Large-Area Atomically Thin Graphene Membranes for Sub-Nanometer Scale Separations

Atomically thin graphene with a high-density of sub-nanometer pores represents the ideal membrane for ionic and molecular separations, offering ultrafast solvent transport and high solute rejection via molecular sieving. However, a single large nanopore can severely compromise membrane performance via non-selective leakage. Forming precise sub-nanometer pores (0.28-0.66 nm) in the graphene lattice over large areas with a high density via scalable processes remains extremely challenging due to differential etching between pre-existing defects/grain boundaries and pristine regions. Here, we show for the first time that size-selective interfacial polymerization after nanopore formation in graphene not only seals larger defects (>0.5 nm) and macroscopic tears effectively, but also successfully preserves sub-nanometer pores (>0.28 nm), thereby enabling fully functional large-area high-performance graphene membranes. Further, low-temperature chemical vapor deposition (CVD) growth followed by mild UV/ozone oxidation allows for facile and scalable introduction of a high density (4-5.5 × 10¹² cm^-2) of useful sub-nanometer pores in the graphene lattice. We demonstrate fully functional centimeter-scale atomically thin membranes with water (~0.28 nm) permeance ~23× higher than commercially available membranes, and excellent rejection to salt ions (~0.66 nm, >97% rejection) and small organic molecules (~0.7-1.5 nm, ~100% rejection) under forward osmosis.