Synthesis and characterization of stable hollow Ti-silica microspheres with a mesoporous shell

Titanium-silica hollow spheres with a mesoporous shell have been synthesized using an inverse multiple oil-water-oil (O/W/O) emulsion. The oil phase consists of kerosene and sorbitan monooleate (Span 80, C24H44O6); the aqueous phase is a viscous sol solution, prepared from ethanol, Ti-Si species, and HNO3 solution. The transparent shells are up to several micrometers thick and are interspersed by a random mesopore network with a high specific surface area of 779 m(2)/g. This improves the stability and surface permeability of the hollow spheres. FTIR, Raman, and UV-vis spectra suggest that part of the Ti atoms is present as isolated Ti sites in the silica framework, together with amorphous titania oligomers. Applications of this novel material as catalyst or host-guest material are anticipated.