Surface modification of TiO2 with Fe2O3 clusters was made through chemisorption of ferric phthalocyaninetetracarboxylate onto TiO2, 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 TiO2 as a noncrystallized cluster, while TiO2 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 TiO2 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 TiO2, mainly ascribed to the increased size of Fe2O3 clusters. In the presence of H2O2, all Fe-containing catalysts were more active than bare TiO2. 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/TiO2 electrode. Present work clearly shows that only Fe2O3 clusters in a small size and at low coverage on TiO2 are beneficial to the photocatalytic reaction, while excess iron oxide is detrimental. Possible mechanism is discussed in the text. (C) 2012 Elsevier B.V. All rights reserved.