Reactivity-Controlled Preparation of Ultralarge Graphene Oxide by Chemical Expansion of Graphite

The production of ultralarge graphene oxide (ULGO) is hindered by sluggish diffusion process of the oxidizing agents into graphite layers, as well as sheet fracture resulting from inhomogeneous oxidation. Previous methods rely on an excess amount of oxidants or multiple oxidation to overcome large diffusion resistance, but at the cost of ULGO yield and environmental risk. Here, we discover the chemical expansion of graphite (CEG) with high solvent-accessible surface areas can effectively boost mass diffusion and facilitate exhaustive oxidation at low oxidant dosage (2 wt equiv). The oxidizing reaction is therefore controlled by the chemical reactivity of graphite with oxidant rather than the diffusion of oxidant, which results in a similar to 100% yield of ULGO nanosheets with an area-average size of 128 pm. The worm-like structure of CEG and its oxide provides a chance to recover excess sulfuric acid using a 100-mesh filter, where subsequent exfoliation to ULGO nanosheets is achieved by mild agitation or shaking in several minutes. The ULGO paper prepared by blade casting exhibits superior mechanical properties (Young's modulus of 11.9 GPa and tensile strength of 110.8 MPa) and electrical conductivity (similar to 613 S/cm after HI reduction).