Adsorption-Assisted Interfacial Polymerization toward Ultrathin Active Layers for Ultrafast Organic Permeation

Thin-film composite (TFC) membranes show exceptional permeation properties of key importance for many separations. However, their design and development need ultrathin and defect-free nanofilms as the active layer to alleviate the bottleneck of permeation–rejection trade-off. Here, a 25 nm thick film is fabricated on a porous support by introducing polydopamine (PDA) as an adsorption layer, imparting a unique adsorption-assisted interfacial polymerization (IP) strategy. The PDA layer efficiently captures and enriches amine monomers even from ultradilute solution toward uniform stacking on the support, thus generating ultrathin and defect-free films after polymerization. This is superior to the defective one from conventional IP. Such an active layer features ultrafast permeation for organics, favorable solute rejection, and excellent operation stability. Particularly, the acetone permeance of this new TFC membrane reaches 96.3 L m^–2 h^–1 bar^–1, which exceeds that from conventional IP by more than 10 times, ranking among one of the highest performances reported to date. More significantly, the pernicious permeation–rejection trade-off of the TFC membrane is thus alleviated. Besides, this strategy is facile, versatile, and easy to scale-up, giving controllable physical and chemical structures to the active layer. This study may pave a way to well-design highly efficient film materials for various transport and separation applications

Incorporating Zwitterionic Graphene Oxides into Sodium Alginate Membrane for Efficient Water/Alcohol Separation

For the selective water-permeation across dense membrane, constructing continuous pathways with high-density ionic groups are of critical significance for the preferential sorption and diffusion of water molecules. In this study, zwitterionic graphene oxides (PSBMA@GO) nanosheets were prepared and incorporated into sodium alginate (SA) membrane for efficient water permeation and water/alcohol separation. The two-dimensional GO provides continuous pathway, while the high-density zwitterionic groups on GO confer electrostatic interaction sites with water molecules, leading to high water affinity and ethanol repellency. The simultaneous optimization of the physical and chemical structures of water transport pathway on zwitterionic GO surface endows the membrane with high-efficiency water permeation. Using dehydration of water/alcohol mixture as the model system, the nanohybrid membranes incorporating PSBMA@GO exhibit much higher separation performance than the SA membrane and the nanohybrid membrane utilizing unmodified GO as filler (with the optimal permeation flux of 2140 g m^–2 h^–1, and separation factor of 1370). The study indicates the great application potential of zwitterionic graphene materials in dense water-permeation membranes and provides a facile approach to constructing efficient water transport pathway in membrane

High-Performance Composite Membrane with Enriched CO₂‑philic Groups and Improved Adhesion at the Interface

A novel strategy to design a high-performance composite membrane for CO₂ capture via coating a thin layer of water-swellable polymers (WSPs) onto a porous support with enriched CO₂-philic groups is demonstrated in this study. First, by employing a versatile platform technique combining non-solvent-induced phase separation and surface segregation, porous support membranes with abundant CO₂-philic ethylene oxide (EO) groups at the surface are successfully prepared. Second, a thin selective layer composed of Pebax MH 1657 is deposited onto the support membranes via dip coating. Because of the water-swellable characteristic of Pebax and the enriched EO groups at the interface, the composite membranes exhibit high CO₂ permeance above 1000 GPU with CO₂/N₂ selectivity above 40 at a humidified state (25 °C and 3 bar). By tuning the content of the PEO segment at the interface, the composite membranes can show either high CO₂ permeance up to 2420 GPU with moderate selectivity of 46.0 or high selectivity up to 109.6 with fairly good CO₂ permeance of 1275 GPU. Moreover, enrichment of the PEO segment at the interface significantly improves interfacial adhesion, as revealed by the T-peel test and positron annihilation spectroscopy measurement. In this way, the feasibility of designing WSP-based composite membranes by enriching CO₂-philic groups at the interface is validated. We hope our findings may pave a generic way to fabricate high-performance composite membranes for CO₂ capture using cost-effective materials and facile methods

Enhanced Interfacial Interaction and CO₂ Separation Performance of Mixed Matrix Membrane by Incorporating Polyethylenimine-Decorated Metal–Organic Frameworks

Polyethylenimine (PEI) was immobilized by MIL-101­(Cr) (∼550 nm) via a facile vacuum-assisted method, and the obtained PEI@MIL-101­(Cr) was then incorporated into sulfonated poly­(ether ether ketone) (SPEEK) to fabricate mixed matrix membranes (MMMs). High loading and uniform dispersion of PEI in MIL-101­(Cr) were achieved as demonstrated by ICP, FT-IR, XPS, and EDS-mapping. The PEI both in the pore channels and on the surface of MIL-101­(Cr) improved the filler–polymer interface compatibility due to the electrostatic interaction and hydrogen bond between sulfonic acid group and PEI, and simultaneously rendered abundant amine carriers to facilitate the transport of CO₂ through reversible reaction. MMMs were evaluated in terms of gas separation performance, thermal stability, and mechanical property. The as-prepared SPEEK/PEI@MIL-101­(Cr) MMMs showed increased gas permeability and selectivity, and the highest ideal selectivities for CO₂/CH₄ and CO₂/N₂ were 71.8 and 80.0 (at a CO₂ permeability of 2490 Barrer), respectively. Compared with the membranes doped with unfilled MIL-101­(Cr), the ideal selectivities of CO₂/CH₄ and CO₂/N₂ for PEI@MIL-101­(Cr)-doped membranes were increased by 128.1 and 102.4 %, respectively, at 40 wt % filler loading, surpassing the 2008 Robeson upper bound line. Moreover, the mechanical property and thermal stability of SPEEK/PEI@MIL-101­(Cr) were enhanced

Hydrogenated Oxygen-Deficient Blue Anatase as Anode for High-Performance Lithium Batteries

Blue oxygen-deficient nanoparticles of anatase TiO₂ (H-TiO₂) are synthesized using a modified hydrogenation process. Scanning electron microscope and transmission electron microscope images clearly demonstrate the evident change of the TiO₂ morphology, from 60 nm rectangular nanosheets to much smaller round or oval nanoparticles of ∼17 nm, after this hydrogenation treatment. Importantly, electron paramagnetic resonance and positronium annihilation lifetime spectroscopy confirm that plentiful oxygen vacancies accompanied by Ti³⁺ are created in the hydrogenated samples with a controllable concentration by altering hydrogenation temperature. Experiments and theory calculations demonstrate that the well-balanced Li⁺/e^– transportation from a synergetic effect between Ti³⁺/oxygen vacancy and reduced size promises the optimal H-TiO₂ sample a high specific capacity, as well as greatly enhanced cycling stability and rate performance in comparison with the other TiO₂

Ultrathin and Vacancy-Rich CoAl-Layered Double Hydroxide/Graphite Oxide Catalysts: Promotional Effect of Cobalt Vacancies and Oxygen Vacancies in Alcohol Oxidation

Co-containing layered double hydroxides (LDHs) are potential non-noble-metal catalysts for the aerobic oxidation of alcohols. However, the intrinsic activity of bulk LDHs is relatively low. In this work, we fabricated ultrathin and vacancy-rich nanosheets by exfoliating bulk CoAl-LDHs, which were then assembled with graphite oxide (GO) to afford a hybrid CoAl-ELDH/GO catalyst. TEM, AFM, and positron annihilation spectrometry indicate that the thickness of the exfoliated LDH platelets is about 3 nm, with a large number of vacancies in the host layers. Fourier transformed XAFS functions show that the Co–O and Co····Co coordination numbers (5.5 and 2.8, respectively) in the hybrid CoAl-ELDH/GO material are significantly lower than the corresponding values in bulk CoAl-LDHs (6.0 and 3.8, respectively). Furthermore, in addition to the oxygen vacancies (V_O) and cobalt vacancies (V_Co), CoAl-ELDH/GO also contains negatively charged V_Co–Co–OH^δ− sites and exposed lattice oxygen sites. CoAl-ELDH/GO shows excellent performance as a catalyst for the aerobic oxidation of benzyl alcohol, with a TOF of 1.14 h^–1; this is nearly five times that of the unexfoliated bulk CoAl-LDHs (0.23 h^–1) precursor. O₂-TPD and DRIFT spectroscopy declare that the oxygen storage capacity and mobility are facilitated by the oxygen vacancies and surface lattice oxygen sites. Meanwhile, DFT calculations of adsorption energy show that benzyl alcohol is strongly adsorbed on the oxygen vacancies and negatively charged V_Co–Co–OH^δ− sites. A kinetic isotope effect study further illustrates that the vacancy-rich CoAl-ELDH/GO catalyst accelerates the cleavage of the O–H bond in benzyl alcohol. Finally, we show that the hybrid CoAl-ELDH/GO material exhibits excellent catalytic activity and selectivity in the oxidation of a range of other benzylic and unsaturated alcohols

Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Molybdenum disulfide (MoS₂) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS₂-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS₂ nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS₂ nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS₂ nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS₂. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS₂ always outperforms the corresponding 2H phase MoS₂ samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS₂ samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS₂ or other layered materials with enhanced HER performance