A �silica-protected annealing� method that allows selective conversion of amorphous TiO2 into anatase TiO2 phase is described. A typical synthesis starts with highly uniform TiO2 microspheres with average diameter of 470 nm, which were then coated by silica (SiO2) through the sol-gel method. The resulting core/shell microspheres (TiO2@meso-SiO2) contain mesoporous silica shells with the thickness of about 30 nm. They were annealed in air at temperatures from 773 to 1173 K, which converted selectively to anatase TiO2 phase (anatase TiO2@meso-SiO2). Rutile TiO2 phase, which is typically observed when TiO2 anneals at temperatures over 873 K, was not observed in the X-ray powder diffraction pattern. This strategy is also useful for protecting active core materials against air-oxidation, in which the silica layer serves as a capping layer. The TiO2@meso-SiO2 microsphere was annealed under the ammonia (NH3) atmosphere, which results in the formation nitrogen-doped titania coated by mesoporous silica shells. The resulting sample was thoroughly characterized using a wide range of techniques, including elemental analysis, thermo gravimetric analysis, transmission electron microscope, scanning electron microscope, energy dispersive spectrometry, UV-visible absorption spectroscopy, and X-ray photoelectron spectroscopy. The nitrogen-doped titania exhibits excellant photocatalytic activity under visible light and persistent stability in water. The capping silica layer not only allows chemical species to reach the surface of nitrogen-doped titania but also plays an important role in the protection of active core material. 

Air-stable nitrogen-doped titania by silica-protected annealing

248th National Meeting (2014)

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