Electron Trap Analysis of Tin(II) Niobate Photocatalyst Particles Using Photoacoustic Infrared Spectroscopy

Abstract

Photoabsorption of tin­(II) niobate (SnNb2O6) photocatalyst particles, which possess the possible band position to allow overall water splitting and visible light absorption (ca. 2.3 eV of bandgap energy), was investigated by photoacoustic infrared spectroscopy (IR–PAS). With excited light irradiation, infrared absorption due to electron accumulation in SnNb2O6 appeared, and its spectral shape was in good agreement with that of tin­(IV) oxide (SnO2) but not that of niobium­(V) oxide (Nb2O5). The spectral matching results suggest that substitutional tetravalent tin (Sn4+) at the pentavalent niobium (Nb5+) site acts as an electron acceptor and that the energy levels of Sn4+ are mainly located at ca. 0.3 eV below the bottom of the conduction band. Therefore, IR–PAS can be used to reveal the energy distribution and origin of electron-trapping sites in multinary oxides such as SnNb2O6.