Visible-light-induced oxidation of trans-ferulic acid by TiO2 photocatalysis

The oxidation of trans-ferulic acid (C10H10O4) in aqueous TiO2 dispersion occurs via the formation of a charge-transfer complex on the TiO2 surface that is able to absorb visible light (kP400 nm). The main product is CO2, whereas secondary oxidation products are organic species such as vanillin, caffeic acid, homovanillic acid, and vanillylmandelic acid. Oxidation through the formation of a charge-transfer complex occurs only in the presence of specific TiO2 samples. Experiments in the absence of oxygen, in the presence of bromate ions and by using a phosphate-modified TiO2, have been carried out for investigating the reaction mechanism. In order to study the interaction between trans-ferulic acid and TiO2 surface and to characterize the charge-transfer complex, UV–Vis diffuse reflectance and FT-IR spectroscopies have been used. FT-IR characterization of TiO2 samples in contact with the aqueous trans-ferulic acid solution indicates that the charge-transfer complex formation occurs via adsorption of bidentate ferulate species.