Hierarchically-structured SiO2-Ag@TiO2 hollow spheres with excellent photocatalytic activity and recyclability.

A new protocol for constructing sandwich-like SiO2-Ag@TiO2 hollow spheres (SAT) is introduced, in which SiO2 acts as an efficient support for the Ag nanoparticles (Ag NPs) immobilization, while TiO2 maintains its hierarchical structure and prevents the aggregation of Ag NPs during the photocatalytic reaction. As a photocatalytic agent, the inner and outer surfaces of TiO2 can be fully occupied by pollutants molecules because of its unique structure, which faster boosts the photo-generated electrons to transfer the substrates, leading to an enhanced photocatalytic performance. Compared with Ag NPs deposited on the surface of SiO2@TiO2 (STA), the as-synthesized SAT exhibits a markedly enhanced visible-light and UV light activity than STA for degrading tetracycline and traditional dyes. The excellent photocatalytic performances are ascribed to the enhanced transport paths of photo-generated electrons, reduced recombination probability of e-/h+ pairs, and decreased threat of oxidation and corrosion. Especially, the SAT still maintains its photocatalytic efficiency after five consecutive runs even though the sample is recovered under visible-light irradiation, far beyond the reusability of STA under the same conditions. Therefore, the outstanding photocatalytic activity and excellent recyclability make SAT more potential to purify aquatic contaminants and to meet the demands of future environmental issues.