Adsorption and photo-oxidation of 3,4-dihydroxy-cinnamic acid on TiO(2) films

The photo-oxidation of 3,4-dihydroxy-cinnamic acid (DHCA) is investigated on TiO(2) films prepared from commercial Degussa P-25 (FP25 films) and from colloidal TiO(2) prepared by the sol-gel method (FSG films). Photo-oxidation rates have been found to be inversely correlated to the amount of adsorbed species. The extent of adsorption increases as the solution pH increases from 1 to 4 and is more pronounced in the case of FP25 samples for which the amount of adsorbed species is 2.7 x 10(-10) Mol cm(-2), i.e. about threefold higher than for the FSG case. Analysis of DHCA adsorption on TiO(2) suspensions provided information complementary to that collected on films. Diffuse reflectance UV-visible and FTIR spectra of adsorbed DHCA are conspicuously different for the two types of films.