Membrane Material Research Articles

Long-term pure- and mixed-gas performance of carbon molecular sieve membranes derived from a tetraphenylethylene-based ladder polymer of intrinsic microporosity (TPE-PIM) for propylene/propane separation

Continuous long-term evaluation of propylene and propane permeation through narrow slit carbon molecular sieve (CMS) membranes is essential for an in-depth study of their steady-state separation performance. CMS membranes are characterized by finely tuned ultramicroporous structures, exceptional thermal and chemical stability, and hold great promise for the energy-intensive separation of propylene and propane. However, the gradual changes in their performance over time due to penetrant-induced structural chain rearrangements have often been overlooked. In this study, we prepared CMS membranes using a polymer of intrinsic microporosity (PIM) with a highly aromatic tetraphenylethylene (TPE) based building block. The presence of bulky and sterically hindered TPE repeat units renders this polymer an excellent precursor for the fabrication of high-performance CMS membranes. The TPE-PIM-based precursor underwent pyrolysis at temperatures ranging from 550 to 700 °C for 1 h. Pure- and mixed-gas permeation tests were accompanied by various characterization techniques to assess the carbonization state of the CMS materials. The CMS pyrolyzed at 700 °C exhibited a decline in pure-gas C3H6/C3H8 selectivity from an initial value of 300 to 161 at steady state over a 20-day period. Even more notable, under equimolar mixed-gas feed conditions, the isotropic CMS film displayed a substantial C3H6/C3H8 selectivity reduction from 214 to 62 over a 24-day period. This performance decline can be attributed to competitive sorption and very slow dilation kinetics, which led to moderately reduced propylene permeability while significantly enhancing propane permeability. Our study suggests that long-term, continuously performed mixed-gas permeation experiments are essential to assess the ‘steady-state’ performance of CMS membranes for mixtures containing highly sorbing feed components, as observed for propylene/propane separation.

Electrospinning-hot pressing technique for the fabrication of thermal and electrical storage membranes and its applications

Electrospinning-hot pressing technique for the fabrication of thermal and electrical storage membranes and its applications

Advancing Artificial Cells with Functional Compartmentalized Polymeric Systems - In Honor of Wolfgang Meier.

The fundamental building block of living organisms is the cell, which is the universal biological base of all living entities. This micrometric mass of cytoplasm and the membrane border have fascinated scientists due to the highly complex and multicompartmentalized structure. This specific organization enables numerous metabolic reactions to occur simultaneously and in segregated spaces, without disturbing each other, but with a promotion of inter- and intracellular communication of biomolecules. At present, artificial nano- and microcompartments, whether as single components or self-organized in multicompartment architectures, hold significant value in the study of life development and advanced functional materials and in the fabrication of molecular devices for medical applications. These artificial compartments also possess the properties to encapsulate, protect, and control the release of bio(macro)molecules through selective transport processes, and they are capable of embedding or being connected with other types of compartments. The self-assembly mechanism of specific synthetic compartments and thus the fabrication of a simulated organelle membrane are some of the major aspects to gain insight. Considerable efforts have now been devoted to design various nano- and microcompartments and understand their functionality for precise control over properties. Of particular interest is the use of polymeric vesicles for communication in synthetic cells and colloidal systems to reinitiate chemical and biological communication and thus close the gap toward biological functions. Multicompartment systems can now be effectively created with a high level of hierarchical control. In this way, these structures can not only be explored to deepen our understanding of the functional organization of living cells, but also pave the way for many more exciting developments in the biomedical field.

Tuning the Properties of Polyvinylidene Fluoride/Alkali Lignin Membranes to Develop a Biocatalytic Membrane Reactor for an Organophosphorus Pesticide Degradation.

It has been observed that the immobilization of a phosphotriesterase enzyme (PTE) onto polyvinylidene fluoride (PVDF) membranes significantly decreased the enzyme activity, and this negative effect was attributed to the hydrophobic character of the membrane. The indirect indication of this reason was that the same enzyme immobilized on other membrane materials bearing hydrophilic character showed better performance. In this work, we provide direct evidence of the mechanism by immobilizing a PTE on a PVDF membrane hydrophilized by blending it with alkali lignin (AL). The PTE was immobilized on PVDF membrane by a covalent bond with the same procedure used in earlier studies to attribute changes in enzyme activity solely to the wettability properties (and not to the material chemistry). The activity of the PTE immobilized on the PVDF membrane hydrophilized with AL was 50% higher than that of the enzyme immobilized on the PVDF hydrophobic membrane. Further improvements of the membrane structure tailored for the development of a biocatalytic membrane reactor (BMR) were also promoted. In particular, the performance of the BMR was studied as a function of the thickness of the membrane, which allowed us to modulate the residence time into the enzyme-loaded membrane pores while maintaining the flow rate through the pores at a constant.

Fabrication of omniphobic PVDF membrane with SiO2–FeOOH hierarchical structures for robust membrane distillation

Omniphobic membrane has been demonstrated as an effective strategy to mitigate membrane wetting and fouling risks in membrane distillation (MD) processes. In this work, novel omniphobic membranes with hierarchical re-entrant surface structure were fabricated. Firstly, the FeOOH nanorods were deposited on the polydopamine (PDA) pre-treated poly (vinylidene fluoride) PVDF membrane. After that, the SiO2 nanoparticles (NPs) were coated on the FeOOH nanorods via electrostatic attraction to form hierarchical structures. Finally, the fluorosilane was utilized to reduce the membrane surface free energy, contributing to PVDF based omniphobic membranes. The effects of reaction time, FeCl3·6H2O and SiO2 NPs concentrations on membrane properties, including membrane surface morphology, average pore size, contact angles (CAs), surface roughness and permeate flux, were investigated in detail. The resulting omniphobic membranes showed high CAs towards various tested liquids, such as 0.4 mM sodium dodecyl sulfate (SDS) solution (143.9 ± 0.8°), hexadecane (113.5 ± 3.2°) and mineral oil (132.5 ± 2.8°). This membrane exhibited outstanding performance in a continuous 50-h vacuum membrane distillation (VMD) process with a 10 wt% NaCl feed solution. Besides, the anti-oil-fouling properties were further assessed with a feed solution containing 200-ppm hexadecane and 3.5-wt% NaCl, the omniphobic membrane exhibited steady permeate flux of above 24.18 kg m−2 h−1 and a 99.99 % rejection rate during 50-h testing. Finally, the omniphobic membrane showed high anti-wetting properties by SDS/salt solution. This work introduces a new strategy for fabricating omniphobic membranes that shows significant potential for treating complex industrial wastewaters.

Development of Multi-Walled Carbon Nanotube-Integrated Recycled Polyethylene Terephthalate Electrospun Antibacterial Face Mask

In this study, electrospun nanofiber membranes were successfully fabricated by modifying recycled polyethylene terephthalate (r-PET) with multi-walled carbon nanotubes (MWCNTs) for face mask applications. The recycling of PET bottles ensures effective waste management, while the electrospinning process facilitates the creation of delicate nano-range fibers. The inclusion of MWCNTs aimed to assess the antibacterial activity of the resulting nanomembranes. The fabricated samples underwent comprehensive characterization, including scanning electron microscopy (SEM), ultimate tensile testing, particulate filtration efficiency (PFE) testing, Fourier transform infrared spectroscopy (FTIR), and antibacterial sensitivity assays, revealing significant findings. MWCNTs incorporation led to minor bead formation in the membranes, with fiber diameters ranging from 446 to 862 nm. However, MWCNTs resulted in reduced stiffness and tensile properties due to the disruption of polymer chain alignment. The nanofiber membranes demonstrated effective filtration of 0.3 µm particulates, achieving filtration rates between 96 to 97%Functional group analysis confirmed the presence of both r-PET and MWCNTs in the composites. Although the r-PET/MWCNTs 12 kV membrane lacked an antibacterial zone of inhibition, it exhibited reductions of 28.64% for S. aureus and 31.9% for E. coli. These results collectively underscore the potential of r-PET/MWCNTs samples as an alternative nanofibrous membrane material for face masks. J. of Sci. and Tech. Res. 5(1): 63-74, 2023

A universal machine learning framework to automatically identify high‐performance covalent organic framework membranes for CH4/H2 separation

AbstractA universal machine learning framework is proposed to predict and classify membrane performance efficiently and accurately, achieved by combining classical density functional theory and string method. Through application of this framework, we conducted high‐throughput computations under industrial conditions, utilizing an extensive database containing nearly 70,000 covalent organic framework (COF) structures for CH4/H2 separation. The best‐performing COF identified surpasses the materials reported in the previously documented MOF and COF databases, exhibiting an impressive adsorption selectivity for CH4/H2 exceeding 82 and a membrane selectivity reaching as high as 248. More impressively, some of the best candidates identified from this framework have been verified through previous experimental works. Furthermore, the automated machine learning framework and its corresponding scoring system not only enable rapid identification of promising membrane materials from a vast material space but also contribute to a comprehensive understanding of the governing mechanisms that determine separation performance.

Sustainable Approaches for the Fabrication of Nanocellulose-Polyamide Membrane Based on Waste Date Palm Leaves for Water Treatment

A vast amount of agricultural waste, such as dried leaves, stems, pits, seeds, etc., are produced by date palm trees in Saudi Arabia each year. This waste is an excellent source of degradable biomass suitable for many uses. Crystalline nanocellulose (CNC) is one of the most important nanomaterials that can be used in various applications. Due to its unique properties, which include biorenewability, optical transparency, high mechanical strengths, and sustainability, nanocrystalline cellulose has become a significant nanomaterial in recent years. In this study, CNC was isolated from the waste date palm leaves and used for the production of PA-modified membranes for water treatment by reverse osmosis membrane technology. The membranes were prepared by surface polymerization with the polyamide as a selective layer on the polysulfone support film. Three membranes were produced, two with 0.01% and 0.02% (w/v) CNC and the third with PA-free CNC for comparison. Each membrane produced was tested using different characterization techniques. The polyamide membrane with 0.01% w/v CNC had a higher water permeability of 43.25 L/m2 h bar than the membranes with 0% w/v CNC (36.25 L/m2 h) and 0.02% w/v CNC (42.85 L/m2 h bar). Under the same conditions, salt retention was also found to be above 98% for both NaCl and MgSO4 for the two modified membranes. The contact angle was found to be 68.04±3.7, 72.83±0.8, and 63.76±5.5 for PA(0%CNC), PA-CNC (0.01% w/v), and PA-CNC (0.02% w/v), respectively. The 0.01% PA-CNC membrane exhibited a higher water contact angle, greater hydrophobicity and lower surface roughness. As a result, the isolated CNC might be appropriate for use as a modifier agent for membrane fabrication and water treatment.

Feasibility of biomass-based flexible and transparent AuNPs-acetylcellulose membrane for multifarious surface-enhanced Raman spectroscopy detection

BackgroundLignocellulosic biomass-based derivatives coupled with surface-enhanced Raman spectroscopy (SERS) technology have emerged as an appealing and indispensable tool in food safety and environmental monitoring for rapidly detecting trace contaminants like pesticide residues. The membrane material, serving as a substrate, ensures both sampling flexibility and test accuracy by directing the diffusion-adsorption process of the molecules. However, the existing membrane substrates, critical for the practical application of SERS, suffer from issues such as costly, intricate fabrication procedures, or restricted detection capabilities. ResultsHerein, we present a flexible, transparent, and biodegradable cellulose acetate membrane with gold nanoparticles (AuNPs) uniformly embedded, fabricated using a simple scraping method. This membrane achieved a limit of detection (LOD) of thiram pesticide in water at 10−8 g mL−1. The unique optical transparency of the substrates allowed for in-situ detection on surfaces, with an LOD of thiram reaching 30 ng cm−2. SignificanceFurthermore, SERS substrates made from corn stover-derived cellulose acetate enable the detection of various contaminants, highlighting their cost-effectiveness and eco-friendliness because of the abundance and low environmental impact of the raw materials.

Fabrication of ultrafiltration membranes based on methacrylate copolymers containing quaternary ammonium and PEG units for dye removal

Abstract Phase inversion involves in a complex process due to numerous factors affecting the membrane formation. Among them, polymer chain entanglement from polymeric membrane materials plays a critical role in regulating membrane structure and is still worth further exploration. Herein, a series of methacrylate copolymers with different contents of poly(ethylene glycol) methacrylate (PEGMA) were designed and synthesized, and ultrafiltration membranes cast from these copolymers were systematically investigated regarding structural evolution and filtration performance. Surface zeta potential of membranes gradually transformed from positive to negative with the increasing PEGMA content due to nonsolvent-induced surface migration of element oxygen, and meanwhile the transformation from finger-like pore structure to sponge-like pore structure in the support layer was observed, which could be attributed to chain entanglement of the PEGMA-rich copolymer. Filtration experiments indicated that sponge-like membranes possessed better separation effect of Victoria blue B compared with finger-like membranes, and the optimized mPP40-15 % showed a retention rate of 99.55 % and permeance of 110.26 L m−2 h−1 bar−1 and displayed good selective separation of dye/salt mixture. Besides, sponge-like membranes also exhibited easy regeneration, anti-fouling property and filtration stability. This work will provide guidance for modulating membrane structure and offer an alternative material for membrane separation in handling dye wastewater.

Fabrication of ultra-permeable membranes with antibiofouling capability by incorporating bifunctionalized zeolite

Poor water permeance and biofouling significantly limit the application of nanofiltration (NF) membranes in wastewater treatment and seawater desalination. Herein, bifunctionalized FAU-Ag-OH zeolites, featuring abundant hydroxyl groups and silver ions on their surface, were designed and incorporated into polyamide (PA) layer of a thin-film nanocomposite (TFN) membrane, effectively enhancing the antibiofouling properties and water permeance of membrane. The plentiful hydroxyl groups and well-dispersed silver ions on the bifunctionalized FAU-Ag-OH zeolites impart the membrane with more negative surface charge, increased hydrophilicity, and superior antibiofouling property. Additionally, the doped FAU-Ag-OH zeolites can retard the diffusion of piperazine during interfacial polymerization (IP) process and have improved chemical compatibility with polymers, which results in desirable membrane structure. Consequently, the optimal M–0.05 membrane containing FAU-Ag-OH zeolites exhibited a 2.3-fold increase in water permeance (18.8 ± 2.0 L m−2 h−1 bar−1) and enhanced antibiofouling ability (with antibacterial efficiency up to 95.4 % and flux recovery ratio up to 85 %) compared with the TFC membrane. The successful fabrication of such membrane with enhanced antibiofouling properties and improved water permeance is expected to promote the application of NF membranes in water treatment.

Superprotonic Conductivity by Synergistic Blending of Coordination Polymers with Organic Polymers: Fabrication of Durable and Flexible Proton Exchange Membranes.

Creation of an efficient and cost-effective proton exchange membrane (PEM) has emerged as a propitious solution to address the challenges of renewable energy development. Coordination polymers (CPs) have garnered significant interest due to their multifunctional applications and moldability, along with long-range order. To leverage the potential of CPs in fuel cells, it is essential to integrate microcrystalline CPs into organic polymers to prepare membranes and avoid grain boundary issues. In this study, we designed and synthesized CPs containing imidazole and sulfonate moieties via gel-to-crystal transformation. The integration of CPs into the PVDF-PVP matrix resulted in superprotonic conductivity in the order of 10-2 S cm-1 at room temperature (30 ºC) and 98% RH. The proton conductivity achieved with CP-integrated composite membrane was 4.69 × 10-2 S cm-1 at 80 °C and 98% RH, the highest among all CP/MOF-integrated PVDF-PVP membranes under hydrous conditions. The excellent compatibility of CPs with PVDF-PVP produced highly flexible membranes with superior mechanical, chemical, and thermal stability. About 25 times higher proton conductivity value was achieved with membrane, compared to intrinsic CPs, at RT and 98% RH. Thus, we present a cost-effective CP-integrated mixed-matrix membrane with superprotonic conductivity and long-term durability for cutting-edge fuel cell development.

Preparation and performance of Rb+ doped La2Ce2O7-δ proton conductor for hydrogen permeation membranes

Compared with perovskite-type proton conductor materials, fluorite-type La2Ce2O7-δ has good tolerance to H2O and CO2, and is a promising candidate material for hydrogen permeation membranes. In this work, Rb+ doped La2Ce2O7-δ was proposed as a means to enhance both the hydrogen permeation flux and electrochemical performance of La2Ce2O7-δ. Experimental findings indicate that the sample exhibits the highest conductivity and hydrogen permeation flux at a doping concentration of 15 % (La1.85Rb0.15Ce2O7-δ). Specifically, the hydrogen permeation flux of Pt-La1.85Rb0.15Ce2O7-δ increased by 1.5 times when the dry sweeping gas was replaced with wet sweeping gas during hydrogen permeation testing. It was observed that variations in membranes thickness resulted in distinct hydrogen permeation control mechanisms. Moreover, La2Ce2O7-δ samples doped with various concentrations of Rb+ exhibited excellent stability in a wet atmosphere containing 20 % CO2, suggesting their potential as ceramic hydrogen separation membranes materials.

A study on preparation of low-cost environment-friendly self-assembled nanocellulose membrane from waste paper

In the context of green development, different types of waste paper were used in this study to prepare environment-friendly nanocellulose membrane by using different pretreatment processes. The results showed that all nanocellulose membranes had a novel microscopic composite morphology: nanocellulose fibers in the middle were tightly arranged and had a certain direction, while nanocellulose fibers at the edge were arranged randomly. Moreover, the type of waste paper affected the formation and property of nanocellulose membranes deeply compared with the pretreatment process. Nanocellulose membrane prepared from office waste paper had a high transmittance (50.8 %) and low oxygen transmission rate (1.548·10−3/cm3mm/(m2·d·KPa)) while that prepared from waste corrugated paper had a high yield (50.63 %), high folding number (81 times), and low water vapor transmission rate (1550.24 g·m−2·day−1). Meanwhile, nanocellulose membrane prepared without any deinking treatment had a significant performance advantage in terms of water vapor barrier and folding resistance. Therefore, in actual application, deinking treatment can be selectivity omitted, which will simplify the preparation process flow and reduce the production cost of nanocellulose membrane. Furthermore, in order to satisfy different application requirements, the appropriate raw materials and treatment processes can be chosen to prepare nanocellulose membranes with different properties. This study provides a simple and low-cost way to prepare high-performance environment-friendly self-assembled nano membrane material, and also achieves the high value utilization of waste paper, which has a certain ecological, economic, and social benefits.

Investigation on the synthesis conditions of poly(4-methyl-1-pentene) hollow fiber membrane with high gas permeability and strong tensile strength

Investigation on the synthesis conditions of poly(4-methyl-1-pentene) hollow fiber membrane with high gas permeability and strong tensile strength

Vapor-phase reduction synthesis of N, S co-doped graphene/MWCNT hybrid membrane for all-solid-state supercapacitors and adsorption of organic pollutants

Owing to the limited reserves of fossil fuels, many researchers are focused on seeking advanced materials to relieve the drawbacks caused by the imbalance between the supply and demand of fossil fuels. In this study, a N, S co-doped graphene/multi-walled carbon nanotubes hybrid membrane (GMHE) was synthesized by flow-directed assembly followed by vapor-phase reduction. The resulting hybrid membrane not only exhibited excellent capacitance performance, but also good adsorption capacity for organic pollutants owing to its high electrochemical activity, well-developed pore structure, and rich surface state. The assembled GMHE all-solid-state symmetric supercapacitor delivered a high power density of 6000 W·kg−1 at an energy density of 16.0 W·h·kg−1 and superior capacitance stability (retaining 97.2 % of its initial capacitance value at 3 A·g−1). The adsorption capacity of the GMHE for organic pollutants was 50 times (chlorobenzene) its own mass. In addition, the hybrid membrane exhibited remarkable reusability over in adsorption–combustion cycles. The judiciously designed bifunctional membrane material developed herein can be directly applied in energy storage and oil pollution cleanup, supporting sustainable economic development.

Mapping the evolution of seawater desalination research (2000–2024): Bibliometric and co-word analysis of 11,000+ publications

Seawater desalination (SWD) can partially mitigate the increasing freshwater needs globally. Although, SWD is multifaceted and involves processes with environmental and economic challenges, research is often analyzed through Literature Reviews (LRs) in specific contexts that may miss general trends. Bibliometric Analyzes (BAs), however, provide researchers with an overview through Co-occurrence Networks (CNs), Strategic Diagrams (SDs), Thematic Subnetworks (TSs), and Thematic Evolution Diagrams (TEDs). Nevertheless, their use in SWD research has been limited, with minimal attention given to them. Thus, we created a bibliometric dataset, compared it with other BAs, and developed CNs, SDs, TSs, and a TED for SWD. Furthermore, key term searches (Energy, Solar, Reverse Osmosis, Modeling and Optimization, Membrane Distillation, Environmental, Economics, Fouling, Nanofiltration, and Ultrafiltration) and their literature are discussed. Geographical analysis shows China and the US lead SWD research, shifting from process design to membrane fabrication and solar energy. Furthermore, RO remains the leading technique despite high energy demands. Solar desalination shows promise but faces cost and scalability challenges. Environmental and economic concerns are discussed, as well as emerging solutions regarding, solar desalination, blue energy, “blue carbon”, and zero liquid discharge. Research gaps include fouling effects and pretreatment incorporation in optimizations are also highlighted.

Bis-tris-based polyester nanofiltration membranes fabricated via one-step interfacial polymerization for desalination

To obtain high-performance polyester (PE) nanofiltration (NF) membranes for desalination, most PE NF membranes are fabricated with high aqueous monomer concentration, or high reaction temperature, or long reaction time. The interfacial polymerization (IP) reaction rate between hydroxyl groups and acyl chloride groups is promoted but the cost of membrane fabrication is also increased. In this work, Bis-tris (bis(2-hydroxyethyl)-amino-tris(hydroxymethyl)methane) with rich hydroxyl groups is first utilized as an aqueous monomer to fabricate PE membranes under conventional IP conditions. The fabricated Bis-tris PE membranes feature strong hydrophilicity, excellent electronegativity, and ultra-thin selective layers, which are conducive to improving desalination performance. The optimized Bis-tris PE membrane shows excellent water permeance of 22.5 L m−2 h−1 bar−1 and a satisfactory Na2SO4 rejection of 96.9 %. Additionally, the Bis-tris PE membrane displays superior long-term stability and chlorine resistance under 96 h cross-flow filtration. This research enlightens the promising potential of Bis-tris as a novel and economic aqueous monomer for the fabrication of high-performance PE NF membranes.

Assembly-Dissociation-Reconstruction Synthesis of Covalent Organic Framework Membranes with High Continuity for Efficient CO2 Separation.

Covalent organic frameworks (COFs), at the forefront of porous materials, hold tremendous potential in membrane separation; however, achieving high continuity in COF membranes remains crucial for efficient gas separation. Here, we present a unique approach termed assembly-dissociation-reconstruction for fabricating COF membranes tailored for CO2/N2 separation. A parent COF is designed from two-node aldehyde and three-node amine monomers and dissociated to high-aspect-ratio nanosheets. Subsequently, COF nanosheets are orderly reconstructed into a crack-free membrane by surface reaction under water evaporation. The membrane exhibits high crystallinity, open pores and a strong affinity for CO2 adsorption over N2, resulting in CO2 permeance exceeding 1060 GPU and CO2/N2 selectivity surpassing 30.6. The efficacy of this strategy offers valuable guidance for the precise fabrication of gas-separation membranes.

Fabrication and performance evaluation of an innovative asymmetric polyethersulfone composite membrane for efficient methyl blue filtration

AbstractGiven the toxicity of wastewater pollutants to both humans and the environment, it is critical to develop a new synthetic membrane with superior permeability and rejection. Herein, a novel asymmetric polyethersulfone (PES) composite filtration membrane was successfully prepared using a simple alternating vacuum‐deposition process with positively charged chitosan and negatively charged cellulose nanofibrils as polycations and polyanions, respectively. As expected, the produced PES composite filtration membranes had a compressed and negatively charged surface, which prevented the anionic dye methyl blue (MB) molecules from infiltrating into the membrane matrix. Consequently, the resulting PES composite filtration membranes exhibited an extremely high MB rejection (99.7%) and a satisfactory flux (37.47 L h−1 m−2 MPa−1). In addition, the composite membrane demonstrated extremely selective removal of anionic dyes in the presence of neutral dyes due to the Donnan effect. Furthermore, the developed PES composite filtration membranes displayed exceptional long‐term stability (99.8% rejection and 36.5 L h−1 m−2 MPa−1 flux after 50 h of filtration) and recycling properties (90.1% flux recovery rate after 3 cycles of running). In conclusion, the PES composite filtration membranes prepared in this study presented great potential in wastewater filtering.