Photocatalysis by illuminated titania: Oxidation of hydroquinone and p-benzoquinone

Photocatalytic oxidation of hydroquinone and p-benzoquinone, the main inter mediates which are formed in the process of phenol oxidation on irradiated titania, was studied. The reaction proceeds via several steps. Some of the intermediates were detected by HPLC and GC-MS; ethanedial, glycerol, and 1, 2,4-trihydroxybenzene. Under illumination in the presence of TiO2, p-benzoq uinone initially transforms partly to hydroquinone, partly oxidizes to unid entified intermediates. The residue, about 4% of the concentration of hydro quinone, undergoes slow oxidation together with the hydroquinone. The rate of hydroquinone photooxidation shows 1(st) order behaviour.