Electronic Structure of Titania Nanosheets With Vacancies Based on Nonadiabatic Quantum Molecular Dynamics Simulations

Abstract

Titania nanosheets (TNSs) are expected to be applied to new, flexible, and high‐performance photocatalytic materials utilizing their two‐dimensional structure. Although it has been indicated that an experimentally synthesized TNS has more than a few Ti vacancies, the effects of these vacancies on the photocatalytic activity of a TNS have not yet been elucidated. Here, we present the results of first‐principles molecular dynamics simulations for various TNS structural models, both with and without a Ti vacancy. The calculated electronic density of states and bandgap energies of the TNSs are compared with those of bulk anatase. Provided that proper models are utilized, we confirm that TNSs have larger bandgap energies than anatase, as is observed experimentally, regardless of the existence of a Ti vacancy. Non‐adiabatic molecular dynamics simulations show that a Ti vacancy induces a spatial separation of the photogenerated electron and hole, and increases their recombination time. Accordingly, there are large differences in photocatalytic activity among the structural models. We therefore conclude that it is crucial to consider the effects of Ti vacancies in order to evaluate the photochemical properties of TNSs precisely.