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.
Ion transport is crucial for biological systems and membrane-based technology. Atomic-thick two-dimensional materials, especially graphene oxide (GO), have emerged as ideal building blocks for ...developing synthetic membranes for ion transport. However, the exclusion of small ions in a pressured filtration process remains a challenge for GO membranes. Here we report manipulation of membrane surface charge to control ion transport through GO membranes. The highly charged GO membrane surface repels high-valent co-ions owing to its high interaction energy barrier while concomitantly restraining permeation of electrostatically attracted low-valent counter-ions based on balancing overall solution charge. The deliberately regulated surface-charged GO membranes demonstrate remarkable enhancement of ion rejection with intrinsically high water permeance that exceeds the performance limits of state-of-the-art nanofiltration membranes. This facile and scalable surface charge control approach opens opportunities in selective ion transport for the fields of water transport, biomimetic ion channels and biosensors, ion batteries and energy conversions.
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•Factors of governing water resistance of porous coordination polymers were surveyed and discussed.•Representative studies were given with emphasis on adsorptive-based gas separations ...by water resistant porous coordination polymers.Representative studies were given with emphasis on membrane-based gas separations by water resistant porous coordination polymers.
Porous coordination polymer (PCP) chemistry has a promising future because of the tunable structures and excellent properties of polymers. However, the strategy for designing and preparing water-resistant PCPs is a considerable challenge. This review surveys and investigates the factors governing water resistance in a hierarchy sequence. Subsequently, representative studies are provided with an emphasis on their adsorptive- and membrane-based gas separations. This review is intended to be useful for researchers who are interested in designing water-resistant PCPs and exploring promising applications for gas separation.
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•Representative studies were given with emphasis on methods for preparation of metal organic framework nanosheets.•Crucial technologies for characterization of metal organic framework ...nanosheets were evaluated.•Series of promising applications by metal organic framework nanosheets were surveyed and discussed.
With infinite assembly and ultrathin nature, metal-organic frameworks nanosheets (MOFNs), as an emerging family of two-dimensional (2D) materials, have attracted extensive interest in fields of material science, chemistry and nanotechnology. Here, we aim to review the recent advances of MOFNs. The assortments of their synthetic methods of top-down, bottom-up and combined strategies are discussed at first, including the comparison of their advantages and limitations. Then, some crucial techniques towards the morphology and microstructure characterization of MOFNs were introduced. We have also discussed the wide ranges of potential applications, especially molecular separation, catalyst, energy conversion, conduction, photofunction, electrochromism and sensing. Finally, the challenges and outlooks for these multi-functional 2D materials were prospected based on current achievements, as well as their unique architectural features.
Recent innovations highlight the great potential of two‐dimensional graphene oxide (GO) films in water‐related applications. However, undesirable water‐induced effects, such as the redispersion and ...peeling of stacked GO laminates, greatly limit their performance and impact their practical application. It remains a great challenge to stabilize GO membranes in water. A molecular bridge strategy is reported in which an interlaminar short‐chain molecular bridge generates a robust GO laminate that resists the tendency to swell. Furthermore, an interfacial long‐chain molecular bridge adheres the GO laminate to a porous substrate to increase the mechanical strength of the membrane. By rationally creating and tuning the molecular bridges, the stabilized GO membranes can exhibit outstanding durability in harsh operating conditions, such as cross‐flow, high‐pressure, and long‐term filtration. This general and scalable stabilizing approach for GO membranes provides new opportunities for reliable two‐dimensional laminar films used in aqueous environments.
Graphene oxide membranes are susceptible to water‐induced effects such as peeling of stacked laminates. A strategy is described for stabilization of graphene oxide membranes with interlaminar short‐chain (amine) and interfacial long‐chain (O=CS) molecular bridges. The bridged membranes demonstrate excellent durability in cross‐flow, high‐pressure, and long‐term filtration and they withstand vibration and sonication treatments.
The state-of-the-art of membrane technology is characterized by a number of mature applications such as sterile filtration, hemodialysis, water purification and gas separation, as well as many more ...niche applications of successful membrane-based separation and processing of fluid mixtures. The membrane industry is currently employing a portfolio of established materials, mostly standard polymers or inorganic materials (not originally developed for membranes), and easily scalable manufacturing processes such as phase inversion, interfacial polymerization and coating. Innovations in membranes and their manufacturing processes must meet the desired intrinsic properties that determine selectivity and flux, for specific applications. However, tunable and stable performance, as well as sustainability over the entire life cycle of membrane products are becoming increasingly important. Membrane manufacturers are progressively required to share the carbon footprint of their membrane modules with their customers. Environmental awareness among the world's population is a growing phenomenon and finds its reflection in product development and manufacturing processes. In membrane technology one can see initial steps in this direction with the replacement of hazardous solvents, the utilization of renewable materials for membrane production and the reuse of membrane modules. Other examples include increasing the stability of organic membrane polymers and lowering the cost of inorganic membranes. In a long-term perspective, many more developments in materials science will be required for making new, advanced membranes. These include “tools” such as self-assembly or micro- and nano-fabrication, and “building blocks”, e.g. tailored block copolymers or 1D, 2D and 3D materials. Such membranes must be fabricated in a simpler manner and be more versatile than existing ones. In this perspective paper, a vision of such LEGO®-like membranes with precisely adjustable properties will be illustrated with, where possible, examples that already demonstrate feasibility. These include the possibility to switch properties using an external stimulus, adapting a membrane's selectivity to a given separation, or providing the ability to assemble, disassemble and reassemble the membrane on a suitable support as scaffold, in situ, in place and on-demand. Overall, it is foreseen that the scope of future membrane applications will become much wider, based on improved existing membrane materials and manufacturing processes, as well as the combination of novel, tailor-made “building blocks” and “tools” for the fabrication of next-generation membranes tuned to specific applications.
•„Evolutionary” and (potentially) „revolutionary” ideas and concepts for membrane materials and fabrication comprehensively discussed.•Advanced or new „building blocks“ and „tools“ for making membranes systematically described and discussed.•Concepts for modular, in situ, in place, on demand assembled membrane systems based on suited scaffolds and building blocks.
As a new family of two-dimensional (2D) materials, MXene, with many attractive physicochemical properties, has attracted increasing attentions and been applied for various applications. Here, for the ...first time, ultrathin MXene membranes with thickness down to several tens of nanometers were developed for pervaporation desalination by stacking synthesized atomic-thin MXene nanosheets. Influences such as lateral size of MXene nanosheets and feed temperature on the resulting membrane performance were systematically investigated. Owing to unique 2D interlayer channels as well as high hydrophilicity, the ultrathin MXene membrane with ~60nm exhibited high water flux (85.4Lm−2h−1) and salt rejection (99.5%) with feed concentration of 3.5wt% NaCl at 65°C. In addition, the MXene membrane showed a good long-term stability and performance in synthetic seawater system. The high-performing ultrathin 2D MXene membrane developed here in this work offers great potential for pervaporation applications.
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•Ultrathin 2D Ti3C2Tx MXene membrane was designed and fabricated.•MXene membrane was first reported for pervaporation process.•Abundant oxygen-containing groups enabled MXene membranes to be hydrophilic.•High water flux (85.4Lm-2h-1) with high salt rejection (99.5%) was realized.
Graphene oxide (GO) has been considered as a promising material to develop advanced nanofiltration membranes benefiting from its extraordinary physicochemical properties. GO membranes for practical ...application need porous substrates to provide sufficient mechanical strength. Compared to extensive studies on the manipulation of GO selective layer, the influence of substrates on the performance of GO membranes has been received much less attention. Actually, significant differences in physical and chemical properties of the substrates should lead to distinct assembly structure of resulting GO membranes with uneven performance. Therefore, the effect of substrate on GO membranes formation and separation are worth study and optimization. Herein, we employed typical inorganic ceramic tube and polymeric polyacrylonitrile (PAN) and polycarbonate (PC) substrates to support GO membranes and studied the effects of their surface morphologies and roughness, surface chemical composition, as well as bulk pore structure on the formation and nanofiltration performance of resulting GO membranes. Substrates properties were revealed to have remarkable impacts on the adhesion and transport property of GO membranes. We found that the surface morphological and chemical structure of substrates induced GO assembly and determined GO adhesion, and the bulk pore structure of substrates dominated the whole transport resistance of GO membrane. Especially, the PAN substrate possessing abundant oxidized functional groups after simple hydrolysis, contributed to a robust interfacial adhesion with GO selective layer and enabled GO membrane to withstand harsh stability measurements including cross-flow, high feed pressure and long-period continuous operation. Besides, the smooth surface morphology along with the bulk highly porous structure of PAN substrate offered a favorable platform for GO assembly, resulting in competitive nanofiltration performance with water permeance of 15.5 Lm−2 h−1bar−1 and dye rejection of 99.5%. Overall, this work gives new insights of design and fabrication of durable GO membranes for practical applications.
•Surface morphology and chemical structure of substrates control GO layer formation.•Bulk pore structure of substrates dominates transport resistance of GO membrane.•Hydrolyzed PAN substrate optimizes formation and NF performance of GO membranes.
As an alternative energy source to fossil fuels, biobutanol has received increasing attention. In this work, new mixed matrix membranes (MMMs) incorporating zeolitic imidazolate frameworks (ZIF-71) ...particles into polyether-block-amide (PEBA) were prepared for biobutanol recovery from acetone–butanol–ethanol (ABE) fermentation broth by pervaporation (PV). FESEM, EDS, XRD, FT-IR, DSC and contact angle measurements were conducted to study the morphologies, physical and chemical properties and surface properties of the MMMs. The PV performance of the prepared MMMs with various ZIF-71 loadings for separating n-butanol from its aqueous solution was investigated. As a result, both separation factor and thickness-normalized flux of the PEBA membranes were improved by incorporating appropriate amount of ZIF-71 (≤20wt%). The membrane with 20wt% ZIF-71 was evaluated in ABE model solution and ABE fermentation broth, and exhibited high n-butanol separation performance. ZIF-71 particles were confirmed as promising fillers to enhance the separation performance for butanol recovery because of their excellent compatibility with polymer and organophilicity. This work demonstrated the ZIF-71/PEBA MMMs could be potential candidates for practical biobutanol production.
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•Hydrophobic ZIF-71 particles were introduced into PEBA to prepare MMMs.•The MMMs improved separation factor and flux simultaneously in aqueous butanol.•The MMMs showed high butanol recovery performance in ABE fermentation broth.
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