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Controlled Synthesis of Monodisperse SiO2[BOND]TiO2 Microspheres with a Yolk–Shell Structure as Effective Photocatalysts



Monodisperse yolk–shell SiO2–TiO2 microspheres were synthesized using core–shell silica microspheres as templates. In the absence of prior surface modifications, a uniform coating of the TiO2 layer on the core–shell silica was achieved through a sol–gel route. Mesoporous silica shells between the outer TiO2 shell and the SiO2 core were selectively removed by using a weak base, yielding yolk–shell SiO2–TiO2 microspheres (ys-SiO2@TiO2). Using the same templates, we synthesized Pt-encased microspheres (SiO2@Pt-TiO2), in which Pt nanoparticles are embedded between the SiO2 core and the TiO2 shell. Selective etching of the silica shells in SiO2@Pt-TiO2 yields Pt-encased yolk–shell SiO2–TiO2 microspheres (ys-SiO2@equation imageTiO2), which contain void spaces suitable for use as nanoreactors. The ys-SiO2@equation imageTiO2 catalyst shows enhanced hydrogen production from water under UV-light irradiation presumably as a result of multiple reflections within the void spaces and can be reused without losing their activity. Moreover, this core–shell template method is effective for the synthesis of other yolk–shell microspheres with different metal oxides.