Variation in the chemistry of the TiO2-mediated degradation of hydroxy- and methoxybenzenes: electron transfer and HO•ads initiated chemistry

The early degradation product distributions from TiO2-mediated photocatalytic degradations of a series of multiply hydroxylated benzenes and their methoxylated analogs is reported. The methoxylated compounds show a distinct trend away from ring-opening reactions that are attributed to electron transfer chemistry towards hydroxylations and demethylations that are attributed to hydroxyl-type chemistry. The initial rates of the reactions suggest that this is not simply due to the availability of the extra carbon sites. It is instead hypothesized that the compounds with hydroxyl groups are bound to the TiO2 in such a way as to facilitate electron transfer and its subsequent chemistry. Addition of isopropyl alcohol to the degradations slows the degradations of the methoxylated compounds more than it does the hydroxylated compounds and particularly inhibits the demethylation and hydroxylation reactions. It is suggested that the question of whether an organic substrate must be bound to the photocatalyst at the time of excitation may be dependent on the type of chemistry being observed. © 2001 Elsevier Science B.V. All rights reserved.