Cerium Oxide Coating of Titanium Dioxide Pigment to Decrease Its Photocatalytic Activity

The use of cerium oxide coating of titanium dioxide pigments to decrease photocatalytic activity was studied. A large decrease in the photocatalytic activity of titanium dioxide particles coated with cerium oxide was obtained even with a tiny coating amount of 0.2 wt %, and these particles were more stable than those with the conventional 2.0 wt % film coating of silicon dioxide or 1.5 wt % aluminum oxide. The combination film coatings of cerium oxide and silicon or aluminum oxide showed smaller decreases in photocatalytic activity. Both Ce(III) and Ce(IV) oxide coatings gave highly decreased photocatalytic activity, even when the cerium oxide coating did not completely cover the surface. It was inferred that the efficient decrease of photocatalytic activity was because the unpaired electrons in the 4f orbital of cerium enabled the coating film to capture electrons and holes that were produced when titanium dioxide was exposed to ultraviolet irradiation.