The Bandgap of TiO2 Nanoparticles from Photo- and Electrochemical Properties – a Theoretical Study

Abstract

Oxide nanoparticles, like TiO2 nanoparticles are often applied in electrodes and photocatalytic systems. The morphology and shape of these nanoparticles can be easily tuned with experimental conditions, which raise the question how much the electro- and photochemical properties are affected by the nanoparticle geometry.We studied the electronic states around the bandgap in anatase-type TiO2 nanoparticles of different shapes with (101) and (001) facets using Density Functional based Tight Binding (DFTB) method. Previous calculation has already shown that most orbitals of the valence and conduction bands forms delocalized band-like orbitals, however there are a significant number localized states at the lower at edge of conduction band, too. These trapping sites may play important role in electrochemistry when placed on the surface of the nanoparticle.Photochemical properties however depend on optical transitions between electronic states with proper symmetry, and mostly dominated by delocalized states of atoms in the bulk. In this talk we analyze the optical spectra on the nanoparticles and compare it to the electrochemically important surface trapping.