Functionalization of graphene sheets by the diazonium chemistry during electrochemical exfoliation of graphite

Abstract

Graphene sheets were spontaneously functionalized with anthraquinone molecules in a one-pot process, during the oxidative electrochemical exfoliation of a graphite electrode in a 0.1 M H2SO4 solution containing anthraquinone diazonium ions. This counterintuitive process involves the electrochemical oxidation of graphite and reduction of diazonium ions and functionalization occurs by spontaneous reaction of freshly generated graphene sheets with diazonium ions. This reaction is faster than the common approach based on the reaction of diazonium ions with pre-exfoliated graphene sheets. Indeed, the grafting yield of our one-pot process is higher than that of a two-step procedure based on functionalization of already produced graphene sheets, presumably due to the higher reactivity of freshly generated graphene sheets during electrochemical exfoliation. As a result of functionalization, the water dispersibility of graphene sheets was improved and an increase of the BET specific surface area was observed. The presence of anthraquinone molecules was confirmed by Fourier transform infrared spectroscopy, electron microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. Thermogravimetric analysis, Raman spectroscopy and electronic conductivity measurements are consistent with the covalent bonding of anthraquinone on the graphene sheets. Thermogravimetric analysis and cyclic voltammetry data allowed the evaluation of the loading of anthraquinone groups on the graphene sheets.