Assessing the evolution of oxygenated functional groups on the graphene oxide surface upon mild thermal annealing in water

Graphene oxide (GO) is known to be a 2D metastable nanomaterial that can be reconstructed under thermal annealing into distinct oxidized and graphitic phases. Up to now, such phase transformation, mainly related to epoxide and hydroxyl functional groups, has been usually achieved by thermally treating layers of GO in the solid state. Here, we present the mild annealing of GO dispersed in an aqueous medium, performed at two temperatures, 50 degrees C and 80 degrees C, for different intervals of time. We show experimental evidences of the epoxide instability in the presence of water by means of XPS, cyclic voltammetry and Raman spectroscopy, demonstrating the reorganization of epoxide and hydroxyl moieties initiated by water molecules. In fact, at 50 degrees C an increase in oxygen content is detected in all annealed samples compared to untreated GO, with a transformation of epoxide groups into vicinal diols. On the other hand, at 80 degrees C the oxygen content decreases towards the initial value since the vicinal diols, previously formed, transform into single hydroxyls and C00000000000000000000000000000000111111110000000011111111000000000000000000000000C bonds. Moreover, the higher temperature annealing likely favours oxygenated functional groups rearrangements and clustering, in accordance with the literature, leading to a higher electron affinity and conductivity of the graphenic network. The fate of epoxide and hydroxyl moieties on the graphene oxide is analyzed under mild thermal conditions (50-80 degrees C range) in water.

Automated summary

This study demonstrates the influence of water on the stability of epoxide functional groups in graphene oxide (GO) under mild annealing. The presence of water triggers the reorganization of epoxide and hydroxyl moieties, leading to the transformation of epoxide groups into vicinal diols. Higher temperature annealing promotes rearrangements and clustering of oxygenated functional groups, resulting in enhanced electron affinity and conductivity of the graphenic network.