Self-doping for visible light photocatalytic purposes: construction of SiO2/SnO2/SnO2:Sn2+ nanostructures with tunable optical and photocatalytic performance

This work explores a hydrothermal route to synthesis of self-doped SiO2/SnO2/SnO2: Sn2+ nanostructures with controlled hierarchical structures and lattice parameters for tunable optical and photocatalytic properties. The effects of Sn2+ self-doping in the SnO2 lattice on the local structure, electronic structure, and photodegradation of methyl orange were systematically investigated. It is found that two layers of SnO2 and SnO2: Sn2+ nanocrystals with thicknesses of 13 and 8 nm were coated on SiO2 spheres showing monodispersed features. By Sn2+ doping, a blue shift of the Sn 3d XPS binding energy was observed, which is thought to be mainly related to the difference in electronegativity of Sn4+, Sn2+ and variation of lattice parameters. In contradiction to the quantum size effect, the self-doped SiO2/SnO2/ SnO2: Sn2+ nanostructures showed an abnormal red shift of band gap energy, which is related to doping effects and variations of lattice parameters. With well-defined lattice structure and electronic structure, the photocatalytic performance of SiO2/SnO2/SnO2: Sn2+ nanostructures can be well regulated and optimized.