Synthesis And Characterization Of Tio₂ -based Nanostructures

This paper focused on the preparation and characterization of perovskite MTiO₃ (M=Ba, Sr, Ca, Mg) nanostructures, porous SrTiO₃ sphere and heteronanostructure of multilayer TiO₂ nanotube@Ag nanoparticles, and explored the electrical properties of MTiO₃, the photocatalytic activity of the porous SrTiO₃ sphere and heteronanostructure of multilayer TiO₂ nanotube@Ag nanoparticles. Transmission electron microscopy(TEM), Scanning electron microscopy(SEM), X-ray diffraction(XRD), UV-visible absorption(UV-vis), Capacitance-voltage(C–V)and Polarization-field(P–E)were systematically studied on the as-obtained nanostructure materials. The results were as follows.Perovskite nanostructures MTiO₃ films were successfully synthesized on Ti foil by a convenient hydrothermal method, including BaTiO₃ nanorings, SrTiO₃ nanocubes, CaTiO₃ micro-rectangulares and MgTiO₃ nanodisks. The effects of reaction temperature, reaction time and alkaline concentration on the phase transition and morphology evolution were studied. The phase change of BaTiO₃ from cubic to tetragonal could be tuned by varying reaction time and temperature. In addition, two types of formation processes were investigated to elucidate the growth mechanisms of MTiO₃ structures. The formation of MTiO₃(M = Ba and Sr)undergoes a"nanowire–tube–ring"growth mechanism with a self-sacrifice of titanate nanowire framework rout, while the formation of CaTiO₃ and MgTiO₃ structures followed an simultaneous epitaxial growth of TiO₂ nanotube on titanate nanowire and self-nucleation of MTiO₃ in the solution (M= Mg and Ca) initially, and then a conversion of the nanowire and nanotube to MgTiO₃/CaTiO₃ nanostructure process. Moreover, the electrical properties of the perovskite MTiO₃ nanostructure including polarization-field hysteresis and capacitance-voltage characteristics were also investigated, the result indicate that the BaTiO₃ shows a good ferroelectric nature, SrTiO₃ and CaTiO₃ have high dielectric constant.Porous SrTiO₃ spheres were successfully synthesized by a convenient hydrothermal method without template agents. The pore size of the as-synthesized SrTiO₃ porous spheres could be tuned by varying reaction time and reaction temperature, and the effect of Ti source on the morphology was also studied, the solid SrTiO₃ sphere could be obtained by employing titanate nanowire as Ti precursor, while the porous SrTiO₃ sphere could be obtained by employing titanate nanotube as Ti precursor. The porous SrTiO₃ spheres exhibited much enhanced photocatalytic activity greatly than that of the solid SrTiO₃ spheres.Firstly, multilayer TiO₂ nanotubes were successfully synthesized by a convenient hydrothermal method, then the multilayer TiO₂ nanotube@Ag nanoparticle heteronanostructures were successfully synthesized by a water-phase precipitation method by depositing Ag nanoparticles on the multilayer TiO₂ nanotube. The size and quantity of the Ag nanoparticles deposited on the nanotube could be tuned by varying reaction time and concentration of Ag+. Multilayer TiO₂ nanotube@Ag nanoparticle heteronanostructures exhibited much enhanced photocatalytic activity greatly than that of titanate nanowire and multilayer TiO₂ nanotube.