Improving TiO₂ Anatase Nanostability Via Interface Segregation: The Role of the Ionic Radius

Titanium dioxide nanoparticles are of particular interest in photocatalysis and artificial photosynthesis studies. Their properties are dependent on parameters such as the crystal polymorph, for example, anatase/rutile phases, the specific surface area, and the capacity to adsorb CO2 and H2O gas molecules. A cause-effect relationship exists between those parameters, the surface thermochemistry, and the performance in application. However, the lack of systematic thermodynamic data has hindered a more comprehensive understanding to enable control. This work investigates the relationship between the surface thermochemistry of alkaline earth metals doped TiO2 and the associated micro and nanostructural features. TiO2 nanoparticles doped with Mg2+, Ca2+, Sr2+, or Ba2+ showed spontaneous segregation of dopants to the nanoparticles' interfaces, leading to incremental surface energy reduction as directly measured by microcalorimetry of adsorption. The phenomenon was a direct function of ionic radius and led to the improved thermal stability of the nanoparticles against coarsening, stabilizing the anatase polymorph, and increasing the specific surface area.