exceptional dehydration performance for isopropanol (IPA)/water solutions (IPA: 90 wt%) in the pervaporation process, achieving a water flux of 0.6 kg/(m2 h) and a separation factor of around 1300. This work demonstrates that the single-pass ultrasonic spray method is an effective strategy for the large-scale production of polymer-supported flexible hybrid silica membranes.

Scale-Up of PTFE-Based Gas Diffusion Electrodes Using an Electrolyte-Integrated Polymer-Coated Current Collector Approach.

Nonconductive porous polymer substrates, such as PTFE, have been pivotal in the fabrication of stable and high-performing gas diffusion electrodes (GDEs) for the reduction of CO2/CO in small scale electrolyzers; however, the scale-up of polymer-based GDEs without performance penalties to technologically more relevant electrode sizes has remained elusive. This work reports on a new current collector concept that enables the scale-up of PTFE-based GDEs from 5 to 100 cm2 and beyond. The present approach builds on a multifunctional current collector concept that enables multipoint front-contacting of thin catalyst coatings, which mitigates performance losses even for high resistivity cathodes. Our improved current collector design concomitantly incorporates a flow-field functionality in a monopolar plate configuration, keeping electrolyte gaps small for increased performance. Experiments with 100 cm2 cathodes were conducted in a one-gap alkaline AEM and acid CEM system. Our design represents an important step forward in the development of larger-size CO2 electrolyzers.

Deoxygenation of CO<sub>2</sub> Solvent Based on Monoethanolamine in Gas–Liquid Membrane Contactors Using Composite Membranes

This work is devoted to the removal of dissolved oxygen from a model solvent based on monoethanolamine (MEA) to prevent its oxidative degradation during the absorption purification of flue gases from carbon dioxide. Composite membranes based on porous ceramic and polymer substrates with a thin selective layer of poly[1-(trimethylsilyl)-1-propyne] and its mixture with polyvinyltrimethylsilane have been developed. Gas-liquid membrane contactors have been created on their basis. It is shown that with their use in the vacuum mode, up to 60% of dissolved oxygen can be removed from the model solvent.

Terahertz Humidity Sensing Based on Surface-Modified Polymer Mesh Membranes with Photografting PEGMA Brush.

A simple and compact intensity-interrogated terahertz (THz) relative humidity (RH) sensing platform is successfully demonstrated in experiments on the basis of combining a porous polymer sensing membrane and a continuous THz electronic system. The RH-sensing membrane is fabricated by surface modification of a porous polymer substrate with hydrophilic and photosensitive copolymer brushes via a UV-induced graft-polymerization process. The intensity interrogation sensing scheme indicated that the power reduction of the 0.4 THz wave is dependent on the grafting density of the copolymer brushes and proportional to the RH percent levels in the humidity-controlled air-sealed chamber. This finding was verified by the water contact angle measurement. Based on the slope of the proportional relation, the best sensitivity of the hydrophilic surface-modified sensing membrane was demonstrated at 0.0423 mV/% RH at the copolymer brush density of 1.57 mg/mm3 grafted on the single side of the sensing membrane. The sensitivity corresponds to a detection limit of approximately 1% RH. The THz RH sensing membrane was proven to exhibit the advantages of low loss, low cost, flexibility, high sensitivity, high RH resolution, and a wide RH working range of 25-99%. Thus, it is a good candidate for novel applications of wearable electronics, water- or moisture-related industrial and bio-sensing.

Characterization of a solid-supported aqueous biphasic system for the sorption of dyes from aqueous solution

An aqueous biphasic system (ABS) comprising solutions of ammonium sulfate and polyethylene glycol-2000 (PEG-2000) in which the latter is supported on a porous polymeric substrate (Amberlite XAD-16) has been characterized by examining its performance in the removal of dyes from aqueous solution. Comparison of its behavior to that of a commercial sorbent (ABEC) consisting of a polyethylene glycol covalently bound to a polymer support indicates that the capacity, uptake kinetics, and efficiency of the supported ABS are comparable or superior to that of the ABEC resin. In addition, results obtained at various PEG-2000 concentrations and with PEGs of a range of molecular weights demonstrate that in contrast to ABEC resin, the behavior of a supported ABS can be readily “tuned” to provide the desired dye retention. The relative retention of various dyes is not generally predictable from their behavior in an analogous liquid-liquid system, however, the apparent result of synergistic effects between the XAD-16 support and the PEG phase.

Hydrogen Isotope Separation Using Graphene-Based Membranes in Liquid Water.

Hydrogen isotope separation has been effectively achieved electrochemically by passage of gaseous H2/D2 through graphene/Nafion composite membranes. Nevertheless, deuteron nearly does not exist in the form of gaseous D2 in nature but as liquid water. Thus, it is a more feasible way to separate and enrich deuterium from water. Herein, we have successfully transferred monolayer graphene to a rigid and porous polymer substrate, PITEM (polyimide track-etched membrane), which could avoid the swelling problem of the Nafion substrate as well as keep the integrity of graphene. Meanwhile, defects in the large area of CVD graphene could be successfully repaired by interfacial polymerization resulting in a high separation factor. Moreover, a new model was proposed for the proton transport mechanism through monolayer graphene based on the kinetic isotope effect (KIE). In this model, graphene plays a significant role in the H/D separation process by completely breaking the O-H/O-D bond, which can maximize the KIE, leading to increased H/D separation performance. This work suggests a promising application for using monolayer graphene in the industry and proposes a pronounced understanding of proton transport in graphene.

Flexible, breathable, and reinforced ultra-thin Cu/PLLA porous-fibrous membranes for thermal management and electromagnetic interference shielding

Electromagnetic interference shielding and thermal management by wearable devices show great potential in emerging digital healthcare. Conventional metal films implementing the functions must sacrifice either flexibility or permeability, which is far from optimal in practical applications. In this work, an ultra-thin (15 µm), flexible, and porous Cu/PLLA fibrous membrane is developed by depositing copper particles on the polymer substrate. With novel acetone & heat treatment procedure, the membrane is considerably stronger while maintaining the porous fibre structure. Its fantastic breathability and super high electrical conductivity (9471.8130 S/cm) enable the composites to have fast electrical heating characteristics and excellent thermal conductivity for effective thermal management. Meanwhile, the porous polymer substrate structure greatly enhances the diffusion of conductive substances and increases the electromagnetic interference shielding effectiveness of the membranes (7797.98 dB cm2/g at the H band and 8072.73 dB cm2/g at the Ku band respectively). The composites present high flexibility, breathability, and strength with the functions of thermal management and electromagnetic shielding, showing great potential for future portable electronic devices and wearable integrated garments.

Porous Polymeric Substrates Based on a Styrene–Divinylbenzene Copolymer for Reversed-Phase and Ion Chromatography

Porous Polymeric Substrates Based on a Styrene–Divinylbenzene Copolymer for Reversed-Phase and Ion Chromatography

In-situ growth of UiO-66-NH2 in porous polymeric substrates at room temperature for fabrication of mixed matrix membranes with fast molecular separation performance

In-situ growth of UiO-66-NH2 in ordinary porous polymeric substrates offers promising opportunities to eliminate interfacial defects in mixed matrix membranes (MMMs). However, this strategy is still hard to be realized because conventional hydrothermal synthesis of UiO-66-NH2 involves harsh conditions (e.g., high temperatures, and polar aprotic solvents), which are destructive to ordinary polymer. Herein, UiO-66-NH2 was in-situ grown in polymeric substrates under room temperature via a successive immersion of a porous polyether sulfones substrate in a Zr4+ formic acid/ethanol solution and a 2-aminoterephthalic acid ethanol/formic acid/water solution. Attenuated total refraction Fourier transform infrared and X-ray diffraction characterizations demonstrated the successful incorporation of UiO-66-NH2 in the substrate. The optimized membrane possessed a high pure water permeance of 209.5 L-2h−1 bar−1 and rejections higher than 99.5% towards small molecules of Congo Red, xylene brilliant cyanin G, and Rose Bengal sodium salt. More importantly, after a 5-day immersion in water or an intense ultrasonication treatment, the membrane showed no significant change in separation performance, suggesting its excellent stability. The novel strategy regarding MMMs with UiO-66-NH2in-situ growth disclosed in this study paves the way to develop advanced UiO-66-NH2 membranes toward sustainable molecular separation in environmental applications.

In-situ formation of asymmetric thin-film, mixed-matrix membranes with ZIF-8 in dual-functional imidazole-based comb copolymer for high-performance CO2 capture

Despite numerous studies on free-standing, mixed-matrix membranes (MMMs), the development of thin-film MMMs with high permeance is still an ongoing challenge. Here, the successful fabrication of ultra-high-permeance thin-film MMMs on a porous polymer substrate is described based on a highly porous zeolitic imidazole framework (ZIF-8) and a dual-functional imidazole-based comb copolymer. The copolymer of poly(vinyl imidazole)-poly(oxyethylene methacrylate) (PVI-POEM) is synthesized via free-radical polymerization, and it exhibits CO2-philicity, strong adhesion, and good interactions with fillers. In contrast to commercial benchmark membranes such as Pebax, the use of the PVI-POEM comb copolymer results in significant improvement in the CO2 permeance without significant loss of selectivity even at high ZIF-8 loadings and low thickness. It is attributed to the in-situ formation of inverse, asymmetric morphology of MMMs and partial infiltration of PVI-POEM chains into ZIF-8 particles. Optimization of the preparation process, such as ZIF-8 loading, substrate type, and coating layer thickness, leads to an extremely high CO2 permeance of 4474 GPU with high CO2/N2 and CO2/CH4 ideal selectivities of 32.0 and 12.4, respectively, which is far beyond the current trade-off limit for membranes. The mechanism behind the exceptionally high CO2 separation performance is delineated by exploring molecular dynamic simulation through morphology, structural, and energetic analyses.

Impact of a Graphene Oxide Reducing Agent on a Semi-Permeable Graphene/Reduced Graphene Oxide Forward Osmosis Membrane Filtration Efficiency.

Graphene has been considered as a material that may overcome the limitations of polymer semi-permeable membranes in water treatment technology. However, monolayer graphene still suffers from defects that cause leakage. Here, we report a method of sealing defects in graphene transferred onto porous polymer substrate via reduced graphene oxide (rGO). The influence of various reducing agents (e.g., vitamin C, hydrazine) on the properties of rGO was investigated by SEM, Raman, FTIR, and XRD. Subsequently, membranes based on graphene/reduced graphene oxide were tested in a forward osmosis system using sodium chloride (NaCl). The effect of the effectiveness of the reduction of graphene oxide, the type and number of attached groups, the change in the distance between the rGO flakes, and the structure of this material were examined in terms of filtration efficiency. As a result, semi-permeable centimetre-scale membranes with ion blocking efficiency of up to 90% and water flux of 20 mL h−1 m−2 bar−1 were proposed.

Alcohol-Treated Porous PTFE Substrate for the Penetration of PTFE-Incompatible Hydrocarbon-Based Ionomer Solutions.

For a mechanically tough proton exchange membrane, a composite membrane incorporated with a porous polymer substrate is of great interest to suppress the ionomer swelling and to improve the dimensional stability and mechanical strength of the ionomers. For the composite membranes, good impregnation of substrate-incompatible ionomer solution into the substrate pores still remains one of the challenges to be solved. Here, we demonstrated a facile process (surface treatment with solvents compatible with both substrate and the ionomer solution) for the fabrication of the composite membranes using polytetrafluoroethylene (PTFE) as a porous substrate and poly(arylene ether sulfone) (SPAES) as a hydrocarbon-based (HC) ionomer. Appropriate solvents for the surface treatment were sought through the contact angle measurement, and it was found that alcohol solvents effectively tuned the surface property of PTFE pores to facilitate the penetration of the SPAES/N-methyl-2-pyrrolidone (NMP) solution into ∼300 nm pores of the substrate. Using this simple alcohol treatment, the SPAES/NMP contact angle was reduced in half, and we could fabricate the mechanically tough PTFE/HC composite membranes, which were apparently translucent and microscopically almost void-free composite membranes.

Decimeter-Scale Atomically Thin Graphene Membranes for Gas-Liquid Separation.

Graphene holds great potential for fabricating ultrathin selective membranes possessing high permeability without compromising selectivity and has attracted intensive interest in developing high-performance separation membranes for desalination, natural gas purification, hemodialysis, distillation, and other gas-liquid separation. However, the scalable and cost-effective synthesis of nanoporous graphene membranes, especially designing a method to produce an appropriate porous polymer substrate, remains very challenging. Here, we report a facile route to fabricate decimeter-scale (∼15 × 10 cm2) nanoporous atomically thin membranes (NATMs) via the direct casting of the porous polymer substrate onto graphene, which was produced by chemical vapor deposition (CVD). After the vapor-induced phase-inversion process under proper experimental conditions (60 °C and 60% humidity), the flexible nanoporous polymer substrate was formed. The resultant skin-free polymer substrate, which had the proper pore size and a uniform spongelike structure, provided enough mechanical support without reducing the permeance of the NATMs. It was demonstrated that after creating nanopores by the O2 plasma treatment, the NATMs were salt-resistant and simultaneously showed 3-5 times higher gas (CO2) permeance than the state-of-the-art commercial polymeric membranes. Therefore, our work provides guidance for the technological developments of graphene-based membranes and bridges the gap between the laboratory-scale "proof-of-concept" and the practical applications of NATMs in the industry.

In-Situ Growth of Uio-66-Nh2 in Porous Polymeric Substrates at Room Temperature for Fabrication of Mixed Matrix Membranes with Fast Molecular Separation Performance

In-Situ Growth of Uio-66-Nh2 in Porous Polymeric Substrates at Room Temperature for Fabrication of Mixed Matrix Membranes with Fast Molecular Separation Performance

A defect-free MOF composite membrane prepared via in-situ binder-controlled restrained second-growth method for energy storage device

Composite membranes with high selectivity and permeability are always essential in diverse fields including batteries and separation. Ultrathin highly-selective layers with well-defined porous structures are deemed as the priority for the composite membranes to break the trade-off effect between selectivity and permeability. Here, we report a binder-controlled restrained second-growth method (BRSM), which directly introduces continuous and uniform metal organic frameworks selective layers (UiO-66/-67) on porous polymer substrates (Daramic) to achieve defect-free composite membranes. In this method, the nucleation and growth of MOF can be well-tuned via controlling MOF nucleation density and the dissolution rates of binders. Composite membranes with UiO-66/-67 layers demonstrate well-controlled selectivities on different ions, confirming the key role of well-ordered pores of MOF. This is further highlighted by the coulombic efficiency (CE) enhanced from 88.4% to 94.5% at a current density of 80 mA cm−2 in zinc-iodine flow battery (ZIFB) demonstration. Additionally, a more even deposition of zinc is induced by MOF surface layer with uniformly pore size distribution, which can suppress the zinc dendrites effectively. This work demonstrates an effective and controllable way to introduce defect-free MOF selective layers on polymer substrates via tuning the MOF nucleation and growth, creating highly selective composite membranes.

High-throughput CO2 capture using PIM-1@MOF based thin film composite membranes

Carbon capture from power plants represents a powerful technique to mitigate increasing greenhouse gas emissions. In this work, we describe a thin film composite (TFC) membrane incorporating a polymer of intrinsic microporosity (PIM-1) and metal organic framework (MOF) nanoparticles for post-combustion CO2 capture. The novel TFC membrane design consists of three layers: (1) a CO2 selective layer composed of a PIM-1@MOF mixed matrix; (2) an ultrapermeable PDMS gutter layer doped with MOF nanosheets; and (3) a porous polymeric substrate. Notably, the PDMS@MOF gutter layer incorporating amorphous nanosheets provides a CO2 permeance of 10,000–11,000 GPU, suggesting less gas transport resistance in comparison with pristine PDMS gutter layers. In addition, by blending nanosized MOF particles (MOF-74-Ni and NH2-UiO-66) into PIM-1 to afford a selective layer, the resultant TFC membrane assembly delivered improved CO2 permeance of 4660–7460 GPU and CO2/N2 selectivity of 26–33, compared with a pristine PIM-1 counterpart (CO2 permeance of 4320 GPU and CO2/N2 selectivity of 19). Furthermore, PIM-1@MOF based TFC membranes displayed an enhanced resistance to aging effect, maintaining a stable CO2 permeance of 900–1200 GPU and CO2/N2 selectivity of 26–30 after aging for 8 weeks. To the best of our knowledge, the high CO2 separation performance presented here is unprecedented for PIM-1 based TFC membranes reported in the open literature.

P109 PASSIVE ECCRINE SWEAT SENSING FOR DUPLEX TEMPORAL DETECTION OF CYTOKINES

Abstract Introduction Sweat based wearable sensors have shown a lot of promise in the recent years due to the ability of tracking the biomarkers in real-time. Among the various biomarkers present in sweat, cytokine concentrations have been shown in comparable range to the blood cytokines. Detection of sweat cytokines can help in monitoring of inflammation in real-time. In this work, we demonstrate a duplex cytokine sweat based sensor for real-time monitoring. The developed sensor can detect interleukin-6 (IL-6) and interleukin-10 (IL-10) in real-time that can aid in prognosis or recovery of inflammation. Materials and Methods The sweat based sensor was developed with semiconducting electrode on porous polymeric substrate on a porous polymer substrate. Affinity capture probes were immobilized on the sensor surface via a thiol-cross linking chemistry. ATR-IR was used to validate immobilization of the capture probes. Electrochemical impedance measurements technique was used to detect the interaction between the specific antibody and target analyte. The impedance response based on the binding interaction was used to quantify the sensor metrics. Results In this work, a sweat sensor platform for the duplex detection of IL-6 and IL-10 has been demonstrated. The conjugation of the antibodies to the sensor surface was confirmed using ATR-IR spectroscopy. Impedance response was used to characterize the sensor performance metrics. Calibration dose response curve was developed with decreasing impedance response for increasing concentrations of target analyte. A limit of detection of 2 pg/mL was obtained with a dynamic range from 2 pg/mL- 200 pg/mL for IL-6. IL-10 demonstrated a limit of detection of 1.5pg/mL with a dynamic range from 1.5- 150pg/mL. The developed sensor demonstrated minimal or no cross-reactivity to non-specific molecules. Conclusion A novel sweat-based biosensor for duplex detection of cytokine markers has been demonstrated. The developed biosensor can detect pro and anti-inflammatory cytokines that can aid in the prognosis or recovery of inflammation.

Atomic layer deposition (ALD) on inorganic or polymeric membranes

Membranes can be defined as physical barriers allowing the selective transport of species. This tutorial aims to provide the basics of membrane technologies and materials, the fundamentals of the atomic layer deposition (ALD) technique, and, most importantly, to describe how to efficiently perform ALD on different membrane substrates. Membrane devices enable a considerable reduction of costs and environmental impacts for many industries, and there is a constant need to improve their operational performance. Atomic layer deposition (ALD) is a deposition technique enabling the preparation of high quality thin films on extremely high-aspect-ratio substrates with an excellent conformality and a thickness control at the nanolevel, a unique capability. Therefore, this technology can be applied for both pore size tailoring and interface engineering in membrane structures. Certain important aspects that must be taken into consideration when carrying out ALD on these highly porous ceramic or polymeric membrane substrates will be addressed, in order to achieve a conformal coating of pore walls. Finally, this tutorial will also provide specific case studies to illustrate how ALD can be applied to various membrane devices and improve their operational performance. Thus, by providing this knowledge of ALD for membrane applications, this tutorial will permit us to better exploit this emerging and growing field.