Oxygen vacancies in nano-sized TiO₂ anatase nanoparticles

Anatase nanoparticles containing surface oxygen vacancies (V_O) and Ti³⁺ are of great importance for applications in photocatalysis, batteries, catalysis, sensors among other uses. The properties of V_O and their dependence on the size of nanoparticles are of great research interest and could allow obtaining advanced functional materials. In this work, a complete set of oxygen vacancies in an anatase nanoparticle of size 1.1 nm was investigated and compared to those of a twice larger nanoparticle, having the same shape and surface hydroxylation pattern. It turned out that the decrease in the size of the anatase nanoparticle strongly facilitated creation of surface oxygen vacancies and Ti³⁺. After their creation, oxygen vacancies undergo three transformation paths — (1) small repulsion of surrounding Ti cations with retention of the vacancy, (2) transfer of oxygen anion, leading to the movement of oxygen vacancy to a more stable position, and (3) collapse of oxygen vacancy accompanied by structure deformation towards Magneli-like phase.