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Silver-modified LTA zeolites are validated to be one of the most efficient nanomaterials applied in adsorptive separation, which is an energy-efficient alternative to the state-of-the-art cryogenic distillation for ethylene and ethane separation. Here, three representative LTA zeolites, Ag modifications via different methods including ion-exchange, mechanical mixing, and acid leaching, are systematically explored by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, H2 temperature-programming reduction, and ultraviolet–visible spectroscopy with the assistance of Grand Canonical Monte Carlo simulations to identify the location of various Ag species in the LTA zeolite and thus to understand the mechanism of promoted separation performance in nature. The performance of these zeolites for the separation of ethylene/ethane is validated via ideal adsorbed solution theory and breakthrough experiments under ambient conditions. It is confirmed that Ag+ can afford selective binding of ethylene via π-complexation. Ag2O nanoparticles encapsulated in the zeolitic channels narrow the pore diameters to the suitable size, excluding ethane via molecular sieving. The synergistic effect of π-complexation and molecular sieving from Ag+ and Ag2O nanoparticles in the zeolitic channels triggers highly selective adsorption of ethylene over ethane. [ABSTRACT FROM AUTHOR]

Ultrafast molecular-sieving graphene-based membranes with selective separation of volatile aromatic compounds (VACs) have great potential in environmental protection, reutilization of expensive materials, and industrial separation processes. However, current graphene-based absorbents suffer from slow removal speed and limited adsorption capacity for VACs. Herein, pristine and Ni2+-controlled graphene oxide membranes (GOMs) with a permeance up to ∼8.0 × 10–6 mol m–2 s–1 Pa–1, being 1–2 orders of magnitude higher than those of previously reported membranes. The GOMs selectively separate VACs from N2 is achieved on ceramic substrates via the size-exclusion effect for the first time. At a high VACs feed concentration, such GOMs show high rejection rates of 99.8, 99.4, 95.9, and 97.3% for phenol, benzaldehyde, benzoic acid, and benzylamine, respectively. X-ray diffraction (XRD) results show the two-dimensional (2D) channel size for gas transportation within the GOMs is 0.44 nm, which can reject the transportation of VACs but have no effect on N2. Interestingly, using improved Ni2+-controlled GOMs, the rejection rates of benzoic acid and benzylamine rejection rates increased from 95.9 to 98.6% and from 97.3 to 99.4%, respectively. Our finding provides a fast and efficient way to filter VACs in air and has potential applications in air purification and industrial processes. [ABSTRACT FROM AUTHOR]

Plasma-induced polymerization of liquid silsesquioxane monomer (1,2-bis-(triethoxysilyl)-ethane, BTESE) at the gas–liquid interface was achieved at room temperature by employing an atmospheric-pressure plasma jet. The polymerization of the liquid monomer under exposure to atmospheric-pressure plasma resulted in the formation of a thin polysilsesquioxane layer at the immediate surface of the porous support. The confined polymerization at the plasma-liquid interface was demonstrated to be beneficial for preparing nanocomposite membranes with a thin selective layer on top of the porous support. The BTESE-derived polysilsesquioxane membrane exhibited high selectivity for gas separation (H2/CH4 = 195) based on the molecular sieving mechanism. [ABSTRACT FROM AUTHOR]

In recent years, extensive research has used molecular dynamics simulations to investigate gas separation through nanoporous graphene (NPG) membranes. However, most studies have considered graphene membranes as rigid, overlooking the impact of their inherent flexibility. This study systematically quantifies the effect of graphene flexibility on gas permeation by comparing the diffusion of various gases through flexible and rigid single-layer NPG models. The results demonstrate that flexibility notably increases permeance, particularly for gases with larger molecular diameters/pore size ratios, by allowing gas molecules greater mobility within the pore. Interestingly, the effect of flexibility boils down to the expansion of the average pore size, and the detail of the membrane's vibrational dynamics is of little importance in quantifying permeance. Our work shows that accounting for flexibility in molecular models improves the alignment of simulation results with experimental data, emphasizing the importance of considering membrane flexibility in predictive models of NPG membrane performance.

Porous single-layer graphene is believed to be an ultimate molecular sieving membrane. One of the bottlenecks in scaling up graphene membranes is the transfer process in which capillary forces as well as the mechanical tensions imposed on the graphene film generate unwanted cracks and tears. Herein, we report a single-step fishing-free transfer technique for the fabrication of a helium-sieving graphene membrane using a spin-coating-assisted approach in which no capillary forces and mechanical tensions are exerted on the graphene film. The porous polysulfone (PS), which is synthesized in this method, is applied as both the graphene protective layer and the porous reinforcing support; thus, eliminating the fishing stage in which the graphene film is scooped onto a supporting substrate. The proposed technique yields a crack-free and large-area (∼1 cm2) graphene film on the porous polymer substrate. This technique also eliminates the issue with polymer residues remaining on the graphene surface during the transfer process. A relatively high gas molecular sieving performance (gas selectivity of 25, 24, and 1.1 for He/CH4, H2/CH4, and He/H2 separation, respectively) was obtained, which demonstrates the presence of sub-nanometer intrinsic defects as well as the absence of cracks and tears in the graphene membrane. Despite the low graphene porosity of 0.002%, agreeable He and H2 permeance (up to 5.18 × 10–8 mol m–2 s–1 Pa–1) was observed, which highlights the success of the developed technique used for the fabrication of graphene membrane in the current work. [ABSTRACT FROM AUTHOR]

Chemical modification of the interior and exterior surfaces of protein nanocages holds promise for various applications such as cosmetics, pharmaceuticals, and catalysts. However, dual-surface modification of these surfaces using different chemicals remains challenging, particularly when the same substituents, such as cysteine thiols, are modified. We recently produced an artificial protein nanocage called TIP60 that has 20 large surface pores. Chemical modification of cysteine residues introduced in the interior surface of TIP60 showed that these pores allow the passage of small molecules from the outside environment to the inside of the nanocage. In this study, we found that the surface pores on TIP60 function as size-dependent molecular filters. Modification experiments using different-sized polymers containing maleimide groups, which specifically react with thiols, showed that macromolecules with diameters larger than that of the pores could not penetrate into the inner cavity. This molecular size discrimination by the pores prompted us to perform stepwise dual-surface functionalization of a double mutant of TIP60 presenting cysteine residues on the interior and exterior surfaces. This was achieved by modifying the exterior cysteine residues with a polymer containing a maleimide group that cannot penetrate to the inside of the nanocage, followed by modification of the interior cysteine residues using thiol-containing small molecules. Dual-functionalized TIP60 released internal small molecules in a redox-responsive manner. This simple approach for dual-surface modification would make TIP60 a useful nanocarrier for a broad range of applications including drug-delivery and molecular filtration systems. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) subnanometer channels allow unique mass transport promising for molecular sieving. New 2D channels of MoS2 nanosheets allow one to understand molecular transmission and separation, unlike the graphene oxide counterpart containing various defects and cationic metal contaminants. Membranes from layered MoS2 platelets show extraordinary stability in an aqueous environment and compatibility with polymer filters, both beneficial to efficient manufacturing. Sharing gas-tightness and unimpeded water vapor permeation with a graphene oxide membrane, our lamellar MoS2 membrane demonstrates a molecular sieving property for organic vapor for the first time. The MoS2 membrane also reveals diffusion selectivity of aqueous ions, attributable to the energy penalty in bulk-to-2D dimensional transition. These newly revealed properties of the lamellar membrane full of angstrom-sized 2D channels point to membrane technology applications for energy and environment. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) is a key reactant in several Fischer-Tropsch processes, including those used in light olefin and methanol syntheses. However, it is highly toxic and causes serious poisoning of noble metal catalysts. Thus, a solid adsorbent that can selectively capture CO, especially at low concentrations, is required. In this study, zeolite Y-based adsorbents in which Cu(I) ions occupy the supercage cation sites (CuCl/Y) are prepared via solid-state ion exchange. Volumetric adsorption measurements reveal that the Cu(I) ions significantly enhance CO adsorption in the low-pressure range by π-complexation. Furthermore, unexpected molecular sieving behavior, with extremely high CO/CO 2 selectivity, is observed when excess CuCl homogeneously covers the zeolite pore structures. Thus, although CO has a larger kinetic diameter, it can penetrate the zeolite supercage while smaller molecules (i.e., Ar and CO 2 ) cannot. Density functional theory calculations reveal that CO molecules can remain adsorbed in pseudoblocked pores by CuCl, thanks to the strong interaction of C 2p and Cu 3d states, resulting in the high CO/CO 2 selectivity. One of the prepared adsorbents, CuCl/Y with 50 wt % CuCl, is capable of selectively capturing 3.04 mmol g -1 of CO with a CO/CO 2 selectivity of >3370.

One scalable and facile dip-coating approach was utilized to construct a thin CO 2 -selection layer of Pebax/PEGDA-MXene on a hollow fiber PVDF substrate. An interlayer spacing of 3.59 Å was rationally designed and precisely controlled for the MXene stacks in the coated layer, allowing efficient separation of the CO 2 (3.3 Å) from N 2 (3.6 Å) and CH 4 (3.8 Å). In addition, CO 2 -philic nanodomains in the separation layer were constructed by grafting PEGDA into MXene interlayers, which enhanced the CO 2 affinity through the MXene interlayers, while non-CO 2 -philic nanodomains could promote CO 2 transport due to the low resistance. The membrane could exhibit optimal separation performance with a CO 2 permeance of 765.5 GPU, a CO 2 /N 2 selectivity of 54.5, and a CO 2 /CH 4 selectivity of 66.2, overcoming the 2008 Robeson upper bounds limitation. Overall, this facile approach endows a precise controlled molecular sieving MXene membrane for superior CO 2 separation, which could be applied for interlayer spacing control of other 2D materials during membrane construction.

Tunable regulation of molecular penetration through porous membranes is highly desirable for membrane applications in the pharmaceutical and medical fields. However, in most previous reports additional reagents or components are usually needed to provide the graphene-based membranes with responsiveness. Herein, we report tunable arch-bridged reduced graphene oxide (rGO) nanofiltration membranes modulated by the applied voltage. Under a finite voltage of 5 V, the rGO membrane could completely reject organic/anionic molecules. With assistance of the voltage, the positive-charge-modified rGO membrane realized the universal rejection of both cationic and anionic dyes, also showing the valid modulation in harsh organic solvents. The efficient electrical modulation depended on the synergetic effects of Donnan repulsion and size exclusion, benefiting from the electric field enhancement in arch-bridged rGO structures. Furthermore, multicomponent separation was achieved by our electrically modulated rGO-based membranes, demonstrating their potential in practical applications such as pharmaceutical industries.

The development of adsorption-based separation processes alternative to the energy-intensive cryogenic distillation for a mixture of propylene and propane remains essential but challenging in gas industries. Molecular sieving separation of C 3 H 6 /C 3 H 8 on stable carbon adsorbents appeals to be promising, while it is quite challenging to realize due to the random distributions and arrangements of the internal pores in common carbons. Herein, a series of polysaccharide-based CD-MOF-derived ultramicroporous carbon adsorbents with their pore size tuned at a subangstrom level were prepared. Molecular sieving separation of C 3 H 6 /C 3 H 8 was realized on the optimal C-CDMOF-2-700 owing to the delicate structure with an appropriate pore size (5.0 Å). Besides, C-CDMOF-2-700 exhibited a high C 3 H 6 uptake of 1.97 mmol g -1 under ambient conditions. An ultrahigh uptake ratio of C 3 H 6 /C 3 H 8 at 1.0 kPa (403) was also achieved, outperforming all reported adsorbents. Kinetic adsorption tests and breakthrough experiments further demonstrate this well-designed carbon adsorbent to be promising in industrial C 3 H 6 /C 3 H 8 separation.

Water-soluble volatile organic compounds (VOCs) are among the most difficult-to-treat species during wastewater treatment. The current purification and removal of high-concentration VOCs still rely on the energy-consuming distillation and high-pressure driven reverse osmosis technology. There is an urgent need for an advanced technology that can effectively remove high-concentration VOCs from water. Here, we report a metal-organic framework (MOF)/polyaniline (PANI) nanofiber array composite photothermal membrane for removal of high-concentration VOCs from water via molecular sieving during a solar-driven evaporation process. The modified zeolitic imidazole framework-8 (ZIF-8) layer grown on a PANI nanofiber array acts as a molecular sieving layer to evaporate water but intercept VOCs. The composite membrane exhibits high VOCs rejection and a high-water evaporation rate for water containing different concentrations of VOCs. When treating water containing VOCs with a concentration of up to 400 mg L -1 , the VOCs rejection rate is up to 99% and the water evaporation rate is 1.0 kg m -2 h -1 under 1 sun irradiation (1 kW m -2 ). Our work effectively combines the molecular sieve effect with a solar-driven evaporation process, which provides an effective strategy for the treatment of water containing VOCs.

Adsorptive separation by porous solids provides an energy-efficient alternative for the purification of important chemical species compared to energy-intensive distillations. Particularly, the separation of linear hexane isomers from its branched counterparts is crucial to produce premium grade gasoline with high research octane number (RON). Herein, we report the synthesis of a new, flexible zinc-based metal-organic framework, [Zn 5 (μ 3 -OH) 2 (adtb) 2 (H 2 O) 5 ·5 DMA] (Zn-adtb), constructed from a butterfly shaped carboxylate linker with underlying (4,8)-connected scu topology capable of separating the C6 isomers n HEX, 3MP, and 23DMB. The sorbate-sorbent interactions and separation mechanisms were investigated and analyzed through in situ FTIR, solid state NMR measurements and computational modeling. These studies reveal that Zn-adtb discriminates the n HEX/3MP isomer pair through a kinetic separation mechanism and the n HEX/23DMB isomer pair through a molecular sieving mechanism. Column breakthrough measurements further demonstrate the efficient separation of linear n HEX from the mono- and dibranched isomers.

Realizing membranes of atomic thickness functioning reliably constitutes a giant leap forward for a plethora of applications where the efficient separation of fluid constituents at the molecular level is critical. Here, by employing density functional theory, we explore the energy landscape of typical gas molecules attempting permeation through graphene nanopores and determine the minimum energy permeation pathways, based on the precise knowledge of the related molecular level interactions. With this approach we investigate two basic permeation routes: direct permeation and surface-based transport. We find that for subnanometer pores, the diffusion barrier of direct and surface transport depends on the pore chemical functionalization, while the molecule pore permeation barrier is independent of the gas-pore approach due to the overlap of surface and direct diffusion paths over the pore center. The overall minimum energy permeation pathway of He, H 2 , CO 2 , and CH 4 molecules, across nanopores of different dimensions and chemical functionalization, defines the pore diameter (∼1.2 nm) below which effusion theory is inaccurate, as well as the critical pore diameter (∼0.8 nm) required to achieve positive permeation barriers driving molecular sieving. We determine that achieving positive permeation barriers required for high selectivity gas separation is inseparably combined with postpermeation desorption barriers due to attractive van der Waals interactions. The discovered permeation energetics are pore-molecule-specific and are incorporated into an analytical model extending existing theory. Our results provide a scientific background for rational pore design in graphene membranes, which can lead to gas separation at a commercially relevant performance level.

In this study, three polymer precursor conformations, dilute, semi-dilute, and concentrated, were used to fabricate carbon molecular sieving (CMS) membranes via a fixed carbonization protocol. The effects of the precursor conformation on the microstructure of the resultant CMS membranes were characterized by Raman analysis. Their ability to separate light gases, such as H 2 /CH 4 and H 2 /N 2 , was assessed with a single-gas system. Additionally, a novel method was proposed to detect the cutoff size of the CMS membranes created in this study. The method combined high-resolution transmission electron microscopy (HR-TEM) and a focused ion beam (FIB) system. Finally, due to the semi-dilute solution's denser polymer chains and lack of severe polymer entanglement, highly graphited CMS membranes with excellent gas separation performance were successfully synthesized using a semi-dilute polyetherimide dope solution. Interlayer distances in the carbon matrix were visualized and measured using our novel probing tool (HR-TEM and FIB) and software. The CMS membrane fabricated with a semi-dilute dope exhibited the best gas separation performance of the tested membranes. It had the most ordered carbon sheet orientation and exhibited a superior selectivity of H 2 /CH 4 = 293 with a hydrogen permeability of 1138.7 Barrer, far surpassing the reported permselectivity of other membranes. We believe that the high H 2 /CH 4 selectivity presented here is unprecedented for CMS membranes reported in the literature.

Highly permselective nanostructured membranes are desirable for the energy-efficient molecular sieving on the subnanometer scale. The nanostructure construction and charge functionalization of the membranes are generally carried out step by step through the conventional layer-by-layer coating strategy, which inevitably brings about a demanding contradiction between the permselective performance and process efficiency. For the first time, we report the concurrent construction of the well-defined molecular sieving architectures and tunable surface charges of nanofiltration membranes through precisely controlled release of the nanocapsule decorated polyethyleneimine and carbon dioxide. This novel strategy not only substantially shortens the fabrication process but also leads to impressive performance (permeance up to 37.4 L m -2 h -1 bar -1 together with a rejection 98.7% for Janus Green B-511 Da) that outperforms most state-of-art nanofiltration membranes. This study unlocks new avenues to engineer next-generation molecular sieving materials simply, precisely, and cost efficiently.

Transmembrane protein channels, including ion channels and aquaporins that are responsible for fast and selective transport of water, have inspired membrane scientists to exploit and mimic their performance in membrane technologies. These biomimetic membranes comprise discrete nanochannels aligned within amphiphilic matrices on a robust support. While biological components have been used directly, extensive work has also been conducted to produce stable synthetic mimics of protein channels and lipid bilayers. However, the experimental performance of biomimetic membranes remains far below that of biological membranes. In this review, we critically assess the status and potential of biomimetic desalination membranes. We first review channel chemistries and their transport behavior, identifying key characteristics to optimize water permeability and salt rejection. We compare various channel types within an industrial context, considering transport performance, processability, and stability. Through a re-examination of previous vesicular stopped-flow studies, we demonstrate that incorrect permeability equations result in an overestimation of the water permeability of nanochannels. We find in particular that the most optimized aquaporin-bearing bilayer had a pure water permeability of 2.1 L m -2 h -1 bar -1 , which is comparable to that of current state-of-the-art polymeric desalination membranes. Through a quantitative assessment of biomimetic membrane formats, we analytically show that formats incorporating intact vesicles offer minimal benefit, whereas planar biomimetic selective layers could allow for dramatically improved salt rejections. We then show that the persistence of nanoscale defects explains observed subpar performance. We conclude with a discussion on optimal strategies for minimizing these defects, which could enable breakthrough performance.

Two-dimensional materials are the essential building blocks of breakthrough membrane technologies due to minimal permeation barriers across atomically thin pores. Tunable pore size fabrication combined with independently controlled pore number density is necessary for outstanding performance but remains a challenge. There is a great need for parallel, upscalable methods that can control pore size from sub-nm to >5 nm, a pore size range required for membranes with effective molecular separation. Here we report a dry, facile, and scalable process introducing atomic defects by design, followed by selective etching of graphene edge atoms able to controllably expand the nanopore dimensions from sub-nm to 5 nm. The attainable average pore sizes at 10 15 m -2 pore density promise applicability to various separation applications. We investigate the gas permeation and separation mechanisms, finding that these membranes display molecular sieving (H 2 /CH 4 separation factor = 9.3; H 2 permeance = 3370 gas permeation units (GPU)) and reveal the presence of interweaved transport phenomena of pore chemistry, surface flow, and gas molecule momentum transfer. We observe the smooth transition from molecular sieving to effusion at unprecedented permeance (H 2 /CH 4 separation factor = 3.7; H 2 permeance = 10 7 GPU). Our scalable graphene membrane fabrication approach in combination with sub-5 nm pores opens a new route employing 2D membranes to study gas transport and effectively paving the way to industrial applications.

Thin-film composite (TFC) membranes are favored for precise molecular sieving in liquid-phase separations; they possess high permeability due to the minimal thickness of the active layer and the high porosity of the support layer. However, current TFC membrane fabrication techniques are limited by the available materials for the selective layer and do not demonstrate the level of structural control needed to substantially advance organic solvent nanofiltration (OSN) membrane technology. In this work, we employ the newly developed thin-film lift-off (T-FLO) technique to fabricate polybenzimidazole (PBI) TFC membranes with porous support layers uniquely tailored to OSN. The drop-cast dense PBI selective layers endow the membranes with an almost complete rejection of common small dye molecules. The polymeric support layer is optimized by a combinatorial approach using four different monomers that alter the cross-linking density and polymer chain flexibility of the final composite. These two properties substantially affect the porogen holding capacity of the reticular polymer network, leading to the formation of different macropore structures. With a 150 nm thick PBI selective layer and fine-tuning of the support layer, the resulting membrane achieves stable and superior permeance of 14.0, 11.7, 16.4, 11.4, 17.1, and 19.7 L m -2 h -1 bar -1 for water, ethanol, methanol, isopropanol, tetrahydrofuran (THF), and acetonitrile, respectively.

Graphene oxide (GO) membranes have great potential for separation applications due to their low-friction water permeation combined with unique molecular sieving ability. However, the practical use of deposited GO membranes is limited by the inferior mechanical robustness of the membrane composite structure derived from conventional deposition methods. Here, we report a nanostructured GO membrane that possesses great permeability and mechanical robustness. This composite membrane consists of an ultrathin selective GO nanofilm (as low as 32 nm thick) and a postsynthesized macroporous support layer that exhibits excellent stability in water and under practical permeability testing. By utilizing thin-film lift off (T-FLO) to fabricate membranes with precise optimizations in both selective and support layers, unprecedented water permeability (47 L·m -2 ·hr -1 ·bar -1 ) and high retention (>98% of solutes with hydrated radii larger than 4.9 Å) were obtained.

Porous membranes play an important role in the separation technologies such as gas purification, solute nanofiltration, and desalination. An ideal membrane should be thin to maximize permeation speed, have optimum pore sizes to maximize selectivity, and be stable in various harsh conditions. Here, we show that the nanometer-thick membrane prepared by means of filtration of functionalized boron nitride (FBN) water suspensions can block solutes with hydrated radii larger than 4.3 Å in water. The FBN membranes with abundant nanochannels reduce the path length of ions. As molecular sieves, the FBN membrane can permeate small ions at an ultrahigh rate-a 25-fold enhancement compared with that of its theoretical diffusion rate and much higher than the graphene oxide membrane. Importantly, the FBN membrane exhibits excellent permeability even when it is immersed in acidic, alkaline, and basic salts solutions because of its intrinsic chemical stability. The molecular dynamics simulations further confirmed that the nanocapillaries formed within the FBN membrane in the hydrated state were responsible for high permeation performance. The simple vacuum filtration fabricated FBN membrane with angstrom-sized channels and ultrafast permeation of ions promises great potential applications in the areas of barrier separation and water purification.

Ultra-thin composite carbon molecular sieve (CMS) membranes were fabricated on well-defined inorganic alumina substrates using a polymer of intrinsic microporosity (PIM) as a precursor. Details of the pyrolysis-related structural development were elucidated using focused-beam, interference-enhanced spectroscopic ellipsometry (both in the UV-vis and IR range), which allowed accurate determination of the film thickness, optical properties as well as following the chemical transformations. The pyrolysis-induced collapse of thin and bulk PIM-derived CMS membranes was compared with CMS made from a well-known non-PIM precursor 6FDA-DABA. Significant differences between the PIM and non-PIM precursors were discovered and explained by a much larger possible volume contraction in the PIM. In spite of the differences, surprisingly, the gas separation properties did not fundamentally differ. The high-temperature collapse of the initially amorphous and isotropic precursor structure was accompanied by a significant molecular orientation within the formed turbostratic carbon network guided by the laterally constraining presence of the substrate. This manifested itself in the development of uniaxial optical anisotropy, which was shown to correlate with increases in gas separation selectivity for multiple technologically important gas pairs. Reduction of CMS skin thickness significantly below ∼1 μm induced large losses in permeability coefficients with only small to moderate effects on selectivity. Remarkably, skin thickness reduction and physical aging seemed to superimpose onto the same trend, which explains and strengthens some of the earlier fundamental insights.

An upsurge in searching membranes with high selectivity, permeability, and stability, which have been considered to be promising in the membrane-based gas separation process, has received huge attentions in academia and industry. In this work, we demonstrated a new molecular sieving ZIF membrane, which has a unique mixed-ligand ZIF structure constructed by two bulk imidazolate linkers within the zeolite GIS topology, resulting in appropriate aperture size, strong affinity to CO 2 , exceptional thermal and chemical stabilities, and superhydrophobic properties. Benefited from these features, the resulting JUC-160 membrane indeed exhibited remarkable separation efficiency and stability, with excellent H 2 /CO 2 selectivity of 26.3 and considerable H 2 permeance of 9.75 × 10 -7 mol m -2 s -1 Pa -1 under high temperature up to 200 °C. Furthermore, owing to its superhydrophobicity, the JUC-160 membrane could maintain its prominent separation performance even with the presence of steam.

Pure metal-organic framework (MOF) layers deposited on porous supports are important candidates for molecular sieving membranes, but their performance usually deviates from theoretical estimations. Here, we combine step-wise scanning electron microscopy imaging, time-resolved synchrotron X-ray scattering, terahertz infrared spectroscopy, and density functional theory calculation to investigate the ZIF-8 membrane formation on two types (polydopamine and TiO 2 ) of functionalized porous supports. Though molecular sieving of ZIF-8 membranes for smaller gases (He, H 2 , and CO 2 ) can be achieved with both types of functionalized supports, we unravel that the strong interaction between MOF and polydopamine can disrupt the formation of "perfect" MOF crystals at the interface, leading to a "contracted" MOF structure with partially uncoordinated imidazolate ligands. This further affects the low-frequency dynamical parameters of the framework and inhibits the effective seeded growth. Eventually, it leads to an unexpected loss of selectivity for the bulkier gases (N 2 and CH 4 ) for ZIF-8 on polydopamine-functionalized supports. This work links the dynamical aspects of MOFs with their gas transport behavior and highlights the importance of regulating the interfacial weak forces to preserve the ideal molecular sieving efficiency of MOF membranes, which also provides guidance for defect engineering of MOF film fabrication for sensing and electronic devices beyond membranes.

Herein, we report the fabrication of hydrogen gas sensors with enhanced sensitivity and excellent selectivity. The sensor device is based on the strategic combination of ZnO nanowires (NWs) decorated with palladium nanoparticles (Pd NPs) and a molecular sieve metal-organic framework (MOF) nanomembrane (ZIF-8). The Pd NPs permit the sensors to reach maximal signal responses, whereas the ZIF-8 overcoat enables for an excellent selectivity. Three steps were employed for the fabrication: (i) coating of a miniaturized sensor with vapor-grown ZnO NWs, (ii) decoration of these NWs with Pd NPs by atomic layer deposition, and (iii) partial solvothermal conversion of the tuned NWs surface to ZIF-8 nanomembrane. The microstructure and composition investigations of the ZIF-8/Pd/ZnO nanostructured materials confirmed the presence of both metallic Pd NPs and uniform ZIF-8 thin membrane layer. The integration of these nanomaterials within a miniaturized sensor device enabled the assessment of their performance for H 2 detection at concentrations as low as 10 ppm in the presence of various gases such as C 6 H 6 , C 7 H 8 , C 2 H 5 OH, and CH 3 COCH 3 . Remarkably high-response signals of 3.2, 4.7, and 6.7 ( R a / R g ) have been measured for H 2 detection at only 10, 30, and 50 ppm, whereas no noticeable response toward other tested gases was detected, thus confirming the excellent H 2 selectivity obtained with such a sensor design. The results obtained showed that the performance of gas sensors toward H 2 gas can be greatly increased by both the addition of Pd NPs and the use of ZIF-8 coating, acting as a molecular sieve membrane. Furthermore, the presented strategy could be extended toward the sensing of other species by a judicious choice of both the metallic NPs and MOF materials with tuned properties for specific molecule detection, thus opening a new avenue for the preparation of highly selective sensing devices.

The separation of carbon dioxide (CO 2 ) from hydrocarbons is a critical process for the production of clean energy and high-purity chemicals. Adsorption based on molecular sieving is an energy-saving separation process; however, most of molecular sieves with narrow and straight pore channels exhibit low CO 2 uptake capacity. Here, we report that a twofold interpenetrated copper coordination network with a consecutive pocket-like pore structure, namely, SIFSIX-14-Cu-i (SIFSIX = hexafluorosilicate, 14 = 4,4'-azopyridine, i = interpenetrated) is a remarkable CO 2 /CH 4 molecular sieving adsorbent which completely blocks the larger CH 4 molecule with unprecedented selectivity, whereas it has excellent CO 2 uptake (172.7 cm 3 /cm 3 ) under the ambient condition. The exceptional separation performance of SIFSIX-14-Cu-i is attributed to its unique pore shape and functional pore surface, which combine a contracted pore window (3.4 Å) and a relatively large pore cavity decorated with high density of inorganic anions. Dispersion-corrected density functional theory calculation and neutron powder diffraction were performed to understand the CO 2 binding sites. The practical feasibility of SIFSIX-14-Cu-i for CO 2 /CH 4 mixtures separation was validated by experimental breakthrough tests. This study not only demonstrates the great potential of SIFSIX-14-Cu-i for CO 2 separation but also provides important clues for other gas separations.

Triethoxyfluorosilane (TEFS), which is a pendant-type alkoxysilane with a Si-F bond, was utilized for the development of a molecular sieving membrane. The effect that a source of fluorine and calcination temperature exerted on gas permeation properties and network pore size was evaluated via single-gas permeation properties across a wide range of temperatures. A TEFS membrane calcined at 350 °C showed high H 2 permeance (2.0 × 10 -6 mol m -2 s -1 Pa -1 ) and high selectivity for H 2 over larger molecules (H 2 /CF 4 : >300; H 2 /SF 6 : >18 000), indicating that this network pore size would be suitable for a H 2 permselective membrane that could promote the process of methylcyclohexane (MCH) dehydrogenation to produce toluene (TOL). Based on the gas permeation properties and the results of XPS and FTIR, network pore size depended on the fluorine concentration incorporated in SiO 2 that existed as Si-F bonds, irrespective of the fluorine source. A TEFS membrane showed approximately the same pore size distribution and level of gas permeance, irrespective of calcination temperature (350 and 550 °C), due to the low Si-OH density in the networks as suggested by the result of FTIR, which can prevent the densification caused by the condensation of Si-OH groups. The pair distribution function also suggested that densification of the network structure for TEFS was apparently suppressed compared with that of a tetraethoxysilane (TEOS)-derived structure.

Two-dimensional (2D) subnanometer channels allow unique mass transport promising for molecular sieving. New 2D channels of MoS 2 nanosheets allow one to understand molecular transmission and separation, unlike the graphene oxide counterpart containing various defects and cationic metal contaminants. Membranes from layered MoS 2 platelets show extraordinary stability in an aqueous environment and compatibility with polymer filters, both beneficial to efficient manufacturing. Sharing gas-tightness and unimpeded water vapor permeation with a graphene oxide membrane, our lamellar MoS 2 membrane demonstrates a molecular sieving property for organic vapor for the first time. The MoS 2 membrane also reveals diffusion selectivity of aqueous ions, attributable to the energy penalty in bulk-to-2D dimensional transition. These newly revealed properties of the lamellar membrane full of angstrom-sized 2D channels point to membrane technology applications for energy and environment.

Perforated single-layered graphene has demonstrated selectivity and flux that is orders of magnitude greater than state-of-the-art polymer membranes. However, only individual graphene sheets with sizes up to tens of micrometers have been successfully fabricated for pressurized permeation studies. Scaling-up and reinforcement of these atomic membranes with minimum cracks and pinholes remains a major hurdle for practical applications. We develop a large-area in situ, phase-inversion casting technique to create 63 cm 2 high-quality single-layered perforated graphene membranes for ultrafast nanofiltration that can operate at pressures up to 50 bar. This result demonstrates the feasibility of our technique for creating robust large-area, high quality, single-layered graphene and its potential use as a pressurized nanofiltration membrane.

Stimuli-responsive membranes that can adjust mass transfer and interfacial properties "on demand" have drawn large interest over the last few decades. Here, we designed and prepared a novel magnetoresponsive separation membrane with remote switchable molecular sieving effect by simple one-step and scalable nonsolvent induced phase separation (NIPS) process. Specifically, poly(ether sulfone) (PES) as matrix for an anisotropic membrane, prefabricated poly(N-isopropylacrylamide) (PNIPAAm) nanogel (NG) particles as functional gates, and iron oxide magnetic nanoparticles (MNP) as localized heaters were combined in a synergistic way. Before membrane casting, the properties of the building blocks, including swelling property and size distribution for NG, and magnetic property and heating efficiency for MNP, were investigated. Further, to identify optimal film casting conditions for membrane preparation by NIPS, in-depth rheological study of the effects of composition and temperature on blend dope solutions was performed. At last, a composite membrane with 10% MNP and 10% NG blended in a porous PES matrix was obtained, which showed a large, reversible, and stable magneto-responsivity. It had 9 times higher water permeability at the "on" state of alternating magnetic field (AMF) than at the "off"-state. Moreover, the molecular weight cutoff of such membrane could be reversibly shifted from ∼70 to 1750 kDa by switching off or on the external AMF, as demonstrated in dextran ultrafiltration tests. Overall, it has been proved that the molecular sieving performance of the novel mixed matrix composite membrane can be controlled by the swollen/shrunken state of PNIPAAm NG embedded in the nanoporous barrier layer of a PES-based anisotropic porous matrix, via the heat generation of nearby MNP. And the structure of such membrane can be tailored by the NIPS process conditions. Such membrane has potential as enabling material for remote-controlled drug release systems or devices for tunable fractionations of biomacromolecule/-particle mixtures.

Two-dimensional (2D) materials with atomic thickness and extraordinary physicochemical properties exhibit unique mass transport behaviors, enabling them as emerging nanobuilding blocks for separation membranes. Engineering 2D materials into membrane with subnanometer apertures for precise molecular sieving remains a great challenge. Here, we report rational-designing external forces to precisely manipulate nanoarchitecture of graphene oxide (GO)-assembled 2D channels with interlayer height of ∼0.4 nm for fast transporting and selective sieving gases. The external forces are synergistic to direct the GO nanosheets stacking so as to realize delicate size-tailoring of in-plane slit-like pores and plane-to-plane interlayer-galleries. The 2D channels endow GO membrane with excellent molecular-sieving characteristics that offer 2-3 orders of magnitude higher H2 permeability and 3-fold enhancement in H2/CO2 selectivity compared with commercial membranes. Formation mechanism of 2D channels is proposed on the basis of the driving forces, nanostructures, and transport behaviors.