The First Precise Determination of Graphene Functionalisation by in situ Raman Spectroscopy

TL;DR

This study uses in situ Raman spectroscopy combined with quantum calculations to precisely monitor covalent functionalization of graphene, revealing new vibrational bands and differentiating between covalent binding and other interactions.

Contribution

First comprehensive in situ Raman analysis of graphene covalent functionalization supported by quantum calculations, providing detailed vibrational assignments and insights into reaction mechanisms.

Findings

Discovery of new D-bands associated with covalent binding

Differentiation between covalent binding and intercalation or oxidation

Application of Raman analysis to various functionalized graphene derivatives

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 ($KC_8$) with $H_2O$ and compared it with the corresponding exposure to $H_2$ and $O_2$. The early stages of graphene hydrogenation are accompanied by the evolution of a series of so far undiscovered D-bands ($D_1$-$D_5$). 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 $KC_8$ to $H_2$ and $O_2$ didn't cause covalent binding, but intercalation of molecular $H_2$ or partial oxidation, respectively. A combination of $H_2O$ and $O_2$ 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.