Fig. 3

Centrifugal methods for purification of exfoliated graphene. a Schematic showing centrifugation based size selection procedure. (b-d) TEM images of exfoliated graphene sheets, (b) without any size selection after direct centrifugation at 500 rpm (c) with size selection centrifuged according to scheme (a) with a rate of 3000 rpm and (d) 500 rpm. a-d reproduced from ref. 37 with permission, © Elsevier). e Thickness sorting of graphene using density gradient ultracentrifugation (DGU). f-g Mean flake thickness histogram measured by AFM of sorted graphene taken from the locations marked in panel. e-g reproduced from ref. 38 with permission, © American Chemical Society)