Thermal annealing of graphite oxide under high pressure: An experimental and computational study
AF da Silva and AM Christmann and TMH Costa and AR Muniz and NM Balzaretti, CARBON, 139, 1035-1047 (2018).
In this work, we investigate the effect of high pressures on thermal reduction of graphite oxide (GO) using a combination of different characterization techniques and atomistic computational simulations. GO samples were submitted simultaneously to different pressures (up to 7.7 GPa) and temperatures (up to 1500 degrees C) using a high-pressure chamber. Reactive molecular dynamics simulations were carried out to provide some insight on the observed structural transformations. The samples annealed at ambient pressure consisted of large sheets of reduced GO, containing defects. In contrast, the morphology of the samples processed at higher pressures and temperatures was similar to those of graphite nanocrystals (significantly smaller than the pristine GO sheets). The simulations results corroborated these observations, and helped to explain the reasons for the differences in the morphology of the material when submitted to different conditions. They showed that higher pressures induced a significant reduction on the interplanar volume, inhibiting the formation of gas molecules and enhancing the diffusion and redistribution of functional groups on the GO surfaces. A sequence of reaction and diffusion pathways led the functional groups to concentrate in some regions, causing the local tearing of the structure and formation of crystalline nanodomains as observed in the experiments. (C) 2018 Elsevier Ltd. All rights reserved.
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