Dr. Uwe Burghaus
Department of Chemistry and Biochemistry
Carbon and Other Flatlands: Graphene & Silicatene
Recently in the literature, the wetting properties of graphene for water were controversially discussed. That dispute was based on contact angle (/engineering) measurements at ambient pressure. However, since the 1990s, it is known from surface science studies that impurities distinctly affect wetting properties. Therefore, we collected data for water adsorption at clean ultra-high vacuum (UHV) measuring conditions. PVD (physical vapor deposited) graphene grown on Ru(0001) at UHV as well as commercial CVD (chemical vapor deposited) graphene/Cu and graphene/SiO2 samples were studied. We propose simple rules based on UHV kinetics data to classify the water-graphene-support interactions. Only for graphene/Cu, the water interaction is hydrophobic. Graphene’s wettability is not directly related to wetting properties of the supports. Therefore, graphene is not transparent to water wetting. Similarly, benzene and alkanes were used as probe molecules, mostly to evaluate support effects of epitaxial graphene. In contrast to polar water, we demonstrate that graphene is nearly transparent for none-polar benzene adsorption on both copper and silica supports, opposed to Ru(0001) where benzene decomposes. In other words, the binding energies of benzene on e.g. graphene/Cu and the Cu support are very similar (, i.e., graphene/Cu is transparent for benzene). First data of two other two-dimensional (2D) systems will briefly be described: graphene oxide as a metal-free catalyst as well as silicatene as a 2D analogy to zeolites. Also for these systems we currently focus on water adsorption. (Interested in details? See, Chemical Communications 50 (2014) 7698; 51 (2015) 11463).