TiO ₂ Surface Engineering to Improve Nanostability: The Role of Interface Segregation

Nanoparticle stability against coarsening is one of the keys to allow better exploitation of the properties of nanoscale materials. The intrinsically high interfacial energies of nanoparticles constitute the driving force for coarsening, and therefore can serve as targets to design materials with improved thermal stability. In this study, we discuss the surface engineering of TiO ₂ nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba ²⁺ ions to the interfaces of TiO ₂ nanocrystals. Ba ²⁺ is a strong candidate for photoelectrocatalytic reduction of CO ₂ and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba ²⁺ content located at both the surface and at grain boundary interfaces and combined with direct calorimetric measurements of surface energies and microstructural studies to demonstrate that Ba ²⁺ excess quantities directly impact coarsening of TiO ₂ nanocatalysts by creating meta-equilibrium configurations defined by the Ba ²⁺ content and segregation potentials at each individual interface. The results establish the fundamental framework for the design of ultrastable nanocatalysts.