Photocatalytic performance of Sn-doped TiO₂/reduced graphene oxide composite materials

Composite materials of Sn-doped TiO₂ nanoparticles (4-6 nm) uniformly anchored onto reduced graphene oxide (RGO) sheets were fabricated by a hydrothermal process. When compared with an undoped TiO₂/RGO composite material, the partial substitution of Sn⁴⁺ for Ti ⁴⁺ in TiO₂/RGO in different doping concentrations not only increased the specific surface area, but also narrowed the band gap energy of the material. It also resulted in a shift in the photoresponse of the material into the visible light region, an increase in the relative intensity of its Raman (D/G) band, and changes in its X-ray photoelectron spectra; these results implied strong interactions between the Sn species and nanosized TiO₂ as well as between the TiO₂ and RGO layers. The presence of RGO led to enhanced adsorptivity of methyl orange onto the material compared with that of either pure TiO₂ or Sn-doped TiO₂. Increasing the Sn dopant content to optimal value facilitated photoactivity under both UV and visible light irradiation. The incorporation of both RGO and Sn dopants significantly modified the electronic structure of TiO₂, altering the electron transfer direction and efficiently prohibiting the recombination of photo-induced charge carriers.