The functionalisation of graphite surfaces with nitric acid: identification of functional groups and their effects on gold deposition

The role of surface oxygen species in the nucleation and reactions of metal nanoparticles on carbon surfaces has been explored using model systems based on graphite supported with DFT calculations. Features in the X-ray photoelectron spectra at characteristic binding energies of 532.6 eV, 531.8 eV, and 533.5 eV were unambiguously assigned to hydroxyl, ketone, and ether groups after selective derivatization. Surfaces treated with nitric acid generate almost exclusively hydroxide groups which on heating to 573 K transform into ketones and ethers. Gold nanoparticles deposited from an aurochloric acid solution show a better dispersion on the hydroxylated surface than on either the clean or the ketone-covered surface and whereas on the hydroxylated surface the adsorbed gold was reduced completely to Au0, a small component attributed to Au3+ was present after deposition at the ketone-/ether-covered surface. DFT calculations confirm that gold atoms adsorb more strongly to a hydroxylated step edge than one functionalised with ketone groups. The results give an insight into the effects of the acid washing of carbon catalysts before loading with the active metal components