Effect of surface Fe2O3 clusters on the photocatalytic activity of TiO2 for phenol degradation in water.

Surface modification of TiO(2) with Fe(2)O(3) clusters was made through chemisorption of ferric phthalocyaninetetracarboxylate onto TiO(2), followed by sintering in air to remove organic moiety. Solid characterization with electron paramagnetic resonance spectroscopy and other techniques showed that ferric oxides were highly dispersed on TiO(2) as a noncrystallized cluster, while TiO(2) phases remained unchanged. For phenol degradation in aerated aqueous suspension, only the sample containing less than 0.3 at.% Fe was more active than bare TiO(2) under UV light, whereas no activity was found under visible light. As anatase thermally transferred into rutile, the Fe-containing catalyst became less active than bare TiO(2), mainly ascribed to the increased size of Fe(2)O(3) clusters. In the presence of H(2)O(2), all Fe-containing catalysts were more active than bare TiO(2). Moreover, similar trend in activity among different catalysts was also observed with the formation of hydroxyl radicals, and with the generation of photocurrent measured under N(2) with Fe/TiO(2) electrode. Present work clearly shows that only Fe(2)O(3) clusters in a small size and at low coverage on TiO(2) are beneficial to the photocatalytic reaction, while excess iron oxide is detrimental. Possible mechanism is discussed in the text.