Visible light photocatalysis in transition metal incorporated titania-silica aerogels

Transition metal salts were added to aerogels of TiO2–SiO2 mixtures. The resulting M–TiO2–SiO2 (M = transition metal, in general present in the form of oxides) materials had very high surface areas (600–1000 m2/g) and pore volumes (1–4 cm3/g), and contained highly dispersed transition metal oxides. Several samples were active photocatalysts for acetaldehyde oxidation to carbon dioxide using visible light; in particular chromium, cobalt, and nickel. These intimate aerogel mixtures were only active when SiO2 was present (i.e. M–TiO2 aerogels were not). High oxidation states of the transition metal ions (e.g. Cr6+, Co3+) appear to be important in bringing about visible light photocatalyst activity.