Studying functional groups in graphene oxide with soft X-ray spectroscopy and density functional theory

Graphene oxide (GO) is a class of chemically derived graphene materials widely used in diverse fields, ranging from electronics to environmental applications. Yet, its detailed structure remains an open question due to the effect of the different synthesis methods on the oxidation level. In this work, we compare our synchrotron radiation based soft X-ray spectroscopy and density functional theory (DFT) calculations to elucidate the relevance of functional groups on the structure and electronic properties of GO, synthesized by modified Hummers’ method. We demonstrate that the position of the hydroxyl groups strongly modulates the structure and local bonding environment. Our results indicate that it is energetically preferable to attach functional groups to only one side of the GO layer, which leads to a largely intact carbon network with 60% C-C regions. We observe that the presence of hydroxyl groups induces charge distortions while epoxide groups weaken the adjacent carbon bonds. Furthermore, our two-dimensional electron density map illustrates the detailed electron localization in various carbon sites within GO. This provides information on the interaction of functional groups, which is essential in order to tailor GO with specific properties for applications in energy storage, sensing, and next-generation electronic devices.