The First Precise Determination of Graphene Functionalisation by in situ Raman Spectroscopy
Abstract
We report, for the first time, a comprehensive study involving in situ Raman spectroscopy supported by quantum mechanical calculations to exactly monitor the covalent binding to graphene with unprecedented precision. As a model reaction we have chosen the hydrogenation of reduced graphite (KC8) with H2O and compared it with the corresponding exposure to H2 and O2. The early stages of graphene hydrogenation are accompanied by the evolution of a series of so far undiscovered D-bands (D1-D5). Using quantum mechanical calculations, we were able to unambiguously assign these bands to distinct lattice vibrations in the neighborhood of the covalently bound addend. Interestingly, the exposure of KC8 to H2 and O2 didn't cause covalent binding, but intercalation of molecular H2 or partial oxidation, respectively. A combination of H2O and O2 treatment led to the formation of additional hydroxyl (-OH) functionalities. The latter reaction represents a very suitable model for the decomposition of graphenides under ambient conditions (hydrogenation and hydroxylation). We have applied this Raman analysis to simulate and satisfactorily characterize a series of additional covalently functionalised graphene derivatives prepared as bulk materials with different composition (e.g. degree of functionalisation and the nature of covalent addend) demonstrating the generality of the concept and the fundamental value for graphene chemistry.