Effective band gap engineering by the incorporation of Ce, N and S dopant ions into the SrTiO3 lattice: exploration of photocatalytic activity under UV/solar light

Cerium, nitrogen, and sulfur ions were doped into SrTiO3 (STO) lattice by sol-gel method. PXRD results confirm the cubic perovskite structure for all the doped samples. Higher Ce dopant concentration leads to the formation of CeO2 as a separate phase. X-ray density calculations show the solid to be of omission solid solution type material. A red shift in the absorption towards the visible region for all the doped samples was due to the formation of various mid-band gap states. FTIR technique confirms the presence of bidentately coordinated SO42- ions on the surface of doped samples. The XPS technique confirms the presence of Ce3+, Ce4+, S6+ and two different types of nitrogen. The surface acidity of the doped catalyst increases by the presence of SO42- and OH- ions favoring efficient trapping of photogenerated electrons. The upward shift in the position of VB of doped samples by almost 0.26 eV reduces the band gap of CeNS-STO samples as confirmed by the VB XPS technique. The lower PL intensity and higher magnitude of photocurrent for Ce0.48N0.19S0.44-SrTiO3 (CeNS-STO (2)) sample corresponds to higher separation efficiency of photogenerated electron-hole pairs. The enhanced photocatalytic activity of CeNS-STO (2) sample under both UV/solar light may be attributed to the synergistic effect between the three dopants Ce4+, N3-, and S6+ narrow band gap, decreased crystallite size, mesoporous structure, and high surface area. Intermediate products were identified by HPLC analysis and a possible degradation reaction mechanism was proposed. Incorporation of metal /nonmetal ions into the SrTiO3 lattice creates donor and acceptor levels within the band gap. The Ce4+/Ce3+ and S6+ dopant energy levels are located below the CB band edge, whereas N(3-)acceptor energy levels are located above the VB band and they are also merged within the VB based on its location in the interstitial or substitutional lattice sites. Figure shows various electronic transitions and possible degradation reaction pathways using CeNS-SrTiO3 photocatalyst under the irradiation of solar light.