Metal oxide nanocrystals, and in particular TiO₂, are employed for many technologically relevant surface applications. Because chemical and photochemical reactivity critically depends on the size and the shape of the crystals, control over these properties represents a key issue in materials' synthesis. Morphologically well-defined nanostructures will be introduced as model systems to establish a correlation between chemical and photochemical reactivity, on one hand, and the abundance of specific surface sites, on the other.

TiO₂ absorbs photons with energies greater than 3.2 eV which leads to the generation of excited electrons and holes. These can either (a) recombine under photoluminescence emission or heat generation, (b) become persistently trapped or (c) undergo redox reactions with molecules at the particle surface. The particle surface largely determines the efficiency of these processes. For this reason, photoexcitation processes have been investigated on different TiO₂ based model systems: TiO₂ anatase nanoparticles produced via chemical vapour deposition[1], titanate nanotubes[2] and TiO₂ nanorods. Persistent charge trapping and oxygen radical formation were studied by electron paramagnetic resonance. The presence of O₂, an electron scavenger, results in charge transfer to the oxygen molecule to generate adsorbed O₂^- radicals.

Quantification in terms of trapped charges per particle was carried out and the influence of the surface structure and properties on the obtained figures will be discussed. Tracking UV-induced reactions on nanomaterials of different size and shape in comparison with studies on the standard TiO₂ P25 represents a valuable approach towards the identification of active sites on nanocrystalline samples.

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1. Oxide Islands on MgO Nanocubes
2. Spectroscopic Properties of adjoined TiO₂ Nanocrystals
3. Chemical Control of Photoexcited States in Titanate Nanostructures
4. Oxide Nanocrystals as Model Systems for Surface Chemistry
5. Manipulation of chemical and optical properties of MgO nanocubes via surface functionalization