Surface graphitization of ozone-treated detonation nanodiamonds

Bifunctional detonation nanodiamonds (NDs) were obtained by vacuum annealing at 750 degrees C of NDs previously oxidized in ozone (ND-ozone). Raman investigations demonstrate a significantly higher amount of sp(2) carbon compared to ND with polyfunctional surface (ND-NRI) annealed in vacuum under the same conditions. In addition to sp(2) 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 (+50mV at pH 6.5), while the starting sample has a high negative zeta potential (-60mV). This supports the oxygen hole-doping model previously proposed to explain the positive zeta potential of NDs after vacuum annealing. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim