  Graphene oxide (GO) membranes continue to attract intense interest due to
their unique molecular sieving properties combined with fast permeation rates.
However, the membranes' use has been limited mostly to aqueous solutions
because GO membranes appear to be impermeable to organic solvents, a phenomenon
not fully understood yet. Here, we report efficient and fast filtration of
organic solutions through GO laminates containing smooth two-dimensional (2D)
capillaries made from flakes with large sizes of ~ 10-20 micron. Without
sacrificing their sieving characteristics, such membranes can be made
exceptionally thin, down to ~ 10 nm, which translates into fast permeation of
not only water but also organic solvents. We attribute the organic solvent
permeation and sieving properties of ultrathin GO laminates to the presence of
randomly distributed pinholes that are interconnected by short graphene
channels with a width of 1 nm. With increasing the membrane thickness, the
organic solvent permeation rates decay exponentially but water continues to
permeate fast, in agreement with previous reports. The application potential of
our ultrathin laminates for organic-solvent nanofiltration is demonstrated by
showing >99.9% rejection of various organic dyes with small molecular weights
dissolved in methanol. Our work significantly expands possibilities for the use
of GO membranes in purification, filtration and related technologies.
