Facile synthesis of monodisperse polymer/SiO2/polymer/TiO2 tetra-layer microspheres and the corresponding double-walled hollow SiO2/TiO2 microspheres.

Monodisperse tetra-layer poly(ethyleneglycol dimethacrylate-co-methacrylic acid) (P(EGDMA-co-MAA))/SiO(2)/P(EGDMA-co-MAA)/TiO(2) tetra-layer microspheres were facilely synthesized by the combination of the distillation precipitation polymerization for the preparation of P(EGDMA-co-MAA) layers and the controlled sol-gel hydrolysis of inorganic precursors for the formation of silica (SiO(2)) and titania (TiO(2)) layers. The thickness of the outer titania shell-layer was well-controlled via altering the feed of titanium tetrabutoxide (TBOT) during the sol-gel hydrolysis, while the size of polymeric layers were facilely controlled via a multi-step addition of ethyleneglycol dimethacrylate (EGDMA) crosslinker and methacrylic acid (MAA) monomer during the polymerization. The corresponding double-walled hollow inorganic microspheres containing SiO(2) inner shell and TiO(2) outer shell with various thickness were obtained after the selective removal of P(EGDMA-co-MAA) components via the calcination of the tetra-layer polymer/SiO(2)/polymer/TiO(2) microspheres under 550 degrees C for 4 h in air. The structure and morphology of the resultant microspheres were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), X-ray photoelectron microscopy (XPS), and thermogravimetric analysis (TGA). Further, the photocatalytic properties of the resultant double-walled hollow SiO(2)/TiO(2) microspheres were studied by photocatalytic degradation of methyl orange (MO) with ultraviolet (UV) irradiation of a 500 W high-pressure mercury lamp.