Effects of Mott–Schottky Frequency Selection and Other Controlling Factors on Flat-Band Potential and Band-Edge Position Determination of TiO2

Abstract

The use of titanium dioxide for tackling environmental pollution has attracted great research interest recently. The potential of a photocatalyst in removing contaminants depends mainly on its conduction and valence-band edges relative to the standard potential of reactive oxygen species. One of the methods used in determining these band-edge positions is via the Mott–Schottky analysis. Thus, the aim of this work was to investigate the influence of the Mott–Schottky frequency and different electrochemical conditions on flat-band potential values and band-edge positions of pure anatase or Degussa P25, calcined or uncalcined in a 0.2 M Na2SO4 solution. The results showed that the shift in the flat-band potential was not so frequency-dependent in the Mott–Schottky analysis, however, other reasons, such as immersion duration leading to thenardite Na2SO4 salt deposition on the surface, irradiation of sources and the change in the pH of the solution (in the range of 1.64–12.11) were also responsible for it. In general, both the calcined anatase and P25 had a less negative value of the flat-band potential compared to the uncalcined. On the other hand, the calcined anatase had a tendency to have a less negative value of the flat-band potential than the calcined P25. From this study, the frequency range for obtaining the flat-band potential within one standard deviation in the Mott–Schottky at a single-frequency analysis was found to be between 200 and 2000 Hz. The energy difference between the Fermi level and the conduction band edge for anatase and P25, either calcined or uncalcined, was 0.097–0.186 and 0.084–0.192 eV, respectively. On the other hand, the band-edge position of anatase or P25 tended to shift upwards when it was repeatedly used in the photoelectrochemical analysis.