INS-, XPS- and SIMS-investigations on the controlled post-oxidation of pigment blacks - Detection of different species of strongly adsorbed water

The generation of oxygen-containing surface groups on furnace blacks and gas blacks has been compared before and after oxidative after-treatments in gas phase (NO2, O-3) and liquid phase (HNO3) procedures by means of X-ray photoelectron spectrometry. Secondary ion mass spectrometry showed that the oxygen concentrations in the near-surface regions were enhanced also, especially due to the influence of ozone. Inelastic neutron scattering was utilized to investigate the overall modification of the blacks at a bulk level. Strongly oxidized blacks even of low primary particle size still showed strong graphite modes and the C-H bending modes of extended basic structural units indicating a minor level of bulk degradation, whereas indications for the removal of molecular-like structures from the surface, Of sp(3) type constituents, and of non-conjugated hydrogen-containing structures was obtained. Inelastic neutron scattering at 20 K was observed to be a suitable probe to detect traces of residual water not only at the surface but also inside the pore system of carbon blacks which could not be removed by long-term drying procedures. The position of the leading edge of the intermolecular librational mode of condensed water in the ice-like state is a sensitive measure for the location of these traces according to their hydrogen bonding. Strongly adsorbed residual water in unrestricted geometry, at the surface of carbon black, leads to ice of type Ih or Ic. Water inside micropores or in a strongly perturbed and loose geometry was indicated by the librational modes of more or less isolated water molecules. This was observed in oxidized carbon black from experiments using ozone. The possibility for direct spectroscopic studies on the hydrogen bonding of strongly adsorbed water even inside the micropores of finely divided, oxidized, electrical conductive and highly absorbing gas blacks seems helpful to complement data from well proven methods for studying interactions between water and carbons. (C) 2001 Published by Elsevier Science Ltd.