(155a) Bottom-up Synthesis of Films Hosting Atom-Thick Molecular-Sieving Apertures

Incorporation of a high density of molecular-sieving nanopores in the graphene lattice by the bottom-up synthesis is highly attractive for high-performance membranes [1-4]. In this presentation, I will discuss our recent success in achieving this by a controlled synthesis of nanocrystalline graphene where incomplete growth of a few nanometer- sized, misoriented grains generates molecular-sized pores in the lattice [5]. The density of pores is comparable to that obtained by the state-of-the-art post-synthetic etching (10¹² cm^-2) and is up to two orders of magnitude higher than that of molecular-sieving intrinsic vacancy defects in single- layer graphene (SLG) prepared by chemical vapor deposition. The porous nanocrystalline graphene (PNG) films are synthesized by precipitation of C dissolved in the Ni matrix where the C concentration is regulated by controlled pyrolysis of precursors (polymers and/or sugar). The PNG film is made of few-layered graphene except near the grain edge where the grains taper down to a single layer and eventually terminate into vacancy defects at a node where three or more grains meet. This unique nanostructure is highly attractive for the membranes because the layered domains improve the mechanical robustness of the film while the atom-thick molecular-sized apertures allow the realization of large gas and proton transport. The combination of gas permeance and gas pair selectivity is comparable to that from the nanoporous SLG membranes prepared by state-of-the-art post-synthetic lattice etching. Overall, the method reported here improves the scale-up potential of graphene membranes by cutting down the processing steps.

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