Enhanced Photocatalytic Degradation of RhB Driven by Visible Light-Induced MMCT of Ti(IV)−O−Fe(II) Formed in Fe-Doped SrTiO₃

It is important to reveal the origin of the visible light-induced photocatalytic activity of transition metal-doped SrTiO₃ in which an isolated energy level is created by the dopant in the forbidden band gap. In this particle, the photocatalytic and photophysical properties of pure SrTiO₃ and Fe-doped SrTiO₃ were investigated comparatively. The Fe-doped SrTiO₃ has been shown to have a much higher photocatalytic activity than pure SrTiO₃ for the degradation of RhB under visible light irradiation. It was showed that doping Fe into SrTiO₃ exhibited an absorption extending up to the visible region in the optical absorption spectrum and established the Ti^IV−O−Fe^II heterobimetallic linkages in the host. Difference diffuse reflectance spectra revealed that the absorption in the visible region is partly attributed to the metal-to-metal charge-transfer (MMCT) excitation of Ti^IV−O−Fe^II linkage formed in the Fe-doped SrTiO₃. The visible light excitation of Ti^IV−O−Fe^II linkage was demonstrated to be the cause of the enhanced degradation of RhB. Furthermore, it was noted that the Ti^IV−O−Fe^II linkages only onto and nearest the surface of the Fe-doped SrTiO₃ behavior as active sites for the visible light-induced photocatalysis.