Comparative study on sandwich-structured SiO2@Ag@SnO2 and inverse SiO2@SnO2@Ag: key roles of shell ordering and interfacial contact in modulating the photocatalytic properties

Sandwich-structured SiO2@Ag@SnO2 and inverse SiO2@SnO2@Ag using SiO2 spheres as cores have been systematically synthesized through hydrothermal treatment. The crystal structure, morphology, size, composition and specific surface area of products were investigated by XRD, SEM, TEM (HRTEM), XPS, UV-vis and N-2 adsorption-desorption instruments. It was found that both Ag nanoparticles and SnO2 layers were successfully decorated or coated on the surface of the matrix. The investigation of photocatalytic properties indicated that the SiO2@Ag@SnO2 heterostructure possessed an excellent photocatalytic ability superior to the SiO2@Ag, SiO2@SnO2 and even the inverse sample SiO2@SnO2@Ag, for the degradation of Rhodamine B (RhB) driven by UV light. The results indicated that Ag nanoparticles acted as the trapping centers for photo-induced electrons, and thus promoted the separation of photoinduced electron-hole pairs and charge migration. The enhanced photocatalytic ability of the heterostructure SiO2@Ag@SnO2 compared to the inverse sample SiO2@SnO2@Ag was possibly due to the larger exposed surface area under UV light irradiation, larger contact interfacial area and larger specific surface area of SiO2@Ag@SnO2 than SiO2@SnO2@Ag. Furthermore, the photocatalyst SiO2@Ag@SnO2 displayed benign recyclability in that its photocatalytic activity was still preserved after 5 cycles.