Potassium intercalation of carbon onions ‘opened’ by carbon dioxide treatment

Abstract

The potassium intercalation of onion-like carbon (OLC) samples consisting of aggregates of carbon onions is studied with photoemission spectroscopy. OLC samples were initially prepared by annealing nanodiamonds (3–20 nm in diameter) at 1800 K in vacuum. The resulting OLC consists of closed fullerene-like shells. The ‘closed’ OLC was subsequently treated with carbon dioxide at 1020 K in order to open the carbon shells by partial oxidation to create ‘opened’ OLC. Core level and valence band photoelectron spectroscopy have been employed in characterizing the changes in electronic structure of the samples. Upon intercalation of the closed OLC with K the C1s core level and valence band features shift to higher binding energies and the density of states at the Fermi level increases, while this effect is significantly smaller for intercalated opened OLC. These results indicate that opening the shells of carbon onions allows potassium to penetrate inside the particles and thus opens up a possible route to fill carbon onions with desired substances and their application as nanocapsules.