The single-layer graphene film, when incorporated with molecular-sized pores, is predicted to be the ultimate membrane. However, the major bottlenecks have been the crack-free transfer of large-area graphene on a porous support, and the incorporation of molecular-sized nanopores. Herein, we report a nanoporous-carbon-assisted transfer technique, yielding a relatively large area (1 mm2), crack-free, suspended graphene film. Gas-sieving (H2/CH4 selectivity up to 25) is observed from the intrinsic defects generated during the chemical-vapor deposition of graphene. Despite the ultralow porosity of 0.025%, an attractive H2 permeance (up to 4.1 × 10−7 mol m−2 s−1 Pa−1) is observed. Finally, we report ozone functionalization-based etching and pore-modification chemistry to etch hydrogen-selective pores, and to shrink the pore-size, improving H2 permeance (up to 300%) and H2/CH4 selectivity (up to 150%). Overall, the scalable transfer, etching, and functionalization methods developed herein are expected to bring nanoporous graphene membranes a step closer to reality.

High-density nanopores with a size resolution of 1 Å were etched on graphene by decoupled defect nucleation and pore expansion.

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Poly(triazine imide) (PTI), a crystalline g-C3N4, hosting two-dimensional nanoporous structure with an electron density gap of 0.34 nm, is highly promising for high-temperature hydrogen sieving because of its high chemical and thermal robustness. Currently, layered PTI is synthesized in potentially unsafe vacuum ampules in milligram quantities. Here, we demonstrate a scalable and safe ambient pressure synthesis route leading to several grams of layered PTI platelets in a single batch with 70% yield with respect to the precursor. Solvent exfoliation under anhydrous conditions led to single-layer PTI nanosheets evidenced by the observation of triangular g-C3N4 nanopores. Gas permeation studies confirm that PTI nanopores can sieve He and H2 from larger molecules. Last, high-temperature H2 sieving from PTI nanosheet–based membranes, prepared by the scalable filter coating technique, is demonstrated with H2 permeance reaching 1500 gas permeation units, with H2/CO2, H2/N2, and H2/CH4 selectivities reaching 10, 50, and 60, respectively, at 250°C.

Etching single-layer graphene to incorporate a high pore density with sub-angstrom precision in molecular differentiation is critical to realize the promising high-flux separation of similar-sized gas molecules, e.g., CO2 from N2. However, rapid etching kinetics needed to achieve the high pore density is challenging to control for such precision. Here, we report a millisecond carbon gasification chemistry incorporating high density (>1012 cm−2) of functional oxygen clusters that then evolve in CO2-sieving vacancy defects under controlled and predictable gasification conditions. A statistical distribution of nanopore lattice isomers is observed, in good agreement with the theoretical solution to the isomer cataloging problem. The gasification technique is scalable, and a centimeter-scale membrane is demonstrated. Last, molecular cutoff could be adjusted by 0.1 Å by in situ expansion of the vacancy defects in an O2 atmosphere. Large CO2 and O2 permeances (>10,000 and 1000 GPU, respectively) are demonstrated accompanying attractive CO2/N2 and O2/N2 selectivities.

Metal-organic framework (MOF) films have recently emerged as highly permselective membranes yielding orders of magnitude higher gas permeance than that from the conventional membranes. However, synthesis of highly intergrown, ultrathin MOF films on porous supports without complex support-modification has proven to be a challenge. Moreover, there is an urgent need of a generic crystallization route capable of synthesizing a wide range of MOF structures in an intergrown, thin-film morphology. Herein, a novel electrophoretic nuclei assembly for crystallization of highly intergrown thin-films (ENACT) approach, that allows synthesis of ultrathin, defect-free ZIF-8 on a wide range of unmodified supports (porous polyacrylonitrile, anodized aluminum oxide, metal foil, porous carbon and graphene), is reported. As a result, a remarkably high H 2 permeance of 8.3 × 10 −6 mol m −2 s −1 Pa −1 and ideal gas selectivities of 7.3, 15.5, 16.2, and 2655 for H 2 /CO 2 , H 2 /N 2 , H 2 /CH 4 , and H 2 /C 3 H 8 , respectively, are achieved from an ultrathin (500 nm thick) ZIF-8 membrane. A high C 3 H 6 permeance of 9.9 × 10 −8 mol m −2 s −1 Pa −1 and an attractive C 3 H 6 /C 3 H 8 selectivity of 31.6 are obtained. The ENACT approach is straightforward, reproducible and can be extended to a wide range of nanoporous crystals, and its application in the fabrication of intergrown ZIF-7 films is demonstrated.

Enhancing the kinetics of liquid–vapor transition from nanoscale confinements is an attractive strategy for developing evaporation and separation applications. The ultimate limit of confinement for evaporation is an atom thick interface hosting angstrom-scale nanopores. Herein, using a combined experimental/computational approach, we report highly enhanced water evaporation rates when angstrom sized oxygen-functionalized graphene nanopores are placed at the liquid–vapor interface. The evaporation flux increases for the smaller nanopores with an enhancement up to 35-fold with respect to the bare liquid–vapor interface. Molecular dynamics simulations reveal that oxygen-functionalized nanopores render rapid rotational and translational dynamics to the water molecules due to a reduced and short-lived water–water hydrogen bonding. The potential of mean force (PMF) reveals that the free energy barrier for water evaporation decreases in the presence of nanopores at the atomically thin interface, which further explains the enhancement in evaporation flux. These findings can enable the development of energy-efficient technologies relying on water evaporation.

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