Spectroscopic and atomic force studies of the functionalisation of carbon surfaces: new insights into the role of the surface topography and specific chemical states

Abstract

The utility of carbon materials in applications as diverse as drug delivery and photocatalysis is often undermined by the complexity of their surface chemistry; different sources of carbon give rise to a varied mixture of functional groups and hence different properties. Considerable efforts have been made to identify specific groups at these surfaces and elucidate the complex interactions that take place but even on materials such as graphene and carbon nanotubes there remains uncertainty about the nature of the components present and their role in the nucleation of other functional materials at the surface. The present study uses highly ordered pyrolytic graphite (HOPG) as a model on which the fundamental properties of specific functional groups and their interactions with deposited nanoparticles can be characterised. We have shown that treatment of HOPG surfaces with low concentrations of hydrochloric acid results in significant topographic changes to the surface and a low concentration of oxygen containing species. From selective derivatization and a comparison of their XP spectra, the latter can be unambiguously identified as surface hydroxyls. DFT calculations have shown that these groups are stable in close proximity to each other. Heating to 573 K leads to conversion of the hydroxyls to mixture of two states, one of which is identified as a ketone whilst the other is proposed to be an ether. Gold deposition on the surface from aqueous solutions of chloroauric acid is shown to be strongly influenced by the nature of the oxygen species present.