Photochemical reduction of carbonate to formaldehyde on TiO2 powder

Photochemical reactions at semiconductor particle surfaces have been used to drive energy uphill reactions to store light energy. Carbonate radical anion was found to be intermediate when carbonate was used to intercept the photogenerated hole on TiO2 by exciting with light energy of more than 3.2 eV. The carbonate anion radical undergoes secondary reactions on the surface to give formaldehyde. The chemical energy stored in this reaction is 580 kj/mole. The quantum yield for the formation of HCHO is 4 × 10−3, but extended irradiation leads to loss of formaldehyde.