| In the various applications in environment remediations, energy storagies, energy transformations, and sensors, titania (TiO2) thin films with one-dimensional nanostructures exhibit unique performances. In this thesis, a facile solution-based technique, which is template-free, was developed to grow vertically aligned TiO2nanowires on arbitarary substrates of stainless steel, glass, silicon wafer, and carbon cloth, at a low temperature and in an open atmosphere.The precursor solution for precipitations of TiO2nanowires was obtained by the interactions of Ti and H2O2solutions with the additives of melamine and nitric acid. A TiO2seed layer was deposited on substrates of glasses (glass rods, glass fibers, FTO and ITO) and metals (stainless steel and nickel foam) by a sol-gel technique. Hydrogen titanate nanowire arrays were then deposited on the substrates by immersing them in the precursor solution. The low-temperature precipitation procedure was controlled via adjusting carefully the reaction parameters of precipitation durations and the seed layer thickness. A subsequent thermal treatment of hydrogen titanate nanowire arrays in air resulted in titania nanowire arrays. Alternatively, titania nanorod arrays were achieved when the hydrogen titanate nanowire arrays were treated with an aqueous HCl solution at80℃. The growth mechanism of the hydrogen titanate nanowire and its phase transition procedure upon the subsequent calcination or HC1treatment was discussed. The morphology, structure, phase composition and photon-induced property of the achieved titania nanostructures were investigated in detail with various techniques of field emission scanning electron microscope (FE-SEM), high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectra (UV-Vis DRS). The photocatalytic activity was evaluated by photodegradation of rhodamine B in water.Follows are the main results obtained:1. Hydrogen titanate nanowire arrays. Hydrogen titanate nanowire arrays were deposited on arbitarary substrates with sol-gel TiO2seed layers by immersing them in the precursor solution prepared by interractions of Ti, H2O2, melamine, and nitric acid at80℃. Under the low temperature of80℃, metallic Ti was oxidized by H2O2and nitric acid, which released hydrated Ti(Ⅳ) ions to the solution. When the concentration of hydrated Ti(IV) ions reached a critical value, hydrogen titanate nanowires were precipiatated on the seed layer. The melamine in the acidic solution decomposed to form cyanuric acid and ammonium ions, which contributed to the formation and stabilization of the layered titanate nanowires. The length of nanowires could be controlled by adjusting the reaction time. Nanowire arrays of3μm in length were obtained by depositing in the precursor solution for48h. The well-aligned nanowire array can also be achieved on glass slides even when the seed layer thickness was further reduced.2. Phase transformation from hydrogen titanate to titania. The calcination of hydrogen titanate at300-550℃achieved well-crystallized TiO2nanowire arrays, which predominantly consisted of anatase, with minor Srilankite. When compared with the arrays calcinated at300-450℃, the nanowires calcinated at550℃exhibited a rough necklace-like appearance, which can be attributed to the further recrystallization and sintering of the anatase crystals. When treated in HC1solution, the morphology changed remarkably and rutile nanorods aligning vertically to the substrate appeared. The low temperature HC1treatment resulted in dissolution of hydrogen titanate nanowire arrays, which then precipitated in the form of aligned rutile nanorods. The band gap of rutile film achieved by the HC1treatment was estimated to be about2.87eV, which is lower than that of bulk rutile (3.0eV). The low temperature HC1treated titania film possessed the best performance in photocatalytic degradations of rhodamine B in water. |
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