Bilayer nanographene reveals halide permeation through a benzene hole

Graphene is a single-layered sp2-hybridized carbon allotrope, which is impermeable to all atomic entities other than hydrogen1,2. The introduction of defects allows selective gas permeation3–5; efforts have been made to control the size of these defects for higher selectivity6–9. Permeation of entities other than gases, such as ions10,11, is of fundamental scientific interest because of its potential application in desalination, detection and purification12–16. However, a precise experimental observation of halide permeation has so far remained unknown11,15–18. Here we show halide permeation through a single benzene-sized defect in a molecular nanographene. Using supramolecular principles of self-aggregation, we created a stable bilayer of the nanographene19–23. As the cavity in the bilayer nanographene could be accessed only by two angstrom-sized windows, any halide that gets trapped inside the cavity has to permeate through the single benzene hole. Our experiments reveal the permeability of fluoride, chloride and bromide through a single benzene hole, whereas iodide is impermeable. Evidence for high permeation of chloride across single-layer nanographene and selective halide binding in a bilayer nanographene provides promise for the use of single benzene defects in graphene for artificial halide receptors24,25, as filtration membranes26 and further to create multilayer artificial chloride channels.