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Carbon molecular sieve (CMS) membranes prepared by carbonization of polymers containing strongly size-sieving ultramicropores are attractive for high-temperature gas separations. However, polymers need to be carbonized at extremely high temperatures (900° to 1200°C) to achieve sub-3.3 Å ultramicroporous channels for H 2 /CO 2 separation, which makes them brittle and impractical for industrial applications. Here, we demonstrate that polymers can be first doped with thermolabile cross-linkers before low-temperature carbonization to retain the polymer processability and achieve superior H 2 /CO 2 separation properties. Specifically, polybenzimidazole (PBI) is cross-linked with pyrophosphoric acid (PPA) via H bonding and proton transfer before carbonization at ≤600°C. The synergistic PPA doping and subsequent carbonization of PBI increase H 2 permeability from 27 to 140 Barrer and H 2 /CO 2 selectivity from 15 to 58 at 150°C, superior to state-of-the-art polymeric materials and surpassing Robeson’s upper bound. This study provides a facile and effective way to tailor subnanopore size and porosity in CMS membranes with desirable molecular sieving ability.

In order to solve the problems of deficient CO2 adsorption sites on Zn/Co zeolitic imidazolate frameworks (ZIFs), Zn/Co ZIFs were thermally treated to promote physical adsorption sites on Zn-N and Co-N bonds and then impregnated with polyethyleneimine (PEI) to promote NH and NH2 chemical adsorption sites. The CO2 adsorption capacity detected on Micromeritics ASAP 2020C increased by 53% to 1.07 mmol/g at 298 K and 1 bar, when Zn/Co ZIF was treated at optimal temperature of 450 °C to obtain the maximum Me-N2 unsaturated adsorption sites. This was because of a partial cleavage of coordination bonds between Zn N, Co N, C N and C N along with dissociation of rationally free methyl groups in the framework ligands, which was supported on density functional theory (DFT) calculation. The Zn/Co ZIF treated at 450 °C and then impregnated with 40 wt% PEI exhibited the highest CO2 adsorption capacity of 1.82 mmol/g under the condition of at 298 K and 1 bar, which was 2.6 times higher than that of raw Zn/Co ZIF. In addition, this adsorbent is proved to be regenerable and stable during 9 cycle CO2 adsorption-desorption tests, therefore, PEI- thermally treated Zn/Co ZIF exhibits a very promising application in CO2 capture from flue gas and natural gas.

Model systems are developed and investigated to better understand the effect of polyether-metal ion interactions on gas separation characteristics. These systems help answer current questions raised by the substantial body of research on metal-organic frameworks (MOFs) dispersed in polyethers to improve gas separation performance, where favorable interactions between the metal centers and polyethers are preferred to improve interfacial compatibility. Specifically, we investigate CO2/gas transport properties of supramolecular networks comprising cross-linked poly(ethylene oxide) (XLPEO) and dissociable salts, including LiClO4, Ni(BF4)2, and Cu(BF4)2. Increasing the salt content increases the glass transition temperature (Tg) and generally decreases gas diffusivity and permeability, which can be successfully described using a Tg-integrated free volume model with an expression similar to the Vogel-Tammann-Fulcher (VTF) equation. Surprisingly, low loadings of LiClO4 and Cu(BF4)2 (2 mass% or less) can increase gas permeability by 30%–70% without affecting the CO2/gas selectivity. This increase correlates with polyether-metal ion dynamics as measured by dielectric spectroscopy. Understanding how interaction-mediated dynamics affect gas transport will be instrumental to designing MOF-based mixed matrix materials for gas separations.

In order to overcome “trade-off” Robeson upper bound 2008 and simultaneously increase the CO2 permeability and selectivity of traditional poly (ethylene oxide) polymer membrane, three anion pillared hybrid ultramicroporous materials (SIFSIX-2-Cu-i, TIFSIX-2-Cu-i and GEFSIX-2-Cu-i) were incorporated into Pebax/PEGDME polymer to fabricate mixed matrix membranes (MMMs). DFT-D2 calculation revealed that the C···F distance (2.62 A) between CO2 molecule and pillared anion (GeF62-) in GEFSIX-2-Cu-i was lower than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. The synergistic effects of C···F van der Waals (vdW) interactions and O···H hydrogen bonding interactions in GEFSIX-2-Cu-i gave a higher CO2 binding energy (34.5 kJ/mol) than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. It was verified that GEFSIX-2-Cu-i with higher CO2 binding energy and specific surface area exhibited higher CO2 adsorption capacity of 5.02 mmol/g than SIFSIX-2-Cu-i and TIFSIX-2-Cu-i. These anion-pillared hybrid ultramicroporous materials with suitable porosity and surface chemistry, enabling multiple host–guest interactions, created unique Rubik’s tube-like “expressway” channels for CO2 molecule passage through the membrane. Results showed that the MMMs with 1 wt% GEFSIX-2-Cu-i nanoparticles exhibited optimal CO2 separation performance in terms of CO2 permeability (460 Barrers) and CO2/H2 (17, an increase of 12.2%), CO2/CH4 (18, an increase of 24.1%), and CO2/N2 (57, an increase of 9.6%) selectivities, as compared with the pure Pebax/PEGDME membrane. As GEFSIX-2-Cu-i loading increase from 1 to 10 wt%, the overall CO2 separation performance decrease due to the aggregation of these nanoparticles. Positron annihilation lifetime spectroscopy (PALS) experiments revealed that the fractional free volume of MMMs with 1 wt% GEFSIX-2-Cu-i nanofillers (FFV = 3.63%) was higher than those of MMMs incorporated with a higher loading (2.5–10 wt%) of GEFSIX-2-Cu-i.

Surface grafting modification was proposed to improve the surface polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane (PDMS) membrane. The initiator 3-aminopropyltriethoxysilane containing one amine group was integrated into PDMS, and polyvinyl pyrrolidone (PVP) with strong polarity was connected to the surface by reacting with amine groups. Surface grafting modification was proven on X-ray photoelectron spectroscopy. The sharp decrease (from ∼98° to ∼28°) in water contact angle of the PDMS membrane indicated the significant improvement in surface polarity after the modification. The surface roughness of the PDMS membrane increased with the modification, and the PDMS surface immersed for 40s was almost covered with PVP. The membrane immersed in PVP solution for 10s improved CO2/H2, CO2/CH4, and CO2/N2 selectivities. While CO2 permeance slightly decreased from ∼2500 GPU to ∼2440 GPU. For the separation of CO2/CH4 and CO2/N2 mixed gases, all CO2/CH4 and CO2/N2 selectivities were improved after the modification. For the separation of CO2/H2 mixed gas, CO2/H2 selectivity was improved when the immersion time was below 30 s.

Despite decades of research, metallic corrosion remains a long-standing challenge in many engineering applications. Specifically, designing a material that can resist corrosion both in abiotic as well as biotic environments remains elusive. Here a lightweight sulfur-selenium (S-Se) alloy is designed with high stiffness and ductility that can serve as an excellent corrosion-resistant coating with protection efficiency of ≈99.9% for steel in a wide range of diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7 orders of magnitude lower than bare metal in abiotic (simulated seawater and sodium sulfate solution) and biotic (sulfate-reducing bacterial medium) environments. The coating is strongly adhesive, mechanically robust, and demonstrates excellent damage/deformation recovery properties, which provide the added advantage of significantly reducing the probability of a defect being generated and sustained in the coating, thus improving its longevity. The high corrosion resistance of the alloy is attributed in diverse environments to its semicrystalline, nonporous, antimicrobial, and viscoelastic nature with superior mechanical performance, enabling it to successfully block a variety of diffusing species.

Mixed matrix materials (MMMs) comprising porous fillers in polymers can exhibit superior gas separation properties, yet their practical use has been limited by poor interfacial compatibility between the two components. Herein we report a bottom-up approach to synthesize the MMMs by dispersing a metal-organic polyhedron (MOP-3) in monomer solutions before rapid photopolymerization to form interpenetrating networks (IPNs), where the porous MOP-3 nanoparticles serve as molecular dopants. Specifically, MOP-3 with particle sizes of ≈5 nm was dispersed in and infiltrated by either a macromonomer of poly(ethylene glycol) diacrylate (PEGDA) or poly(1,3 dioxolane) acrylate (PDXLA). The introduction of the MOP-3 in the polyethers decreases their glass transition temperatures and even induces the crystallization of polyPDXLA at high loadings. Increasing the MOP loading increases CO2 permeability with a slight decrease in CO2/gas selectivity. For example, as the MOP content increases from 0 to 30 mass% in polyPDXLA, CO2 permeability increases from 190 Barrer to 580 Barrer, and CO2/N2 selectivity decreases from 70 to 62 at 35 °C. These IPNs-based MMMs exhibit separation properties above the Robeson's upper bounds for CO2/N2 and CO2/H2 separation. As the MOPs are soluble in solvents, this approach can be easily integrated into industrial membrane fabrication processes to produce MMMs-based composite membranes in large-scale.

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.

To improve the permeation performance of a ceramic hollow fiber-supported poly (amide-b-ethylene oxide) (Pebax)/polyethylene glycol dimethylether (PEGDME) composite membrane during CO2 separation from biohydrogen, a room temperature ionic liquid (RTIL), namely, [P66614][2-Op], with a high CO2 capacity, was adopted to blend in the selective layer. An RTIL-blended selective layer without defects was prepared on the surface of the ceramic hollow fibre. The physicochemical properties and CO2/H2 separation performance of the Pebax/PEGDME/RTIL composite membrane were then compared with those of the Pebax/PEGDME composite membrane. Intermolecular hydrogen bonds were produced after blending RTIL with the Pebax/PEGDME selective layer, and the surface roughness of the composite membrane increased. The CO2 permeation rate increased by ∼35% and reached up to ∼75 GPU at 50 °C, and the CO2/H2 selectivity was maintained at a high value of ∼15 at 30 °C. Blending RTIL with the selective layer inhibited the positive effect of CO2-induced plasticisation on H2 permeability. However, this process improved CO2/H2 selectivity in mixed gases relative to the ideal selectivity by enhancing competitive sorption among gas molecules.

To upgrade the mixed gas of fermentative hydrogen and methane for the preparation of biohythane as a gaseous fuel for vehicles, a composite membrane of poly(amide-b-ethylene oxide) (Pebax® MH 1657) and polyethylene glycol dimethylether (PEGDME) coated on a porous ceramic hollow fiber was originally proposed for CO2 separation. The Pebax/PEGDME selective layer with high CO2 selectivity was closely adhered and evenly distributed to the porous ceramic hollow fiber as a highly permeable support. The ideal CO2/H2 selectivity of the composite membrane increased from 12 ± 0.7 to 26 ± 1.7 when the temperature decreased from 50 °C to 10 °C. Competitive sorption between different gas molecules was found in the composite membrane. The fast diffusion of small molecular gas (H2) through the nanopores in the selective layer improved the diffusion of relatively large molecular gases (CO2 and CH4) in the gas mixture. On the contrary, the slow diffusion of large molecular gas (CH4) worsened the diffusion of relatively small molecular gases (CO2 and H2).

Surface grafting modification was proposed to improve the surface polarity of polyacrylonitrile hollow fiber-supported polydimethylsiloxane (PDMS) membrane. The initiator 3-aminopropyltriethoxysilane containing one amine group was integrated into PDMS, and polyvinyl pyrrolidone (PVP) with strong polarity was connected to the surface by reacting with amine groups. Surface grafting modification was proven on X-ray photoelectron spectroscopy. The sharp decrease (from ∼98° to ∼28°) in water contact angle of the PDMS membrane indicated the significant improvement in surface polarity after the modification. The surface roughness of the PDMS membrane increased with the modification, and the PDMS surface immersed for 40s was almost covered with PVP. The membrane immersed in PVP solution for 10s improved CO