TiO₂ 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 TiO₂ nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba²⁺ ions to the interfaces of TiO₂ nanocrystals. Ba²⁺ is a strong candidate for photoelectrocatalytic reduction of CO₂ and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba²⁺ 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 Ba²⁺ excess quantities directly impact coarsening of TiO₂ nanocatalysts by creating meta-equilibrium configurations defined by the Ba²⁺ content and segregation potentials at each individual interface. The results establish the fundamental framework for the design of ultrastable nanocatalysts.