Surface graphitization of ozone-treated detonation nanodiamonds

Abstract

Bifunctional detonation nanodiamonds (NDs) were obtained by vacuum annealing at 750 °C of NDs previously oxidized in ozone (ND-ozone). Raman investigations demonstrate a significantly higher amount of sp2 carbon compared to ND with polyfunctional surface (ND-NRI) annealed in vacuum under the same conditions. In addition to sp2 carbon caps, thermal desorption mass spectroscopy analysis revealed a higher oxygen concentration at the ND-ozone surface with abundant carbonyl and carboxylic acid anhydride groups. The supernatant of ND-ozone annealed in vacuum exhibits a positive zeta potential (+50 mV at pH 6.5), while the starting sample has a high negative zeta potential (−60 mV). This supports the oxygen hole-doping model previously proposed to explain the positive zeta potential of NDs after vacuum annealing.