Photoanodic response of iron oxide electrode in aqueous solution and its application to Pb2+ removal under visible light irradiation

The iron oxide electrode was prepared from thermal oxidation of iron at 600 °C for 3 h in air atmosphere. This electrode with the structure of Fe3O4 and α-Fe2O3 showed the response of photoanodic current to the light with wavelength shorter than 600 nm. The band gap energy of this electrode was 1.99 eV. The onset potential of distinct steady photocurrent and also the flatband potential were 0.80 and 0.09 V vs. Ag/AgCl, respectively, in 0.1 M HNO3 aqueous solution. The cell consisting of the iron oxide photoanode in HNO3–Pb(NO3)2 and the graphite cathode in H2SO4–Ce(SO4)2 caused the PbO2 deposit on the surface of the former electrode due to visible light irradiation without application of voltage. By holding the potential of this electrode at more positive value than 0.90 V, the photoanodic removal rate of Pb2+ in HNO3–Pb(NO3)2 solution was higher than that observed when Ce4+ was used as electron acceptor.