Bottom-up synthesis of graphene films hosting atom-thick molecular-sieving apertures

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 37; pp. 1 - 10
• Main Authors: Villalobos, Luis Francisco, Goethem, Cédric Van, Hsu, Kuang-Jung, Li, Shaoxian, Moradi, Mina, (赵康宁), Kangning Zhao, Dakhchoune, Mostapha, Huang, Shiqi, (沈悦卿), Yueqing Shen, Oveisib, Emad, Boureaub, Victor, Agrawal, Kumar Varoon
• Format: Journal Article
• Language: English
• Published: Washington National Academy of Sciences 14.09.2021
• Series: Membrane Separations Science Special Feature
• Subjects: Apertures; Chemical synthesis; Chemical vapor deposition; Crystal defects; Density; Etching; Gas transport; Graphene; Lattice vacancies; Membranes; Nanocrystals; Physical Sciences; Polymers; Pores; Prepolymers; Pyrolysis; Selectivity; Thick films
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.2022201118

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. Herein, we achieve 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. The density of pores is comparable to that obtained by the state-of-the-art postsynthetic 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 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 postsynthetic lattice etching. Overall, the method reported here improves the scale-up potential of graphene membranes by cutting down the processing steps.