Substitutional or Interstitial Site-Selective Nitrogen Doping in TiO2 Nanostructures

Herein, we report a colloidal wet-chemical approach enabling control on dopant concentration and location in a nanocrystal host lattice. Growth-doping and nucleation-doping, driven by primary and tertiary amines, respectively, were identified as predominant doping mechanisms responsible for the introduction of nitrogen impurities in interstitial and substitutional sites in highly branched rutile TiO2 nanostructures. High-resolution X-ray photoelectron spectroscopy was used to distinguish the two nitrogen occupational lattice sites and, in combination with UVvis absorption spectroscopy, to investigate the impact of the nitrogen impurities on the optoelectronic properties. The implementation of the nitrogen-doped titania nanostructures in photoelectrodes for water oxidation suggests that these atomically defined building blocks can function as a platform to investigate the impact of the nitrogen occupational sites on the photocatalytic properties. By deliberately choosing precursors and reaction conditions, instead of relying on the most common high temperature annealing of preformed metal oxide in ammonia, we emphasize the importance of understanding the chemistry behind doping to achieve an unprecedented level of control on effective dopant introduction and, therefore, property tunability.