Urea Photosynthesis from Inorganic Carbon and Nitrogen Compounds Using TiO₂ as Photocatalyst

Urea was successfully synthesized by illuminating size-quantized TiO 2 nanocrystals (Q-TiO 2 ) immobilized in polyvinylpyrrolidinone gel film in CO 2 -saturated propylene carbonate containing NO 3 - and 2-propanol, the latter of which served as a hole scavenger. Commercially available TiO 2 (Degussa P-25) also showed activities for the urea photosynthesis, though the production rate of urea was lower. The use of HCOOH or CO in place of CO 2 also yielded urea. The same was true for the replacement of the nitrogen source from NO 3 - to NH 2 OH or NO. The urea production was accompanied by production of other reduction products such as NH 4 + and methanol, but their amounts were largely influenced by the kind of reaction substrates used. The sum of quantum efficiencies obtained for the reduction products showed good accordance with the quantum efficiency obtained for the sole oxidation product of acetone.