Membrane Separation Research Articles

Multifunctional membranes with super-wetting interface and in-situ Fenton-like sites for efficient oil-in-water emulsion separation

The surge in oil-in-water (O/W) emulsions poses a threat to the ecological environment. Membrane separation technology can achieve complete O/W emulsion separation through size sieving; however, its efficiency is limited by membrane fouling. In this study, an efficient O/W separation membrane with passive and positive anti-fouling properties was fabricated using Fe3O4 functionalized attapulgite (ATP) nanofibers. The anti-fouling mechanism of the multifunctional membranes for the separation of various O/W emulsions was studied. During separation process, a hydration layer, which mitigates oil adhesion with binding energy as low as −169 kcal·mol−1, forms on the interface of Fe3O4-ATP. When a cationic surfactant is present, positively charged oil droplets are attracted to the membrane surface, where they compress against each other, leading to demulsification and escape. Synergistic effects including electrostatic shielding, interaction energy, and steric hindrance were demonstrated through characterization and simulation. Our findings showed that the membrane exhibited a high filtration efficiency with an oil rejection of over 99 % and a steady flux of over 73 % of its initial value. After filtration, oil fouling degraded into smaller sizes and escaped from the membrane structure through the Fenton-like catalytic function of Fe3O4, resulting in a flux recovery ratio of up to 90 %. This study provides a reference for the construction of multifunctional membranes for efficient separation processes and advancing anti-fouling research on membrane interfaces.

Bioinspired hierarchical and dual-morphology humic-acid/pectin/chitosan composite aerogels for efficient removal of pollutants from wastewater

How to solve the contradiction between the efficiency and adsorption rate of porous materials in adsorbing pollutants has always been one of the focus issues. In this study, the small landscape cypress trees structure like biomimetic of a hierarchical and dual morphology 3D porous HA-based aerogel was designed and synthesized to use humic acid (HA), pectin (PE) and chitosan (CTS) as raw materials, which it was formed by the disorderly overlapping of lamella composed of fiber networks in 3D space. Due to its special microstructure, it can be used like separation membrane, which allowing for rapid adsorption of pollutants in the water while the water flow passes through quick. In general, this work provides a new concept for owning fast adsorption rate and efficient adsorption of porous materials of preparation to use green method.

Construction of multiple interpenetrati ng network electric field-assisted healing hydrogel composite damage-resistant membrane

Inspired by the intrinsic self-healing ability of organisms, this study proposes to incorporate healing properties into separation membranes that are susceptible to physical damage during installation, operation, maintenance, and cleaning. The polyacrylic acid (PAA) hydrogel-modified layer was first obtained by in situ cross-linking and free radical polymerization in this research. After that, the construction of multiple interpenetrating three-dimensional (3D) network hydrogel-modified layers was realized via inserting amininated carbon nanotubes (CNTs-NH2) and Fe3+. Under the external effect of the electric field, the reversible dynamic linkage bonded in the conductive network constructed by CNTs-NH2 and Fe3+ benefited the rearrangement and diffusion of PAA molecular chains at the fractured interface. The dye separation performance of the composite membrane was restored to ca. 90 % of the initial level without affecting the dynamic operation after damage. The hydrogel-modified layer can be structurally stabilized for as long as 100 days. The Fe3+/CNTs-NH2/PAA/PES hydrogel composite membrane maintained a pure water flux of as high as 124.66 L m−2 h−1∙bar−1. This coating also exhibited excellent electrical conductivity (714.33 Ω/sq), mechanical strength (4.31 Mpa), repair, and screening capabilities. It provides a theoretical basis for achieving industrial scale-up and demonstrates good application prospects and empowerment potential.

Uncovering the membrane and pore formation mechanisms of the lysozyme membrane made via the amyloid-like assembly

Biomimetic protein membranes have attracted increasing interests because of their distinctive separation properties in the membrane field. Low-cost and stable protein lysozyme has been intensively invetigated to fabricate high-performance sepration membranes via a facile and scalable method of amyloid-like assembly. However, the pore formation mechnism of the lysozyme membrane remains unclear. Herein, the lysozyme membranes were fabricated and the membrane formation mechnism and separation properties were investigated experimentally. Molecular dynamics simulation (MDS) was also employed to reveal the pore formation mechanism of the lysozyme membrane. The fabricated lysozyme membrane achieved a stable high water permeance of 10.2 L m−2 h−1 bar−1, as well as a relatively high separation factor (9.5) towards antibiotic and sodium chloride. MDS results found that the membrane pore size is governed by the amino acid compositions and is negatively dependent on the intermolecular forces among amino acids around the pores. Selective pores with 0.54 nm in diameter are primarily formed by these amino acids including alanine (35 %), aspartic acid (25 %), arginine (15 %), phenylalanine (11 %), and lysine (7 %), in which half of them have hydrophobic side chains with no charge, and another half have hydrophilic side chains with balanced charges. This work may stimulate the development of highly permeable and selective protein membranes by carefully engineering their amino acid compositions with optimal charges and hydrophobicity for generation of numerous selective pores.

Smart anti‐fouling and self‐repairing polymer brushes for efficient oil–water separation

AbstractThe increasing water pollution problem poses a demand for oil–water separation materials, but preparing separation materials with high efficiency and excellent durability remains a great challenge. In this work, we use a diblock polymer brush of polydimethylsiloxane (PDMS) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) based on cotton fabric to prepare oil–water separation membranes with high efficiency, good durability, and intelligent self‐repairing properties. Lubricating PDMS brushes reduces the fouling adhesion due to its low surface energy and high flexibility. pH‐responsive PDMAEMA brushes provide good hydrophobicity and an intelligent self‐repairing effect. The prepared Co‐PDMS‐PDMAEMA has high oil flux (>30,000 L m−2 h−1) and high separation efficiency (>99%) even after 10 cycles and its surface character can be recovered under acidic conditions. Overall, the modified cotton fabric made by such a versatile technique is promising in oil–water separation.

High-Performance Crown Ether-Modified Membranes for Selective Lithium Recovery from High Na+ and Mg2+ Brines Using Electrodialysis

The challenge of efficiently extracting Li+ from brines with high Na+ or Mg2+ concentrations has led to extensive research on developing highly selective separation membranes for electrodialysis. Various studies have demonstrated that nanofiltration membranes or adsorbents modified with crown ethers (CEs) such as 2-OH-12-crown-4-ether (12CE), 2-OH-18-crown-6-ether (18CE), and 2-OH-15-crown-5-ether (15CE) show selectivity for Li+ in brines. This study aims to develop high-performance cation exchange membranes (CEMs) using CEs to enhance Li+ selectivity and to compare the performance of various CE-modified membranes for selective electrodialysis. The novel CEM (CR671) was modified with 12CE, 18CE, and 15CE to identify the optimal CE for efficient Li+ recovery during brine electrodialysis. The modification process included polydopamine (PDA) treatment and the deposition of polyethyleneimine (PEI) complexes with the different CEs via hydrogen bonding. Interfacial polymerization with 1,3,5-benzenetricarbonyl trichloride-crosslinked PEI was used to create specific channels for Li+ transport within the modified membranes (12CE/CR671, 15CE/CR671, and 18CE/CR671). The successful application of CE coatings and Li+ selectivity of the modified membranes were verified through Fourier-transform infrared spectroscopy, zeta-potential measurements, and electrochemical impedance spectroscopy. Bench-scale electrodialysis tests showed significant improvements in permselectivity and Li+ flux for all three modified membranes. In brines with high Na+ and Mg2+ concentrations, the 15CE/CR671 membrane demonstrated more significant improvements in permselectivity compared to the 12CE/CR671 (3.3-fold and 1.7-fold) and the 18CE/CR671 (2.4-fold and 2.6-fold) membranes at current densities of 2.3 mA/cm2 and 2.2 mA/cm2, respectively. At higher current densities of 14.7 mA/cm2 in Mg2+-rich brine and 15.9 mA/cm2 in Na+-rich brine, the 15CE/CR671 membrane showed greater improvements in Li+ flux, approximately 2.1-fold and 2.3-fold, and 3.2-fold and 3.4-fold compared to the 12CE/CR671 and 18CE/CR671 membranes. This study underscores the superior performance of 15CE-modified membranes for efficient Li+ recovery with low energy demand and offers valuable insights for advancing electrodialysis processes in challenging brine environments.

Novel mixed matrix membranes containing calixarene for enhanced CO2/N2 separation

Calixarene possessing advantages of small intrinsic cavity size, small particle dimension, and facile dispersion or dissolution in common solvents, is promising filler candidates in mixed matrix membranes (MMMs) for gas separation. Herein, the supramolecular C-propylpyrogallol[4]arene (PgC3) was successfully synthesized via a phenolic resin condensation reaction. It was then incorporated into a polyether-polyamide block copolymer (Pebax-1657) to prepare mixed matrix membranes (MMMs) with varying PgC3 loadings for CO2/N2 separation. The formation of hydrogen bonds between PgC3 and Pebax facilitated the uniform dispersion of PgC3 within the polymer matrix, enhancing interfacial compatibility. The incorporation of PgC3 significantly enhanced the CO2/N2 selectivity of the Pebax while preserving its permeability. The 1 wt% PgC3/Pebax MMMs performs the best CO2/N2 selectivity of 58.6, substantially higher than that of pristine Pebax membrane (32.4). This improvement can be attributed to the strong affinity between the abundant –OH groups in PgC3 and CO2 molecules. Moreover, the PgC3/Pebax MMMs exhibited exceptional stability under operating pressures of up to 5 bar, maintaining its performance consistently throughout a demanding100-hour test. The good separation performance together with the excellent stability enables PgC3 a promising filler in MMMs for CO2/N2 or other gas separations.

Study of interfacial competitive distribution and synergistic permeation in nanofiltration separation of Salvia divinorum acids from the aqueous extract

The contact between solution and membrane during nanofiltration separation produces the interfacial layer fluid, and the competitive distribution laws of solutes in the interfacial layer are difficult to be analyzed, giving rise to diversified separation results that are challenging to explain using traditional nanofiltration separation theory. Four Salvia divinorum phenolic acid components—sodium salvinorin, protocatechuic aldehyde, rosmarinic acid, and salvianolic acid B—which have gradient relative molecular masses and dissociation constants, were selected as the objects of study. The nanofiltration separation parameters, such as membrane flux and permeation rate of the Salvia divinorum phenolic acids and their variability with the monomer solution under the complex solution environment were systematically analyzed. Based on the correlation between the concentration of the interfacial layer and the initial concentration, membrane flux and mass transfer coefficient in the theory of concentration polarization, the concentration of the interfacial layer of the nanofiltration membrane was calculated. This was combined with the state of association characterized by the distribution of particle sizes in the solution, the research model based on the ‘Associative State-Interfacial Competition-Separation Behavior’ was constructed, and the competitive and synergistic membrane separation regulations of the constituents of salvia phenolic acids were clarified. In acidic solutions, van der Waals forces dominate the interfacial competition, and of the four phenolic acids, salvinorin acid B diffused most easily to the membrane surface, showing that the component with the larger relative molecular mass inhibited the penetration of the smaller component; In alkaline solution, Coulomb force and Van der Waals force together dominate the interfacial competition, and the more acidic sodium salvinorin, etc., would preferentially react with hydroxide. At the same time, combined with the feature that the more molecular states in the particle size distribution of the solution are more likely to form aggregates, it was proven that the dissociation of protocatechuic acid aldehyde was inhibited, and its molecular state was more complete. It was shown that the more acidic sodium salvinorin and others facilitated the less acidic protocatechuic aldehyde to pass through the membrane.

Adsorptive membrane separation for eco-friendly decontamination of chlorpyrifos via biochar-impregnated cellulose acetate mixed matrix membrane.

In this work, the phase inversion approach is used to synthesize a blended mixed matrix membrane from cellulose acetate polymer and sugarcane bagasse biochar. The experiments were carried out to estimate the extent of chlorpyrifos (CPS) pesticide removal. The results showed that the removal rate was more than 99% in making the filtered water suitable enough for domestic use. The physical and functional characteristics of the membranes, such as permeability, and contact angle were identified. The changes in the membrane characteristics were observed using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction both before and after the experimental trials. Experiments were conducted to assess not only the rejection characteristics of CPS, as a function feed concentration, but also the effect co-ions on the rejection used to analyze the composition both before and after filtration. The effects of initial CPS concentration, biochar loading, and co-ions on the membrane were investigated. The membranes showed contact angles between 70° and 97° and a permeability between 0.25 × 1010 m Pa-1 s-1 and 0.31 × 1010 m Pa-1 s-1. The effective removal of CPS from the contaminated aqueous stream was attributed to a combination of adsorptive uptake and membrane-based separation. CPS was found to get adsorbed onto the membrane matrix through an intraparticle diffusion mechanism along with an irreversible monolayer adsorption. The membrane-solute adsorptive interaction was represented by Langmuir isotherm and intraparticle diffusion models with a maximum adsorption capacity of 192.3 mg g-1. The findings indicated the efficacy of biochar-cellulose acetate mixed matrix membrane for sustainable and eco-friendly treatment of chlorpyrifoscontaminated water.

Surface functionalization of cellulose derived from hemp by tetraethyl orthosilicate (TEOS) and poly vinylidene fluoride (PVDF)-based composite separator membrane for lithium-ion batteries (LIBs)

Separators play a crucial role in enhancing the electrochemical performance of lithium-ion batteries (LIBs). However, achieving separators with exceptional electrochemical performance and high stability remains a significant challenge. In this study, we meticulously designed composite membranes based on polyvinylidene fluoride (PVDF) with varying contents of microcrystalline cellulose/tetraethyl orthosilicate (MCC/TEOS). The increase in hydrophilicity of PVDF by adding MCC-TEOS weight contents endowed the 3 wt% MCC/TEOS-based PVDF separator membrane with superior electrolyte absorption and reduced resistance, resulting in an impressive ionic conductivity of 0.514 mS/cm higher than the pristine PVDF membrane (0.253 mS/cm). Furthermore, the LIB cell utilizing the 3 wt % MCC/TEOS-based PVDF separator membrane consistently demonstrated stable charge/discharge profiles at a rate of 0.2C, achieving a specific capacity of 98 mAh/g, compared to only 43 mAh/g for the pristine PVDF membrane. These findings underscore the significant potential of MCC/TEOS as a biofiller for bio-membranes, making it an optimal choice for applications in LIBs.

Superhydrophobic microporous membrane based on modified microfibrillated cellulose framework for efficient oil-water separation

The preparation of stable and efficient cellulose-based oil/water separation membranes is of great significance in solving the problem of industrial oily wastewater. Herein, rod-like hydroxyapatite (HAP) modified microfibrillated celluloses (MFCs) are used to form the fibrous framework to produce a microporous PDMS-MFC-HAP membrane. The membrane shows good superhydrophobicity with a water contact angle of 151.6°. It exhibits the oil-water separation performance for various water-in-oil emulsions. The separation flux of the membrane is up to 3665.3 L·m−2·h−1·bar−1 under 0.5 bar pressure with a separation efficiency of over 99.6 %. The PDMS-MFC-HAP membrane could maintain a high separation efficiency of 98.6 % after 20 cycles. This study provides a simple and effective method to fabricate cellulose-based superhydrophobic membranes, which have a greater potential to achieve oil-water separation for oily wastewater treatment with high efficiency.

HYDROGEN GAS RECOVERY THROUGH THE PERMEATION MEMBRANE BASED BIMETALLIC PALLADIUM ALLOY

Generally, the H2 gas produced from the industrial processes is not in a pure state but is mixed with other compounds. For example, the off-gas produced in the oil refinery process still contains CH4, H2, and other gases. Thus, the process of separating as well as recovering the valuable H2 gas from other gas compounds is of essential process. Currently, the H2 separation process is being developed with relatively low costs with good efficiency, namely using the permeation membranes separation process, in which the compounds with high permeability tends to be more easily separated. Here we report the hydrogen recovery process from the mixed H2/N2 off-gas contains 61 % hydrogen and 39% balancing nitrogen, by using the bimetallic Pd-Ag membrane, where the effect of the gas feed pressure (1 and 2 bar) and operating temperature (373.15, 423.15, 473.15, and 523.15, 573.15 K) on the resulting permeate flux is comprehensively studied. We found that the flux and permeability increased with the increase in the gas feed pressure and temperature. Under the same gas temperature of 373.15 K, the permeation flux at the 2 bar gas feed pressure was found to be 2.047 mol.s-1.m-2, which was 166% greater than that of 1 bar pressure, i.e. 1.204 mol.s-1.m-2. Meanwhile, under the same gas feed pressure of 2 bar, the permeation flux at the operating temperature of 573.15 K was found to be 2.103 mol.s-1.m-2, which is 104,9% greater than that of 373.15 K operating temperature, i.e. 2.047 mol.s-1.m-2. These findings suggest the breakthrough advantages of the Pd-Ag alloy membrane for its high hydrogen permeability at low pressure.

Preparation and regulation of high-strength and high-permeability porous ceramic/PDMS composite membranes for gas-liquid separation

Methane detection is crucial in identifying combustible ice within the energy sector. The gas–liquid separation membrane, a key component of methane sensors, plays a critical role in effectively separating methane and water. It significantly enhances the efficiency and stability of detecting methane concentration in situ. However, the related permeability and mechanical property present conflicting requirements in order to achieve optimal membrane performance. This work proposes an investigation into the mass transfer performance of a high-strength composite membrane, utilizing PDMS as the functional layer and porous ceramics as the supporting layer. By adjusting the pore distribution of the porous ceramics, particularly through the use of spherical graphite as a porogen, the study examines the impact of spherical graphite (SG) on the support layer’s morphology and its ability to regulate pore structure. Results indicate that incorporating spherical graphite with a porogen content of 10 wt% and a particle size of 25 μm enhances connections between ceramic grains, resulting in a flexural strength of 56.36 MPa and a permeability coefficient of 1861.57 barrer. This configuration demonstrates good waterproof and breathable performance. Overall, this research presents a novel approach for fabricating methane-water separation membranes, offering valuable insights for underwater methane detection efforts.

Polydopamine-assisted minute fabrication of vertically aligned ZIF-L membranes for CO2/N2 separations

Metal-organic framework (MOF) membranes demonstrate significant potential for industrial gas separations, yet fabricating vertically aligned two-dimensional (2D) MOF membranes on polymer substrates remains a considerable challenge due to the weak adhesion and difficulty in achieving precise alignment. This study presents a one-step method for the rapid synthesis of vertically aligned ZIF-L membranes, using a polydopamine (PDA)-assisted approach. This method enables the rapid formation of homogenous, thin but defect-free membranes on polymer substrates within 5 min, drastically reducing the preparation time by over 200 times. The vertically aligned ZIF-L membranes, characterized by the interlayer galleries facing the gas mixtures, exhibit an excellent CO2 permeance exceeding 1200 GPU and a CO2/N2 selectivity of 14.5. The versatility of this approach allows for its application on various flat-sheet or even hollow fiber supports. Our findings highlight the potential of PDA-assisted synthesis for efficient, scalable preparation of high-performance MOF membranes for industrial gas separations.

Biogenic formation of amorphous carbon in anaerobic digestion: Discovery and regulation with exogenous CO2 and zero valent iron

Anaerobic digestion (AD), a pivotal technology for organic waste reduction and biogas production, has recently gained notable attention for its role in CO2 bioconversion. As membrane separation technologies mature, methane separated from biogas is integrated into natural gas grid, while CO2 can be recycled back into AD reactors, promoting methane production. However, the biogenic formation of amorphous carbon from CO2 in AD is scarcely reported. This study confirmed the presence of amorphous carbon in AD and successfully regulated its growth via exogenous CO2 and zero valent scrap iron (ZVSI), proposing a potential method for CO2 fixation in AD. The results indicated that ZVSI promoted amorphous carbon formation, further boosted by CO2 introduction. Reactors with 80 g/L ZVSI exhibited a 31.4 % increase in amorphous carbon content compared to the control. Concurrently, methane production was also enhanced, with reactors containing 40 g/L ZVSI marking an increase between 9.6 % and 29.8 % over the control. This was attributed to the introduced inorganic carbon, which was further enhanced by the electron donors. Isotopic tracing revealed that the majority of the introduced inorganic carbon was channeled into methane, while a portion formed amorphous carbon. An in-depth microbial community analysis associated potential methanogens (Methanobacteriales, Methanosarcinales, and Methanomicrobiales) with the biogenic formation of amorphous carbon. A potential formation pathway of amorphous carbon was proposed according to metagenomic sequencing analysis. Based on the concept of low carbon, this study breathes new life into traditional anaerobic digestion and also identifies novel pathways for biological CO2 fixation.

Low-crystallinity ZIF-8/dcIm membranes for CO2 sieving

Metal-organic framework membranes have shown great potential for efficient separation applications. However, unavoidable grain boundary defects and the inconstant pore size due to framework flexibility hinder the application of MOF membranes for gas separation. Herein, low-crystallinity ZIF-8/dcIm-x membranes are synthesized via fast current-driven synthesis. The competitive coordination of 4,5-dichloroimidazole (dcIm) linker leads to the formation of a low-crystallinity MOF with reduced grain boundary defects for better gas separation performance. Meanwhile, the in-situ substitution of the mIm linker by dcIm narrows the pore size and transforms the ZIF-8 structure in the stiffened Cm polymorph, allowing precise CO2 sieving. Consequently, the low-crystallinity ZIF-8/dcIm-14 membrane exhibits a promising CO2/CH4 selectivity of 32.4 with a CO2 permeance of 1.73 × 10−8 mol m−2 s−1 Pa−1, which surpasses other membranes. Furthermore, the membrane presents a remarkable pressure resistance up to 3 bar and stable temperature-swing operation between room temperature and 125 °C over 120 h.

Hierarchical and defect-free metal-organic framework membranes deep-rooted within flexible nanofiber substrate

Defect-free MOFs membrane on flexible substrate is challenging and promising for industrial applications. In this work, electrospun nanofiber substrates were employed to construct deep-rooted and defect-free ZIF-8 membranes by a symbiotic layer composed of interpenetrated nanofibers and ZIF-8. Nanofibers provide sufficient nucleation sites to construct an interpenetrated “symbiotic layer”, which further supports ZIF-8 growing to be defect-free. Importantly, benefiting from this symbiotic layer, the rigidity difference between substrate and ZIF-8 is well balanced, resulting in ZIF-8 membrane deep-rooted within the support. Furthermore, tannic acid (TA), was combined to modulate the surface chemistry and inter-crystalline defects of ZIF-8 membranes. Finally, a hierarchical ZIF-8 membrane with nanofibers as flexible substrates were obtained. The prepared PAN/TA2-NZIF-80.25 membrane exhibits H2 permeance of 2408 GPU and H2/CO2 selectivity of 21.80. Specifically, compared with the reported MOFs membrane for H2 separation, the H2 permeance of this work locates in a very high region, while proper H2/CO2 separation factor is still remained, exceeding the 2008 upper bound of H2/CO2 separation. Importantly, this membrane presents stable microstructures and separation performance after twisting. The proposed deep-rooted and defect-free ZIF-8 membrane on flexible substrate is competitive to achieve industrial application.

Ionic nanoporous membranes from self-assembled liquid crystalline brush-like imidazolium triblock copolymers.

There is a need to generate mechanically and thermally robust ionic nanoporous membranes for separation and fuel cell applications. Herein, we report a general approach to the preparation of ionic nanoporous membranes through custom synthesis, self-assembly, and subsequent chemical manipulations of ionic brush block copolymers. We synthesized polynorbornene-based triblock copolymers containing imidazolium cations balanced by counter anions in the central block, side-chain liquid crystalline units, and sidechain polylactide end blocks. This unique platform comprises: (1) imidazolium/bis(trifluoromethanesulfonyl)imide (TFSI) as the middle block, which has an excellent ion-exchange ability, (2) cyanobiphenyl liquid crystalline end block, a sterically hindered hydrophobic segment, which is chemically stable and immune to hydroxide attack, (3) polylactide brush-like units on the other end block that is easily etched under mild alkaline conditions and (4) a polynorbornene backbone, a lightly crosslinked system that offers mechanical robustness. These membranes retain their morphology before and after backbone crosslinking as well as etching of polylactide sidechains. The ion exchange performance and dimensional stability of these membranes were investigated by water uptake capability and swelling ratio. Moreover, the length of the carbon spacer in the imidazolium/TFSI central block moiety endowed the membrane with improved ionic conductivity. The ionic nanoporous materials are unusual due to their singular thermal, mechanical, alkaline stability and ion transport properties. Applications of these materials include electrochemical actuators, solid-state ionic nanochannel biosensors, and ion-conducting membranes.

How Can the Filler-Polymer Interaction in Mixed Matrix Membranes Be Enhanced?

Mixed matrix membranes (MMMs) constitute a type of molecular separation membranes in which a nanomaterial type filler is dispersed in a given polymer to enhance its selective permeation ability. The key issue in MMMs is the establishing of a proper filler-polymer interaction to avoid non-selective transport paths while increasing permeability but also to improve other membrane properties such as aging and plasticization. Along the pass years several strategies have been applied to enhance the physicochemical interaction between the fillers (e.g. silicas, zeolites, porous coordination polymers, carbonaceous materials, etc.) and the membrane polymers: increase of external surface area, priming, use of intrinsically more compatible fillers, in situ synthesis of filler, in situ polymerization, polymer side-chain modification and post-synthetic modification of filler.

Oxidation two-dimensional porous carbon membrane for efficient and precise separation of mixed dyes solution

In actual production, dye wastewater typically contains a mixture of two or more dyes. Therefore, developing efficient and precise separation techniques for mixed dyes solution is of great value but still faces great challenges. In this study, we prepared two-dimensional porous carbon sheets (PCS) using Ti3C2 as the precursor through halogenation etching technology. Subsequently, the PCS was oxidized with nitric acid at room temperature to obtain oxidized porous carbon sheets (OPCS). When mixed dyes solution RB/MO and RB/MB were screened using OPCS vacuum filtration self-assembled porous carbon membrane (OPCSM), the rejection rate for the larger dye RB was 99.9 %, while the permeation rates for the smaller dyes MO and MB were 91.0 % and 99.5 %, respectively. Notably, OPCSM also exhibited much higher water flux than the previously reported. The combination of high water flux and precise screening make OPCSM a highly promising membrane for the separation and reuse of mixed dyes.