Nature Nanotechnology | 2021
Gas separation with porous grapheme
Abstract
Membrane-based gas separation has been attracting wide attention due to its high energy efficiency. Separation membranes based on new materials and design approaches progressed quickly during the past decades. Early in 2009, it was computationally predicated that an atomically thin porous graphene sheet can be highly permeable and selective for gas separation1. Writing in Nature Nanotechnology in 2012, Koenig et al. from the University of Colorado, Boulder, reported the fabrication of micrometre-sized, atomically thin, porous graphene membranes with ultraviolet-induced oxidative etching2. By measuring the transport of a range of gases with a pressurized blister test (pictured) and mechanical resonance, they experimentally demonstrated the selective molecular sieving properties of the fabricated porous graphene membranes, though the selectivity did not meet expectations. Koenig et al. fabricated two porous graphene membranes and named them Bi-3.4 Å and Bi-4.9 Å as these two bilayer graphene membranes can sieve molecules above and below the kinetic diameters of Ar (3.4 Å) and SF6 (4.9 Å), respectively. This was one early attempt to control the kinetic diameter cutoff of gas-separation graphene membranes by slow etching. Koenig et al. also suggested that only a low density of size-selective pores participated in gas transport across the graphene membrane. This was consistent with the later finding by Yuan et al. from MIT published earlier this year3. They found the permeance was dominated by a small fraction of large nanopores due to their low pore-crossing energy barriers. There are now more and more gas separation membranes based on various porous materials like zeolites, MOFs, COFs, graphene/graphene oxide and their composites with polymers. But until now only a handful of traditional polymeric membranes have been commercialized. With better control over pore size and size distribution, membranes with new materials can be more promising for gas separation in the future. ❐