Graphene oxide membranes with hierarchical structures used for molecule sieving.

• A hierarchical structured membrane was achieved for nanofiltration applications. • This membrane exhibits an organic solvent permeance of 2038 L m−2 bar−1 h−1. • This membrane shows above 90% rejections towards dye molecules. Lamellar graphene oxide (GO) membranes show exceptional molecular sieving properties for many applications. For nanofiltration, GO membranes made by different flake sizes present obviously distinct mass transport and molecule sieving performances. Typically, GO membranes stacked by nanosized sheets have high water fluxes but low rejection, while GO membranes stacked by microsized sheets have low water fluxes but high separation efficiency. In this study, we propose to assemble both of nanosized and microsized GO flakes into one GO membrane through three different stacking modes. By comparisons, we discovered that microsized GO sheets stacking on the multi-layered nanosized GO sheets was the most beneficial assembly structure for gaining high fluxes and rejection. The permeances of pure water and organic solvents by this membrane with a thickness of 10 nm achieve 254 and 2038 L m−2 bar−1 h−1, respectively. For separation properties, this membrane exhibits a promising water and isopropanol permeance of 126 and 151 L m−2 bar−1 h−1 respectively for filtering methylene blue (0.9 nm) solutions, while retaining a quite high rejection of above 90%. We believe this hierarchical assembly structure can be further extended into other two-dimensional laminates to pursue higher nanofiltration performances. [ABSTRACT FROM AUTHOR]