A photoelectrochemical and spectroscopic study of phenol and catechol oxidation on titanium dioxide nanoporous electrodes

The photoelectrochemical behavior of TiO2 nanoporous thin film electrodes has been studied in the presence of phenol and catechol. Voltammograms, both in the dark and under illumination, as well as photocurrent transients were combined with Attenuated Total Reflection Infrared measurements. Particular attention has been paid to the way that photocurrent is sensitive to the organics concentration. A non-monotonic, unusual tendency has been observed in all cases. For low organics concentration (lower than 0.1 mM), there is a deactivation of the electrode toward the water photooxidation process. Parallel spectroscopic measurements prove that, in this concentration range, the amount of adsorbed phenol (or catechol) is very small (undetectable), which supports the existence of a low coverage of surface active sites for the water photooxidation process. In the high concentration range, an increase of the organics concentration leads to an unexpected decrease in the stationary photocurrent. This behavior, attributed to both the build-up of an intermediate acting as a recombination center and a fouling of the oxide surface, has rarely been observed in TiO2 heterogeneous photocatalysis.