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The construction of robust (quasi)-solid-state electrolyte (SSE) for flexible lithium-metal batteries is desirable but extremely challenging. Herein, a novel, flexible, and robust quasi-solid-state electrolyte (QSSE) with a "tree-trunk" design is reported for ultralong-life lithium-metal batteries (LMBs). An in-situ-grown metal-organic framework (MOF) layer covers the cellulose-based framework to form hierarchical ion-channels, enabling rapid ionic transfer kinetics and excellent durability. A conductivity of 1.36 × 10

Facilitated transport membranes, with a uniform distribution of facilitated transport carriers, are highly desirable to reduce the separation energy barrier. Nevertheless, the disordered and random assembly of membrane building materials/blocks makes it hard to obtain the controlled uniform distribution of carriers within membranes. Covalent organic frameworks (COFs), equipped with a regular structure and tailored functionality, provide a favorable platform for the uniform distribution of carriers. Herein, we report an ion-exchange strategy to achieve a uniform distribution of facilitated transport carriers within a cationic COF membrane for efficient carbon capture. With the assistance of a small amount of flexible graphene oxide (GO), the potential defects between the junctions of cationic COF nanosheets were eliminated, and ultrathin (20–60 nm), defect-free COF membranes were obtained. By synergistically intensifying the diffusion selective and facilitated transport mechanisms within membranes, the optimized COF membrane exhibits a CO2 permeance of 164.2 GPU with a CO2/CH4 selectivity of 27, both of which exceed those of pure COF membranes in most literature studies. Our findings may stimulate further research on functionalized COF membranes and other kinds of organic framework membranes with uniformly distributed carriers for molecule separation.

Microporous polymer membranes hold great promise in carbon capture. However, engineering a continuous CO2-selective microporous network to achieve ultrahigh gas permeance and desirable selectivity remains a grand challenge. Aiming to manipulate the pore architecture and pore chemistry to implement efficient separation, knitted microporous polymer membranes are fabricated by in situ knitting composite membranes comprised of polyphenylene oxide (PPO) polymer and benzyl alcohol (BnOH). Specifically, the crosslinkers, formaldehyde dimethylacetal, bridge the neighboring aromatic backbones of PPO chains and BnOH to construct a highly crosslinked network with microporosity. By increasing the structural bridge density, the BET surface area of membranes increases from 4 to 538 m2 g−1. The formation of a highly interconnected microporous network provides remarkably increased permeability. Meanwhile, BnOH as a hydroxyl-containing functional building unit is knitted into micropore skeletons, which can directly tune the pore size and improve the CO2-philicity for enhanced selectivity. The resulting membrane displays an ultrahigh permeability of 4651.2 barrer with a CO2/CH4 selectivity of 27, and demonstrated good resistance to plasticization (up to 30 bar) and aging (for 190 days). This knitting strategy enabling versatile combination of building units with different structures and special functionalities may set up an innovative platform for fabricating a broad range of advanced membranes.

Well-connected transport pathways play a critical role in high performance CO2-facilitated separation membranes. Inspired by ionic cluster network in polymer electrolyte membranes (PEMs) for fast i...

Two-dimensional (2D) nanosheets have emerged as promising functional materials owing to their atomic thickness and unique physical/chemical properties. By using 2D nanosheets as building blocks, diverse kinds of two-dimensional nanochannel membranes (2DNCMs) are being actively explored, in which mass transport occurs in the through-plane and interlayer channels of 2D nanosheets. The rational construction and physical/chemical microenvironment regulation of nanochannels are of vital significance for translating these 2D nanosheets into molecular separation membranes and ionic separation membranes. Focusing on the recent advances of 2DNCMs, in this review, various porous/nonporous 2D nanosheets and their derived nanochannels are first briefly introduced. Then we discuss the emerging top-down and bottom-up methods to synthesize high-quality 2D nanosheets and to prepare high-performance 2DNCMs. As the major part of this review, we focus on three types of nanochannels, which are based on nonporous nanosheets, intrinsically porous nanosheets and perforated nanosheets. The strategies for regulating the physical and chemical microenvironments in the nanochannels are emphasized. The representative applications of 2DNCMs in molecular separations (gas separation, liquid separation) and ionic separations are presented. Finally, the current challenges and future perspectives are highlighted.

Manufacturing advanced solid-state electrolytes (SSEs) for flexible rechargeable batteries becomes increasingly important but remains grand challenge. The sophisticated structure of robust animal dermis and good water-retention of plant cell in nature grant germane inspirations for designing high-performance SSEs. Herein, tough bioinspired SSEs with intrinsic hydroxide ion (OH

Although one of the most mature battery technologies, lithium-ion batteries still have many aspects that have not reached the desired requirements, such as energy density, current density, safety, environmental compatibility, and price. To solve these problems, all-solid-state lithium batteries (ASSLB) based on lithium metal anodes with high energy density and safety have been proposed and become a research hotpot in recent years. Due to the advanced electrochemical properties of 2D materials (2DM), they have been applied to mitigate some of the current problems of ASSLBs, such as high interface impedance and low electrolyte ionic conductivity. In this work, the background and fabrication method of 2DMs are reviewed initially. The improvement strategies of 2DMs are categorized based on their application in the three main components of ASSLBs: The anode, cathode, and electrolyte. Finally, to elucidate the mechanisms of 2DMs in ASSLBs, the role of in situ characterization, synchrotron X-ray techniques, and other advanced characterization are discussed.

Polymers of intrinsic microporosity (PIMs) exhibit high permeability but moderate selectivity, which limits their industrial application in membrane gas separations. Here, a novel CO2-philic perflu...

Covalent organic frameworks (COFs) hold great promise in molecular separations owing to their robust, ordered and tunable porous network structures. Currently, the pore size of COFs is usually much larger than most small molecules. Meanwhile, the weak interlamellar interaction between COF nanosheets impedes the preparation of defect-free membranes. Herein, we report a series of COF membranes through a mixed-dimensional assembly of 2D COF nanosheets and 1D cellulose nanofibers (CNFs). The pore size of 0.45–1.0 nm is acquired from the sheltering effect of CNFs, rendering membranes precise molecular sieving ability, besides the multiple interactions between COFs and CNFs elevate membrane stability. Accordingly, the membranes exhibit a flux of 8.53 kg m−2 h−1 with a separation factor of 3876 for n-butanol dehydration, and high permeance of 42.8 L m−2 h−1 bar−1 with a rejection of 96.8% for Na2SO4 removal. Our mixed-dimensional design may inspire the fabrication and application of COF membranes., The fabrication of defect-free covalent organic framework (COF) membranes for the separation of small molecules is challenging. Here, the authors report robust COF membranes with precise molecular sieving through a mixed-dimensional assembly, exhibiting high performance for alcohol dehydration and salt rejection.

Membranes with fast CO2 transport pathways have attracted intense attention due to their outstanding CO2 permeability, showing potential for industrial application. Regulating the spatial distribution of CO2-philic groups in polymer-based membranes is expected to be a promising strategy to achieve the fast CO2 transport pathways. In membrane matrix, the interconnected network of concentrated domains of CO2 facilitated transport groups provides membranes with specific CO2 transport pathways and finally leads to their high separation performance. In this study, a novel kind of polyelectrolyte membrane, quaternary ammonium polysulfone with interconnected ionic clusters, is prepared to enhance the CO2 permeability. The hydrophilic quaternary ammonium groups tend to aggregate spontaneously to create ionic clusters. Furthermore, under humidified conditions, these ionic clusters are connected by water to form an ionic cluster network in the membrane matrix. The ionic cluster network plays the crucial role in accelerating the selective transport for CO2 molecules over CH4 by the reversible interaction between CO2 and ion pairs. By tuning the quaternization degree of polysulfone, a series of polyelectrolyte membranes with different size of ionic clusters were developed. Membranes with hydrated ionic clusters (5–9 nm) show dramatic enhancement in CO2 separation performance, especially in CO2 permeability. The as-prepared quaternary ammonium polysulfone membrane with 8.98 nm ionic clusters exhibited the high CO2 permeability of 1109.44 Barrer and a high CO2/CH4 selectivity of 29.70, which exceeds 2008 Robeson upper bound limit. The optimized separation performance of QA-PSf membranes is attractive for potential application such as CO2 capture from flue gas and natural gas.

Mixed matrix membranes (MMMs), which are fabricated by incorporating dispersed fillers into a continuous polymeric matrix, have been broadly utilized in gas separation due to their unique hierarchical structures and enhanced separation performance. Fillers of intrinsic nanopores (FINs) have drawn considerable attention because they not only can provide additional molecular transport channels but also have a potential size-sieving property. Although many excellent reviews about MMMs have been published, quite few of them are specifically designed for MMMs containing FINs. This Review focuses on three kinds of FINs, covalent organic frameworks (COFs), zeolites, and metal–organic frameworks (MOFs), as the representatives of organic, inorganic, and inorganic–organic FINs. The typical physical and chemical features of these three kinds of FINs are introduced. Afterward, methods to prepare FIN-based MMMs are briefly introduced. Particularly, solutions to prevent the aggregation and improve the dispersion of FIN...

For high-performance mixed-matrix membranes (MMMs), it is crucial to design gas transport channels in fillers to rationally manipulate the structure-property relationship. In this study, the novel porous organosilicon nanotubes (PSiNTs) were incorporated into Pebax to prepare MMMs for biogas purification (CO2/CH4 separation). After comparing the separation performance of MMMs containing PSiNTs and MMMs containing non-porous organosilicon nanotubes (SiNTs)，it can be found that the porous structure on wall of organosilicon nanotubes had a significant effect on the improvement of the gas permeability. In addition, the amino-modified PSiNTs (N-PSiNTs) were prepared and introduced into membranes to significantly enhance the CO2 permeability and CO2/CH4 selectivity. Firstly, the porosity of N-PSiNTs afforded rapid gas transport channels in MMMs and intensified the diffusion mechanism, increasing the CO2 permeability. Secondly, the reversible reaction between amino groups and CO2 in MMMs intensified the facilitated transport mechanism, increasing the CO2/CH4 selectivity. In particular, the Pebax-N-PSiNTs with 0.5 wt% and 1 wt% N-PSiNTs exhibited the optimal separation performance, which surpassed 2008 upper bound and were superior to the MMMs incorporated with other kinds of nanotubes.

In this study, a kind of functionalized graphene oxide (GO) membranes was fabricated. GO nanosheets were pre-coated by polydopamine (PDA) via spontaneous polymerization of dopamine (DA) and then cross-linked with zinc ions (Zn2+) via dopamine-mediated complexation reaction. The PDA coating rendered GO nanosheets a large number of evenly distributed oxygen-containing functional groups, which are beneficial to bond zinc ions effectively and to create favorable microenvironments of the nanochannels in GO membranes. Both PDA and Zn2+ acted as cross-linkers to tune the interlayer spacing of GO nanosheets. Zinc ions also afforded facilitated transport ability towards CO2 in dry state. Taking CO2/CH4 separation as the model system, the GO-PDA-Zn2+ membrane exhibited significantly enhanced CO2 permeance of 175 GPU with CO2/CH4 selectivity of 19.1 in dry state owing to the large transport channels and facilitated transport carriers. Moreover, the GO-PDA-Zn2+ membrane exhibited high CO2/CH4 selectivity of 32.9 in wet state owing to the stable intergalleries and moderate interlayer spacing. It is envisioned that the synergistic manipulation of PDA and metal ions can be utilized to exploit a variety of 2D membranes with superior gas separation performance.

Graphene oxide (GO) membranes display fascinating properties in molecular and ionic separation. The interlayer distance between adjacent GO nanosheets determines the separation efficiency. Currently, the interlayer distance is mostly tuned using small molecule or polymer crosslinkers, which often lead to a relatively low permeation flux due to the considerable channel occupancy. Inspired by the vein structure in nature, we propose a strategy of using vein-like supramolecular dendrimers as crosslinkers to tune the interlayer distance of GO membranes. We chose primary amine-terminated polyamidoamine (PAMAM) dendrimers with a medium molecular weight, a regularly branched structure and multiple peripheral amine groups. At a low adding amount (4 wt% PAMAM Generation 0 and equal molar of Generation 1 and 2) of dendrimers, the interlayer distance can be tuned in the range of 0.43–0.76 nm in the wet state. The resulting GO-based membranes exhibited a permeation flux of 124 kg m−2 h−1 and a NaCl rejection rate of >99.99% in simulated seawater desalination, as well as a permeation flux of 9108 g m−2 h−1 and a separation factor of 2941 in butanol dehydration, far beyond the performance of state-of-the-art membrane counterparts. Moreover, the membrane remains stable for 168 h and exhibits outstanding mechanical stability. Our study provides a novel avenue to robust and high-performance 2D nanosheet separation membranes.

Covalent organic frameworks (COFs) hold great promise in molecular separation. However, since the aperture size of most COFs is in the range of 0.8–4.9 nm, constructing COF membranes with a smaller aperture size is thus in urgent demand yet remains a grand challenge. In this study, a Bronsted acid mediated one-step self-assembly method for the fabrication of COF membranes is proposed by segregating the organic phase (containing Bronsted acids and aldehydes) from the aqueous phase (containing amines) with a polymeric support and implementing an interfacial polymerization reaction thereby. Bronsted acids, serving as a versatile mediator, can facilitate the amorphous-to-crystalline transformation, ensure the confined membrane growth at the interface and regulate the assembly behavior of COF subunits, and thus play a critical role in manipulating the microstructure evolution of COF-JLU2 membranes. More intriguingly, a correlation among membrane structures, separation performance and the partition coefficient (log P) of Bronsted acids was established. When log P lies in between 1.0 and 3.0, the COF membranes with continuous active layers, tunable thickness (50–400 nm) and small aperture size (0.49–0.51 nm) can be fabricated, achieving superior alcohol dehydration performances to all the reported membrane counterparts. Our findings may stimulate further research on bottom-up construction of COF membranes and other kinds of organic framework membranes (XOF membranes).

Mixed matrix membranes (MMMs) hold great promise in overcoming the tradeoff between membrane permeability and selectivity. The rational design of fillers to well coordinate physical and chemical selectivities remains challenging. Here, we explore a heterostructured filler by in-situ growth of ZIF-8 on LDH surface (ZIF-8@LDH), which was then embedded into Pebax to fabricate MMMs for CO2/CH4 separation. The proximity effect of the heterostructured filler endows MMMs with superior gas separation performance compared with the control MMMs containing single filler ZIF-8, LDH and dual fillers (where ZIF-8 and LDH are separately incorporated). On one hand, ZIF-8 and abundant hydroxyl groups on LDH afford favorable affinity toward CO2, significantly enhancing the physical selectivity of CO2/CH4. On the other hand, the oriented distribution of ZIF-8 on LDH elevates CO2 concentration around LDH and increases the efficiency of CO2 facilitated transport, leading to remarkably enhanced chemical selectivity. Particularly, the optimum separation performance is achieved for MMMs containing 2 wt% of ZIF-8@LDH with a CO2 permeability of 1307 Barrer and a CO2/CH4 selectivity of 31.6. The unique attributes of heterostructured filler may be extended to fabricate a variety of MMMs for high performance molecular separations.

The authors gratefully acknowledge the financial support from the National Key R&D Program of China (2017YFB0603400), the National Natural Science Foundation of China (No. 21576189, 21490583 and 21621004), Natural Science Foundation of Tianjin (16JCZDJC36500), the National Science Fund for Distinguished Young Scholars (No. 21125627), Program of Introducing Talents of Discipline to Universities (B06006), State Key Laboratory of Organic-Inorganic Composites (oic-201701004).

Graphene oxide quantum dots (GOQDs), which inherit the monolayer of sp2 carbon atoms structure and hydrophilic groups as graphene oxide (GO) sheets, but with a quantum lateral size less than 100 nm, may hold great promise in membrane preparation. In this study, a novel nanocomposite membrane by mixing GOQDs with sodium alginate (SA) matrix was prepared for ethanol dehydration. GOQDs with an average lateral dimension around 3.9 nm provided additional shorter and less tortuous transport pathways for water molecules to penetrate the membrane compared to microsized GO sheets. Benefiting from the nanosize and high hydrophilicity of GOQDs, the nanocomposite membrane exhibited favorable ethanol dehydration performance with a total permeation flux of 2432 ± 58 g m−2 h−1, which was 60% higher than that of pristine alginate membrane, and a separation factor of 1152 ± 48. Incorporating GOQDs into the membranes can be an effective approach to improving the water permeation for water-permselective pervaporation membranes.

In this study, novel kinds of MMMs were fabricated by incorporating ZIF-67 nanoparticles into polymers of intrinsic microporosity (PIM-1). ZIF-67 (Co substituted ZIF-8) displays stiffer Co-N bond as compared with the Zn-N bond in ZIF-8, which might led to the slightly smaller effective pore aperture of ZIF-67. Good compatibility between ZIF-67 nanoparticles and PIM-1 matrix rendered ideal interfacial morphology. The intrinsic separation performance of ZIF-67 was estimated from our experimental separation results based on the Maxwell model. The calculation demonstrated its superior CO2/CH4 selectivity of 45, which is twice compared with that of ZIF-8, supporting the high molecular sieving efficiency of PIM-1/ZIF-67 MMMs. Particularly, the CO2 and H2 permeability increased by 15.1% and 59.6% for PIM-1 membrane with 20 wt% ZIF-67 loading, meanwhile CO2/CH4 and H2/CH4 selectivity increased by 34.4% and 86.96%, respectively. The strategy of incorporating highly selective ZIFs into polymers of intrinsic microporosity may have promising potential in fabricating high performance membranes for efficient gas separation.

The urgent demand of capturing CO 2 from energy relevant applications stimulated researchers to develop novel high-performance membrane materials. PIM-1, a representative class of polymers of intrinsic microporosity (PIMs), possesses high permeability but low selectivity due to its highly twisted ladder-like structure. A facile approach to improve CO 2 separation performance of PIM-1 is to implant CO 2 -philic fillers. In this study, a novel nano-sized filler Poly(ethylene glycol) functionalized Polyhedral oligomeric (PEG-POSS), with PEG anchored on POSS was incorporated into PIM-1 membrane at nanoscale level to increment CO 2 selectivities of the membrane. The as-prepared PIM-1/PEG-POSS mixed matrix membranes (MMMs) were characterized by Fourier transform infrared (FT-IR) spectra, thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Single gas permeabilities of N 2 , CH 4 and CO 2 were measured by the time-lag method. PIM-1/PEG-POSS membranes showed enhanced CO 2 selectivity over CH 4 and N 2 at high PEG-POSS loadings. Specifically, the PIM-1/PEG-POSS membrane with 10 wt% PEG-POSS nanoparticles exhibited the optimal separation performance, of which the CO 2 permeability reached 1300 Barrer and CO 2 /CH 4 selectivity increased by 150% compared with the pristine PIM-1, which surpassed the 2008 Robeson upper bound. The as-prepared PIM-1/PEG-POSS MMMs show great potential for CO 2 capture.

Achieving high membrane performance in terms of gas permeance and carbon dioxide selectivity is an important target in carbon capture. Aiming to manipulate the channel affinity towards CO2 to implement efficient separations, gas separation membranes containing CO2 -philic and non-CO2 -philic nanodomains in the interlayer channels of graphene oxide (GO) were formed by intercalating poly(ethylene glycol) diamines (PEGDA). PEGDA reacts with epoxy groups on the GO surface, constructing CO2 -philic nanodomains and rendering a high sorption capacity, whereas unreacted GO surfaces give non-CO2 -philic nanodomains, rendering low-friction diffusion. Owing to the orderly stacking of nanochannels through cross-linking and the heterogeneous nanodomains with moderate CO2 affinity, a GO-PEGDA500 membrane exhibits a high CO2 permeance of 175.5 GPU and a CO2 /CH4 selectivity of 69.5, which is the highest performance reported for dry-state GO-stacking membranes.

Polymers of intrinsic microporosity (PIMs) exhibit the inherent superior permeability over traditional commercial polymers, however, the relatively low selectivity restrict their broad application in gas separation. In this study, novel kinds of mixed matrix membranes (MMMs) combined covalent organic frameworks (COFs) and PIMs were prepared and utilized for improving the selectivity of carbon capture process. Covalent organic framework (SNW-1) was synthesized via Schiff base chemistry and incorporated into polymer of intrinsic microporosity (PIM-1) to prepare MMMs. Pure gas permeation tests and mixed gases separation performances of the MMMs were conducted. Owing to its proper porosity characteristics and good compatibility with PIM-1 matrix, the incorporation of SNW-1 significantly intensified the diffusion process of CO2 within the membrane. Compared with pure PIM-1 membrane, the prepared MMMs showed an increment of 27.4% and 37.6% in selectivity of CO2/CH4 and CO2/N2 along with an enhancement of 116% in CO2 permeability. The strategy of incorporating COFs into polymers of intrinsic microporosity may hold promising potential in preparing high performance MMMs for gas separation.

Biological membranes possess hierarchical channels and thus exhibit ultrahigh permselectivity for molecules and ions. Intrigued by the delicate structure and transport mechanisms in biochannels, polymer composite membranes with selective transport channels are successfully fabricated for diverse energy- and environment-related applications. This tutorial review aims to present the latest progress in the design and construction of selective molecule/ion transport channels within polymer composite membranes with emphasis on the regulation of the physical and chemical microenvironments of these channels. The concluding remarks are presented with a tentative perspective on the future research and development of highly efficient channel-facilitated molecule/ion transport across polymer composite membranes.

Harvesting energy from biogas is a potential way to retard the depletion of fossil fuels and fight against global warming simultaneously. Membrane technology holds great promise to achieve cost-effective biogas upgrading, along with advantages of low energy consumption and environmental friendliness, which leads to extensive exploration in fabricating CO2 membranes with high separation performance. In this study, mixed matrix membranes are fabricated by incorporating exfoliation-free layered double hydroxides laminates intercalated with amino acids (Phe with hydrophobic side chains and Glu with hydrophilic side chains) into a low-cost commercial Pebax (poly (amide-b-ethylene oxide)) polymer. Both amino and carboxyl groups can facilitate the transport of CO2 through quadrupole moment interaction, enlarged interlayer spacing and reversible reaction. Particularly, MMM containing 5 wt% AA-LDH exhibits an optimal permeability of 790 Barrer and a promising CO2/CH4 selectivity of 31, which is 64.6% and 83.9% higher than the pristine Pebax membrane, respectively. The distinct advantages in terms of facile fabrication and processability confer the LDH-based membrane with great potential for large-scale CO2 capture and separation.

High-performance membrane materials are urgently demanded for efficient membrane-based biogas upgrading. Polyelectrolytes with convertible ionic groups, spontaneously forming interconnected facilitated transport pathways for gas molecules via microphase separation, exhibit promising potential in membrane-based separation. However, there is a great challenge to further enhance the gas permeability and selectivity simultaneously due to the limited microphase separation and low free volume generated by the strong interaction between ionic groups. Herein, we demonstrate a novel strategy to construct the tunable hollow quaternary ammonium (-N+(CH2CH3)3) clusters with good CO2 affinity via sacrificial template method in quaternized polysulfone (QAPSf) membranes for achieving the fast transport of CO2. The templates (POSS) induce the formation of –N+(CH2CH3)3 clusters through forced microphase separation in the membranes and then are etched away to generate hollow CO2-philic clusters to increase the fractional free volume in membranes and thus improve CO2 diffusion. After that, the B(OH)4- as counterions by ion exchange endow the hollow CO2-philic clusters with high CO2-facilitating ability, which simultaneously enhance the CO2 permeability and CO2/CH4 selectivity. The resultant QAPSf-B(POSS-2) membrane exhibits superior separation performance with an optimal permeability of 1113 Barrer and a CO2/CH4 gas selectivity of ~45, i.e. 334% and 73% higher than the pristine QAPSf membrane, respectively, breaking the trade-off between permeability and selectivity and surpassing the Robeson 2008 upper-bound.

Plasticization and physical aging due to the undesirable deformation of chain microstructure under high pressure or long-term operation hamper the practical application of polymer membranes. Fixing the polymer chain architecture without sacrificing the internal free volume and thereby the membrane permeability remains a grand challenge. The venation architecture in plant leaf, featured by its stable vein structure with abundant interveinal spaces, offers us an inspiration for designing a highly permeable and stable chain architecture. Here, we construct a venation-like chain architecture in polyphenylene oxide (PPO) membrane by introducing numerous interchain crosslinking bridges using Friedel-Crafts-based hypercrosslinking reaction. These crosslinking bridges rigidify the chains and prevent them from dense packing, inhibiting the microstructural deformation, while simultaneously generating abundant free volume. The resulting membranes display ultrahigh CO2 permeability of 5130 Barrer (73-fold higher than pristine PPO membrane), along with superior structural stability. Particularly, the plasticization is fully suppressed under high pressure even up to 70 bar and the physical aging-induced loss of CO2 permeability is reduced remarkably down to as low as 19% after 360 days, transcending most of the state-of-the-art membranes. This venation-like chain architecture opens a new avenue to solving the current permeability-stability dilemma for the implementation of polymer membrane technology.

The acceleration of electron transfer through the regulation of coordination environment of active sites is an effective way to improve reaction performances. Herein, cobalt layered double hydroxide decorated with sub-1 nm platinum clusters (Pt/Co-LDH) were synthesized for oxygen evolution reaction (OER). The integration of platinum unexpectedly induced unique nanocage structures assembled by ultra-thin LDH nanosheets via an in-situ redox process. The as-prepared Pt/Co-LDH nanocages exhibit high OER activity with a low overpotential of 265 mV at 10 mA cm−2. Experiments and density functional theory calculations indicate the high catalytic activity is mainly attributed to the strong interactions between Pt and Co-LDH, which can regulate the local coordination environment and electronic structures of cobalt. The well-defined Co–Pt−OH structures could help promote the adsorption energy of water molecules and reduce the energy barrier of rate-limiting step, benefiting from the enhanced electron transfer during the electrocatalytic process, playing the role of “electronic pump”. Furthermore, the novel in-situ redox synthetic strategy also presents a facile universality to obtain metal-doped (Pt, Au, Pd) Co-LDH nanocage structures.

Membrane separation is an energy-efficient technology to achieve biogas upgrading. However, their broad application is limited by the relatively low gas permeability and thus the large membrane area. Polymers of intrinsic microporosity (PIMs), as a kind of highly permeable polymers, hold great promise to solve this problem but are restricted by their relatively low selectivity. In this study, significant enhancement in the selectivity of highly permeable PIM-1 membranes was achieved through incorporating amino-functionalized zeolitic imidazolate framework ZIF-7 to prepare mixed matrix membranes (MMMs). NH2-ZIF-7 exhibits not only excellent intrinsic CO2/CH4 separation ability but also favorable interaction with the PIM-1 polymer. The fortified interfacial interaction generates the rigidification of polymer chains at the interface and partial blockage of NH2-ZIF-7 particles, which both contributes to the enhancement of CO2/CH4 diffusion selectivity. Notably, the CO2/CH4 selectivity of the mixed matrix membrane containing 20 wt% NH2-ZIF-7 increased to 20.6 with CO2 permeability of 2953 Barrer, which transcended the reported 2008 upper bound of polymer membranes. To analyze the gas transport behavior within MMMs and explain the enhanced selectivity, a modified Maxwell model considering rigidified polymer region and partially blocked particle skin was proposed and validated by the good consistency between the experimental and predicted data.

Membrane-based separations are of energy-efficient and environmentally benign attributes for biogas energy developments. Membranes from polymers of intrinsic microporosity (PIMs) often suffer from low selectivity. In this study, remarkable enhancements in CO2/CH4 selectivity of PIM-1 membranes are achieved by incorporating nano-sized ZIF-67 (ZIF-S) filler with a larger specific surface area and a better compatibility, thereby fortifying the interactions with PIM-1 matrix and effectively alleviating nonselective interfacial voids. For the resulting PIM-1/ZIF-S membranes, a maximum CO2/CH4 selectivity of 21.1 was acquired with 15 wt% loading of ZIF-S, an increase of 69.40% compared with the pristine PIM-1 membrane, along with an associated CO2 permeability above 2800 Barrer. To elucidate gas transport behaviors within membranes, a modified Maxwell model is developed and the calculation results match well with the experimental data. The strategy of incorporating framework nanofillers into membranes may find promising applications in enhancing the selectivity of highly permeable polymer membranes.

Development of high-performance membranes for biogas upgrading is an urgent demand for the application of membrane technology in the field of renewable energy. Covalent organic frameworks (COFs) exhibit promising potential in membrane-based separation for their highly ordered crystalline porous structure, total organic backbone and tailored functionality. However, the limited functional groups on frameworks and relatively larger pore size of existing COFs restrict further improvement in the separation efficiency especially for gas mixtures. This work reports a novel strategy for modifying the pore of COF-300 with imidazolium-based ionic liquid [bmim][Tf2N] by post-impregnation and then incorporate the composite particles IL@COF-300 into Pebax matrix to prepare mixed matrix membranes (MMMs). The IL decreases the pore size of COF-300 from 1.28 nm to 1.09 nm and increases the diffusion coefficient difference (DCO2/DCH4) between CO2 and CH4. Moreover, the presence of IL with high CO2 solubility endows the COF-300 pores with CO2-facilitating ability and thus increasing the solubility difference (SCO2/SCH4). The dual functions of IL lead to an enhanced separation performance of the resultant IL@COF-300/Pebax MMMs with an optimal permeability of 1601 Barrer and a CO2/CH4 gas selectivity of ~39, i.e. 209% and 87% higher than the pristine Pebax membrane, respectively, breaking the trade-off between permeability and selectivity and surpassing the Robeson 2008 upper-bound. The membrane also exhibits superior long-term operation stability during two months.

2D material membranes with well-defined interlayer nanochannels hold great promise for precise molecular separation, where the size and surface chemical property of the channel determine the separation efficiency. The currently reported 2D material membranes for efficient CO2 separation are primarily built by introducing crosslinkers or intercalators into the interlayer channel. In this study, we demonstrate a novel 2D material membrane with inherent CO2-selective transport channels based on layered double hydroxide (LDH). The intrinsic breathing effect of LDH toward CO2 enables the spontaneous incorporation of CO2 molecules into the interlayer nanochannels and subsequent conversion/transport in the form of CO32− species which are released as CO2 at the downstream side of membrane. Moreover, the intercalated CO32− ions with an ionic radius of 0.136 nm narrow down the nanochannel size from 0.7 nm to 0.3 nm by electrostatic interaction with LDH layers, conferring the membrane a distinct molecular sieving ability for CO2/CH4 separation. The unique breathing effect and size-sieving effect jointly contribute to the high membrane separation performance with CO2 permeance of 150 GPU and CO2/CH4 selectivity of 33. This study is anticipated to extend the materials and strategies for design of the CO2 preferential transport channels in membranes.

Graphene oxide (GO) membranes with two-dimensional (2D) interlaminar channels display fascinating properties in gas separation where the separation efficiency is governed by the size and interlayer interactions of 2D channels. Incorporating intercalators into GO interlayers is recognized as an effective strategy to create appropriate microenvironments for biogas upgrading (remove CO2 from raw biogas, specifically CO2/CH4 separation). Herein, we proposed a strategy of using a kind of nanocage, amino-functionalized polyhedral oligomeric silsesquioxane (POSS–NH2), as versatile intercalator to regulate the channel structure and afford favorable microenvironments for CO2/CH4 separation in GO membranes. The channel size of GO membranes was reduced from 9.1 A to 4.7 A by POSS-NH2 crosslinking, which could elevate the diffusion selectivity of CO2/CH4. The amino groups on POSS-NH2 are able to react with CO2 reversibly, facilitating the transport of CO2. Through synergistically intensifying diffusion selective and facilitated transport mechanisms, the optimized membrane CO2/CH4 selectivity reached 74.5, which is superior to most reported values of 2D membranes. Moreover, we selected another POSS intercalator without amino groups, in order to distinguish the contribution of physical and chemical mechanisms to selectivity. Our study may provide a novel avenue in designing versatile intercalators to construct high-performance 2D membranes.

Correction for ‘Brønsted acid mediated covalent organic framework membranes for efficient molecular separation’ by Hongjian Wang et al., J. Mater. Chem. A, 2019, 7, 20317–20324.