Photo-oxidation mechanism of l-alanine in TiO2 photocatalytic systems as studied by proton NMR spectroscopy

Photocatalytic decomposition of alanine as a representative amino acid was investigated in detail for nine different kinds of TiO2 powders by proton NMR spectroscopy. Acetic acid was detected as a stable major intermediate via a fragile intermediate of acetaldehyde. Pyruvic acid was formed on rutile surface, while acetamide was detected on anatase surface. Pyruvic acid was formed directly from alanine, whereas acetamide was produced likely from acetaldehyde and ammonia, which are the decomposition components of alanine. In addition, small amount of formaldehyde and formic acid was formed and decomposing to CO2.