Dominated factors for high performance of Fe3+ grafted metal doped TiO2 based photocatalysts

Abstract

We examined dominated factors for visible light driven performance of the Fe3+ grafted metal doped TiO2 based photocatalyst (Fe/Me:TiO2) by means of ESR spectroscopy and active oxygen detection. For the performance of the Fe/Me:TiO2, in addition to a direct electron transfer from TiO2 valence band to the grafted Fe3+, indirect electron transfers to the Fe3+ are important. In this work, it was revealed that the electron acceptor state formed close to the redox potential of the grafted Fe3+ to Fe2+ by doping metal ions leaded to enhancement of the photocatalytic activity because the efficiency of the indirect electron transfer via acceptor level to the Fe3+ was high. The other indirect electron transfer via metal ions of donor state to the Fe3+ did not lead to large enhancement of photocatalytic activity. A two-step electron excitation from TiO2 valence band to conduction band via defect level under visible light irradiation was a path with high recombination rate of electron–hole and therefore could not contribute to the photocatalytic activity. Moreover the defect level decreased the efficiency of the direct electron transfer from the TiO2 valence band to the Fe3+, resulting in decrease of photocatalytic activity.