Fluorescence development during 514 nm irradiation of catechol adsorbed on nanocyrstalline titanium dioxide

Irradiation of a catechol/TiO2 film with a 514 nm laser produced a fluorescent, surface-adsorbed species. The reaction was slow, taking approximately 20–60 min to reach completion under the conditions of this study. A laser power study indicated that the rate of reaction was approximately proportional to the square-root of the laser power. The kinetics of fluorescence development could be modelled by a simple, first-order rate law for the nitrogen-sparged solution only. When air was bubbled through the solution the initial rate increased, and a transient peak in the fluorescence could be observed for θ = 0.49 (the lowest coverage in this study). The kinetics of the air-sparged system could be reproduced with a model that included both a persistent fluorescent species and a transient species, which converted to a non-fluorescent product in a subsequent, photochemical reaction. Raman spectra of the fully reacted surface did not reveal any new, adsorbed, organic molecule, indicating that the reaction results in the desorption of the organic molecule. It was concluded that fluorescent species was a modification of the titania surface, likely a partially reduced titanium ion.