Visible-light-induced photoelectrochemical behaviors of Fe-modified TiO2 nanotube arrays

Fe-modified TiO2 nanotube arrays (TiO2 NTs) were prepared by annealing amorphous TiO2 NTs whose surface was covered with Fe3+ by a dip-coating procedure, and characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV-visible reflectance spectroscopy. The photoelectrochemical properties were evaluated by the photocurrent response and photoelectrocatalytic (PEC) degradation of methylene orange (MO) and 4-chlorophenol in water under visible-light irradiation (lambda > 420 nm). The results showed that a Fe-modified TiO2 NTs electrode exhibited a larger photocurrent response and higher PEC activity for the degradation of organic pollutants than a pure TiO2 NTs electrode. At a bias potential of 0.4 V, the photocurrent response of a 0.5 M Fe-modified TiO2 NTs electrode exceeded that of a pure TiO2 NTs electrode by a factor of about 10, and the PEC degradation rates of MO and 4-chlorophenol on a 0.5 M Fe-modified TiO2 NTs electrode exceeded those on a pure TiO2 NTs electrode by a factor of about 2.5. The larger photocurrent response and higher PEC activity of Fe-modified TiO2 NTs could be attributed to the enhancement of separation of charge-carriers at the external electric field and the extension of the light response range of TiO2 to the visible-light region with the narrowing of the band gap.