Morphology of TiO2 nanoparticles as fingerprint for the transient absorption spectra: implications for photocatalysis

Abstract

Understanding the relationship between structural properties and the character of the charged carriers in photoactive TiO2 nanoparticles is fundamental to improving their photocatalytic activity. Transient absorption spectroscopy (TAS) is often used to explore the character of the charge carriers, but carrying out experiments on well-defined nanoparticles with a given morphology and selected size is extremely difficult. Here, hybrid time-dependent density functional theory based calculations carried out for realistic TiO2 nanoparticles (NPs) with bipyramidal, truncated, and spherical morphologies reveal that the electron-trapped carriers are quite sensitive to the NP morphology. In particular, these carriers are shallowly trapped in faceted NPs whereas they are deeply trapped in those exhibiting a spherical morphology. In addition, the simulated absorption spectra can be compared directly to experimental ones obtained by TAS, thus allowing additional information to be provided regarding the morphology of the TiO2 NPs in a given sample. Note that although the present study focuses on TiO2 nanoparticles, it can be easily extended to other photoactive materials such as ZnO or WO3 NPs thus allowing the extraction of information regarding the relationship between the NP morphology and the nature of the low-lying excited states.