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A high-performance MOF-based mixed matrix membrane was constructed via incorporating o-BA modified ZIF-8 nanoparticles into PIM-1 matrices. The synergistic effect of molecular sieving and adsorption inhibition of the obtained membrane offers good chance for efficient mixed O 2 /N 2 separation. [Display omitted] • High-performance MOF-based MMMs were developed for mixed O 2 /N 2 separation. • The synergistic effect of size sieving and adsorption inhibition promotes excellent separation performance. • The modification of o-CB on the outer surface of ZIF-8 contributes to the improved interfacial compatibility. • The optimal membrane exhibits a mixed O 2 /N 2 selectivity of 8.9 with O 2 permeability of 796.5 Barrer. Oxygen/nitrogen (O 2 /N 2) separation is of great importance but faces huge challenges owing to their similar molecular size and close polarity. In this work, we construct a polymer of intrinsic microporosity (PIM-1) based mixed matrix membrane (MMM) for efficient O 2 /N 2 separation by using ZIF-8 as the sieving filler along with surface modification of o-carborane (o-CB) to strengthen selective N 2 adsorption fixation as well as polymer-filler interfaces. Markedly, the o-CB on the outer surface of ZIF-8 not only affords the requisite interfacial compatibility in molecular sieving MMMs, but also increases the diffusion difference between O 2 and N 2 by the preferential adsorption with N 2 molecules. This synergistic effect of molecular sieving and adsorption inhibition achieves efficient O 2 /N 2 diffusion differential separation. As expected, the optimal membrane with o-CB-ZIF-8 loading of 35 wt% exhibits an O 2 permeability of 796.5 Barrer and a mixed O 2 /N 2 selectivity of 8.9 with O 2 /N 2 (20:80, vol.) mixtures, exceeding the latest 2015 upper bound limits. Moreover, the according membrane module with o-CB-ZIF-8 loading of 20 wt% also displays moderate O 2 permeability of 391.7 Barrer and O 2 /N 2 selectivity of 5.5 under pressure of 1 bar. This work may provide a feasible platform for designing high-performance MOF-based membranes in air separations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Structure of organosilica membranes was tailored via controlling the unsaturated degree of bridges. • Membranes exhibited satisfied separation performance for the n-butanol/water mixtures. • Pervaporation performance can be predicted by the gas permeation properties. In the petroleum industry, the mixing of ethanol (EtOH), isopropanol (IPA), and n-butanol (n-BuOH) with water is a prevalent occurrence in both production and recovery phases. Obtaining the required degree of purity via dehydration poses a significant challenge that needs to be addressed. Pervaporation has emerged as a promising method for separating azeotropic mixtures due to its energy efficiency and independence from vapor-liquid equilibrium constraints. In this study, organosilica precursors, namely 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)ethylene (BTESEthy), and 1,2-bis(triethoxysilyl)acetylene (BTESA), were utilized for the fabrication of organosilica membranes using the sol–gel method. Subsequently, these membranes were employed for pervaporation dehydration of EtOH, IPA, and n-BuOH. This study investigates the effect of the degree of unsaturation of the bridged group, feed composition, and C atom count of alcohol on membrane dehydration performance. The membranes demonstrated superior separation performance for the n-butanol/water mixtures compared to other alcohol/water systems investigated. In this particular context, BTESE membrane exhibited a significant separation factor, although accompanied by a reduced permeation flux. Conversely, BTESA membrane demonstrated a decreased separation factor but an increased permeation flux. The comparison between gas permeation and pervaporation highlighted that the separation mechanism was primarily governed by molecular sieving through the organosilica membranes. [ABSTRACT FROM AUTHOR]

• A stable and cost-effective MOF was prepared for benchmark CO 2 capture. • High CO 2 capacity with record CO 2 /N 2 and CO 2 /CH 4 selectivity was achieved. • Impressive CO 2 capacity of 2.60 mmol/g in CO 2 /N 2 breakthrough experiments. • MOF beads were granulated with high MOF loading and retained separation performance. The design of porous materials for CO 2 capture from flue gas and natural gas is highly demanded. However, it is challenging to target materials that combine high CO 2 capacity and CO 2 selectivity. In this work, we report a robust metal–organic framework (MOF) Zn-ox-mtz with one dimensional channels and narrow windows for excellent CO 2 capture from CO 2 /N 2 (simulated flue gas) and CO 2 /CH 4 (simulated natural gas) with high selectivity. Zn-ox-mtz exhibits a high CO 2 capacity (58.0 STP cm3 g−1 at 15 kPa), excellent CO 2 /N 2 (15/85, S > 106) and CO 2 /CH 4 (50/50, S > 105) selectivity and good chemical stability. In addition, the practical separation performance is demonstrated by breakthrough experiments under various process conditions. A efficient separation is achieved with the impressive CO 2 capacity of 2.60 ± 0.12 mmol g−1 at 298 K. Importantly, the outstanding performance is sustained under high humidity. The molecular sieving mechanism investigated by theoretical calculations indicated that CO 2 with small molecular size is tightly trapped by multiple C = O···H-C hydrogen bonding and O = C···O forces in the cavity while CH 4 and N 2 with larger molecular size display overlarge energy barrier to cross the contract pore windows. Moreover, the granulation of Zn-ox-mtz by hydroxypropyl cellulose is realized with high MOF loading (93.8 %) and the granulated Zn-ox-mtz beads retained the excellent CO 2 /N 2 and CO 2 /CH 4 separation performance. [ABSTRACT FROM AUTHOR]

The discharge of wastewater containing dyes not only causes serious environmental pollution but also poses a severe threat to human health. The selective separation of dyes and reuse of inorganic salts are vital in the textile industry. In this work, nitrogen-doped graphene quantum dots (N-GQDs) was successfully synthesized via the "one-step solvothermal method", and the N-GQDs composite membranes were innovatively fabricated by constructing a thin selective layer top the modified multi-walled carbon nanotubes (MWCNTs) matrix membrane via interfacial polymerization process. The pore size of the N-GQDs membranes could be flexibly modulated by regulating the contents of the N-GQDs. The suitable N-GQDs membrane (M4, 0.35 wt % of N-GQDs) possessed over 96 % rejection rate for diverse charged dyes, which was higher than that of the piperazine polyamide (PA3) membrane. Notably, the rejection of the smaller molecular weight of Methylene Blue by the M4 membrane reached ∼98.93 %, which was higher than that reported in most literature, mainly owing to the relatively smaller average pore size and stronger electronegativity of the membrane. Especially compared with our previous work, the prepared M3 and M4 membranes exhibited an enhancement of ∼37.79 % and 39.48 % in rejection of Methylene Blue, ∼ 78 % and 19 % in pure water permeability, respectively. On account of the size sieving and charge effect, the N-GQDs membrane (M4) could maintain high rejection for dyes and exhibited efficient separation for dye/salt with a separation factor of 115 for the Congo Red/sodium chloride mixture after continuous cross-flow filtration for 24 h in the simulated wastewater condition. Furthermore, the N-GQDs membrane also exhibited favorable acid-base resistance and satisfactory anti-fouling performance. Importantly, the N-GQDs membranes presented excellent decolorization efficiency for the practical textile wastewater. These results revealed that the as-prepared N-GQDs membrane possessed great potential for actual textile wastewater advanced treatment and purification. This study also offers a new candidate to rationally manipulate the separation properties of nanofiltration membranes adopting new aqueous monomers. [Display omitted] • The pore size of the membrane could be flexibly regulated by N-GQDs contents. • The custom-tailored N-GQDs membrane was suitable for efficient dye separation. • N-GQDs membranes show worthy durability and selectivity even in harsh conditions. • N-GQDs membranes present superior decolorization for actual dye wastewater. [ABSTRACT FROM AUTHOR]

• MOPs and their breakthroughs in membrane application are systematically summarized. • The development, synthetic means and structural design of MOPs is presented. • The challenges in preparing precise molecular sieving MOPs membrane are discussed. Microporous organic polymers (MOPs) are ideal candidates for designing highly efficient and precise molecular sieving separation membranes due to their exceptional porosity, rigid pore structure, pore size designability, and ease of functionalization. These materials encompass COFs, POCs, PAFs, PIMs, CMPs, and HCPs. However, the path to utilizing MOPs as separation membrane applications has encountered obstacles. Several studies have been conducted to fully exploit the exceptional properties of these polymers. The better application of MOPs materials should be considered in terms of material design and synthesis, membrane formation, and membrane task-specific applications. This review objectively reclassifies MOPs materials based on the latest research and material ordering and provides a systematic summary of MOPs material synthesis and design, MOPs-based membrane fabrication difficulties, and current novel MOPs-based membrane design. Additionally, it introduces in detail the preparation of different types of MOPs-based membranes. The applications of MOPs-based membranes in separation applications are also thoroughly summarized. Finally, this review summarizes the challenges of current MOPs-based membrane development, proposes future opportunities and potential applications in the separation and purification field. [ABSTRACT FROM AUTHOR]

• Novel method for rGOA production by dithionite (DTN) driven reduction induced self-assembly. • The optimal DTN to GO ratio is 2:1 by mass based on Raman, FTIR, and nitrogen adsorption results. • Limited access of hexane isomers to pores and the surface of rGOAs dependent on the molecule kinetic diameter. • Hexane isomers can be separated in rGOAs based on molecular kinetic sieving effect. • Aromatic C6 hydrocarbon establish strong specific interactions with the rGOA surface. The ability of reduced graphene oxide aerogels (rGOAs) for challenging gas-phase separation was investigated with hexane isomers and benzene (C6 hydrocarbons) using inverse gas chromatography (IGC). For the first, rGOAs were synthesized with sodium dithionite (DTN) as a reductant. Experiments revealed that the most optimal DTN to graphene oxide mass ratio was 2:1, resulting in the highest specific surface area of 432.3 m2 g−1 and the highest degree of graphitization among analyzed samples. C6 hydrocarbon adsorption tests demonstrated the dominant role of the kinetic effect for the adsorption of branched and cyclic hexane isomers - the partition coefficient decreased as the molecule kinetic diameter increased. The contribution of thermodynamic effects was distinguished for molecules with uneven charge distribution. A comparison of the partition coefficient ratios for different pairs of hydrocarbons demonstrated the potential of rGOAs in separating various C6 hydrocarbons. The selectivity, calculated from binary-component adsorption tests of benzene (Bz)/cC6 equimolar mixture, was 13.7, 8.5 and 2.8 for DTN4, DTN2, and DTN1. The research indicates that rGOAs may have potential as adsorbents for the selective separation of hydrocarbons, however, the competitive adsorption and performance at high surface coverages of adsorbates have to be accounted for in further research to assess the applicability of rGOAs reliably. [ABSTRACT FROM AUTHOR]

Organic solvent nanofiltration (OSN) membranes with precise molecular-sieving performance have become increasingly important in chemical and pharmaceutical industries, desiring superior membranes with both high permeability and selectivity. Herein, the V-shape Tröger's base (TB) structure is incorporated in the polyamide network to engineer microporosity as well as the molecular-sieving performance of the thin-film composite (TFC) polyamide membrane for organic solvent nanofiltration (OSN). The TFC membrane containing the TB structure features a rigid and contorted chain structure, which affords high and stable methanol permeability in OSN applications. Furthermore, the H-bond interaction between the H of amide groups and N in TB reinforces the interchain interaction, endowing the membrane with a precise selectivity to organic solutes. The as-prepared TFC membrane demonstrated high methanol permeance of 16.6 L m−2 h−1 bar−1 and sieving performance to organic molecules with molecular weight cut-off (MWCO) down to 349 Da. Furthermore, the membrane demonstrates shape selectivity for organic solutes, exploiting the fine microporous structure. This study may provide insights into the molecular design of TFC membranes by finely tuning the molecular features for precise solute separations. TFC membranes prepared by interfacial polymerization using TBDA as an aqueous monomer with a V-shape structure were selected for the formation of trapped nanovoids in the polymer network. [Display omitted] • The V-shape TBDA was explored as aqueous phase to incorporate contorted polymer chains in the polymer network. • The PA-TBDA TFC membranes with a fine microporous structure exhibit both size and shape selectivity for organic solutes. • The PA-TBDA TFC membranes show excellent methanol permeance of 16.6 L m−2 h −1 bar −1 with MWCO down to 349 Da. • The PA-TBDA TFC membranes demonstrate excellent long-term stability and can be operated at 10 bar for 7 days in DMF. [ABSTRACT FROM AUTHOR]

[Display omitted] • Scale-up preparation of Cu(BF 4) 2 (4-DPDS) 2 using room temperature and green solvent. • Simultaneously achieves extremely high selectivity for binary components of C 2 H 4 /C 2 H 6 , C 3 H 6 /C 3 H 8 , and C 2 H 2 /CO 2. • Calculations verified the dynamic diffusion behavior of olefins in the flexible gourd channel. • Simultaneously capture and separation of C 2 H 4 and C 3 H 6 from seven-component cracking gases at ambient conditions. • Extraordinarily stable structure enables multiple cycles of gas separation under 75% humidity. Simultaneously capturing and separating high-purity C 2 H 4 and C 3 H 6 from cracked gas mixtures presents a significant challenge. Herein, a robust metal–organic framework (Cu(BF 4) 2 (4-DPDS) 2) was designed featuring a gourd-shaped one-dimensional channel. Its specific alkenes match structure can only adsorb alkenes while completely excluding alkanes. With a remarkable adsorption selectivity of 76,203 for equimolar C 2 H 4 /C 2 H 6 and high selectivity of 159 for equimolar C 3 H 6 /C 3 H 8 , Cu(BF 4) 2 (4-DPDS) 2 not only achieves >99 % purity separation of C 2 H 4 and C 3 H 6 from binary mixtures but also simultaneously captures and separates these compounds from seven-component cracking gases at ambient conditions. Its performance stability remains intact even under 75 % RH conditions, thanks to its robust framework. Based on the particular gourd-shaped channel, it can also achieve efficient C 2 H 2 /CO 2 separation. Ab initio Molecular Dynamics simulations demonstrate the dynamic diffusion process of gas molecules in the structure, and in situ infrared analyses reveal the framework's rich C-H•••F and S•••π binding sites with C 2 H 4 and C 3 H 6. This material's robust structure, exceptional alkene sieving capabilities, and repeatable separation performance comprehensively showcase Cu(BF 4) 2 (4-DPDS) 2 as a unique metal–organic framework for simultaneous recognition and capture of C 2 H 4 and C 3 H 6. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recent advances in MOFs for C 3 H 6 - and C 3 H 8 -selective separation were reviewed. • Mechanisms for C 3 H 6 - and C 3 H 8 -selective separation by MOFs were discussed. • Parameters influencing C 3 H 6 /C 3 H 8 -selective separation by MOFs were investigated. Due to their similar physicochemical characteristics, the separation of propylene (C 3 H 6) from propane (C 3 H 8) is a challenging but essential process in the petrochemical industry. Currently, the majority of known techniques use either one-sided thermodynamic or kinetic separation. However, purification under ambient conditions is possible via adsorption-based separation using porous particles, which may have positive energy and environmental effects. Metal–organic frameworks (MOFs) are the most promising option for selectively separating C 3 H 6 and C 3 H 8 due to their ability to control pore shape and functionality. This review discusses the different separation processes, key separation variables, and benchmarked C 3 H 6 /C 3 H 8 separation variables, including the current state of C 3 H 6 /C 3 H 8 selective separation using MOFs. It also examines the primary challenges and opportunities associated with using MOFs for the effective separation of C 3 H 6 /C 3 H 8. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks with programmed surface charge enable tunable permeation behaviors of water permeation of 15.5 to 34.5 L m−2 h−1 bar−1 and dye removal up to 99%. This is attributed to the modulation of wetting and solid surface energy which provide further insight into controllable molecular transport and design of nanomaterials for sieving, water treatment, and energy conversion. [Display omitted] Molecular separation is critical to mitigating the issues of water contamination and shortage and currently focuses on the use of framework materials fabricated by special building blocks. However, developing a simple and tunable synthesis methodology for materials with alternative permeation and selectivity remains challenging. Here, we fabricate a series of nanochannel membranes composed of uniform spherical covalent organic frameworks (COFs). Diversified spherical COFs have diameters ranging from ∼150 to ∼800 nm, therefore demonstrating a programmable surface charge distribution from −24 to −63 mV. COF membranes with tailor-made surface charge enable different surface energy levels and allow increasing water permeation of 15.5 to 34.5 L m−2 h−1 bar−1. Furthermore, COFs can also act as filters, achieving up to 99.7% rejection and separation of the opposite charged dyes. We expect these COFs with tunable surface charge to be applicable to variety of fields, including sieving, batteries, and water treatments. [ABSTRACT FROM AUTHOR]

Two-dimensional graphene oxide (GO) membranes exhibit great potential for environmental aqueous separation and purification. However, their viability and performance are greatly limited under cross-flow conditions due to the enlargement of interlayer spacing and peeling of stacked GO laminates in aqueous environments. Herein, inspired by natural nacre structure, we present a dual-functional and ultra-stable β-cyclodextrin (β-CD) -polyacrylic acid (PAA) -GO composite membrane, with a constant d-spacing in both wet and dry states. Nanosheets and chain polymers construct a typical "brick-mortar" structural configuration, which exhibits great anti-swelling property compared with other reported GO membranes. By rationally optimizing and tuning the membrane structures, the ultrathin GO membrane (∼50 nm) exhibits outstanding stability in cross-flow and long-term filtration. Moreover, the designed membrane shows dual functions (high-throughput enantioselectivity and excellent dyes rejection) with the increase of molecular size. This strategy boosts the ongoing research in designing robust lamellar membrane materials for practical engineering applications in aqueous environments. [Display omitted] [ABSTRACT FROM AUTHOR]

• A series of chitosan-derived ultramicroporous carbons were prepared using activating reagents-free method. • CNC-700 possesses excellent C 2 H 4 /C 2 H 6 molecular sieving performance. • High purity of C 2 H 4 can be produced via one-step adsorption–desorption process. • The good stability and scalability make CNC-700 a promising adsorbent for industrial applications. The selective separation of C 2 H 4 /C 2 H 6 pair is of paramount importance in the petrochemical industry, which is yet challenged by their similar polarities, shapes, and kinetic diameters. The use of carbonaceous adsorbents with molecular sieving capability holds great promise in achieving the desired selectivity and economically feasibility. However, such progress has been hindered by the typically wide pore size distribution observed in traditional carbons. Herein, we report a series of chitosan-based ultramicroporous carbons with C 2 H 4 /C 2 H 6 molecular sieving performance through an activating reagents-free method. The hydrothermal process of chitosan was initially employed to prepare condensed carbonaceous hydrochar rich in heteroatoms. The subsequent thermal etching led to the formation of sieving-based ultramicropores, stemming from the decomposition of heteroatoms and hot-shrinkage of pores at high temperature. The as-synthesized optimal CNC-700 sample achieved a high C 2 H 4 uptake of 32.3 cm3 (STP) g−1 and negligible C 2 H 6 adsorption at 298 K and 1.0 bar. The isosteric heat of C 2 H 4 on CNC-700 reached 34.5 kJ mol−1, significantly lower than other thermodynamically driven carbonaceous adsorbents. The fixed-bed breakthrough experiments further validated the efficient separation of equimolar C 2 H 4 /C 2 H 6 mixture under dynamic conditions. This work provides an important guideline to fabricate carbons with adjustable ultramicropore size derived from biomass for the highly effective separation of light hydrocarbons via molecular sieving. [ABSTRACT FROM AUTHOR]

Highly selective methane sensing remains a formidable challenge in the field of metal oxide semiconductor (MOS)-based gas sensors. To address this issue, zeolitic imidazolate framework (ZIF) modulation is considered as an effective approach because of its pore size sieving and polarity sieving effects. In this work, core-shell ZnO/Pd@Co node-replaced ZIF-8 (ZIF-8/67) nanorods were synthesized by self-sacrificial template method, followed by post-synthetic modification of ZIF-8. When the replacement ratio of Co nodes reached 12.4%, ZnO/Pd@ZIF-8/67 exhibited a response of 12.2% to 500 ppm CH 4 at 210°C but no response to 50 ppm CO, 50 ppm NH 3 and 5 ppm NO 2 , showing excellent selectivity. By limiting rotational freedom of 2-methylimidazole, Co node replacement decreased the effective pore size from 4.0 to 4.2 Å to 3.8–4.0 Å and hindered the diffusion of NO 2 with the dynamic diameter of 4.5 Å, thus enhancing the pore size sieving effect. Moreover, polarity sieving effect is also enhanced due to the favourable adsorption of polar CO (3.76 Å) and NH 3 (2.6 Å) by ZIF. Therefore, the selectivity of nonpolar CH 4 (3.8 Å) was improved. This work provides a new strategy for reasonably controlling and modulating the ZIF structure to achieve high selectivity in MOS-based sensors. • ZnO/Pd@ZIF-8/67 nanorods were synthesized via self-sacrificial template method and Co node replacement of ZIF-8. • ZnO/Pd@ZIF-8/67 exhibited excellent CH 4 sensing selectivity against CO, NH 3 and NO 2. • Enhanced size- and polarity-induced sieving effects of ZIF by Co node replacement improved the selectivity of CH 4. [ABSTRACT FROM AUTHOR]

Positively charged composite membranes with polyethylene-based antimicrobial separation layers are conveniently developed herein for precise molecular sieving. Quaternization cross-linking between hyperbranched polyethylene- graft -poly(diethylaminoethyl methacrylate) and 1,2-dibromoethane constructs porous networks with abundant quaternary ammonium groups. Modified membranes exhibit different interception capabilities for anions, cations, and neutral molecules. We explain the possible sieving mechanisms with respect to size exclusion, the Donnan effect, and the intrapore energy barrier. A strongly positively charged separation layer introduces the electrostatic interaction which has different effects on cationic, anionic, and neutral molecules during filtration. Membranes prepared by the simple quaternization cross-linking strategy can efficiently separate molecular mixtures with different dimensions or charges. Moreover, the plentiful quaternary ammonium groups endow the membranes with favorable antimicrobial activity against Gram-positive E. coli and Gram-negative S. aureus. [Display omitted] • The graft copolymer HBPE- g -PDEAEMA was successfully synthesized by ATRP. • Hyperbranched polyethylene was used to moidify membranes for the first time. • Quaternization cross-linking was used to prepare molecular sieving membranes. • The membranes can precisely distinguish molecules with different charges or sizes. • The polyethylene-based separation layer showed favorable antimicrobial activity. [ABSTRACT FROM AUTHOR]

A bridged-type organosilica, bis(triethoxysilyl)methane (BTESM) membrane was evaluated in detail for single-gas permeation at temperatures ranging from −130 to −200 °C, and for binary (O 2 /He, O 2 /N 2) separation at 30 and -115 °C, respectively. The permeance of He, Ar, and N 2 demonstrated a trend of activated diffusion as permeance increased with an increase in the temperature; O 2 permeance, however, reached its maximum value at about −80 °C. O 2 permeance increased with a decrease in the temperature (30 to −80 °C), and permeance then gradually decreased (−80 to −130 °C), which demonstrates surface diffusion. In the case of O 2 /He binary separation, both O 2 and He permeated according to molecular sieving at 30 °C, but at −115 °C, O 2 /He selectivity was enhanced approximately 10-fold due to permeation blockage by adsorbed O 2. On the other hand, in the case of O 2 /N 2 binary separation at −115 °C, the effect of permeation blocking by adsorbed O 2 permeance was lessened due to the effect of competitive adsorption, which translated to a level of O 2 /N 2 selectivity that was only 1.5-fold higher than that at 30 °C. [Display omitted] • Hydrophobic organosilica membranes suppressed decreases in gas permeance at temperatures as low as −130 °C. • Organosilica membranes showed dependable stability at −130 °C. • Adsorption of O 2 at extremely low temperatures enhanced the O 2 separation performance. • Molecular sieving dominated the O 2 separation mechanism at 30 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The multipoint coordination mode of ligand provides a rigid 1D channel for IPM-101. • IPM-101 exhibits molecular-sieving n-C 4 H 10 adsorption over iso -C 4 H 10. • The n-C 4 H 10 adsorption capacity of IPM-101 exceeds the most benchmark adsorbents. • DFT calculations reveal the molecular-sieving separation mechanism of IPM-101. • IPM-101 shows efficient n-C 4 H 10 / iso -C 4 H 10 separation in breakthrough experiments. Molecular-sieving separation of isomeric C4 paraffins, n-butane (n-C 4 H 10) and isobutane (iso -C 4 H 10), is highly desired but challenging because of their very close molecular sizes and physical properties. However, most of the MOF adsorbents often undergo framework flexibility or ligand rotation or swing, leading to the variation of pore size and the loss of the molecular-sieving effect. In this work, an adenine-based MOF with a suitable window size and rigid narrow 1D channel, namely IPM-101, was selected for n-C 4 H 10 / iso -C 4 H 10 separation. Adsorption experiments demonstrate that IPM-101 can sensitively adsorb n-C 4 H 10 in the low-pressure region (0–0.05 bar) and reach a saturation state at 0.1 bar while iso -C 4 H 10 is excluded by the size-exclusion effect. Owing to the high porosity, IPM-101 exhibits a high n-C 4 H 10 adsorption capacity (51.6 cm3 g−1) at 1 bar and 298 K. Density functional theory (DFT) calculations clearly reveal the molecular-sieving mechanism that n-C 4 H 10 molecule can diffuse into the pore channel of IPM-101 easily but the diffusion of iso -C 4 H 10 in IPM-101 is kinetically forbidden for its high diffusion energy barrier. The breakthrough experiments show that n-C 4 H 10 and iso -C 4 H 10 can be efficiently separated and iso -C 4 H 10 with a purity of up to 99.9 % can be directly collected. The regeneration experiments show that IPM-101 has good cycling stability for n-C 4 H 10 adsorption and n-C 4 H 10 / iso -C 4 H 10 separation. Therefore, the high separation efficiency, excellent regeneration ability, and low cost indicate that IPM-101 has great application potential for practical n-C 4 H 10 / iso -C 4 H 10 separation in industry. [ABSTRACT FROM AUTHOR]

Molecular intercalation has been widely used for graphene oxide (GO) nanosheets to control interlayer spacing (d -spacing). However, further research is necessary to refine and enhance the precision of d -spacing control. In this study, we demonstrate a versatile strategy to create chitosan (CS) intercalated GO (GO@CS) nanosheets, whose d -spacing can be finely controlled by numbers of linked CS unit. This means the concentration of CS solution directly influences d -spacing of GO, and we can get the desired d -spacing for various applications by modulating the CS concentration. This is benefited from the linear structure of CS ensuring a consistent molecular length. The simulation of molecular structures with different numbers of linked CS unit supports this model. Then, the nanofiltration membranes prepared by these GO@CS nanosheets show high hydrophilicity, strong chemical bonding force, and abundant negative charges, which enhances permeability (water permeance of 91 L m−2 h−1 bar−1), stability, and anti-fouling ability during dye separation processes, even though they are ultrathin (∼70 nm). Notably, the contrasting filtration efficiencies observed for oppositely charged dye molecules indicate a great potential use in molecular sieving. [Display omitted] • A versatile strategy is used for chitosan intercalated graphene oxide nanosheets. • Interlayer spacing is finely controlled by numbers of linked chitosan unit. • Laminar membranes have good hydrophilicity and tunable surface charge. • Membranes have high water permeance of 91 L m-2 h-1 bar-1 and dye rejection of 95 %. • Membranes show various filtration efficiencies of oppositely charged dye molecules. [ABSTRACT FROM AUTHOR]

• One-step CVD of propylene was performed on carbon hollow fiber membranes. • Coated carbon membranes had high carbon contents and were hydrophobic. • Propylene coating greatly improved the ideal selectivities of the carbon membranes. • The propylene volume fraction and CVD time affected the gas separation performance. In this study, we investigated the effects of one-step chemical vapor deposition (CVD) of propylene on the pore structures and gas separation performances of carbon hollow fiber membranes derived from sulfonated poly(phenylene oxide) (SPPO). The CVD is performed by feeding a 5–100% of propylene gas at the carbonization peak temperature. The obtained CVD carbon membranes had higher carbon concentrations and were hydrophobic. Their water permeances were considerably lower than those of uncoated membranes in pervaporation experiments. The gas permeances of the CVD membranes also decreased but the ideal selectivities greatly improved, especially for H 2 /CH 4 from 130 to 1625 with the membrane prepared by pyrolysis at 650 °C for 60 min in combination with CVD of 100% propylene for 5 min. We found that the gas separation performance could be easily controlled by changing the propylene volume fraction and CVD time. The highest H 2 /CH 4 selectivity of 29,940 was obtained for a membrane pyrolyzed at 700 °C for 20 min with CVD using 10% propylene for 20 min. [ABSTRACT FROM AUTHOR]

Highlights • A chabazite aluminosilicates coated with a siliceous chabazite layer was synthesized. • Adsorption rate of 1-butanol was decreased by the pure silica chabazite coating. • Coated chabazite showed an even more pronounced exclusion of 1-butanol. • Pure silica chabazite coating layer acts as a diffusion barrier. Abstract Due to its shape selective properties, the narrow pore chabazite zeolite is an interesting material for the separation and purification of 1-butanol from ABE (acetone-butanol-ethanol) fermentation broth, as it selectively traps ethanol from the mixture of acetone, ethanol and butanol. In order to improve the separation performance of chabazite zeolite in humid conditions, we synthesized a core-shell structured chabazite type zeolite, with a chabazite aluminosilicate core coated with a pure silica chabazite layer. This material was evaluated in the vapor phase separation of 1-butanol using a model ABE vapor mixture. Unexpectedly, a broader breakthrough profile of ethanol was obtained on the coated chabazite, resulting in a lower 1-butanol recovery. It was found that the adsorption rate of 1-butanol was decreased by the pure silica chabazite coating. In breakthrough experiments, the coated chabazite showed an even more pronounced exclusion of 1-butanol as compared to the parent material, resulting in a larger separation factor of ethanol over 1-butanol. The pure silica chabazite coating layer acts as a kind of diffusion barrier against 1-butanol rather than ethanol, enhancing the molecular sieving effect. [ABSTRACT FROM AUTHOR]

Energy-efficient CO 2 /C 2 H 2 separation by membranes is critical for producing acetylene by partial combustion of natural gas. Separating CO 2 and C 2 H 2 by membranes is challenging because they have the same kinetic diameter and similar dimensions. Here we demonstrate for the first time high-silica chabazite (CHA) zeolite membranes with surprisingly high CO 2 selectivity over C 2 H 2. Both unary permeation and binary mixture permeation data demonstrated consistent high CO 2 permselectivity >30. Equilibrium adsorption isotherms indicate only a slight adsorption selectivity for C 2 H 2 , implying that a high diffusion selectivity for CO 2 is required for the effective separation. The dynamic uptake data, however, points to slight C 2 H 2 diffusion selectivity in CHA zeolite crystals. Hypotheses are proposed to explain the inconsistency between crystal and membrane diffusion results. [Display omitted] • Highly CO 2 /C 2 H 2 selective membranes are demonstrated for the first time. • No CO 2 /C 2 H 2 adsorption or diffusion selectivity was observed in the bulk phase of CHA zeolite. • The high selectivity is likely from the microstructure at intercrystalline boundaries of the polycrystalline membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D-printed carbon-based monoliths were studied in adsorptive alkane isomer separation. • Fixed bed breakthrough experiments were conducted for C5/C6 isomer feed mixtures. • The pristine monolith shows a near molecular sieving effect for the branched alkanes. • The CO 2 -activated monoliths significantly adsorbed all the alkane isomers. • A dynamic fixed bed adsorption model is developed to simulate the experimental data. Hierarchically structured 3D printed porous carbons monoliths, exhibiting cylinder structures composed of tetragonal cubic centered unit cells, were studied for their applicability in adsorptive pentane (C5) and hexane (C6) alkane isomers separation (linear/branched). Three materials of the same macroscopic shape were employed in the study, which varied in the micro- and mesoporosity by changing the final CO 2 activation step: non-activated and activated at 1133 K for 6 and 12 h, respectively. Fixed bed breakthrough experiments were conducted for C5/C6 isomer feed mixtures, covering 373, 423, and 473 K temperatures and total alkane partial pressure up to 50.0 kPa. Results demonstrated that the initial porosity for the non-activated monolith enables the complete separation of linear from their respective branched isomers (slightly adsorbed) via a near molecular sieving effect, showing the following sorption hierarchy order (nC6 > nC5) ≫>≫ (2MP > 3MP > 23DMB ≈ iC5 > 22DMB). Regarding the CO 2 -activated monoliths, both showed a completely different picture, being all the alkane isomers adsorbed (much higher loadings) following the sorption hierarchy order: nC6 > 3MP > 2MP > 23DMB > 22DMB > nC5 > iC5. These results indicate that besides enhancing the microporosity and available specific surface area, the pore sieving effect of branched alkanes is lost due to the pore widening during the CO 2 activation. The breakthrough data for the non-activated monolith is also numerically fitted with a convenient, dynamic adsorption model. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conditions and parameters controlled in the fabrication of carbon molecular sieve membranes (CMSMs) are summarized. • Mass transfer properties of CMSMs are discussed. • Gas separation properties of CMSMs are summarized. • Current challenges in and future directions for practical application of CMSMs are surveyed. Carbon molecular sieve membranes (CMSMs) have drawn substantial research attention in recent years due to their ability to overcome the trade-off limitation between permeability and selectivity that is commonly observed in polymeric membranes used for gas separation. The performance of CMSMs is governed by various factors, such as the choice of polymeric precursors and their pre-treatment, pyrolysis, and post-treatment conditions. This review examines the critical aspects in the process of developing CMSMs based on polyimide precursors for gas separation. In addition, the mass transfer mechanism and characterization methods of CMSMs are discussed. Then, the performances of various CMSMs developed so far are examined against the Robeson upper bound limit, and pilot-scale applications and an economic analysis of CMSM-based gas separation are provided. Finally, the challenges and perspective are presented as the concluding remarks. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have demonstrated their superiorities as molecular sieve membranes for strategic gas separations. The promotion of these 2D membranes is confronted with great challenges such as elaborate fabrication procedures and expensive raw materials. Layered hydroxide salts (LHSs) are a kind of lamellar material involving economical ingredients and are quite easy-to-fabricate. However, they have yet to be developed into gas separation membranes and their separation potential has not been investigated, despite their merits. Here, we report the successful fabrication of ultrathin Zn 5 (OH) 8 (NO 3) 2 ·2H 2 O membranes by using a rapid and facile in situ growth strategy at room temperature. By virtue of the few-layered membrane thickness, the obtained membranes exhibited intriguing surface undulations, which endowed the membranes with extremely tortuous interlayer channels and therefore an auspicious molecular sieving ability. Consequently, these membranes showed an optimal H 2 /CO 2 mixture separation selectivity of 792 ± 38 and a remarkable H 2 permeance of 1607 ± 99 GPU. Moreover, with a demonstration of a gentle framework dehydration, the molecular sieving capacity of the LHS membrane was further sharpened at 150 °C owing to the narrowed interlayer channels. This work introduced a low-cost 2D membrane and manifested the advantages of fabricating few-layered 2D membranes, opening a new avenue for membrane future scale-up. [Display omitted] • 2D Zn 5 (OH) 8 (NO 3) 2 ·2H 2 O (ZHNH) membrane is fabricated by using in situ growth method. • ZHNH membrane exhibits surface undulation which provide tortuous transfer pathways. • ZHNH membrane exhibits superior H 2 /CO 2 separation performance via molecular sieving. • Dehydrated membrane demonstrate H 2 /CO 2 separation factor of 355 at 150 °C. [ABSTRACT FROM AUTHOR]

Carbon membranes are a potentially attractive candidate for the in-situ removal of water vapor in CO 2 hydrogenation reactions. Their hydrophilicity and pore structure can be tuned by properly adjusting the synthesis procedure. Herein, we assess the effect of the carbonization temperature (450–750 °C) on the performance of supported CMSM in terms of vapor/gas separation, in correlation with changes in their surface functionality and porous structure. FTIR spectra showed that the nature of the functional groups changes with the evolution of the carbonization step, leading to a gradual loss in hydrophilicity (i.e., OH stretching disappears at T carb ≥ 600 °C). The extent of water adsorption displays an optimum at T carb of 500 °C, with the membrane carbonized at 650 °C being the least hydrophilic. We found that the pore size distribution strongly influences the water permeance. At all T carb , adsorption-diffusion (AD) is the dominant transport mechanisms. However, as soon as ultra-micropores appear (T carb : 600–700 °C) molecular sieving (MS) contributes to an increase in the water permeance, despites a loss in hydrophilicity. At T carb ≥ 750 °C, MS pores disappear, causing a drop in the water permeance. Finally, the permeance of different gases (N 2 , H 2 , CO, CO 2) is mostly affected by the pore size distribution, with MS being the dominant mechanism over the AD, except for CO 2. However, the extent and mechanism of gas permeation drastically change as a function of the water content in the feed, indicating that gas/vapor molecules need to compete to access the pores of the membranes. [Display omitted] • Effect of the carbonization temperature on the hydrophilicity of carbon membranes. • In situ FTIR analysis used to study the membrane interaction and affinity to water. • Significant CO 2 surface adsorption, increasing with the carbonization temperature. • Adsorption diffusion is the dominant mechanism for water, methanol and CO 2 permeation. • Membranes carbonized at 600–700 °C show highest permeability due to the pores in the molecular sieve region. [ABSTRACT FROM AUTHOR]

Selectivity remains the biggest challenge for metal oxide semiconductor (MOS)-based gas sensors, especially for inactive gases such as CH 4. In this work, the core-shell structured ZnO/Pd@ZIF-8 was fabricated via the self-templated method and the sensor based on the ternary hybrid showed excellent CH 4 selectivity against NH 3 , CO and NO 2. ZIF-8 was critical for the selectivity enhancement via dual filtering effects: a) size-induced sieving, where NO 2 with a larger kinetic diameter of 4.5 Å can be hindered by ZIF-8 with an effective aperture size of 4.0–4.2 Å; b) polarity-induced sieving, where NH 3 (2.6 Å) and CO (3.76 Å) with larger polarity showed stronger interaction with ZIF-8 and their diffusion is therefore retarded. Therefore, the selectivity of nonpolar CH 4 (3.8 Å) is improved. The present insight about the dual filtering effects of ZIF-8 may provide a new insight to improve MOS sensing selectivity by rational designing MOF structures. [Display omitted] • Facile synthesis of ZnO/Pd@ZIF-8 core-shell structure. • Excellent CH 4 sensing selectivity against CO, NH 3 and NO 2. • New insight into dual sieving effect of ZIF-8 induced by size and polarity. [ABSTRACT FROM AUTHOR]

Triethoxysilane (TRIES), which consists of three ethoxy groups and a Si-H bond as a pendant-type alkoxysilane, was utilized as a Si precursor for the fabrication of a gas separation membrane. The effect of membrane fabrication parameters such as sol preparation conditions and calcination temperatures on Si-H groups and network structures was evaluated. The degree of dehydrogenation of Si-H groups in aqueous solution was independent of the H 2 O/Si molar ratio in the sol, but the degree of hydrolysis and polymerization of ethoxy groups (-OEt) depended on the H 2 O molar ratio. TRIES membranes calcined at 550 °C under N 2 showed a decrease in network size with an increase in the H 2 O/Si molar ratio in the sol. The TRIES-derived network pore size also depended on the calcination temperature, and the network size was decreased under lower calcination temperatures. For example, a TRIES membrane calcined at 550 °C showed high selectivity for He/N 2 and H 2 /N 2 at approximately 1000 and 600, respectively, however, in the case of calcination at 300 °C, Knudsen diffusion dominated for small molecules (H 2 /N 2 selectivity: 4.3) and molecular sieving favored large molecules (H 2 /CF 4 : >100, H 2 /SF 6 : >400). When a TRIES membrane was fabricated by calcination at 300 °C, most Si-H groups were still present in the networks, the estimated network pore size for the TRIES membrane was 0.577 nm, which was larger than that of a tetraethoxysilane (TEOS) membrane calcined at 350 °C (0.426 nm). On the other hand, when TEOS and TRIES membranes were fabricated at 550 °C, both membranes showed approximately the same network pore size (TEOS: 0.385 nm, TRIES: 0.382 nm), due to the dehydrogenation of Si-H groups in the formation of Si-OH groups as well as for the forming of a Si–O–Si bond. [ABSTRACT FROM AUTHOR]

The solute separation in reverse osmosis/nanofiltration (RO/NF) membrane processes is mainly controlled by both the diffusivity in a pore and the steric partition factor, and the latter is defined by the geometrical probability at which a solute can be accessible into a pore. The rejection of alcohols has been estimated semi-empirically by using the steric partition factor derived by the approximation of molecular shape as a rectangular parallelepiped. However, the approach was not suitable for crown ethers, and in this work the shape of crown ethers was approximated as a disk: the disk radius and disk thickness were developed as new shape parameters. The calculated rejections of crown ethers by using the disk-shaped model corresponded well to the observed rejections, where the used pore radius was calculated on the basis of the rejections of alcohols. Boric acid in non-dissociated form is also assumed to be a disk-shaped molecule, but the calculated rejection by the disk-shaped model was smaller than the observed one. The results suggest that boric acid transports through membrane pores with hydrated water molecules. [ABSTRACT FROM AUTHOR]

Developing new techniques and materials for ethylene (C 2 H 4) and ethane (C 2 H 6) separation is an industrially significant but challenging task. Here we report two isoreticular pillar-layer metal-organic frameworks, Co(aip)(bpy) 0.5 and Co(aip)(pyz) 0.5 , for the separation of C 2 H 4 /C 2 H 6. The pore apertures of the pillar-layer metal-organic frameworks are rationally controlled by changing the length of the pillar ligands. Significantly, Co(aip)(pyz) 0.5 with a shorter pillar ligand shows reduced pore size and molecular sieving separation of C 2 H 4 from C 2 H 6. Co(aip)(pyz) 0.5 has a moderate C 2 H 4 capacity of 1.78 mmol/g but ultrahigh C 2 H 4 /C 2 H 6 selectivity exceeding 2000 at ambient conditions. The molecular simulation revealed that large torsion angle between the organic linker plane and Co–O bond leads to the high energy barrier for C 2 H 6 to enter into the pore, which results in the molecular sieving separation of C 2 H 4 /C 2 H 6. Dynamic breakthrough experiments confirmed the high selectivity of Co(aip)(pyz) 0.5 for C 2 H 4. And high-purity C 2 H 4 (>97%) with a C 2 H 4 productivity of 19.1 l/kg can be obtained through the desorption process. Meanwhile, the excellent reusability and moisture stability endow it great potential for applications in adsorptive separation. [Display omitted] • The pore apertures of the pillar-layer MOFs are rationally controlled. • Co(aip)(pyz) 0.5 showed the molecular sieving separation of C 2 H 4 /C 2 H 6. [ABSTRACT FROM AUTHOR]

Membrane separation technologies featuring environmentally friendly and highly efficient processes have been widely adopted for sustainable development. Non-linear macromolecules, represented by aromatic poly(amidoamine) dendrimers (ArPD), have good potential for increasing the porosity of the active layer in thin-film composite (TFC) membranes. However, they are often difficult to use as the sole monomer in interfacial polymerization to prepare membranes with high separation accuracy. Herein, the DMF/H 2 O system was determined to resolve the problem of ArPD dissolution, and the behavioral differences of ArPD for different generations in film-forming were then elucidated. For G4 (the fourth generation of ArPD) -TMC (trimesoyl chloride) membranes, the good sieving performance is attributed to the relatively dense polyamide networks from interfacial polymerization, and the continuous pore channels from the tightly packed macromolecules. Therefore, the final polyamide layer shows significant heterogeneity. Moreover, a "patching" strategy was employed to further improve the separation performance. The ArPD-based membranes exhibit about 3 times higher permeance than MPD (m-phenylenediamine)-based membranes under the comparable NaCl rejection. For the repaired membrane, the water permeance reaches 3.2 L m−2 h−1 bar−1 with the NaCl rejection of about 94.9%, which is advantageous compared with reported macromolecule-based membranes. The repaired membrane also shows excellent performance in the removal of small organics in organic solvent system. For example, the methanol permeance achieves 1.5 L m−2 h−1 bar−1 with the rejection to potassium cinnamate (186.25 g mol−1) about 90.3%. This work provides a typical paradigm for the application of macromolecules in the preparation of TFC membranes. [Display omitted] • An aromatic poly(amidoamine) dendrimer (ArPD) served as the sole amine monomer to participate in IP reaction. • The active layer of G4 (the fourth generation of ArPD) -TMC membrane shows significant heterogeneity. • A "patching" strategy was used to further improve the separation performance. • ArPD-based membranes show good performance in desalination and removal of organics. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new strategy was developed to prepare graphene sheets with tunable layer-number. • Sieving performance of membranes assembled from the graphene sheets was studied. • The membranes assembled from thin graphene sheets behaved better sieving performance. • An insight into optimizing the nanochannel structure in the membrane was proposed. Graphene oxide (GO)-based membranes have attracted extensive attention in water purification but still face great challenge due to their poor service life. To overcome this issue, weakly oxidized graphene nanosheets have been chemically exfoliated from natural graphite via a newly-developed strategy for preparing layer-tunable graphene. When an 80 μm-thick graphene membrane is assembled from the graphene nanosheets with an average layer number of 3, it exhibits a high rejection rate of 99.9 % for Rhodamine B and a water flux of up to 3452.6 L m−2 h−1 bar−1. This should be ascribed to the unique hierarchically nanochannel structure within the membrane. This finding may provide a new insight into the design and fabrication of the thick membrane having excellent sieving performance. Furthermore, the rejection rate of RB can be maintained at 99.9 % even after 24 cycles of filtrations, demonstrating a superior service performance for the membrane. [ABSTRACT FROM AUTHOR]

Using the secondary growth method, a continuous zeolite Y film was prepared on a conducting FTO glass substrate. The synthetic gel composition was optimized to contain no cracks. This method provides a simple and effective way of controlling the thickness of zeolite Y films and expands the possible range of applications for molecular sieve films. Therefore, as presented in this study, zeolite Y film on a transparent conducting oxide glass such as FTO glass can furnish electrodes with size and ionic selectivity. [ABSTRACT FROM AUTHOR]

The aim of this study is to determine the optimal carbonization conditions for carbon hollow fiber membranes for hydrogen purification. To this end, it is a prerequisite to obtain the best permselectivity of the resultant membrane. Three different carbonization atmospheres (vacuum, helium flow, and argon flow) were examined, while their effects on the changes in the microstructure and gas permeation properties of the as-synthesized carbon membranes were elucidated using a pure gas permeation test, coupled with an array of characterizations, including Raman spectroscopy and XPS. Moreover, the issue of vacuum degree was addressed to maintain the best reproducibility of the carbon membrane. The results revealed that CHFM-HV exhibited the best separation capability for H 2 /CH 4 of 516.90, thereby indicating distinct hydrogen purification characteristics. Such good performance was driven by the attractive synergism of the ordered microstructure and larger pore volume. Notably, the recovery of permselectivity for CHFM-HV reached 90% after four months, thus suggesting its aging resistance. Hence, the demonstrated approach is efficient for altering the microstructure of the carbon membrane, thereby strengthening the separation performance and long-term stability. Overall, it is suitable for broad applications of diverse polymer precursors and prolonged the lifespan of the as-prepared carbon membrane. [Display omitted] • Carbonization atmosphere affects the microstructure of carbon membrane. • Lower vacuum degree will help to improve reproducibility of carbon membrane. • The resulting CHFM manifests the outstanding permselectivity toward hydrogen purification • Excellent aging-resistance of carbon membrane was achieved after 4 months. [ABSTRACT FROM AUTHOR]

Ultra-thin membranes have significant potential for the gas separation. However, the fabrication of ultra-thin membrane with high selectivity and permeance remains a challenge. Herein, we develop a high-performance hydrogen separation membrane using atomic layer deposition (ALD) method to deposit ultra-thin Al 2 O 3 layer (ALD-Al 2 O 3) on a porous anodic aluminum oxide (AAO) support. The pore openings of the AAO substrate were fully covered, but not sealed, by the Al 2 O 3 overlayer after 260 ALD cycles. Due to the low deposition temperature (50 °C), angstrom-scale pores were formed within the Al 2 O 3 overlayer. Single gas permeance results revealed that the size of the pores to be smaller than 0.364 nm, but larger than the kinetic diameter of molecular H 2 (0.289 nm). This membrane at room temperature, exhibits high H 2 permeance of ∼3.03 × 10−7 mol m−2 s−1 Pa−1 and high H 2 selectivity for H 2 /CO 2 (5148.2), H 2 /O 2 (120.7), H 2 /N 2 (161.5) and H 2 /CH 4 (219.5), showing great potential for industrial H 2 purification and recovery. [Display omitted] • Ultra-thin hydrogen separation membrane was prepared by atomic layer deposition. • Ultra-thin membrane shows ultrahigh gas-pair selectivity. • Molecular sieving effect results in the high gas separation performance. [ABSTRACT FROM AUTHOR]

An efficient membrane for helium separation from natural gas is quite crucial for cryogenic industries. However, most experimentally available membranes fail in separating helium from small molecules in natural gas, such as H 2 , as well as in 3 He/ 4 He isotopes separation. Using first-principles calculations, we theoretically demonstrated that the already-synthesized graphitic carbon nitride (g-C 3 N 4 ) has high efficiency in helium separation from the gas molecules (H 2 , N 2 , CO and CH 4 ) in natural gas and the noble gas molecules (Ne and Ar). The selectivity of He over H 2 molecule at room temperature is calculated to be as high as 10 7 . More interestingly, the g-C 3 N 4 membrane can also serve as a quantum sieving membrane for 3 He/ 4 He separation with a predicted transmission ratio of 18 at 49 K, thus offers a combined means of both He and 3 He isotope separation. [ABSTRACT FROM AUTHOR]

An ultramicroporous metal–organic framework (Cu-F-pymo) with dual functionalities achieved sieving separation of CO 2 from N 2 and CH 4 with remarkably high selectivity (>107) and high adsorption capacity (69.2 cm3 cm−3). Cu-F-pymo with small pore size around 3.3 Å also exhibited enhanced binding affinity toward CO 2 through electrostatic and hydrogen-bonding interactions, which was verified from GCMC modeling studies. The high sieving CO 2 separation performance was further confirmed by cycling column breakthrough tests with good productivity (1078 mmol kg−1 and 941 mmol kg−1). [Display omitted] • An ultramicroporous metal–organic framework with dual-functionality. • The MOF exhibits extremely high sieving separation of CO 2 from N 2 and CH 4. • The MOF exhibits a very high adsorption capacity at ambient conditions as well. • Accordingly, the material shows very high productivity for CO 2 removal. The removal of carbon dioxide from fuel gases and N 2 -rich flue gas are critical for chemical energy industry, and reduction of carbon emission. Adsorptive size-sieving based gas separation is highly desired to maximize the separation efficiency but rarely reported. Herein, an ultramicroporous metal–organic framework built from copper(II) and 5-fluoropyrimidin-2-olate, termed as Cu-F-pymo , has been studied for the separation of CO 2 from CH 4 and N 2. Cu-F-pymo can exclusively capture CO 2 over CH 4 and N 2 with significant high IAST selectivity (>107) and a high adsorption capacity of 69.2 cm3 cm−3. Such molecular size-sieving effect is attributed to the small pore size of Cu-F-pymo (∼3.3 Å), which can only allow the diffusion of CO 2. The oxygen moieties decorated on the channel surface enforced the binding affinity toward CO 2 through electrostatic and hydrogen-bonding interactions as confirmed by molecular simulation studies. The outstanding size-sieving CO 2 separation performance was further confirmed by cycling column breakthrough tests, which demonstrated the dynamic CO 2 capture capacity of 1078 mmol kg−1 and 941 mmol kg−1 for CO 2 /CH 4 (50:50), CO 2 /N 2 (15:85) mixtures, respectively. More importantly, the mild regeneration feature of Cu-F-pymo underlies its potentials for practical carbon capture applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrokinetic energy conversion combined with organic molecular sieving was investigated. • The surface charges of MXene-based nanochannels were successfully transferred from negative to positive. • The integrated nanochannels displayed efficient dye rejection and high output current. • The effects of the various parameters on energy conversion and molecular separation were discussed. With the development of nanofabrication and nanomaterials, electrokinetic nanofluidic energy conversion has been studied in nanometre-scale, even sub-1-nm channels, which can sieve organic molecules. However, achieving simultaneous nanofluidic energy conversion and organic molecular sieving still remains a challenge. In this work, functional MXene-based membranes were prepared for simultaneous electrokinetic energy conversion and organic molecular sieving. The surface charges of MXene-based membranes were successfully transferred from negative to positive by functionalizing poly (diallyldimethylammonium chloride) (PDDA) polycation chain. The positively charged PDDA-MXene (PMXene) composite membranes displayed good rejection (greater than 99 %) for positively charged methylene blue (MB) molecules. The streaming currents through PMXene and MXene membranes were opposite, indicating the successful modification of the surface charge in the nanochannels of the membranes. In addition, the output current improved around four times from ∼ 95 nA (50 kPa) to ∼ 380 nA (150 kPa) through the PMXene membranes. The flux and rejection of the membranes can also be enhanced by tuning the applied pressure and the thickness of the membranes. Given the superior selective transport of ions and molecules, functional MXene-based membranes can offer many exciting opportunities for self-powered and energy recovery systems during the separation process. [ABSTRACT FROM AUTHOR]

[Display omitted] • The prepared membranes exhibited long-term stability via CHZ crosslinked with GO nanosheets. • The composite membranes displayed ultra-high water permeance and excellent dyes rejection (99%). • The composite membranes can separate mixed dye solutions completely. As natural resources become more and more limited, it is exceptionally essential to decrease energy consumption in membrane separation processes, which makes membranes with ultra-high water permeance increasingly expected. Graphene oxide (GO) membranes have exhibited an unsurpassed future for wastewater purification. However, it is two key challenges to greatly increase the water permeance while retaining the removal efficiency of contaminants and improve the enduring stability of membranes in aqueous solution. In this work, the membranes with ultrafast water permeability were prepared by self-assembly vacuum filtration method using carbohydrazide (CHZ) as reducing and cross-linking agent. The obtained lamellar rGO/CHZ nanofiltration membranes exhibited water permeance bigger than 1600 L m-2h−1 bar−1, and outstanding separation efficiency, e.g., Congo Red (CR), Malachite Green (MG), and Crystal Violet (CV) removal rate of 99%. More importantly, the composite membrane exhibited efficiently selective separation of various mixed dyes. Such as binary mixed dyes of MG/MO, the removal rate of MG is 99%, while the removal rate of MO is merely 23%. In addition, the membrane still showed excellent stability after long-term immersion in solutions of various pH values. The separation performance in terms of complete rejection of single dyes and selective filtration of mixed dyes makes them one of the promising materials for dye separation, purification, and reuse. [ABSTRACT FROM AUTHOR]

The molecular sieving effect of tetrahydrofuran (THF) clathrate hydrate was experimentally investigated. The capture and release of seven gases, i.e., helium (He), hydrogen (H 2 ), neon (Ne), nitrogen (N 2 ), xenon (Xe), methane (CH 4 ), and ethane (C 2 H 6 ), in THF clathrate hydrate were investigated. For gases with a diameter smaller than the window diameter, the order of the gas uptake rates in the THF clathrate hydrate was in accordance with the order of their van der Waals diameters, except for He. This result indicates that the gas uptake rate is generally controlled by the size of the gas molecules. The apparent diffusion coefficients for these gases in the THF clathrate hydrate were estimated. The van der Waals diameters of CH 4 and Xe are larger than the window diameter. However, gas uptake by THF clathrate hydrate was observed for both gases. This can be attributed to the formation of the type I clathrate hydrate of these gases. No significant gas uptake of ethane was observed. Based on the results, H 2 /N 2 and H 2 /C 2 H 6 separation experiments were conducted. Gas separation of H 2 /N 2 by THF clathrate hydrate was successfully achieved using the difference in their gas uptake rates of the gases, and the separation ratios were in the range 4–16 mol/mol. Gas separation of H 2 /C 2 H 6 was also achieved utilizing the molecular sieving effect of THF clathrate hydrate. [ABSTRACT FROM AUTHOR]

• A flexible molecular sieving strategy developed for efficient C 2 H 2 /CO 2 separation. • A new cost-effective MOF was prepared with unprecedented topological structure. • High C 2 H 2 capacity and high C 2 H 2 /CO 2 uptake selectivity achieved by ZNU-3. • Excellent C 2 H 2 /CO 2 separation performance confirmed by breakthroughs. The separation of C 2 H 2 /CO 2 is an important process in industry but challenged by the trade-off of capacity and selectivity owning to their close physical properties and identical kinetic molecular size. Herein, we reported a new metal organic framework ZNU-3 (ZNU = Zhejiang Normal University) with flexibility controlled by abundant hydrogen-bonds for highly selective molecular sieving of C 2 H 2 from CO 2 , CH 4 , C 2 H 4 and C 2 H 6 using commercially available cost-effective ligands. At 1.0 bar and 298 K, the uptake capacity of C 2 H 2 is 81.0 cm3 (STP) g−1, while the CO 2 , C 2 H 4 , C 2 H 6 , CH 4 , N 2 uptake capacities are only 5.4, 5.3, 1.0, 1.1, 1.1 cm3 (STP) g−1, respectively. Such high uptake ratios of C 2 H 2 over other C2 and C1 gases have rarely been achieved. Particularly, the C 2 H 2 /CO 2 uptake ratio of 14.9 is only secondary to that of the benchmark UTSA-300a and much higher than those of all other porous materials. Dynamic breakthrough experiments with equimolar C 2 H 2 /CO 2 mixtures showed that the retaining time of C 2 H 2 is nearly 2 fold of that of CO 2 , indicating the excellent practical separation performance of ZNU-3 for C 2 H 2 /CO 2 mixtures. Modeling studies indicated that C 2 H 2 is mainly trapped by two opposite carboxylic groups with additional small contribution from π···π packing between pyridine ring and planar C≡C moiety. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular sieving of CO 2 from CH 4 and N 2 were achieved on M−gallate (M = Mg, Co, Ni). • Unique S-shaped isotherms with ultrahigh uptake of CO 2 (4.96 mmol g−1) on Mg-gallate at 313 K and 1 bar enables a high working capacity in high-temperature separation process of flue gas. • Multiple hydrogen bonds ensure a dense packing of CO 2 within MOF structure verified by DFT calculations. • Robust structure and cycling stability as well as facile scale-up synthesis guarantee M−gallate promising in practical applications. Carbon capture and sequestration are vital industrial processes that not only mitigate the greenhouse effect but also promote upgrading of low-quality natural gas. Porous adsorbent-based adsorption separation process appeals to be promising, while it still remains a great challenge to develop adsorbents with high adsorption uptake and selectivity of CO 2 as well as high working capacity in practical applications. In this work, a group of gallate-based metal-organic frameworks with aperture size of 3.52 to 3.65 Å were reported for molecular sieving of CO 2 from N 2 and CH 4. Remarkably, Mg-gallate exhibited a record-high uptake of CO 2 (5.05 mmol g−1) among all reported molecular sieving adsorbents combined with ultrahigh uptake ratio of CO 2 /CH 4 (29.7) and CO 2 /N 2 (84.2) at 1 bar and 298 K. Multiple O-H...C and O...H-O interactions afford dense packing of CO 2 molecules in the framework structure with a density up to 1.06 g cm−3 on Mg-gallate, verified by density function theory calculations. Experimental breakthrough experiments confirmed the superb separation performance of flue gas and natural gas over a wide range of temperature. Robust structure and cycling stability along with facile scale-up synthesis method further offer great potential of M−gallate in industrial applications. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) are typically fabricated by mechanically mixing presynthesized polymers and fillers together in a solvent to form a membrane solution, which often causes poor filler dispersion in the polymer matrix. In this work, an in situ polymerization method was proposed by which 2,6,14-triaminotriptycene (Trip), octanedioyl chloride, and graphene oxide (GO) reacted in the polymerization to form a polyamide@GO mixed matrix polymer. Different characterization methods, such as Raman analysis, XRD (X-ray diffraction), and TGA (thermogravimetric analysis), were used to verify the chemical linking between GO and polyamide. The performance of the polyamide@GO membrane in the separation of cyclohexane/nitrogen mixtures was evaluated and compared with that of pure polyamide membranes and mechanically mixed polyamide + GO membranes. The polyamide@GO membrane with a GO content of 0.3 wt% exhibited the highest separation performance. The permeability increased from 427 Barrer to 1098 Barrer under the same rejection (99.4%) conditions compared with that of the pure polyamide membrane. Because incorporation of GO disrupted the efficient stacking of polyamide chains, more amorphous domains were formed, providing more transport channels. This work provides an alternative way to overcome the trade-off phenomenon in the synthesis of new MMMs. [Display omitted] • GO mixed microporous triptycene-based polyamide was synthesized in situ. • GO in the polyamide can increase the inter-chain distance of polyamide chains. • Higher permeability with greater than 99% rejection can be observed after the addition of GO. [ABSTRACT FROM AUTHOR]

Abstract: SAPO-34 membranes that have CO2/CH4 separation selectivities of ~100 at 295K and pressures up to 4.6MPa also show high molecular sieving separations of mixtures containing i-butane (0.50-nm kinetic diameter) or CF4 (0.47nm). The separation selectivities were 15,000–20,000 for CO2/i-butane from 295 to 420K, and 12,000–20,000 for CO2/CF4 for feed pressures up to 0.5MPa at 295K. These may be the highest gas-phase separation selectivities reported for zeolite membranes, and they are likely lower limits because of concentration polarization, leakage around O-rings, and i-butane diffusion through the silicone O-rings. The low defect concentration was also confirmed by spatial defect distributions measured with i-butane. Thus, less than 1% of the CH4 permeation during CO2/CH4 separations is through defects larger than 0.47nm. Isobutane, even though it is too large to adsorb in SAPO-34 pores (0.38-nm diameter), appeared to inhibit CO2 permeation by adsorbing on the external surface. These SAPO-34 membranes also separated H2/i-butane with lower limits on selectivities of 6000 at 295K and 10,000–14,000 at 423K, and they were also selective for He/CH4 separation (selectivity=20) and H2/CH4 separation (selectivity=35–45). In these separations, both He and H2 appear to speed up CH4 permeation, as expected from molecular simulations reported previously. Also, CH4 appears to slow diffusion of CO2, He, and H2. [Copyright &y& Elsevier]

Highlights: [•] SAPO-5 crystal plates of about 1μm in side length and 200nm in thickness were prepared. [•] C-oriented SAPO-5 crystal monolayer was deposited on α-Al2O3 coated with a PVA film. [•] SAPO-5 seed layer was grown to continuous 1.5μm thick, c-oriented membrane. [•] SAPO-5 membranes show high permeability and excellent separation characteristics. [Copyright &y& Elsevier]

Abstract: A facile, versatile and reproducible sol–gel process to make microporous organosilica membranes by using 1,2-bis (triethoxysilyl) ethane (BTESE) as a precursor is reported. The influence of process parameters on sol particle size and rheology of BETSE-derived sols was investigated to produce defect-free composite membranes by a single dipping procedure and subsequent calcination. The microporous structure of a BTESE layer on mesoporous alumina supports enabled selective molecular sieving of gas molecules. Single gas permeation (SGP) experiments, performed at 200°C, showed that a H2/CH4 permselectivity of 24 was reproducibly achieved. No SF6 gas permeance through these membranes proof the presence of a defect-free microstructure. SEM cross-section analysis showed a hybrid selective layer with a thickness dependent on the sol precursor concentration. [Copyright &y& Elsevier]

Hybrid membranes with 2D vertical continuous channels are expected to achieve high separation performance, but remain unexplored. In this study, 2D vertical continuous channels from layered double hydroxide (LDH) array were constructed in hybrid membranes for pervaporation dehydration. Vertically aligned LDH array that anchored onto the polyacrylonitrile substrate via in situ hydrothermal synthesis was employed to provide intrinsic continuous channels with an interlayer distance between water and ethanol. Sodium alginate impregnated into interstitial space of LDH array ensured a leakage-free and mechanical strength of membranes. The height of LDH array within hybrid membranes could be facilely manipulated from 1.5 μm to 3.6 μm through altering the hydrothermal reaction time and Co2+/Al3+ ratio. Comparing hybrid membranes with randomly oriented LDH, the hybrid membrane with vertically aligned LDH array exhibites optimal water permeability of 7742 Barrer together with a desirable selectivity of 1903 when the reaction time is 10 h, and Co2+/Al3+ ratio is 2. This study provided an innovative avenue to fabricating high-performance hybrid membranes with 2D vertical continuous channels. [Display omitted] • 2D vertical continuous channels from LDH array are constructed in hybrid membranes. • 2D vertical continuous channels afford precise molecular sieving. • The height of LDH array can be tuned by hydrothermal reaction conditions. • The hybrid membrane exhibits superior selectivity and permeability. [ABSTRACT FROM AUTHOR]

The scarcity of freshwater is of great challenge that the world is facing nowadays. The advances of nanomaterial based on the reverse osmosis (RO) technology provide new possibilities for desalination. In this study, using molecular dynamics simulation, we propose and design an excellent RO membrane composed of fluorinated graphene (F-GRA) nanochannels, by which the exceptionally high water permeation (reaching up to 61.1 L/cm2/day/MPa) and the almost complete ion rejection are achieved. Notably, F-GRA nanochannel membranes exhibit a desalination performance much more promising than many other nanomaterials in previously theoretical studies. This superior desalination performance of F-GRA channels is attributed to the negatively charged surface and hydrophobicity of F-GRA, where the electrostatic interactions (attraction or repulsion) between ions and F-GRA surface cause the ideal ion rejection and the ultralow water friction on F-GRA mediated by its hydrophobicity results in the excellent water penetration. Moreover, potential of mean force calculations further reveal that the water molecule reflects the lowest free energy barrier relative to ions when traversing through the F-GRA channel, indicating the energetical favorability of the successful water transport instead of ions. Our theoretical study offers a fascinating approach of molecular sieving design usable for future desalination. • Fluorinated graphene (F-GRA) nanochannel based membrane is constructed. • The F-GRA membrane presents an excellent desalination performance with the high water permeability and the high ion rejection. • The superior water permeability and ion rejection are resulted from the negatively charged surface and hydrophobicity of F-GRA. • The desalination performance of F-GRA nanochannel is investigated from the molecular level. [ABSTRACT FROM AUTHOR]

Abstract: The present work describes the adsorption and separation of xylene isomers by ZIF-8. Although the formal pore diameter of ZIF-8 is much smaller than the molecular diameter of the xylene isomers, ZIF-8 is able to separate the isomers by molecular sieving. A structural study indicates that the diffusion of the xylenes into the pore structure of ZIF-8 happens via a transitory deformation of the pore aperture which is based on a tilt of the imidazolate linkers, followed by a return to the initial conformation. The rate of adsorption depends on the size of the isomer, i.e. it decreases from para- to meta- and to ortho-xylene. The separation of the xylene isomers is good in the gas phase. In liquid phase breakthrough experiments, the quality of the separation is deteriorated. Moreover, as expected for a separation based on molecular sieving, para-xylene cannot be well separated from ethyl-benzene. [Copyright &y& Elsevier]

Abstract: The performance of carbon hollow fiber membranes derived from sulfonated poly(phenylene oxide) (SPPO) was investigated with respect to the dehydration of aqueous alcohol solutions. SPPO carbon hollow fiber membranes were prepared by pyrolysis of precursor polymer membranes at 600°C, which possess sufficient membrane flexibility and excellent gas separation performance. In pervaporation tests, SPPO carbon membranes exhibited high flux and high separation factors in the separation of water and larger alcohol molecules, indicating that the main permeation mechanism is molecular sieving. In addition, water permeance was much higher than that of H2, which is similar in size to water, suggesting that surface diffusion occurred. Water adsorption measurements and surface analysis by ESCA indicate the presence of oxygen-containing functional groups on the surface of the carbon membrane as adsorption sites. Increasing the temperature resulted in lower water permeances for water/2-propanol systems, though flux exhibited opposite tendencies. The activation energy for water permeation was negative, supporting the likelihood of adsorption effects. Furthermore, water permeance gradually increased with water concentration. Temperature and concentration did not have much influence on ideal selectivity, and maintained a value over 10000 for the range of conditions investigated. [Copyright &y& Elsevier]

Abstract: Metal-organic frameworks (MOFs) which offer a variety of topologies, porous networks and high surface areas are promising and have potential for the applications of specific adsorption, isomerization, catalysis and separation. UIO-66 is the first MOF that has been observed to have reverse shape selectivity. However, such reverse shape selectivity of MOFs has never been explored for capillary gas chromatographic separation. Here we report the fabrication of MOF UIO-66 coated capillary column and exploration of the reverse shape selectivity and molecular sieving effect of such column for capillary gas chromatographic separation of alkane isomers and benzene homologues with excellent selectivity and precision. The adsorption enthalpies and entropies on the interaction between hydrocarbons and UIO-66 were measured to illustrate the energy effect on the separation of alkane isomers and benzene homologues on the UIO-66 coated capillary column. UIO-66 coated capillary column gave preferential retention of branched alkane isomers over their linear isomer, showing reverse shape selectivity, making UIO-66 coated capillary column attractive for capillary gas chromatographic separation of alkane isomers. iso-Propylbenzene (branched) eluted after n-propylbenzene on the UIO-66 coated capillary column again shows reverse shape selectivity. However, much bulkier 1,3,5-trimethylbenzene eluted earlier than n-propylbenzene and iso-propylbenzene on the UIO-66 coated capillary column, exhibiting molecular sieving effect. The combination of reverse shape selectivity with molecular sieving effect makes the UIO-66 coated capillary column promising for the separation of structural isomers. [Copyright &y& Elsevier]

Abstract: Nanoporous membranes with antifouling properties and narrow pore size distribution targeted at a nanometer and subnanometer separation capacity hold great promise in high end value molecular sieving and bioseparation. Herein a novel strategy is presented for preparation of well-defined nanoporous membranes with tunable nanopores via click chemistry. The graft polymerization based on copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) was successfully conducted at ambient conditions to tether monodispersed propargyl poly(ethylene glycol)s (pro-PEGs) onto a microporous polysulfone (PSF) membrane anchored with azide groups. The solute transport method indicates that a series of nanoporous membranes with narrowed pore size distribution and the mean pore diameter of 1.20nm, 0.82nm and 0.69nm were obtained. The protein filtration experiments show that membrane surface can be endowed with antifouling properties by the densely grafted PEG. The membrane effectively rejects emulsified oil at 0.5MPa with less fouling than the thin film composite membrane. The molecular sieving capacity is demonstrated through separation of dyes varying in several angstroms. [Copyright &y& Elsevier]