Monolithic Crystalline Swelling of Graphite Oxide: A Bridge to Ultralarge Graphene Oxide with High Scalability

The large-scale preparation of ultralarge graphene oxide (ULGO) is urgently needed for developing advanced devices and high-performance nanocomposites. However, it is extremely difficult to produce ULGO in an industrially viable, high-efficiency manner because of the inevitable sheet fragmentation and significant gelation behavior occurred in existing methods. We propose a stationary oxidation-monolithic crystalline swelling strategy that can completely convert graphite to ULGO. This new stationary oxidation method minimizes the sheet fracture and prevents the exfoliation of oxidized layers without sacrificing the oxidation rate, resulting in oxidized flakes with high crystalline and lateral sizes the same as raw graphite. The oxidized graphite flakes undergo a monolithic crystalline swelling during the purification, leading to the formation of a three-dimensional ordered structure without peeling. This enables graphite oxide to be purified by spontaneous sedimentation within 1 h as gelation is avoided and to be exfoliated exhaustively into single-layered ULGO sheets through mild mechanical shaking, with an average size of 108 μm and the largest size of 256 μm. These ULGO sheets can form liquid crystals at a record dispersion concentration (as low as 0.2 mg/mL). The ULGO papers show outstanding mechanical properties and electrical conductivities (after HI reduction) that outperform the reported results.