Atomic Insights into Oxygen Vacancy Generation of Titania Nanoparticles via High-Temperature Gas-Phase Synthesis Routes

Vacancy engineering in metal oxides is recognized as a key method for precisely tuning band structures, improving photocatalytic efficiency, and creating stable anchoring sites for atomically dispersed metal catalysts. Particularly, high-temperature gas-phase synthesis is a promising approach for synthesizing nanoparticles (NPs) with surface vacancies. Nevertheless, the vacancy formation and migration mechanisms in the high-temperature synthesis remain poorly understood up to now. In this study, we elucidate the atomic-scale thermodynamic and transport principles governing the oxygen vacancy (Ov) formation in TiO₂ NPs based on the reactive force field molecular dynamics simulations. By employing the Hungarian algorithm for lattice rotation pattern recognition, we further clarify the distribution and in-lattice migration of oxygen vacancies (Ovs) within the NPs. From a thermodynamic perspective, we propose a theoretical model demonstrating that elevated temperatures promote Ov formation through surface desorption, where the thermal effect dominates over the size effect. From the transport perspective, detailed statistical analyses reveal that the Ov distribution is anisotropic, and in-lattice migration of the Ovs is hindered by an energy valley resulting from an Ov-induced Ti-rich zone. Additionally, Ov formation also changes the crystal structure of “core–shell” NPs by promoting the expansion of the amorphous shell through distorting the crystal lattice. Insights from the study bridge the atomic-scale dynamics to high-temperature gas-phase synthesis, providing quantitative guidelines for designing vacancy-engineered nanocrystals.