  TiO2 nanotube arrays grown by anodization were coated with thin layers of
polydopamine as visible light sensitizer. The PDA-coated TiO2 scaffolds were
used as photocatalyst for selective oxidation of benzyl alcohol under
monochromatic irradiation at 473 nm. Benzaldehyde was selectively formed and no
by-products could be detected. A maximized reaction yield was obtained in
O2-saturated acetonitrile. A mechanism is proposed that implies firstly the
charge carrier generation in polydopamine as a consequence of visible light
absorption. Secondly, photo-promoted electrons are injected in TiO2 conduction
band, and subsequently transferred to dissolved O2 to form oxygen radical
anions. These radicals react with benzyl alcohol and lead to its selective
dehydrogenation oxidation towards benzaldehyde.
