Controlling surface defects and photophysics in TiO₂ nanoparticles

Titanium dioxide (TiO₂) is widely used for photocatalysis and solar cell applications, and the electronic structure of bulk TiO₂ is well understood. However, the surface structure of nanoparticulate TiO₂, which has a key role in properties such as solubility and catalytic activity, still remains controversial. Detailed understanding of surface defect structures may help explain reactivity and overall materials performance in a wide range of applications. In this work we address the solubility problem and surface defects control on TiO₂ nanoparticles. We report the synthesis and characterization of ∼4 nm TiO₂ anatase spherical nanoparticles that are soluble and stable in a wide range of organic solvents and water. By controlling the temperature during the synthesis, we are able to tailor the density of defect states on the surface of the TiO₂ nanoparticles without affecting parameters such as size, shape, core crystallinity, and solubility. The morphology of both kinds of nanoparticles was determined by TEM. EPR experiments were used to characterize the surface defects, and transient absorption measurements demonstrate the influence of the TiO₂ defect states on photoinduced electron transfer dynamics.