The effect of acid treatment on the surface chemistry and topography of graphite
Emir Bouleghlimat, Philip R. Davies, Robert J. Davies, Rebecca Howarth, Jiri Kulhavy, David J. Morgan, Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom
The effect of acid treatment on the surface chemistry and topography of graphite. Preliminary data suggests gold nanparticles may deposit around the 'nanobubbles'
A novel study into the effect of surface treatments on the local topography of model carbon catalyst supports has been published in Carbon.
Carbon based materials, including graphite and “activated carbon”, are commonly used as a supports for heterogeneous catalysts because of their relatively low cost, high surface area and the ease with which precious metals can be reclaimed from the support at the end of the catalyst’s active life. However, in nearly all cases, carbon supports are acid washed, typically with HCl and/or HNO3, before the adsorption of the active component. The wash has two purposes; it removes unwanted contaminants that accumulate on the carbon surface during preparation; and it is also thought to introduce hydrophilic functional groups that modify the behaviour of the carbon towards the active component and the reaction solvent. There has been considerable discussion in the literature about the nature of these modified carbon surfaces.
Our approach has been to employ a combination of atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to study the effect of acid treatments using highly oriented pyrolytic graphite (HOPG) to allow us to study the topography at a nanoscale level. HOPG is often used as a model carbon surface for studies under ultra-high vacuum conditions despite the lack of functional groups that would exist on real catalyst surfaces. For this reason the present study can also be regarded as bridge between the idealised UHV systems and the practical catalysts
We have discovered that the acid based modification of the HOPG surface occurs through intrusion by the acid into the graphite, causing weakening and breakage of the interplanar bonds. Leading to “bubbles” under the graphite surface. The results may have implications for our understanding of carbon based catalysts since functional groups generated under the surface would be less effective at stabilising nanoparticles of active material deposited onto the graphite.