Surface Structures of Fe-TiO₂ Photocatalysts for NO Oxidation

Commercial rutile TiO₂ particles capped with Al₂O₃ and ZrO₂ layers, which are widely used in white pigments, can serve as a starting material for the fabrication of visible light-responsive photocatalysts toward gas-phase NO oxidation. The as-received TiO₂ with iron impurities exhibited reduced photocatalytic activity, and the activity was boosted by the deposition of additional iron comparable in quantity to the intrinsic iron impurity level. Analyses using X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectroscopy, and low-energy ion scattering spectroscopy revealed that the deposited iron and intrinsic impurity iron are dissimilar in terms of location, oxidation states, and interaction with TiO₂. This suggests that tracking the structure and impurity levels of photocatalyst elements can be crucial for understanding structure-activity relationships of real catalysts.