Hydrogen activation at TiO2 anatase nanocrystals

The chemical activation of small molecules like hydrogen or oxygen at the surface of UV excited nanocrystals can provide valuable insights into the solid's photoactivity. We investigated the interaction of dehydroxylated TiO2 anatase nanocrystals with atomic as well as molecular hydrogen using electron paramagnetic resonance spectroscopy. Electron transfer from atomic hydrogen occurs spontaneously at T = 77 K and produces a charge separation state which is characterized by surface adsorbed protons and trapped electrons forming paramagnetic Ti3+ (d1) states. While there is no significant activation of molecular H2 at the surface of dehydroxylated particles in the absence of UV light, H2 acts as an efficient scavenger of photogenerated hole centers. These reactions are compared with charge carrier trapping at p < 10−5 mbar and discussed in the light of experiments which were carried out on frozen colloidal nanoparticle suspensions as described in the literature.