Minimizing electron-hole recombination in modified TiO2photocatalysis: electron transfer to solution as rate-limiting step in organic compounds degradation

Abstract

4-Stilbenecarboxaldehyde (4SCA) at pH 3 was added to TiO2 anatase to form a new catalyst where the aldehyde carbonyl group reacts with the TiO2-OH to form the corresponding acetal (4SCA-TiO2). 4SCA-TiO2 significantly retards the electron recombination when it is illuminated with ultraviolet B light because of the formation of a stable radical anion·−4SCA-TiO2 that we have detected spectroelectrochemically. The light excited electron on the catalysis is transferred relatively slow to solution. Therefore, the electron transfer to solution is the rate-limiting step for water-dissolved organic compound degradation when 4SCA-TiO2 is used as photocatalyst. For instance, degradation rate constants using naphthalene (Naph) and p-nitrophenol (PNP) in an ample pH range support the proposal. Accordingly, rate constants are faster when the standard redox potential of the involved electron acceptor in the solution increases. In fact, this condition can be tuned to promote reactivity. The affinity between the organics being degraded and 4SCA-TiO2 also influences on the degradation rate constants.