Separation Performance Of Membranes Research Articles

Huge improved gas separation performance of carbon molecular sieve membrane by forming a double crosslinked polyimide precursor

A vital issue in searching for advanced gas separation membranes is understanding the precursor structure-gas separation properties of carbon molecular sieve (CMS) membranes. Here, we reported two crosslinked polyimides and used as CMS precursors, in which, the DCPI-4 is a double cross-linkable polyimide with 4 % triptycene triamine as a crosslinker (Type I) and COOH group that can be crosslinked at 350 °C by decarboxylation (Type II), whereas the DCPI-0 with COOH (Type II). After pyrolysis at 550 °C, the DCPI-4-CMS showed a higher SBET (812 vs 713 m2g-1), larger ultra-microporosity ratio (26.6 % vs 17.8 %), larger d-spacing (4.08 vs 3.94 Å), less graphitization (sp3/sp2 of 0.156 vs 0.118), 5.5 times higher CO2 permeability (7573 vs 1391 Barrer) and same CO2/CH4 selectivity (∼62) than DCPI-0-CMS. We consider this is due to the type I crosslinking enhances the rigidity of the polyimide backbone, and inhibits the collapse of micropores during the carbonization, which causes improved ultra-microporosity and ultra-micropore ratio that both enhances the gas diffusion and solubility coefficient as well activation energy difference of gas pairs. Conclusively, this double crosslinking method provides a good perspective for achieving CMS membranes with excellent gas separation performance.

Efficient separation of linear and mono-branched hexane isomers using large-area silicalite-1 membranes

Membrane-based hydrocarbon isomer separation is a promising and energy-saving alternative to distillation. For the first time, tubular silicalite-1 membranes with large areas of 180 cm2 were employed in this study to separate linear and mono-branched hexane isomers. The membrane had a thickness of around 8 μm and showed highly (h0h) orientation. In binary and ternary mixtures of n-hexane (n-C6), 2-methylpentane (2MP), and 3-methylpentane (3MP), the effects of temperature and partial pressure on the separation performance of silicalite-1 membrane were examined. Moreover, the long-term stability of the membrane in binary and ternary mixture separation was also investigated. The large-area membrane showed a n-C6 permeance of 2.4 × 10-8 mol/(m2 s Pa) and n-C6/2MP and n-C6/3MP separation factors of 36 and 74 in the ternary n-C6/2MP/3MP (2.8 kPa/2.9 kPa/2.8 kPa) mixture with N2 as the balanced gas at 100 kPa absolute and 303 K, respectively. The scaling-up membranes demonstrated good and stable separation performance during the long-term test, highlighting the effectiveness and potential application of using large-area silicalite-1 membranes for the separation of hexane isomer mixtures.

Construction of low-resistance nano-transport channels with UiO-66-(NH2)2 “transmembrane” in polyamide layer structure for efficient nanofiltration

Metal-organic frameworks (MOFs) is always a research hotspot as the modifier for fabrication of thin-film nanocomposite (TFN) membrane due to their excellent chemical tunability and suitable pore size. However, the traditional strategy for the involvement of MOFs into interfacial polymerization (IP) process has its limitations, as the addition of MOFs only serve to modulate the structure of the polyamide (PA) layer and to optimize the transport path of water molecules, rather than play an important role in selectively sieving solutes. To solve the problem that MOF embedded under the PA layer cannot directly participate in solute sieving, this study designed a “transmembrane” structure of MOF in the PA layer. Here, the feasibility of 1,3,5-Benzenetricarbonyl chloride modified UiO-66-(NH2)2 was verified based on Gibbs free energy calculations. By adding chlorinated UiO-66-(NH2)2 nanomaterials in the dual IP process, a high-throughput nanofiltration membrane was innovatively constructed. In contrast to conventional thin-film composite membrane prepared by only one IP process, the sieving mechanism no longer relied solely on the free volume of the PA chain segments. Instead, it was determined by the combination of the pore channels of UiO-66-(NH2)2 and the matrix gaps. Based on density functional theory (DFT), the calculated diffusion energy barriers of H2O and Na2SO4 in UiO-66-(NH2)2 and PA matrices reveal the reasons for the improvement of water flux and changes in retention rate of TFN membranes. In addition, the gap size between PA-MOFs was determined by comparing the solvation and de-solvation structures of dye molecules. This work provides a new theoretical basis for explaining the changes in the separation performance of TFN membranes, and offers new ideas for the development of novel TFN membrane structures.

Anti-fouling ternary zwitterionic coating membrane with strong surface hydration and salt resistant for efficient long-term emulsion separation in high salinity marine environment

Membrane separation has been acknowledged as an advanced technology to handle the oil spills. However, most of the superhydrophilic/underwater superhydrophobic membranes currently applied for oil/water separation would lose their superwettability when exposed to salty marine environments, leading to serious membrane plugging and separation performance deterioration. Herein, inspired by seawater fish and mussels, a simple, green, and versatile one-step co-deposition strategy is proposed for fabricating a ternary zwitterionic coating with strong surface hydration on diverse membranes, showing excellent anti-fouling properties in high salinity environments, even in the saturated NaCl solution. Moreover, the modified membrane performs well in the long term when separating surfactant-stabilized oil-in-seawater emulsion and with impressive recyclability. The ternary zwitterionic coating membrane exhibits great potential in treating oily wastewater in marine.

Constructing the electrostatic potential microenvironment in MMMs by poly(ionic liquid)s functionalized metal–organic frameworks for efficient CO2/CH4 separation

The construction of electrostatic potential microenvironment in MOF is an effective strategy to improve the separation performance of mixed matrix membranes (MMMs). Different functional groups of poly(ionic liquid)s (PIL-F, F=OH, COOH, NH2) are used to modify MOF to synthesize the PIL-F@MIL-101, which were incorporated into Pebax MH 1657 (Pebax) to prepare MMMs for CO2/CH4 separation. PIL-F@MIL-101 possess positive charge, and their order of positive charge is PIL-OH@MIL-101 > PIL-COOH@MIL-101 > PIL-NH2@MIL-101. The MMMs doped with 7.0 wt% PIL-OH@MIL-101 represented the optimal CO2 permeability of 1480.7 Barrer and CO2/CH4 selectivity of 35.2. The performance of Pebax/PIL-OH@MIL-101 approached the 2019 upper bound. It mainly considered to the following reasons: on one hand, the positively charged filler constructed the positively electrostatic potential microenvironment in MMMs, enhancing the electrostatic attraction with the negatively charged O atoms of CO2 and promoting the preferential transport of CO2. On the other hand, the positively electrostatic potential microenvironment in MMMs obstructs the transport of positively charged H atoms of CH4, improving the CO2/CH4 selectivity. The design on constructing electrostatic potential microenvironments in MMMs provides a promising strategy for efficient CO2 separation.

Biomimetic interlayer brought unexpected enhancement in permeability and rejection of polyamide nanofiltration membrane

Construction of interlayer between porous substrate and polyamide (PA) layer has been proved to be an effective way in improving membrane separation performance by the regulation of membrane structure and chemical properties. In present study, biomimetic material—1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) lipid bilayer was selected to serve as the interlayer prepared by suction filtration due to its unique advantages such as smooth, continuous, uniform and hydrophilic surface. The results showed that DOPE interlayer effectively lowered the diffusion rate of piperazine (PIP) from membrane surface to organic phase and thus contributing to the thinner and smoother PA layer. The permeability of the interlayer-based PA membrane reached 35.9 L/m2·h·bar, which was 190 % higher than pure PA NF membranes. More important, the interlayer-based PA membrane exhibited excellent Na2SO4 rejection about 99.8 % accompanied by a good separation selectivity between univalent and bivalent ions. Besides, the interlayer-based PA membrane possessed good stability to the changes of operating pressure, concentration and pH of feed solution, and the long-term NF test. Meanwhile, it performed well in removing NTU, TOC, Mg2+ and SO42− in the treatment of surface water and showed its potential in the practical application. In all, the present work brought new interlayer material in fabricating high-performance NF membrane.

Mixed-matrix membrane designed with water channels and sieving effect for effective removal of heavy metals

The challenge of eliminating heavy metal ions from water has been addressed using Polysulfone (PSf) membranes, which have demonstrated significant potential in treating contaminated solutions. This research aimed to improve the permeability and separation performance of PSf membranes by incorporating Al2SiO6 into their structure. The introduction of Al2SiO6 into the membrane matrix was achieved through the nonsolvent-induced phase separation (NIPS). The resulting mixed-matrix membrane (MMM) exhibited improved efficiency in water filtration. The inclusion of Al2SiO6 led to desirable changes in membrane properties such as hydrophilicity, contact angle and porosity, thereby enhancing the performance of heavy metal ion removal capability. Under a pressure of 2 bar, the mixed matrix membranes achieved rejections exceeding 95 % for lead and 70 % for arsenic. Furthermore, the occurrence of Al2SiO6 enhanced the anti-fouling assets of the PSf membrane by increasing its hydrophilic nature and facilitating the development of a hydration layer, which tends to prevent the interactions between the membrane surface and foulant. These properties make these membranes suitable candidates for separating toxic ions from water.

ZIF-8 membranes for efficient C3H6 recovery from the Hydrogen Peroxide to propylene oxide process

The ZIF-8 membrane has emerged as a promising candidate for C3H6/C3H8 separation. However, the feasibility of ZIF-8 membranes for applications has rarely been investigated with gas provided directly by the industry sector. Herein, the C3H6/C3H8 mixture collected from the backend of the Hydrogen Peroxide to Propylene Oxide (HPPO) process was applied as feed gas to examine the separation performance of tubular ZIF-8 membranes. The membranes exhibited excellent separation performance and long-term stability under 9 bar and 50 °C. Noticeably, upon scaling up to a membrane area of 452.16 cm2 by connecting six three-channel modules in series (multi-step membrane), its separation performance satisfied the C3H6 circulation requirements during the HPPO process (purity ≥97.5 % and recovery rate ≥85 %). Furthermore, a simulation of membrane operation under industrial working conditions (22 bar and 56.3 °C) was performed. By fixing the separation factor at 15, a minimum membrane area of 800 m2 met the requirements at the cost of membrane permeance with 120 GPU. The corresponding economic calculation indicated a maximum of 91.8 % annual capital cost saving compared with the distillation process, paving the way for the practical application of membranes.

Ionic liquid fluoropolymer membranes for the separation of R-410A: Understanding the effect of ionic liquid on membrane characteristics and separation performance

Environmental legislation such as the American Innovation and Manufacturing Act will phase out today's generation of high-global warming hydrofluorocarbon refrigerants over the next two decades. Energy-efficient technologies are needed to separate these often azeotropic and complex mixtures. Membrane technology and extractive distillation with ionic liquids as entrainers have been individually developed for the separation of azeotropic refrigerant mixtures. This study provides details for the separation of R-410A through combining the benefits of glassy, amorphous polymers with ionic liquids to form ionic liquid polymer membranes. Two different classes of ionic liquid polymer membranes are considered: polyvinyl acetate composite membranes with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, and 1-hexyl-3-methylimidazolium chloride, and Hyflon AD 60 with 1-ethyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide. The membranes are characterized with FTIR, helium pycnometry, differential scanning calorimetry, and a high-pressure view-cell to characterize the effect of ionic liquid on polymer properties. The Hyflon AD 60 composite membranes were evaluated for the separation of R-410A through pure-gas permeability, selectivity, solubility, and diffusivity measurements, which show exceptional selectivity for separation of R-410A. Results provide insights on the effect of ionic liquid on the separation of R-410A and indicate that improved separation performance of glassy polymers can be achieved with the addition of ionic liquid.

Carbon quantum dots (CQDs) incorporated dual-layer hollow fibers for pervaporative dehydration of ethanol

Pervaporative ethanol dehydration is a promising approach to concentrate ethanol from biofuel stocks. In this study, we have fabricated high performance dual-layer cellulose triacetate (CTA)/Ultem hollow fiber membranes incorporated with a small amount of superhydrophilic carbon quantum dots (CQDs) via the immiscibility induced phase separation (I2PS) method. The flow rates of the inner- and outer-layer dopes were firstly optimized. Subsequently, various small amounts of CQDs were added into the inner- and outer-layer dope solutions to explore their impacts on membrane structure and separation performance. It was found that the incorporation of a reasonably small amount of CQDs, whether to the inner or outer layer of I2PS membranes, could significantly enhance the mechanical properties and pervaporation performance by altering their structures. The most effective membrane containing 0.2 wt% CQD in the outer layer (0.2CQD_OL) demonstrated exceptional pervaporation performance. Using an 85 wt% ethanol feed solution, this membrane achieved a total flux of 4306 ± 130 g m−2h−1 (equivalent to a water permeance of 33.28 mol m−2h−1 kPa−1) and a water content of approximately 95 wt% (equivalent to a mole-based selectivity of 153) in the permeate over a 172 hr long-term test. A comparison with literature underscores the superior performance of this newly developed I2PS membrane, particularly in terms of water permeance. In summary, the CQD-embedded CTA/Ultem HF membranes demonstrate substantial potential for industrial applications in the pervaporative ethanol dehydration.

Fabrication of polydopamine/graphene oxide composite membranes for effective radionuclide removal

As the energy consumption surges in the past few decades, the utilization of reliable and cost-effective energy resources with minimum greenhouse gas emission is highly desirable, for which nuclear energy has gained intensive attention. The proper treatment of radioactive process water yet remains challenging, but is of vital importance due to its significant threats to environment and public health. In this work, a polydopamine/graphene oxide (PDA/GO) membrane was developed for radionuclide-contaminated water treatment. By the incorporation of PDA, the interlayer spacing of the GO membrane is regulated, as well as an improved anti-swelling property is achieved. At optimal preparation conditions, the PDA/GO has exhibited a high rejection of 99.9 % towards thorium ions with a satisfying water flux of 5.0 L·m−2h−1. Moreover, the influence of solution pH and thorium concentration on the membrane separation performance is studied. Results have indicated that the PDA/GO membrane presents a new promise for the treatment of radionuclide-contaminated water.

A high-performance TFN membrane prepared by a novel PE support layer, a polydopamine interlayer, and a doped MoS2 quantum dots@ZnO nanocomposites-incorporated polyamide active layer

Herein, thin film nanocomposite (TFN) membranes were prepared with excellent chemical stability and separation performance for organic solvent nanofiltration (OSN) applications. The support membrane was synthesized via a new approach, in which a blend of two immiscible polymers, i.e. high density polyethylene (HDPE)-polystyrene (PS), which were compatibilized with styrene-ethylene-butylene-styrene (SEBS), was prepared through mixing by a Brabender, followed by fabricating blend sheets through a hot press machine. The PE support was then prepared by extracting the PS/compatibilizer phase from the blend sheet. The hydrophilicity of the PE support membrane was considerably enhanced with a polydopamine (PDA) layer. Different nanoparticles including nanoflower (NF) ZnO, nanosphere (NS) ZnO, MoS2 Quantum dots-nanoflower ZnO nanocomposite (QDs@NF ZnO), and MoS2 Quantum dots-nanosphere ZnO nanocomposite (QDs@NS ZnO) were incorporated into the polyamide (PA) active layer of the membranes to enhance the performance of the TFN membranes. The separation performance of the TFN membranes was investigated for rejecting different dyes dissolved in methanol. Our results demonstrate outstanding separation performance, with a dye rejection of 99.6 %, 99.6 %, 99.8 %, and 99.9 % for methylene blue, crystal violet, rhodamine B, and methyl green, respectively. Additionally, the TFN membranes incorporated with QDs@NF ZnO nanoparticles showed great solvent resistance, with a methanol permeance up to 6.7 L/m2.h.bar after activation with dimethylformamide.

CFD simulation for CO2 separation using diamond-structured thermally rearranged (TR) polymer membrane: Effect of CO2 feed concentration, feed pressure and temperature

Abstract CO2 separation in natural gas purification is important in improving the properties of natural gas such as energy content, volume and corrosivity. Membrane separation using TR-450 polymer membrane is a potential approach to remove CO2 from natural gas efficiently. The study of CO2/CH4 binary gas mixture separation was simulated using a thermally-rearranged (TR) HAB- 6FDA membrane at 450 °C with a partial part of Schwarz Diamond structure because it exhibits advanced mechanical properties with low stiffness for relatively high strength. TR-450 membrane exhibits excellent separation performance that has the potential to exceed the Robeson plot 1991. Computational fluid dynamics (CFD) was used to simulate the fluid behavior within the geometry created using CAD software. The effect of feed pressure, temperature and CO2 feed concentration on the separation performance of TR-450 membrane was also studied. The results indicated that an increase in feed pressure leads to a decrease in CO2 recovery, hence the lower separation performance. It was also found that increasing the feed temperature leads to an increase in CO2 recovery. Concerning the concentration of CO2 in the feed, elevated levels impact the performance of membrane separation. The enhanced membrane separation performance demonstrated by the TR-450 membrane under various conditions underscores the necessity for additional investigation to unveil its potential in industrial gas separation applications.

Chitin-augmented wetting resistance and water-in-oil emulsion separation performance of silane-modified polyketone membrane

The utilization of membrane technology for separating water-in-oil (W/O) emulsions necessitates a membrane possessing high hydrophobic properties. However, the use of naturally hydrophobic membrane materials, such as polyvinylidene fluoride, is undesirable due to the persistence of fluorine-containing compounds in the environment. Polyketone (PK) membranes present a potential alternative, but their inherent hydrophilic properties can hinder the W/O emulsion separation process. To address this issue, hydrophobic modification of PK membranes can improve their performance in separating W/O emulsion. Natural hydrophobic materials like chitin offer a more sustainable alternative compared to synthetic materials. Chitin was introduced onto the membrane surface along with hexadecyltrimethoxysilane (HDTMS) subsequent to the initial reaction of the PK membrane with tetraethyl orthosilicate (TEOS). Comparative analysis revealed that the mixed chitin and HDTMS modification resulted in the lowest surface wettability compared to membrane modification using only TEOS, HDTMS, and chitin. Examination of membrane performance through toluene emulsion separation demonstrated increased permeability after modification, with permeate toluene purity over 99.8 %. Additionally, the chitin and silane-modified PK membrane exhibited a two-fold increase in filtration process permeability, indicating outstanding fouling resistance. These findings underscore the potential of natural compounds in imparting desired hydrophobic properties to membranes while minimizing reliance on synthetic materials.

Strategic small molecule engineering: Unleashing the full potential of Kevlar aramid membrane in organic solvent nanofiltration

Kevlar aramid fiber (KANF), renowned for its exceptional solvent resistance, holds immense potential in fabricating of solvent-resistant membranes. However, the well-ordered structure of its rigid polymeric chains, coupled with intense intermolecular forces, significantly impedes the transport of solvents. Here, we propose a methodology utilizing small molecule polyethylene glycol (PEG) to mediate an interlayer structural reconstruction of KANF membranes, thereby enhancing solvent permeation. PEG, functioning as a nanostructure regulator, effectively inhibits the diffusion of DMSO into non-solvents during the phase inversion process. This intervention results in the multi-directional polymerization of aramid nanofibers and the emergence of distinctive interconnected microporous structures between layers, which notably accelerates the transport speed of solvents within the membrane. Concurrently, preserving of the dense layer on the surface ensures superior separation performance for the KANF membranes. This research underscores the possibility of modulating the internal microstructure of KANF membranes and highlights the prospective utility of KANF-PEG membranes in the organic solvent nanofiltration field.

Influences of substrate pore size on the morphology and separation performance of MoS2-interlayered thin-film nanocomposite membranes

Recent studies reveal the enhancement in water permeability for thin-film nanocomposite (TFN) membranes that incorporate an interlayer (TFNi), mainly when developed using substrates with larger pores. Nevertheless, the impact of substrate pore size on the membrane's morphology and separation performance requires further exploration. The study systematically investigates how the pore size of polycarbonate track-etched (PCTE) substrates influences these factors. Findings suggest that larger pores lead to rougher membrane surfaces and higher water permeance by reducing hydraulic transport resistance. However, optimal performance on larger pores requires a thicker MoS2 interlayer, leading to a thinner polyamide layer. Specifically, on PCTE-200 substrates, the MoS2 interlayer made up of large MoS2 nanosheets creates a more tortuous path for water molecules, limiting permeance. Conversely, smaller pores than the MoS2 nanosheets' dimensions obstruct the storage and diffusion of PIP monomers, negatively affecting the polyamide film and salt rejection. These findings underscore the significance of choosing the suitable substrate and adjusting interlayer thickness for creating TFN membranes with desired separation characteristics. The study provides valuable insights into the role of substrate selection and interlayer thickness in TFNi membrane design, offering guidelines for developing high-performance membranes for various separation tasks.

Fluorinated ZIF-71 with adjusted pore size to enhance separation performance of mixed matrix membrane for recovering R32 from R410A

Due to the high Global Warming Potential (GWP) of hydrofluorocarbons (HFCs), the Kigali Amendment to the Montreal Protocol explicitly calls for the phase-out or limited use of HFCs, and the replacement of HFCs by hydrofluoroolefins (HFOs) is imminent. Therefore, it is particularly significant to develop new technology to separate valuable difluoromethane (R32, GWP = 675) from the near-azeotropic refrigerant blend R410A (GWP = 2088), because the traditional distillation is not applicable. In this work, aiming to enhance the separation performance of mixed matrix membrane (MMMs) for R410A, 5-fluorobenzimidazole was introduced into ZIF-71 by the solvent assisted linker exchange (SALE) method for the first time to reduce the pore size of fluorinated ZIF-71 by benzene rings and form hydrogen bonds between R32 with ZIF-71. A novel series of MMMs consisting of fluorinated ZIF-71 and Poly(ether-block-amide) ®1657 (Pebax®1657) polymer were prepared to separate the components of the R410A. The separation performance of the MMMs was investigated at different feed pressures and filler loading. The results showed that the introduction of 5-fluorobenzimidazole contributed to a significant increase in R32 permeability and R32/R125 selectivity of the MMMs compared to pure Pebax membrane. The 15 wt% ZIF-71-F/Pebax MMM showed the best separation performance with R32/R125 selectivity up to 26.6, four times that of pure Pebax membrane and twice that of ZIF-71/Pebax MMM. The ZIF-71-F/Pebax MMM have outstanding data on R32/R125 selectivity and no significant disadvantage in permeability, far exceeding the reported separation performance of membranes for R410A. This confirms that the application of fluorinated metal organic frameworks (MOFs) to the separation of refrigerant blends is a promising strategy.

A photocatalyst coupled amphiphobic membrane with enhanced antifouling and self-regenerating properties for oily aerosol filtration

Oily aerosols as the most adhesive particles in the air can cause irreversible fouling of filters. Amphiphobic surface of filters can to some extent reduce membrane fouling, but complex oil fouling will still adhere to the membrane surface, leading to a decrease in membrane separation performance over long-term use. Herein, a silicon carbide (SiC) membrane with amphiphobic properties and catalytic functions was developed to collaboratively combat pollution. Low surface free energy 1H,1H,2H,2H perfluorooctyltrichlorosilane (FOTS) monomer and TiO2 nanoparticles were individually applied to the SiC membrane. PDMS was utilized to protect the monomer from degradation by the catalyst. The membrane exhibits good anti-adhesion and photocatalysis performance for oily aerosols. The membrane exhibits excellent oily aerosol filtration efficiency (98.6 %) with a comparative low filtration resistance of 6.4 kPa, as well as a high capacity for regeneration. Under UV light, the membrane can degrade oily fouling to recover its amphiphobic property. After 5 cycles of filtration, it still maintains good repeatability for oily matter separation and degradation. This study offers a practical approach to designing a membrane that enables long-term and efficient cleaning of oily aerosols.

Fabrication of hollow fiber composite membranes via opposite transmission reaction method for dye/salt separation

The separation layer prepared by the conventional coating-crosslinking method is typically thick and prone to forming defective macropores, significantly affecting the water permeability and dye/salt separation performance of membranes. This work presented a novel method to prepare hollow fiber composite membranes for dye/salt separation based on the opposite transmission reaction of crosslinker. In this method, the macromolecule in situ reacted with a small‐molecule crosslinker at the openings of membrane pore channels, forming a separation layer with discontinuous sheet-like and granular structure. Compared to the conventional forward coating-crosslinking method, the separation layer prepared by the opposite transmission reaction method exhibited an ultra-thin thickness of 29.1 nm. Consequently, the composite membrane exhibited a high water permeability of 72.7 L·m−2·h−1·bar−1, which was 2.3 times higher than that of conventional methods. Moreover, the prepared composite membrane presented a more uniformed pore structure, completely retaining the VBB (100%) with a low Na2SO4 rejection of 4.3%, demonstrating excellent dye/salt separation performance. Additionally, the prepared composite membrane exhibited superior anti-fouling properties compared to that prepared by the conventional method. Therefore, the opposite transmission reaction method proposed in this study held promising applications in the preparation of hollow fiber composite membranes for efficient dye/salt separation.

Polyoxometalates decoration combining with solvent activation for enhanced separation performance of nanofiltration membrane

Nanofiltraion (NF) membranes are promising candidates for overcoming critical global issues of access to clean water. However, current NF membranes are hampered by the trade-off between the water permeability and selectivity as well as the fouling propensity. In this work, a facile surface decoration simultaneously combined with solvent activation strategy was adopted for the NF membrane modification via simply immersing membrane into the polyoxometalates (POMs) ethanol solution. The introduction of POMs by coordination assembly increases the membrane hydrophilic and electronegativity, and the ethanol loosens the membrane selective layer, leading to the enhanced membrane perm-selectivity and anti-organic fouling property. The permeance and Na2SO4 rejection of the optimized modified NF membrane are 14.90 ± 0.21 LMH/bar and 99.20 ± 0.38 %, which are ∼20 % and more than 3 % increments compared with those of the control membrane, respectively. The modified NF also reveals a lower permeance decline as well as a higher flux recovery toward both positive and negative charged foulants. In addition, benefiting from the biocidal activity of the POMs, the membrane anti-biofouling property is also significantly improved under an extremely low loading of POMs. More importantly, the chemical stability of the modified NF membrane is reinforced due to the protection from the introduced POMs. Our work contributes to revitalizing the prospect of developing NF membranes with excellent filtration performance and antifouling property.