Facile synthesis of hollow anatase titania prepared by charged polymeric nanosphere template

Abstract

Two main synthetic routes have been employed to produce inorganic-coated polymer nanoparticles. The first approach is to precipitate to form a thin inorganic shell of hydrolyzed metal oxide precursors onto the polymeric template. The second approach is a layer-by-layer(LBL) deposition technique to form alternate layers of oppositely charged inorganic and organic species on the core materials. Various inorganic materials, including silica, titania, zirconia, clay and iron oxide, are used as a coating material. Among them, titania has attracted a great deal of recent attention, due to their application in catalysis, photovoltaics and photoelectronics. Titaniacoated particles are particularly useful as catalysts, white pigments and electrophoretic particles. These inorganic-coated polymer nanoparticles have been also used to prepare inorganic hollow nanoparticles, which are prepared by removal of the polymer core either by etching in solution or by calcination at high temperature. Hollow titania spheres have been prepared by the LBL manipulation of preformed inorganic nanoparticles onto polymeric colloidal. Recently, templated syntheses of hollow titania spheres was reported based on sulfonated polystyrene particles, which were prepared by seed emulsion polymerization, followed by treatment in concentrated sulfuric acid. We also reported the preparation of hollow titania nanospheres, based on the cationically-charged copolymer core, comprised of styrene, butyl acrylate and cationic [2-(methacryloxy) ethyl]trimethyl ammonium chloride (MOTAC), was prepared by soap-free emulsion polymerization. Cationically-charged polystyrene nanospheres were prepared by using an ionogenic initiator of 2,2’-azo bis(2methylpropionamidine)dihydrochloride (AIBA). The formation of the organic-inorganic hybrids was achieved by adsorption of titania through the hydrolysis of titania precursor. In the present study, to achieve the rapid and sufficient adsorption of inorganic precursor species onto the surfaces of polymer nanospheres, we synthesize positively-charged, monodisperse polymeric cores which are easily associated with negatively-charged inorganic titania precursors by charge density matching. To enhance the charge density of the polymer nanospheres, the polymer cores were prepared by surfactant-free emulsion copolymerization of methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA) and methacryloxyethyltrimethyl ammonium chloride (MOTAC) in the presence of azo bis(isobutylamidine) hydrochloride (AIBA) as an initiator. Unlike our previous study, the component monomers used in the present work are all acrylic, relatively-large amount of the cationic MOTAC monomer can be incorporated within the polymer backbone, which results in the increase in the charge density onto the surface of the polymer core in an attempt to achieve the sufficient adsorption of negatively-charged titania and obtain hollow titania nanospheres with adequate shell thickness.