Surface and volume characterization of TiO2 nanomaterials by 44Ti time differential perturbed angular correlation

Various TiO2 nanomaterials with primary particle sizes well below 10 nm and TiO2 nanotubes with the anatase structure were studied via the nuclear quadrupole interaction (NQI) of 44Ti(EC)44Sc by time differential perturbed angular correlation. In general two different NQIs were observed, the lower one attributed to the volume fraction because of the similarity to bulk values and the higher one to probes closest to the surface. Rather broad distributions of the strength of the interaction were observed which were different for nominally identical particles, contrary to the axial symmetry which is preserved to a very large extent. These distributions are interpreted as disorder arising from surface tension. These complications affect the interaction between these nanomaterials with biological systems and the environment and render toxicological assessments problematic. Dissolution studies in a synthetic body fluid mimicking blood plasma at 37 C for 4 weeks exhibited a very low solubility, but surprisingly slight changes in the volume fraction, probably due to surface adsorbates. (orig.)