| In this thesis, titania nanowire arrays and hollow polyhedra were fabricated sucessfuly through direct oxidation of metallic titanium by hydrogen peroxide solutions. The related growing procedure was disclosed and the photocatalytic activity of the resultant nanostructured titania was evaluated.Titania nanowire arrays were deposited on Ti substrates by the interactions of Ti and H2O2 solutions with the additives of melamine and nitric acid, through controlling the low-temperature growth via adjusting carefully the reaction parameters. Titania polyhedra were fabricated by the reactions between metallic Ti and and H2O2 solutions containing NaF and nitric acid, followed by calcination and water-washing. Hollow titania polyhedra were achieved directly by oxidation of Ti with H2O2 solutions containing melamine, NaF and nitric acid, followed by a subsequent calcination. The structure, morphology and photon-induced property of the achieved titania were investigated in detail with various techniques of field emission scanning electron microscope (FE-SEM), high-resolution transmission electron microscope (HR-TEM), X-ray diffaraction (XRD), UV-Vis diffuse reflectance spectra (UV-Vis DRS), Raman spectra, X-ray photoelectron spectra (XPS), differential thermogravimetric (DTG) and N2 adsorption. The photocatalytic activity of the achieved titania was evaluated by photodegradation of rhodamine B in water.Follows are the main results obtained:1. Titania nanowire arrays. An approach to fabricate titania nanowire arrays on Ti substrates was developed succesffuly. The method is simple and can be scaled-up easily, with good reproducibility and involves no templates or catalysts. Under the low temperature of 80℃, metallic Ti was oxidized by H2O2 to form a porous amorphous titania film on the surface. Hydrated Ti(Ⅳ) ions were released to the solution at the same time. Once the Ti(Ⅳ) ions in the solution reached a critical concentration, titania precipitated from the solution, predominantly through heterogeneous nucleation on the titania film formed previously on the Ti substrates. On the other hand, the melamine in the acidic solution decomposed to from cyanuric acid, which was adsorbed on the precipitated titania nanocrystals through bridging by-OH groups. Because of the various densities of-OH groups on different planes of the titania nanocrystals, the selective absorption of cyanuric acid is possible. As a result, the precipitated titania nanocrystals, although poorly-crystallized, self-assembled to form nanowires with an average diameter of 25 nm and an aspect ration of ca.40, through the "oriented attachment" mechanism. The crystallinity of the nanowires was improved significantly by a subsequent calcination in air at 450℃The nanowire arrays possessed an activity to assist photodegradation of rhodamine B in water higher than that of the P25 counterpart.2. Titania (hollow) polyhedra. With the additives of certain amounts of NaF and nitric acid in the H2O2 solution, polyhedra mainly consisted of Na3TiF6 were achieved on the Ti surface while maintaining at 80℃for 10 min to 96 h. The initial reaction for 30 min resulted in cubes, which evolved to octahedron with the prolonged reaction duration. Most of Na3TiF6 decomposed to NaF and TiO2, which inititated at 209℃, during the subsequent calcination. The later was titania thin plates with a thickness of ca.20 nm that interlocked with each other to form a polyhedron. After a further water-washing to remove NaF and the remained Na3TiF6, phase pure TiO2 can be achieved. The titania polyhedra, which exhibited an indirect band gap of 3.11 eV, possessed a high specific surface area of 196.3 m2/g. The remarkable photocatalytic activity was confirmed by photodegradation of rhodamine B in water. Hollow titania polyhedra were achieved directly by oxidation of Ti at 80℃for 72 h, with H2O2 solutions containing melamine, NaF and nitric acid, followed by a subsequent calcination.
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