Multifunctional Roles of TiO2 Nanoparticles for Architecture of Complex Core−Shells and Hollow Spheres of SiO2−TiO2−Polyaniline System

Nanoparticles are often used as seeds to grow one-dimensional nanomaterials or as core materials to prepare core−shell nanostructures. On the other hand, the presynthesized inorganic nanoparticles can also be used as starting building blocks to prepare inorganic−polymer nanocomposites. In this work, we explore the roles of metal-oxide nanoparticles (anatase TiO 2 ) in the area of constructional synthesis of highly complex core−shell and hollow sphere nanostructures comprising SiO 2, TiO 2, and polyaniline (PAN). In particular, multifunctional roles of oleate-surfactant-protected TiO 2 nanoparticles have been revealed in this study: they provide starting sites for polymerization of aniline on the surface of SiO 2 mesospheres; they land on the inner surface of polyaniline shell to form a secondary material phase; they work as initial crystalline seeds for homogeneous growth of interior TiO 2 shell; and they serve as primary nanobuilding blocks to form exterior TiO 2 shell on the polyaniline via self-assembly. With the assistance of the TiO 2 nanoparticles, a total of six complex core−shell and hollow sphere nanocomposites (SiO 2 /TiO 2, SiO 2 /TiO 2 /PAN, SiO 2 /TiO 2 /PAN/TiO 2, TiO 2 /PAN, TiO 2 /PAN/TiO 2, and TiO 2 /TiO 2 ) have been made in this work through controlled self-assembly, templating growth, polymerization, and homogeneous seeded growth. Applicability of these nanostructures in photocatalytic applications has also been demonstrated by our preliminary investigations. The easy separation of used catalysts after reaction seems to be advantageous because of relatively large external diameters of the lightweight nanocomposites.