Graphite oxide has become an important precursor for graphene oxide, reduced graphene oxide, and a wide range of other graphene-based materials or composites. In numerous Hummers’ methods for the preparation of graphite oxide, water is added to promote the oxidization reaction but causes problems of tedious purification and liquid waste, which raises concerns of environment processing cost in the large-scale production of graphite oxide. Herein, we propose a highly efficient oxidization of chemical expandable graphite (CEG) for one-step preparation of graphite oxide while water is not added during the oxidization. This method features a direct separation of the solid reactant from the liquid oxidant, allowing the reuse of waste acid and quick centrifugal washing of products close to neutral pH. This strategy also benefits the highly efficient utilization of the oxidant potassium permanganate (KMnO4), indicated by the high monolayer/bilayer yield (∼90%) of graphene oxide for a KMnO4/CEG mass ratio as low as 2.5. Without the hydration reaction, which generally leads to etching of graphitic sheets, the graphene oxide platelets made from this strategy readily maintain a large size of 30∼110 μm for the CEG of 80 mesh grids (∼175 μm), making the current method suitable for the preparation of thermally and electrically conductive graphene films. This work provides a more efficient and environmentally friendly preparation technique for the industrial production of graphite oxide and relevant materials.

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Among many phase-changing materials, graphite is probably the most studied and interesting: the rhombohedral (3R) and hexagonal (2H) phases exhibit dramatically different electronic properties. However, up to now the only way to promote 3R to 2H phase transition is through exposure to elevated temperatures (above 1000 °C); thus, it is not feasible for modern technology. In this work, we demonstrate that 3R to 2H phase transition can be promoted by changing the charged state of 3D graphite, which promotes the repulsion between the layers and significantly reduces the energy barrier between the 3R and 2H phases. In particular, we show that charge transfer from lithium nitride (α-Li3N) to graphite can lower the transition temperature down to 350 °C. The proposed interlayer slipping model potentially offers the control over topological states at the interfaces between different phases, making this system even more attractive for future electronic applications.