Membrane Material Research Articles

Facile fabrication of multifunctional superhydrophilic composite membranes for efficient oil-in-water emulsion separation

Numerous superwetting separation membranes have been designed for the management of oily wastewater due to their highly efficient oil/water separation efficiency. However, the long-term stability of these developed membranes is still restricted by membrane fouling. In this study, we synthesized multifunctional superhydrophilic membranes with superior anti-adhesive and anti-biofouling properties through simple co-deposition of dopamine, polyethyleneimine and CoFe2O4 (CFO) photocatalyst on the porous PVDF substrates for sustainable management of oil-in-water emulsion. The resultant optimal composite membranes showed the superhydropilicity with an underwater oil contact angle of 162.4° and achieved ca. 99.51 % oil/water separation efficiency with a maximum permeability of 232.2 L·m−2·h−1 in the treatment of oil-in-water emulsions driven by gravity. Moreover, the outstanding antibacterial performance of composite membrane was demonstrated by a nearly 100 % antibacterial rate during the exposure in 120-min visible light irradiation. Based on the synergistic effect of superhydrophilicity and photocatalysis, the fabricated composite membranes experienced a stable gravity-driven oil/water separation (oil rejection: >99.46 %) even after a 50-cycle filtration. Such an impressive filtration performance of the polydopamine/PEI/CFO composite membranes highlights their promising potential for sustainable and efficient treatment of oily wastewater.

Purification of Liquid Fraction of Digestates from Different Origins-Comparison of Polymeric and Ceramic Ultrafiltration Membranes Used for This Purpose.

Circular economy, clean technologies, and renewable energy are key to climate protection and modern environmental technology. Recovering water and valuable minerals from the liquid fraction of digestate is in line with this strategy. Digestate, a byproduct of anaerobic methane fermentation in biogas plants, is a potential source of water, minerals for fertilizers, and energy rather than waste. This study examined digestate from municipal and agricultural biogas plants and highlights the need for research on both due to their differences. The use of membrane techniques for water recovery from liquid digestate offers an innovative alternative to conventional methods. This study used standalone membrane filtration and an integrated system to produce water suitable for agricultural use. Ceramic membranes with cut-offs of 1, 5, 15, and 50 kDa and polymeric membranes of polyethersulfone and regenerated cellulose with cut-offs of 10 and 30 kDa were tested. The results showed that the membrane material significantly affects the transport and separation properties. Higher cut-off values increased permeate flux across all membranes. Ceramic membranes were more susceptible to fouling in standalone ultrafiltration, but were more effective in purifying digestate than polymeric membranes. The best results were obtained with a ceramic membrane with a 1 kDa cut-off (for example, for the integrated process and the municipal digestate, the retention rates of COD, BOD5 and DOC were 69%, 62%, and 75%, respectively).

Investigation on sulfonated PVC/polymethyl methacrylate (PMMA)/polystyrene sulfonate (PSS) polymer blends as proton-conducting membrane

AbstractThe design and development of cost-effective and increased methanol permeable and proton-conductive membranes are critical concerns in the fabrication of polymeric electrolyte membranes (PEM). A solution-casting process was used to create a low-cost PEM based on sulfonated polyvinyl chloride (SPVC)-Polymethyl methacrylate (PMMA) blended with varying concentrations of Poly(sodium 4-styrenesulfonate) (PSS). The contact angle, oxidative stability, swelling ratio, water uptake, and methanol uptake of SPVC/PMMA/PSS membranes were investigated as a function of PSS molar ratio. FT-IR examination, 1H NMR spectra, Raman spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), and scanning electron microscope micrographs were additionally utilized for confirming the chemical structure, morphology, and thermal stability of SPVC/PMMA/PSS membranes. Furthermore, the ion exchange capacity (IEC), proton conductivity, and methanol permeability of SPVC/PMMA/PSS membranes were investigated depending on the PSS concentration. The results showed a significant increase in proton conductivity from 1.80 × 10–2 for SPVC/PMMA/1%PSS to 4.7 × 10–2 S/cm for SPVC/PMMA/5%PSS at ambient temperature. On the other hand, the methanol permeability (P = 8.53 × 10–8 cm2/s) was noticeably lower than that of Nafion 117 (3.39 × 10–6 cm2/s). Additionally, the IEC of the manufactured membrane was 1.38 ± 0.7 meq g−1 for SPVC/PMMA/5%PSS compared to 0.91 meq g−1 for Nafion 117 membranes. The maximum water uptake of the synthesized membranes was 48.37 ± 2.27%, whereas Nafion 117 membrane absorption was 65.44%. According to conductivity studies and the membrane efficiency factor, the ideal PSS content in a polymer matrix is 4 wt.%. Finally, the developed SPVC/PMMA/PSS polyelectrolytic membranes show improvements in essential properties such as methanol permeability, proton conductivity, and IEC when combined with low-cost materials, making them an attractive contender as PEM for DMFCs. Graphical abstract

Polyelectrolyte-modified covalent organic framework membranes for multivalent cation removal

Covalent organic framework (COF) has become a promising membrane material in chemical separations. However, the application of COF membranes for ion separation is still challenging, due to the mismatch between the pore size of COFs (1–5 nm) with the diameter of hydrated ions (<1 nm). Herein, a cationic polyelectrolyte surface modification strategy of COF membranes was proposed, by assembling a cationic polyelectrolyte (PEI, PDDA, PAH) layer on the surface of an anionic COF (TpPa-SO3H) membrane via dip coating. The cationic polyelectrolytes on the membrane surface offered abundant positive charges and reduced the surface pore size, leading to the synergistic enhancement of the size sieving and the electrostatic repulsion. Accordingly, effective rejection of multivalent cations was realized with a significantly increased rejection rate of 97.1 % for MgCl2, compared to that of TpPa-SO3H membrane (10.3 %). Furthermore, the polyelectrolyte-modified COF membrane exhibited desirable separation performance for heavy metal ions in water. The rejection rates for heavy metal salts, including CrCl3, CdCl2, CuCl2, PbCl2 and NiCl2, reached 98.5 %, 97.3 %, 97.0 %, 96.2 %, and 96.0 %, respectively, and remained above 95 % during the 7-day long-term operation test.

Enhanced solar desalination with photothermal hydrophobic carbon nanotube-infused PVDF membranes in air-gap membrane distillation

This work aims to increase the efficiency of the solar powered-air gap membrane distillation (SP-AGMD) process; a desalination method driven by solar energy, providing an eco-friendly and sustainable approach to addressing global water shortages. The innovation lies in integrating photothermal hydrophobic multiwalled carbon nanotubes (h-MWCNTs), in varying weight percentages from 5 % to 60 %, into polyvinylidene fluoride (PVDF) membranes using the phase inversion membrane fabrication technique. The h-MWCNTs were synthesized through oxidation and functionalization with oleylamine (OL) to improve their photothermal properties. Their successful integration was confirmed via scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The h-MWCNTs-based SP-AGMD membranes were further evaluated for wettability, liquid entry pressure (LEP), surface temperature, and solar absorbance, demonstrating significant solar light absorption and localized surface heating. This generated the necessary driving force for the AGMD process. Performance metrics such as vapor flux, salt rejection, specific thermal energy consumption, photothermal efficiency, and temperature polarization (TP) coefficient were significantly improved, especially with a 20 % h-MWCNTs addition, which tripled the solar-energy-driven flux and increased photothermal efficiency by 326 % under standard solar conditions, compared to unmodified membranes. All h-MWCNTs-based SP-AGMD membranes achieved over 99 % salt rejection. Lastly, the membranes were tested with real seawater to confirm their applicability for desalination. This photothermal approach offers a scalable, sustainable solution for water purification, making a significant advancement in membrane distillation technology.

Enhancing the Separation Performance of Cellulose Membranes Fabricated from 1-Ethyl-3-methylimidazolium Acetate by Introducing Acetone as a Co-Solvent

Cellulose, a sustainable raw material, holds great promise as an ideal candidate for membrane materials. In this work, we focused on establishing a low-cost route for producing cellulose microfiltration membranes by adopting a co-solvent system comprising the ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) and acetone. The introduction of acetone as a co-solvent into the casting solution allowed control over the viscosity, thereby significantly enhancing the morphologies and filtration performances of the resulting cellulose membranes. Indeed, applying this co-solvent allowed the water permeability to be significantly increased, while maintaining high rejections. Furthermore, the prepared cellulose membrane demonstrated excellent fouling resistance behavior and flux recovery behavior during a challenging oil-in-water emulsion filtration. These results highlight a promising approach to fabricate high-performance cellulose membranes.

Cross-Linked Metathesis Polynorbornenes Based on Nadimides Bearing Hydrocarbon Substituents: Synthesis and Physicochemical Properties.

Metathesis homo- and copolymerization of bifunctional monomers bearing two norbornene moieties was studied. The monomers were synthesized from cis-5-norbornene-exo-2,3-dicarboxylic anhydride and various diamines (hexamethylenediamine, decamethylenediamine, 1R,3S-isophoronediamine). The metathesis homopolymerization of these bis(nadimides) in the presence of the second-generation Grubbs catalyst afforded glassy cross-linked polymers in more than 90% yields. The metathesis copolymerization of the bis(nadimides) and a monofunctional norbornene derivative containing the β-pinene fragment also resulted in insoluble cross-linked polymers in nearly quantitative yields. The structures and purity of the synthesized polymers were confirmed via IR spectroscopy and CP/MAS NMR spectroscopy. Conditions for the fabrication of mechanically strong solution-cast thin films based on copolymers synthesized from the comonomers mentioned above were determined by varying the content of the cross-linking agent. It was shown that the films made in this way are stable in a range of organic solvents and could be useful as semipermeable or membrane materials for use in liquid organic media. The permeability of the polymer films in question to 1-phenylethanol and mandelic acid was studied. The results obtained are discussed along with the data from the DSC, TGA, and powder X-ray diffraction studies of the properties of the synthesized metathesis homo- and copolymers.

Dendritic cells and type I and II interferon production in the local microenvironment of sinonasal tumors

The subpopulations of dendritic cells and their functional potential determined by endogenous interferon status in tumor microenvironment is an important stage in tumor-specific T-lymphocytes effector reactions development. In this regard, understanding the patterns of sinonasal neoplasms immune cells changes is important in the context of the search for biomarkers of the tumor process which may open up new opportunities for targeted therapy. This study is the first to provide a comparative description of dendritic cells subsets and the type I and type II interferon production in patients with malignant and benign sinonasal tumors.Tumor tissue from 30 patients with neoplasms – main group (15 patients with malignant tumors and 15 patients with inverted papilloma) and biopsy material of the mucous membrane from 15 patients with polypous rhinosinusitis (comparison group) were used. Tumor-infiltrating immune cells were isolated from tissue using automated and enzymatic cell dissociation. The surface and intracellular cells phenotype was assessed using monoclonal antibodies and flow cytometry. The production of α- and γ-interferons was determined by enzyme-linked immunosorbent assay. Statistical data analysis was proceeded in Statistica 10.0.An increase of tumor-infiltrating myeloid dendritic cells number was found in patients with malignant tumors as compared to control group what correlated with the stage of the pathological process (R = -0.67; p = 0.01). There was an increase in both myeloid and plasmacytoid dendritic cells in the neoplasm tissue in patients with inverted papilloma relative to the comparison group. The microenvironment of malignant growth was characterized by an increase in α- and γ-interferons production in combination with a pronounced decrease in IFNγ-producing T cells percent while a decrease in both intracellular and extracellular production of γ-interferons was detected in tumor tissue of patients with inverted papilloma as compared with control group.In patients with sinonasal tumors changes in dendritic cells subpopulations as well as a decrease in the reserve capacity of γ-interferon synthesis were revealed what may characterize the involvement of these mechanisms in the formation of the antitumor immune response failure and requires further research to establish their pathogenetic role.

Scientific evaluation on biodegradable and biofunctional polyurethane incorporated chitosan/elastin electrospun membranes in compared with synthetic polymeric expanded polytetrafluoroethylene and polyethylene terephthalate vascular membranes

Cardiovascular disease is a life-threatening health problem. Employing vascular membranes is one of the treatment options in cardiovascular surgery to replace damaged vascular tissues. However, certain limitations associated with synthetic polymeric vascular membranes (expanded polytetrafluoroethylene (e-PTFE) and polyethylene terephthalate (PET)) such as low biodegradability and biofunctional, may lead to thrombosis, inflammatory response, and tissue necrosis. Polyurethane (PU) is commonly applied in vascular engineering, owing to its good biocompatibility and biodegradability. Incorporating chitosan (CS) and elastin (EL) into the PU matrix, specifically in the design of electrospun nanofibrous membrane, is expected to enhance the biological properties of PU. These improvements are crucial to overcome the limitations of synthetic vascular membranes. Previously, there was no scientific comparison between synthetic vascular membranes and the improved design of PU-based nanofibrous membranes. This scientific comparison is pivotal to allow more research exploration on biodegradable and biofunctional materials towards the fabrication of vascular membranes. Herein, the physicochemical, biodegradability, and biofunctional capability of the electrospun PU-based electrospun membranes and two synthetic membranes were compared. Both PU and PU/CS/ES electrospun membranes were annotated with N–H, C–H, and C–N groups with the appearance of elongated fibers. The –CF2 group was presented in the e-PTFE membranes with the view of expanded fibril structure and interconnecting nodes. Whereas for the PET membranes, C=C, C=O, and C–O groups were noticed with the appearance of homogeneous knitted morphology. The PU/CS/ES membranes were found to be more hydrophilic than the PU and the synthetic membranes. The incorporation of CS and EL in the matrix of electrospun PU has improved the PU's biodegradability up to 23.86 ± 5.86 % at 60 days of incubation with the view of swollen and degraded elongated fibers, following the degradation test. Both synthetic polymeric membranes were declared non-biodegradable with less than 7 % degradation at similar incubation timepoint. The PU/CS/ES membranes were also found biofunctional with the most 82 ± 0.49 % of cell viability, protruded cell filopodia, and 44.24 ± 13.99 % scratch cell closure within 24 h of incubation. The incorporation of CS and EL into the PU matrix has improved the biodegradability and biofunctionality compared to the pure PU and synthetic polymeric membranes. Thus, highlight the suitability of PU/CS/ES electrospun membranes to be applied in cardiovascular tissue engineering.

Controllable Design of Polyamide Composite Membrane Separation Layer Structures via Metal-Organic Frameworks: A Review.

Optimizing the structure of the polyamide (PA) layer to improve the separation performance of PA thin-film composite (TFC) membranes has always been a hot topic in the field of membrane preparation. As novel crystalline materials with high porosity, multi-functional groups, and good compatibility with membrane substrate, metal-organic frameworks (MOFs) have been introduced in the past decade for the modification of the PA structure in order to break through the separation trade-off between permeability and selectivity. This review begins by summarizing the recent progress in the control of MOF-based thin-film nanocomposite (TFN) membrane structures. The review also covers different strategies used for preparing TFN membranes. Additionally, it discusses the mechanisms behind how these strategies regulate the structure and properties of PA. Finally, the design of a competent MOF material that is suitable to reach the requirements for the fabrication of TFN membranes is also discussed. The aim of this paper is to provide key insights into the precise control of TFN-PA structures based on MOFs.

Light at the end of the tunnel: FRAP assays combined with super resolution microscopy confirm the presence of a tubular vacuole network in meristematic plant cells

Abstract Plant vacuoles play key roles in cellular homeostasis, performing catabolic and storage functions, and regulating pH and ion balance. Despite their essential role, there is still no consensus on how vacuoles are established. A model proposing that the endoplasmic reticulum is the main contributor of membrane for growing vacuoles in meristematic cells has been challenged by a study proposing that plant vacuoles are formed de novo by homotypic fusion of multivesicular bodies (MVBs). Here, we use the Arabidopsis thaliana root as a model system to provide a systematic overview of successive vacuole biogenesis stages, starting from the youngest cells proximate to the quiescent center. We combine in vivo high- and super-resolution (STED) microscopy to demonstrate the presence of tubular and connected vacuolar structures in all meristematic cells. Using customized fluorescence recovery after photobleaching (FRAP) assays, we establish different modes of connectivity and demonstrate that thin, tubular vacuoles, as observed in cells near the quiescent center, form an interconnected network. Finally, we argue that a growing body of evidence indicates that vacuolar structures cannot originate from MVBs alone but receive membrane material from different sources simultaneously.

Hydroxy salt induced CoAl-LDH nanosheet composite membrane for pervaporation desalination

Pervaporation is a promising desalination technology. Developing high-performance and stable pervaporation membranes with high continuity structure remains a significant challenge. This study reports the development of a novel layered double hydroxide (LDH) nanosheet composite membrane fabricated using a hydroxyl salt induction method. This approach facilitated the in-situ nucleation and growth of the CoAl-LDH nanosheets on polyvinylidene fluoride (PVDF) substrate, reducing precursor concentration and enhancing preparation efficiency. The resulting cross-compatible architecture closely integrated the dense LDH nanosheet separation layer with the flexible PVDF support. The microstructure and morphology of the hydroxyl salt layer and its transformed CoAl-LDH composite membrane were comprehensively investigated. The optimized membrane was applied for pervaporation desalination (3 wt% NaCl, 50 °C), achieving a high flux of 38.4 kg·m−2·h−1 and exceptional NaCl rejection of 99.9 %. It also demonstrated excellent tolerance to a wide salinity range, maintaining 99.6–99.9 % rejection even at 20 wt% NaCl, while the flux remained stable at 26.7 kg·m−2·h−1. Long-term testing confirmed the consistent separation performance and operational stability, underscoring the great potential of this advanced membrane material for practical pervaporation desalination applications.

Designing new sulfate ionophores for potentiometric membrane sensors: Selectivity assessment and practical application

Developing potentiometric chemical sensors for sulfate determination is a rather challenging task due to a considerable hydrophilicity of this anion and its poor affinity to lipophilic plasticized polymeric membranes – one of the most popular sensor membrane materials nowadays. Not too many research works were devoted to this problem in the last years. Here we report on the successful development of several novel sulfate ionophores based on the synthetic modification of the commercially available sulfate ionophore I. The newly developed sensors outperform commercial analogue in terms of elelctrochemical sensitivity and selectivity. We have highlighted certain problems with numerical selectivity assessment in case when primary and interfering ions have different charges. The counterintuitive results yielded by conventional selectivity quantification methods implies the relevance of using alternative approach – visualizing sensor response curves towards primary ion in the presence of interfering ions. Novel sulfate sensors were applied for direct potentiometric measurements of sulfate content in river water samples demonstrating real applicability of the developed sensor membranes.

Fabrication and Customization of Highly Porous PLGA Membranes Utilizing Near‐Field Electrospinning, Thermal Transitions, and Multilayer Strategies

Polymer porous membranes are crucial in various applications, including water filtration, tissue engineering, and drug administration. Conventional far‐field electrospinning (FFES) is widely used for producing polymeric membranes due to its cost‐effectiveness, scalability, and flexibility in using many polymers. However, FFES has limitations in controlling pore form and size, as it produces randomly oriented fibers that lead to inconsistent and noncustomizable pore sizes. To address these limitations, this work combines near‐field electrospinning (NFES) with thermal treatment of polymer fibers and membranes. NFES offers more precise control over fiber placement and alignment, producing well‐defined fiber patterns with consistent and customizable pore sizes without compromising the thickness of membranes. By exploring the interplay between polymer behavior, thermal effects, and capillary action, the differences in pore area under various temperatures and fiber spacings are characterized. Additionally, this study investigates the influence of multilayer infusion on pore size and geometric arrangement by examining multilayer configurations stacked at various angles. The results indicate that increasing the number of layers leads to decreased pore size, while the alignment of infused fibers affects pore shape. This integrated approach enhances control over membrane characteristics, improving the performance and consistency of polymer porous membrane fabrication across various applications.

Fabrication of cellulose nanocrystals-incorporated dense Janus membranes for enhanced desalination and oily saline wastewater treatment via membrane distillation

Conventional hydrophobic membranes used in membrane distillation (MD) face significant challenges, such as severe membrane fouling and wetting, when treating surfactant-containing oily wastewater. Current strategies to modify surfaces for anti-fouling and anti-wetting purposes are often complex and time consuming, potentially compromising the flux in MD. This study investigates the characteristics and performance of novel fabricated Janus membranes for the treatment of oily hypersaline wastewater in membrane distillation applications. Janus membranes, which have a dense polyamide layer containing cellulose nanocrystal nanoparticles, were synthesized using the reverse interfacial polymerization (R–IP) method on a polyvinylidene fluoride (PVDF) substrate. Characterization using scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) revealed that the modified Janus membranes exhibited an enhanced hydrophilicity and structural integrity due to the incorporation of cellulose nanocrystal nanoparticles. The fabricated membranes showed a dense surface layer without visible pores or cracks, with micron-scale patterned structures and widely distributed wrinkles, particularly at higher concentrations of cellulose nanocrystal nanoparticles. The desalination performance was evaluated in an air gap membrane distillation setup, where the modified Janus membranes demonstrated higher water vapor fluxes and stable salt rejection, even in the presence of surfactants. The wettability and fouling resistance of the Janus membranes were evaluated, with the PVDF-RIP0.5C membrane showing the highest hydrophilicity and underwater oleophobicity, thereby preventing oil adhesion and membrane fouling. These results underline the potential of Janus membranes with incorporated cellulose nanocrystal nanoparticles for efficient desalination and treatment of oily saline wastewater in the MD process.

Heterostructure ZIF-8@MXene with sieving effect in mixed matrix membranes for CO2 separation

At the present time, the realm of gas separation membranes is predominantly centered on the development of membrane materials that simultaneously exhibit exceptional gas permeability and selectivity. Mixed Matrix Membranes (MMMs) hold significant promise in addressing the long-standing challenge of balancing membrane selectivity with permeability. By incorporating a molecular sieving mechanism, an enhanced gas separation process is achieved. In this research endeavor, single-layer MXene nanosheets serve as an ideal substrate for the direct growth of ZIF-8 nanoparticles, yielding heterogeneously structured nanofillers, coined ZIF-8@MXene. The composite filler, ZIF-8@MXene, maintains a two-dimensional lamellar structure reminiscent of MXene, while also integrating ZIF-8 nanoparticles with their optimal pore size of 3.4 Å. This optimal pore size efficiently facilitates the unimpeded passage of CO2 molecules through the channels, creating a preferential pathway. Conversely, N2 molecules encounter greater difficulty traversing these channels, effectively coupling the solubility-diffusion mechanism with the molecular sieving mechanism to enhance selectivity in gas separation processes. Consequently, the mixed matrix membrane exhibits a remarkable enhancement in gas selectivity. Particularly, under sub-ambient conditions (−20 °C), the PEO/ZIF-8@MXene-0.3 % membrane achieves an exceptional CO2/N2 selectivity of 294.1, accompanied by a high CO2 permeability of 115.58 Barrer. This outstanding performance surpasses the 2019 upper bound, underscoring the significant potential of heterostructured nanofillers to be harnessed in advancing various mixed matrix membranes (MMMs) towards high-performance gas separation capabilities.

Novel polyamide nanofiltration membrane PEI-(β-CD@g-C3N5)/TMC based on microfiltration substrate for efficient separation of lithium and magnesium

With the development of industry, the scarcity of lithium resources is becoming increasingly prominent. Therefore, the development of high-performance nanofiltration (NF) membranes for lithium extraction from salt lakes has become crucial. Herein, β-Cyclodextrin (β-CD) and amino-rich graphitic carbon nitride (g-C3N5) sol were uniformly mixed to form β-CD@g-C3N5, which was then mixed with polyetherimide (PEI) monomer and subjected to interfacial polymerization (IP) reaction with trimesoyl chloride (TMC) on a 0.22 μm microfiltration (MF) membrane to prepare the PEI-(β-CD@g-C3N5)/TMC composite NF membrane. Through thin plate theory and gradient operation pressure filtration tests, it was found that the composite NF membrane prepared on the MF membrane substrate was not only defect-free but also exhibited superior compression resistance. In Li+/Mg2+ filtration tests, the PEI-(β-CD@g-C3N5)/TMC membrane showed superior NF performance, with a Li+/Mg2+ selectivity coefficient of 38.85 and a permeability of 8.91 L·m−2·h−1·bar−1. This was attributed to the effect of β-CD@g-C3N5, which could thin the separation layer, slightly enlarge and more uniformly distribute the pores, increase hydrophilicity, and enhance positive charge; meanwhile, the cavity structure provided by β-CD helped to effectively separate Li+/Mg2+. Furthermore, under conditions of mixed salt solutions with different Mg2+/Li+ mass ratios and 80 h of continuous filtration, the membrane exhibited excellent stability. This work introduces innovative membrane materials and design concepts to the field of lithium extraction via NF, potentially paving the way for the industrial application of NF technology.

A transition in diffusion behaviors of organic liquid mixtures in dense polymer membranes

Multi-component mass transfer frameworks, such as the Maxwell-Stefan approach, parameterized with the pure component diffusion and sorption behaviors of different substances in polymer materials have been used in predicting complex mixture permeation through polymer membranes. However, a change in the physical state of a polymer membrane (e.g., swelling) or the polymer dynamics (e.g., plasticization) is likely when the membrane is exposed to a high activity organic solvent mixture with strong chemical affinity for the polymer. These changes complicate the accurate estimation of diffusion coefficients for mixtures of solvents based on knowledge of pure component diffusivities within the polymer. Here, we present 120 organic solvent reverse osmosis (OSRO) permeation test results for hydrocarbon liquid mixtures with varying compositions in three different polymers and compare the experimental results to the predictions of a Flory-Huggins coupled Maxwell-Stefan model with two different diffusion modalities. The effect of the chemical affinity between the mixture and the membrane – estimated by the Hansen solubility difference – on the diffusion behaviors of individual solvents permeating through the membrane was investigated via the usage of this model. Our work demonstrates that polymer membranes undergo a reduction for the effectiveness of diffusion-based separation near a specific threshold level of solubility difference (8 MPa0.5) from the mixture and that this difference is consistent across several different membrane materials.

Trefoil-like COFs membrane fabricated by interfacial polymerization for dye/salt separation

Covalent organic frameworks (COFs) with β-ketoenamine structure have shown notable effectiveness in water treatment. In general, COFs can be constructed by the interfacial polymerization (IP) between a C2 symmetry monomer with para-position reaction groups and a C3, C4 and C6 symmetry functionalized monomer. The constrained availability of para-position monomers limits the diversity of COFs synthesis options, necessitating exploration into non-para-position alternatives. Herein, 2,4,6-triformylphloroglucinol (Tp) and ortho-position monomer o-phenylenediamine (OPD) are employed to fabricate a composite membrane featuring COFs with a special trefoil-like structure by interfacial polymerization method. The optimal OPD-Tp COFs/Nylon nanofiltration (NF) membrane has 99.8 % rejection for CR and only 3.2 % rejection for NaCl. Meanwhile, the pure water permeation flux is 132 L m−2 h−1 bar−1. This study shows the significant potential for dye/salt separation of the prepared COFs composite NF membrane and broadens the monomer selective range for the COFs membrane fabrication.

Enhancement of antifouling and separation properties of poly(m-phenylene isophthalamide) hybrid ultrafiltration membrane using highly crystalline poly(heptazine imide) nanosheets

A highly crystalline phase g-C3N4, namely poly (heptazine imide) (PHI) was synthesized using molten salts. A high-performance ultrafiltration membrane was prepared by blending PHI nanosheets with Poly(m-phenylene isophthalamide) (PMIA) to obtain casting solution, and further prepared by phase conversion method. Hybrid PMIA membranes were prepared by incorporating 0.02–0.10 wt% of PHI, which were further characterized by SEM, AFM, XRD, FTIR, XPS, TGA and surface zeta potential. The hydrophilicity, water flux, and rejection of bovine serum albumin (BSA) of the membrane significantly increased. For instance, the water permeability of M4 (264.6 Lm−2h−1bar−1) was about 2.3 times that of bare PMIA membrane (113.6 Lm−2h−1bar−1), while maintaining a BSA rejection of 94.7 % for a 1000 mgL−1 BSA feed solution. Moreover, the M4 membrane showed excellent antifouling performance with a flux recovery rate of up to 88.7 % and lower irreversible fouling of 11.3 %. This study may provide reference for the modulation of highly crystalline g-C3N4 structure and its application in membrane fabrication for water treatment.