Controlled Synthesis of Monodisperse SiO2-TiO2 Microspheres with a Yolk-Shell Structure as Effective Photocatalysts

Monodisperse yolkshell SiO2TiO2 microspheres were synthesized using coreshell silica microspheres as templates. In the absence of prior surface modifications, a uniform coating of the TiO2 layer on the coreshell silica was achieved through a solgel route. Mesoporous silica shells between the outer TiO2 shell and the SiO2 core were selectively removed by using a weak base, yielding yolkshell SiO2TiO2 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 yolkshell SiO2TiO2 microspheres (ys-SiO2@${ \char60 {\rm{Pt}} \char62 }$TiO2), which contain void spaces suitable for use as nanoreactors. The ys-SiO2@${ \char60 {\rm{Pt}} \char62 }$TiO2 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 coreshell template method is effective for the synthesis of other yolkshell microspheres with different metal oxides.