Advanced membranes that combine mechanical robustness with fast permeation are crucial to many applications such as water purification, ions selectivity, and gas separation. Graphene sheets offer a promising opportunity to fabricate thin, high-flux, and pressure-endurable membranes because of their unique 2D morphology, oxidizable surface, and electrical conductivity. We herein report a highly effective yet simple approach to the fabrication of graphene membranes featuring controllable oxidation degrees and thus tunable structures and properties. The graphene sheets comprise a single or a few layers with a lateral dimension of 50-100 nm; their C/O ratios can be manipulated from 4.1 for graphene with a low degree of oxidation (low-oxidation graphene) to 2.5 for medium-oxidation graphene to 1.3 for high-oxidation graphene, by controlling the proportion of phosphoric acid during the 60 min fabrication. Fabricated by simple vacuum filtration, the membranes exhibited various water flux from 200.0 to 20.0 L/m(2)·h·bar at 3 bar of pressure and mechanical robustness (Young's modulus can be up to 20 GPa and tensile strength to 100 MPa). When these membranes were used as electrodes for supercapacitors, specific capacitances of 58.8 F/g and 23.5 F/cm(3) were recorded for the low-oxidation graphene membrane at 1 A/g by a two-electrode configuration; the capacity values retained ∼95% after 800 cycles; the high capacitance would be caused by moderate wettability and high electrical conductivity.
Keywords: composites; graphene membranes; graphene oxide; water permeation and specific capacitance.