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Membranes with high permeance and high rejection for di- and multivalent cation removal are highly desired for efficient brackish water and industrial water treatment. In this work, we report a facile strategy for constructing ultrathin nanofiltration (NF) membranes by in situ cross-linking of amine which is confined in a network film. The network made of single-walled carbon nanotubes (SWCNTs) serves as a framework for poly(ethylene imine) (PEI) to attach and stay, facilitating the formation of a polyamine (PA) layer with high quality and controlled thickness. Benefiting from the ultrathin thickness of the SWCNT network (∼31 nm), an active layer (∼34 nm thick) comes with a high permeance of 27 L m

Covalent organic framework (COF)-based membranes are burgeoning candidates for separation technologies owing to their well-ordered channel structures. The exponential interest in the stability of the COF membrane on exposure to harsh organic solvents is directed to develop a composite membrane for dye separations in polar aprotic solvents. Here, we reported a nanocomposite membrane composing of a single-walled carbon nanotube (SWCNT)/COF (an imine-based COF) hybrid on a commercial polytetrafluoroethylene (PTFE) substrate, with a thickness of ∼58 nm prepared in a diffusion cell. This membrane displayed high permeability and stability toward nonpolar and aprotic solvents. It exhibited high permeability for lower viscous organic solvents such as hexane (66 L m

Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Achieving such a precise separation using membranes requires Angstrom scale pores with a high level of pore size uniformity. Herein, we demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization (SARIP). The dynamic, self-assembled network of surfactants facilitates faster and more homogeneous diffusion of amine monomers across the water/hexane interface during interfacial polymerization, thereby forming a polyamide active layer with more uniform sub-nanometre pores compared to those formed via conventional interfacial polymerization. The polyamide membrane formed by SARIP exhibits highly size-dependent sieving of solutes, yielding a step-wise transition from low rejection to near-perfect rejection over a solute size range smaller than half Angstrom. SARIP represents an approach for the scalable fabrication of ultra-selective membranes with uniform nanopores for precise separation of ions and small solutes., Separating molecules or ions with sub-Angstrom scale precision is important but technically challenging. Here, the authors demonstrate that precise solute-solute separation can be achieved using polyamide membranes formed via surfactant-assembly regulated interfacial polymerization.

Recently, ultrathin polyamide nanofiltration membranes fabricated on nanomaterial-based supports have overcome the limitations of conventional supports and show greatly improved separation performance. However, the feasibility of the nanomaterial-based supports for large-scale fabrication of the ultrathin polyamide membrane is still unclear. Herein, we report a controllable and saleable fabrication technique for a single-walled carbon nanotube (SWCNT) network support via brush painting. The mechanical and chemical stability of the SWCNT network support were carefully examined, and an ultrathin polyamide membrane with thickness of ∼15 nm was successfully fabricated based on such a support. The obtained thin-film composite (TFC) polyamide nanofiltration membranes exhibited extremely high water permeability of ∼40 L m-2 h -1 bar-1, a high Na2SO 4 rejection of 96.5%, and high monovalent/divalent ion permeation selectivity and maintained highly efficient ion sieving throughout 48 h of testing. This work demonstrates a practical route toward the controllable large-scale fabrication of the TFC membrane with an SWCNT network support for ion and molecule sieving. This work is also expected to boost the mass production and practical applications of state-of-the-art membranes composed of one-dimensional and two-dimensional nanomaterials as well as the nanomaterial-supported TFC membranes.

The development of membranes with a superior antifouling property and high-permeation flux is extensively considered but still a challenge for handling emulsified oil foulants in wastewater. Herein, a zwitterionic nanohydrogel-grafted PVDF (ZNG- g-PVDF) nanofibrous membrane was fabricated via a simple surface activation and amide reaction. By tailoring the parameters for electrospinning, PAA-g-PVDF nanofibrous membranes with interpenetrated nanofibers and microsphere structure were formed, and the membrane surface was endowed with high roughness on the micrometer scale. Combined with the strong hydration ability of the grafted zwitterionic nanohydrogels, the obtained ZNG- g-PVDF nanofibrous membrane exhibited a superhydrophilic property and nearly zero adhesion to crude oil under water. It thus showed an extremely high removal efficiency (∼98.7%) for gravity-driven separation of the crude oil-in-water emulsion. Both the water-permeating flux and oil content in the collected filtrate (lower than 13 ppm) showed little change during 10 cycles of the filtration experiment, indicating superior crude oil foulant repellency performance of the ZNG- g-PVDF nanofibrous membrane. Considering the high energy saving of the gravity-driven separation process, this novel ZNG- g-PVDF nanofibrous membrane possesses broad applications in the field of emulsified crude oil foulant cleanup in an aquatic environment.

Nanofiltration (NF) membranes with ultrahigh permeance and high rejection are highly beneficial for efficient desalination and wastewater treatment. Improving water permeance while maintaining the high rejection of state-of-the-art thin film composite (TFC) NF membranes remains a great challenge. Herein, we report the fabrication of a TFC NF membrane with a crumpled polyamide (PA) layer via interfacial polymerization on a single-walled carbon nanotubes/polyether sulfone composite support loaded with nanoparticles as a sacrificial templating material, using metal-organic framework nanoparticles (ZIF-8) as an example. The nanoparticles, which can be removed by water dissolution after interfacial polymerization, facilitate the formation of a rough PA active layer with crumpled nanostructure. The NF membrane obtained thereby exhibits high permeance up to 53.5 l m−2h−1 bar−1 with a rejection above 95% for Na2SO4, yielding an overall desalination performance superior to state-of-the-art NF membranes reported so far. Our work provides a simple avenue to fabricate advanced PA NF membranes with outstanding performance., Nanofiltration membranes are important for water desalination technologies, but designing membranes that achieve both high permeance and high salt rejection remains challenging. Here, the authors use sacrificial nanoparticles in the membrane fabrication process, leading to crumpled structures with ultrahigh permeance.

Developing an effective and sustainable solution for cleaning up or separating oily water is highly desired. In this work, we report a completely inorganic mesh membrane made up of cupric phosphate (Cu3(PO4)2) in a special intersected nanosheets-constructed structure. Combing the hierarchical structure with strong hydration ability of Cu3(PO4)2, the nanosheets-wrapped membrane exhibits a superior superhydrophilic and underwater anti-oil-fouling and antibio-fouling property for efficient oil/water separation to various viscous oils such as heavy diesel oil, light crude oil, and even heavy crude oil with underwater oil contact angles (CAs) all above 158° and nearly zero underwater oil adhesive force even when a large preload force of up to 400 μN was applied on the oil droplet. Simultaneously, the membrane exhibits a high chemical and thermal stability and outstanding salt tolerance. Continuous separation operated on a cross-flow filtration apparatus demonstrates a large separation capacity and long-term st...

A hydrogel-embedded tight ultrafiltration membrane composed of sodium polyacrylate-modified polyacrylonitrile (PAAS-m-PAN) is fabricated by a modified phase inversion process. The as-prepared membrane with excellent anti-dye-fouling property can effectively separate dyes from salts with permeance as high as >140 L m−2 h−1 bar−1, which is several times that of traditional polymeric filtration membranes with a similar rejection performance.

Because of weak hydrophilicity, membranes always experience fouling problems during separations. This phenomenon seriously impedes the development of membrane technologies for practical industrial-oil wastewater treatment. In this work, we successfully fabricated a superhydrophilic zwitterionic poly(vinylidene fluoride) (PVDF) membrane using a two-part process with an in situ cross-linking reaction during nonsolvent-induced phase separation and a subsequent sulfonation reaction. To prepare this zwitterionic PVDF membrane, a copolymer poly(dimethylaminoethyl methacrylate-co-2-hydroxyethyl methacrylate) (PDH) was synthesized as a zwitterionic polymer precursor and used as an additive in membrane preparation. This zwitterionic additive is well-immobilized in the membrane using in situ cross-linking to ensure the long-term stability of the membrane, and subsequent sulfonation transforms the precursor to a zwitterionic polymer to produce a superhydrophilic membrane. This superhydrophilic zwitterionic PVDF membrane exhibits high water permeation flux and good antifouling properties for separating oil-in-water emulsions with high separation efficiency.

Highly sensitive responsiveness is vital for stimuli-responsive membranes. However, it is a great challenge to fabricate stimuli-responsive membranes with ultrahigh gating ratio (the ratio of the salt solution permeating flux to the pure water permeating flux) and high response speed simultaneously. In this work, a salt-responsive membrane with an ultrahigh gating ratio is fabricated via a facile strategy by grafting zwitterionic nanohydrogels onto a poly(acrylic acid)-grafting-poly(vinylidene fluoride) (PAA-g-PVDF) microporous membrane. Due to the synergistic effect of two functional materials, PAA chains and zwitterionic nanohydrogels tethered on PAA chains, this stimuli-responsive membrane exhibits an ultrasensitive salt responsiveness with a gating ratio of up to 8.76 times for Na+ ions, 89.6 times for Mg2+ ions, and 89.3 times for Ca2+ ions. In addition, such zwitterionic nanohydrogels-grafted PAA-g-PVDF (ZNG-g-PVDF) membranes exhibit very rapid responses to stimuli. The permeating flux changes swiftly while altering the feed solution in a continuous filtration process. The excellent salt-responsive characteristics endow such a ZNG-g-PVDF membrane with great potential for applications like drug delivery, water treatment, and sensors.

Accurately monitoring blood glucose in real-time is highly required for diabetes. Utilizing membrane to realize fast separation of a trace of blood is significant for accurately testing blood glucose. In this work, we designed a Janus membrane with thin film composite structure by electrospinning polyurethane (PU) on Ca3(PO4)2-coated nylon mesh. This Janus membrane exhibited directional liquid transport performance and liquid wastage reduction during separation through optimizing the surface wettability, pore parameters and asymmetric structures of membrane. When a trace of water with volume as small as 3 μL was dipped on the hydrophobic side with pore size of around 1.1 μm, this water droplet could easily penetrate through the Janus membrane within 2.9 s under only gravity and liquid wastage reduction was achieved at the same time (D2/D1 = 1.27), suggesting an excellent liquid transportation performance. The blood glucose meter integrated with this Janus membrane could efficiently remove red blood cells from 10 μL blood within 7.2 s. As a result, the sensitivity of the blood glucose meter increased by 4.5%.

The wide application of lithium batteries in consumer electronics and electric vehicles bring about ever-rising demand of lithium resources globally. Nanofiltration (NF) membranes with high Mg2+/Li+ selectivity could achieve highly efficient separation of lithium from natural brines, which provides a good alternative for steady lithium supply. In this work, we developed a dual-skin layer nanofiltration membrane comprised of a polyethylene-imine (PEI) layer grafted on a polyamide layer. The polyamide layer was prepared via interfacial polymerization to endow the NF membrane with sub-nm pores, while the PEI layer was grafted on the polyamide surface via amidation reaction to further equip the membrane with enhanced positive charge. With the synergistic effect of size sieving from the polyamide layer and electrostatic exclusion from the PEI layer, the dual-skin layer NF membrane exhibits a high rejection of 98.5% to MgCl2 and a low rejection of 46.2% to LiCl, suggesting a high Mg2+/Li+ selectivity. As using this dual-skin layer NF membrane for separating Li+ from a simulated brine, a high Mg2+/Li+ separation factor (SMg,Li) up to 33.4 was achieved, which is the highest value among the pressure-driven polymeric nanofiltration membranes reported so far.

Traditional polymer membranes prepared by phase inversion process have the problems of low flux and serious fouling when they were used for oil/water separation. In this work, an alkaline-induced phase inversion process is developed for the superhydrophilic/underwater superoleophobic polyacrylonitrile (PAN) ultrafiltration membrane. The as-prepared PAN ultrafiltration membrane could effectively separate oil-in-H2O emulsions with a high flux up to 2270 L/m2 h bar and an extremely high rejection while the oil residual in filtrate after one-time separation is lower than 10 ppm. Also, the PAN membrane showed ultralow oil adhesion and antifouling properties and can be easily recycled with flux recovery ratio of 85%. This new PAN membrane has a great potential for treating oily wastewater.

Fabricating nanofiltration (NF) membranes with high permeating flux and simultaneous high rejection rate for desalination is rather significant and highly desired. A new avenue is reported in this work to design NF membrane by using polydopamine wrapped single-walled carbon nanotube (PD/SWCNTs) ultrathin film as support layer instead of the use of traditional polymer-based underlying layers. Thanks to the high porosity, smooth surface, and more importantly optimal hydrophilic surface of PD/SWCNTs film, a defect-free polyamide selective layer for NF membrane with thickness of as thin as 12 nm is achieved. The obtained NF membrane exhibits an extremely high performance with a permeating flux of 32 L m-2 h-1 bar-1 and a rejection rate of 95.9% to divalent ions. This value is two to five times higher than the traditional NF membranes with similar rejection rate.

Flux decline of filtration membranes caused by oil pollutants is one of the most serious challenges for oil/water separation. Aiming at improving the anti-fouling property as well as the cyclic stability, a mineralized membrane was fabricated by growing cupric phosphate [Cu3(PO4)2] nanoparticles onto polyacrylic acid-grafted-poly (vinylidene fluoride) (PAA-g-PVDF) microfiltration membrane via soaking mineralization process for oil-in-water emulsion separation. The uniform distribution of Cu3(PO4)2 nanoparticles on both the membrane surface and the inner pores endows the membrane with rigid structure and superhydrophilic property, and thus outstanding anti-oil-fouling performance. The Cu3(PO4)2/PAA-g-PVDF mineralized membranes exhibit low decay rate of permeating flux during 2 h continuous test and a nearly 100% recovery ratio for the separation of various oil-in-water emulsions. Moreover, the membranes possess good mechanical and chemical stability toward ultrasonic, salts and wide pH range, which is promising for treating practical oily wastewater.

Hydrophilically-modified mesh filter membranes have been widely researched for oil/water separation due to their high permeating flux and excellent separation efficiency. However, the low oil pressure resistance of mesh membrane is a major drawback limiting its practical oil/water separation applications. In this work, we report an ultrathin microporous membrane developed via the decoration of a stainless steel mesh filter with electrospun poly(acrylic acid) grafted poly(vinylidene fluoride) (PAA-g-PVDF) nanofibers. The network structure of the nanofiber layer reduces the pore size of the stainless steel mesh to improve its oil pressure resistance, and simultaneously maintains a high active separation area to preserve the highly permeable feature of the mesh filter membrane. Therefore, this composite membrane exhibits high permeating flux (up to 53574 L m−2 h−1 under gravity) and high oil intrusion pressure (>6000 Pa) at the same time. Satisfactory permeating flux and separation efficiency are achieved in various oil/water separation experiments and multiple operating cycles, which demonstrate the great potential of the membrane for practical oily wastewater treatment applications.

Membranes with excellent water permeance and high dye removal efficiency are highly desired for textile industry wastewater treatment. However, the high acidity and salinity in such wastewater impose great challenges in dye removal efficiency for conventional polyamide-based membranes. This study presents a type of acid-tolerant polyarylate (PAR) nanofiltration (NF) membrane that tackles such challenges. The PAR active layer is produced via interfacial polymerization using 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) and isophthaloyl dichloride (IPC) as monomers, and formed on top of a single-walled carbon nanotube (SWCNT) nanofilm. The supporting SWCNT layer contributes to the ultrathin thickness of the PAR active layer and the extremely high membrane permeating flux of ~210 L m−2 h−1 bar−1, while the inclusion of TTSBI monomer grants the PAR active layer surface negatively charged that makes a high dye rejection of >99% at a wide range of feed solution pH and salinity possible. Furthermore, a high selectivity for dye and NaCl was observed with a stable NaCl retention of ~10%, when the membrane is tested at a pH ranging from 2 to 9 and feed NaCl concentration ranging from 1000 to 5000 ppm. The PAR NF membrane is therefore a promising tool for the highly efficient treatment of acidic and high salinity textile dye wastewaters.

In this work, ultrasmall metal-organic frameworks (MOFs) nanoparticles, UIO-66-NH2 nanoparticles were synthesized and embedded in an ultrathin polyamide (PA) active layer via the interfacial polymerization reaction on a polydopamine-wrapped single-walled carbon nanotube film. A thin-film nanocomposite nanofiltration (TFN NF) membrane with a PA/UIO-66-NH2 active layer as thin as 20 ± 3 nm was thus fabricated. The loading mass of the nanoparticles in the TFN NF membrane could be tuned by controlling the nanoparticles concentration in aqueous phase. Benefiting from the ultrathin thickness of active layer and the high loading mass of the MOFs nanoparticles, water permeability up to 46 L m−2 h−1 bar−1 along with a Na2SO4 rejection of 97.1% was achieved, which is 53% increase of the TFC NF membrane without the addition of UIO-66-NH2 nanoparticles. Our membrane owns the thinnest active layer in the category of TFN NF membranes reported so far and exhibits outstanding desalination performance.

A novel Janus membrane integrating an omniphobic substrate and an in-air hydrophilic, underwater superoleophobic skin layer was developed to enable membrane distillation (MD) to desalinate hypersaline brine with both hydrophobic foulants and amphiphilic wetting agents. Engineered to overcome the limitations of existing MD membranes, the Janus membrane has been shown to exhibit novel wetting properties unobserved in any existing membrane, including hydrophobic membranes, omniphobic membranes, and hydrophobic membranes with a hydrophilic surface coating. Being simultaneously resistant to both membrane fouling and wetting, a Janus membrane can sustain stable MD performance even with challenging feed waters and can thus potentially transform MD to be a viable technology for desalinating hypersaline wastewater with complex compositions using low-grade-thermal energy.

With the growing demand for small- and large-scale bioprocesses, advanced membranes with high energy efficiency are highly required. However, conventional polymer-based membranes often have to sacrifice selectivity for permeability. In this work, we report the fabrication of a thermoresponsive composite ultrathin membrane with precisely controlled nanopores for high-throughput separation. The composite membrane is made by grafting a PEG analogue thermoresponsive copolymer onto an ultrathin single-wall carbon nanotubes (SWCNTs) membrane via π-π interaction with no use of the common "grafting from" synthesis approach. The composite membrane exhibits ultrahigh water permeation flux as high as 6430 L m(-2) h(-1) at 40 °C, and more importantly, the pore size of the membrane could be finely adjusted by utilizing the thermoresponsive property of the grafted copolymer. With the temperature changing below and above the lower critical solution temperature (LCST) of the copolymer, the effective pore size of the membrane can be tuned precisely between approximately 12 and 14 nm, which could be applied to effectively separate materials with very small size differences through size sieving.