The iron(III)-ion doped TiO2 (Fe3+-TiO2) with different doping Fe3+ content were prepared via a sol-gel method. The as-prepared Fe3+-TiO2 nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe3+-TiO2 catalysts with different Fe3+ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe3+-TiO2 was revealed: that is, the Fe3+ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti <= 0.03 mol%); while Fe3+ dopant content exceeds 0.03 mol%, Fe2O3 became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe2O3 with TiO2 leads to that the photoinduced electrons and holes of TiO2 transfer to Fe2O3 and recombine quickly, which is unfavorable to the photocatalytic reaction. (c) 2006 Elsevier B.V. All rights reserved.