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 hydrogen^1,2. The introduction of defects allows selective gas permeation^3-5; efforts have been made to control the size of these defects for higher selectivity^6-9. Permeation of entities other than gases, such as ions^10,11, is of fundamental scientific interest because of its potential application in desalination, detection and purification^12-16. However, a precise experimental observation of halide permeation has so far remained unknown^11,15-18. 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 nanographene^19-23. 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 receptors^24,25, as filtration membranes²⁶ and further to create multilayer artificial chloride channels.