Colossal Pressure-Induced Lattice Expansion of Graphite Oxide in the Presence of Water

摘要

Expansion of structure upon compression is a rare phenomenon that has been observed in so-called auxetic materials, and is due to incorporation of liquid media into nanopores. Herein, we present a new class of auxetic materials with unusual compressibility anomaly. The unit-cell volume of graphite oxide (GO) pressurized in the presence of water continuously increases, reaching a maximum at 1.3-1.5 GPa. Expansion of the lattice by 28-30 % significantly exceeds all previously known examples and is due to gradual pressure-induced water insertion into the interlayer space of graphite oxide structure. Solidification of water is observed at 1.3-1.5 GPa and correlates with a sharp downturn in the pressure dependence of the unit-cell volume of the graphite oxide. The effect is reversible, resulting in a unique "breathing" of the structure upon pressure variation.