TiO₂ is a common component of electrode surfaces and photocatalytic systems. Depending on the preparation, the oxide can be formed in different shapes and morphology which can effect the selectivity and efficiency of the electrode [1]. Since the morphology and shape of the nanoparticles can be easily tuned with experimental conditions, this may offer a new, unexplored strategy to improve electrode properties in these systems. The goal of our computational studies is to understand better how charge carriers behave in these oxide nanoparticles.

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) and DFT methods. The previous calculation has already shown that most orbitals of the valence and conduction bands form delocalized band-like orbitals; however, there are a significant number of localized states at the lower edge of the conduction band, too. The calculations clearly show the position of these trapping sites when we compare the electron density of neutral and charged nanoparticles.

Reference:

[1] Selectivity enhancement in the electrochemical reduction of oxalic acid over titanium dioxide nanoparticles achieved by shape and energy-state control. H Eguchi, K Kato, G Juhasz, M Yamauchi - Catalysis Science & Technology, 2021

Figure 1. The electron density difference between negatively charged and neutral nanoparticle (left); electron density difference reflected in Mulliken charges of the atoms (right).