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Control over nanopore size and 3D structure is necessary to advance membrane performance in ubiquitous separation devices. Here, inorganic nanoporous membranes are fabricated by combining the assembly of cylinder-forming poly(styrene-block-methyl methacrylate) (PS-b-PMMA) block copolymer and sequential infiltration synthesis (SIS). A key advance relates to the use of PMMA majority block copolymer films and the optimization of thermal annealing temperature and substrate chemistry to achieve through-film vertical PS cylinders. The resulting morphology allows for direct fabrication of nanoporous AlO_x by selective growth of Al₂O₃ in the PMMA matrix during the SIS process, followed by polymer removal using oxygen plasma. Control over the pore diameter is achieved by varying the number of Al₂O₃ growth cycles, leading to pore size reduction from 21 to 16 nm. 3D characterization, using scanning transmission electron microscopy tomography, reveals that the AlO_x channels are continuous through the film and have a gradual increase in pore size with depth. Finally, the ultrafiltration performance of the fabricated AlO_x membrane for protein separation as a function of protein size and charge is demonstrated.

Nanoporous inorganic membranes are fabricated from cylinder-forming block copolymer templates. Sequential infiltration synthesis followed by oxygen plasma etching converses polymer domains into uniform alumina pores with tunable pore size. The resulting cylindrical channels are continuous through the film thickness. The created membrane shows excellent protein separation ability. This fabrication route holds great promise in making multifunctional membranes.

In article number 1604572, Zi Chen, Yongfeng Mei and co-workers demonstrate that diamond in the form of nanocrystalline nanomembranes, with thinning-reduced flexural rigidities, can be shaped into various 3D architectures, such as tubes, jagged ribbons, nested tubes, helices, and nested rings. Rolled-up tubular diamond microcavities exhibit pronounced defect-related photoluminescence with whispering gallery mode resonance and high thermal stability.

Multilayered or stacked lipid membranes are a common principle in biology and have various functional advantages compared to single-lipid membranes, such as their ability to spatially organize processes, compartmentalize molecules, and greatly increase surface area and hence membrane protein concentration. Here, a supramolecular assembly of a multilayered lipid membrane system is reported in which poly-l-lysine electrostatically links negatively charged lipid membranes. When suitable membrane enzymes are incorporated, either an ubiquinol oxidase (cytochrome bo ₃ from Escherichia coli) or an oxygen tolerant hydrogenase (the membrane-bound hydrogenase from Ralstonia eutropha), cyclic voltammetry (CV) reveals a linear increase in biocatalytic activity with each additional membrane layer. Electron transfer between the enzymes and the electrode is mediated by the quinone pool that is present in the lipid phase. Using atomic force microscopy, CV, and fluorescence microscopy it is deduced that quinones are able to diffuse between the stacked lipid membrane layers via defect sites where the lipid membranes are interconnected. This assembly is akin to that of interconnected thylakoid membranes or the folded lamella of mitochondria and has significant potential for mimicry in biotechnology applications such as energy production or biosensing.

Layer-by-layer assembly of lipid bilayers is used to multiply the surface concentration of electroactive membrane enzymes at electrodes. The interconnected membrane multilayers, akin to that of thylakoid membranes, are investigated using cyclic voltammetry to reveal a linear increase in biocatalytic activity with each additional membrane layer containing a ubiquinol oxidase or an oxygen-tolerant hydrogenase.

Ionic liquids (ILs) acting as new functional solvents have significant impact in both synthetic and materials chemistry. However, the usage of volatile organic solvents in both synthesis and recycling of ILs usually imposes environmental issues. In this study, according to intrinsic wetting threshold theory, a membrane-based approach assisted by superwettability is developed for efficient, convenient, and economical purification of water-immiscible ILs. By precisely tailoring surface energy, the porous membrane is capable of hydrophobicity and superILphilicity (defined as IL contact angle close to zero), selectively allowing ILs to pass through. This kind of functional membrane can not only separate IL/water mixtures, but also IL/water systems containing inorganic salts, organic compounds, amino acids, and proteins.

A membrane-based approach relying on intrinsic wetting threshold theory for highly efficient, convenient, and economical ionic liquid (IL)/water separation has been presented. By precisely tailoring surface energy, the porous membrane is capable of hydrophobicity and superILphilicity, and can separate not only mixtures of different ILs and water, but also IL/water systems containing inorganic salts, organic compounds, amino acids, and proteins.

Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well-intergrown UiO-66 metal-organic framework membranes fabricated on prestructured yttria-stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m⁻² h⁻¹ and excellent separation factor (>45 000) for separating water from i-butanol (next-generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.

Novel membranes for pervaporation: Well-intergrown metal-organic framework UiO-66 membranes are developed on prestructured yttria-stabilized zirconia hollow fibers. The membranes provide excellent performance for purifying typical biofuels, biochemicals, and organics under harsh environments.

The layer-by-layer method is an attractive technique for the fabrication of ultrathin nanostructured polyelectrolyte multilayer membranes (PEMM). A simple two-step procedure is described here for the preparation of an ultrathin, nanostructured membrane comprising a 5–7 nm thick selective layer, consisting only of one single bilayer of poly(diallyldimethylammoniumchloride) and hyperbranched sulfonated poly(aryleneoxindole). These single bilayered membranes exhibit an outstanding solvent-resistant nanofiltration performance, which is superior to that of commercial membranes as well as to previously reported multilayer membranes having 10–20 bilayers. A comparative study between hyperbranched polyelectrolyte (HPE) and linear polyelectrolyte supports the role of the specific 3D structure of the hyperbranched polyelectrolyte in these excellent separation properties. The work thus encompasses the use of HPEs as an ideal choice for PEMMs, which opens up a new route to significantly decrease the overall membrane preparation time while realizing excellent filtration properties.

Reducing the number of bilayers, in combination with increasing flux and retention, is an important objective in the emerging field of layer-by-layer membranes. By exploiting the unique features of a properly tuned hyperbranched polyelectrolyte as polyanion, a simple and very efficient two-step strategy is proposed for the synthesis of polyelectrolyte multilayer membranes with outstanding solvent-resistant nanofiltration properties.

“Aqua materials” that contain water as their major component and are as robust as conventional plastics are highly desirable. Yet, the ability of such systems to withstand harsh conditions, for example, high pressures typical of industrial applications has not been demonstrated. We show that a hydrogel-like membrane self-assembled from an aromatic amphiphile and colloidal Nafion is capable of purifying water from organic molecules, including pharmaceuticals, and heavy metals in a very wide range of concentrations. Remarkably, the membrane can sustain high pressures, retaining its function. The robustness and functionality of the water-based self-assembled array advances the idea that aqua materials can be very strong and suitable for demanding industrial applications.

A tough aqua material for a tough application: The hybrid membrane's components self-assemble to synergistically enhance each other's structure and properties to result in a tough membrane that efficiently purifies water of heavy metals and organic molecules.

The incorporation of metal–organic frameworks (MOFs) into membrane-shaped architectures is of great importance for practical applications. The currently synthesized MOF-based membranes show many disadvantages, such as poor compatibility, low dispersity, and instability, which severely limit their utility. Herein, we present a general, facile, and robust approach for the synthesis of MOF-based composite membranes through the in situ growth of MOF plates in the channels of anodized aluminum oxide (AAO) membranes. After being used as catalysis reactors, they exhibit high catalytic performance and stability in the Knoevenagel condensation reaction. The high catalytic performance might be attributed to the intrinsic structure of MOF-based composite membranes, which can remove the products from the reaction zone quickly, and prevent the aggregation and loss of catalysts during reaction and recycling process.

A MOF reactor: A general, facile, and robust approach is presented for the preparation of MOF-based composite membranes through the in situ growth of MOF plates in the channels of anodized aluminum oxide membranes. The MOF-based composite membranes were used as membrane catalysis reactors, and showed excellent catalytic performance and stability in the Knoevenagel condensation.

Arsenic-free drinking water, independent of electrical power and piped water supply, is possible only through advanced and affordable materials with large uptake capacities. Confined metastable 2-line ferrihydrite, stable at ambient temperature, shows continuous arsenic uptake in the presence of other complex species in natural drinking water and an affordable water-purification device is made using the same.

Carbon nanomembranes (CNMs) are synthetic 2D carbon sheets with tailored physical or chemical properties. These depend on the structure, molecular composition, and surroundings on either side. Due to their molecular thickness, they can be regarded as “interfaces without bulk” separating regions of different gaseous, liquid, or solid components and controlling the materials exchange between them. Here, a universal scheme for the fabrication of 1 nm-thick, mechanically stable, functional CNMs is presented. CNMs can be further modified, for example perforated by ion bombardment or chemically functionalized by the binding of other molecules onto the surfaces. The underlying physical and chemical mechanisms are described, and examples are presented for the engineering of complex surface architectures, e.g., nanopatterns of proteins, fluorescent dyes, or polymer brushes. A simple transfer procedure allows CNMs to be placed on various support structures, which makes them available for diverse applications: supports for electron and X-ray microscopy, nanolithography, nanosieves, Janus nanomembranes, polymer carpets, complex layered structures, functionalization of graphene, novel nanoelectronic and nanomechanical devices. To close, the potential of CNMs in filtration and sensorics is discussed. Based on tests for the separation of gas molecules, it is argued that ballistic membranes may play a prominent role in future efforts of materials separation.

Carbon nanomembranes (CNMs) are made by radiation-induced crosslinking of aromatic self-assembled monolayers and their subsequent release from the substrate. CNMs are molecularly thin, mechanically stable, and chemically functionalizable films with tunable electrical, mechanical, and biofunctional properties. Large-area CNMs can be prepared with sizes of up to 25 cm × 25 cm on solid supports, and 500 µm × 500 µm free-standing.

Two-dimensional (2D) materials of atomic thickness have emerged as nano-building blocks to develop high-performance separation membranes that feature unique nanopores and/or nanochannels. These 2D-material membranes exhibit extraordinary permeation properties, opening a new avenue to ultra-fast and highly selective membranes for water and gas separation. Summarized in this Minireview are the latest ground-breaking studies in 2D-material membranes as nanosheet and laminar membranes, with a focus on starting materials, nanostructures, and transport properties. Challenges and future directions of 2D-material membranes for wide implementation are discussed briefly.

Separation goes small: Two-dimensional materials of atomic thickness have emerged as high-performance separation membranes. The latest advances in the design and fabrication of 2D-material membranes are reviewed, along with a discussion about the challenges for future applications.

Metal–organic framework (MOF) materials have an enormous potential in separation applications, but to realize their potential as semipermeable membranes they need to be assembled into thin continuous macroscopic films for fabrication into devices. By using a facile immersion technique, we prepared ultrathin, continuous zeolitic imidazolate framework (ZIF-8) membranes on titania-functionalized porous polymeric supports. The coherent ZIF-8 layer was surprisingly flexible and adhered well to the support, and the composite membrane could sustain bending and elongation. The membranes exhibited molecular sieving behavior, close to the theoretical permeability of ZIF-8, with hydrogen permeance up to 201×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ and an ideal H₂/CO₂ selectivity of 7:1. This approach offers significant opportunities to exploit the unique properties of MOFs in the fabrication of separation and sensing devices.

Molecular sieving behavior, with a high hydrogen permeance and a H₂/CO₂ selectivity of 7:1, is shown by ultrathin, continuous zeolitic imidazolate framework (ZIF-8) membranes prepared on polymeric supports. The ZIF-8 layer is flexible and adhered well to the support. This approach offers significant opportunities to exploit the unique properties of metal–organic frameworks in the fabrication of separation and sensing devices.

Superhydrophobic/superoleophilic composites HFGO@ZIF-8 have been prepared from highly fluorinated graphene oxide (HFGO) and the nanocrystalline zeolite imidazole framework ZIF-8. The structure-directing and coordination-modulating properties of HFGO allow for the selective nucleation of ZIF-8 nanoparticles at the graphene surface oxygen functionalities. This results in localized nucleation and size-controlled ZIF-8 nanocrystals intercalated in between HFGO layers. The composite microstructure features fluoride groups bonded at the graphene. Self-assembly of a unique micro-mesoporous architecture is achieved, where the micropores originate from ZIF-8 nanocrystals, while the functionalized mesopores arise from randomly organized HFGO layers separated by ZIF-8 nanopillars. The hybrid material displays an exceptional high water contact angle of 162° and low oil contact angle of 0° and thus reveals very high sorption selectivity, fast kinetics, and good absorbencies for nonpolar/polar organic solvents and oils from water. Accordingly, Sponge@HFGO@ZIF-8 composites are successfully utilized for oil–water separation.

Pores for effect: The superhydrophobic and simutaneously superoleophilic HFGO@ZIF-8 composite were utilized for the oil–water separation. In this material zeolitic imidazolate (ZIF) nanocrystals serve as pillars between nanosheets of highly fluorinated graphene oxide.

A free-standing nanofiber membrane can be simultaneously fabricated, patterned, and integrated with electrolyte-assisted electrospinning (ELES). The fluidic nature of the electrolyte collector enables flexible patterning and facile integration of the free-standing nanofiber membrane on complex substrates from a 2D flat surface to a 3D curved geometry via ELES. The structural integrity and performance of the free-standing nanofiber membrane are verified, and this plays a crucial role for future applications, including organ-on-a-chip, tissue scaffolds, and biosensors.

Membrane technology offers the best options to “drought proof” mankind on an increasingly thirsty planet by purifying seawater or used (waste) water. Although desalination by reverse osmosis (RO) and wastewater treatment by membrane bioreactors are well established the various membrane technologies still need to be significantly improved in terms of separation properties, energy demand and costs. We can now define the ideal characteristics of membranes and advances in material science and novel chemistries are leading to increasingly effective membranes. However developments in membranes must be matched by improved device design and membrane engineering. It is likely that limitations in fluid mechanics and mass transfer will define the upper bounds of membrane performance. Nevertheless major advances and growth over the next 20 years can be anticipated with RO remaining as the key to desalination and reclamation, with other membrane processes growing in support and in niche areas.

Membrane technology offers the best options to “drought proof” mankind on an increasingly thirsty planet by purifying seawater or used water. The driving forces for development of membranes for water production are described in this Review. An update is provided for developments in the various preparation techniques for the range of membrane types.