| As an effective way to solve energy and environmental problems, the development of photocatalytic technology is of great significance for sustainable human developments. In the current investigation, a novel strategy to synthesize morphology-controlled and metal-ion-doped TiO2 thin films was developed by combining an intermediate thermal treatment and the subsequent sulfuric acid treatment of titanate nanowires. The morphology, structure, phase composition, and photon-induced property of the achieved titania thin films 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), Raman spectra, X-ray photoelectron spectra (XPS), and UV-Vis diffuse reflectance spectra (UV-Vis DRS). The morphology transition mechanism of the titanate nanowire arrays in the sulfuric acid solution was discussed.Follows are the main results obtained:1. Morphology-controlled synthesis of TiO2 thin films. Morphology controlled TiO2 thin films was obtained by calcining titanate nanowires at different temperatures followed by immersing in diluted H2SO4 solution with pH=2.0 at 80℃ for 72 h. With increasing heating temperatures, the resultant TiO2 films changed from nanoflowers to branched nanowires. Once reaching a critical temperature, titanate nanowires decomposed directly to anatase TiO2 during the intermediate calcination, with the nanowire morphology retained unchanged during the final sulfuric acid treatment. The size of nanoflowers and branches increased with decreasing pH values from 2.0 to 1.0. Meanwhile, the critical temperature for the intermediate calcination to retain the nanowire morphology increased from 280℃ to 300℃. Morphology controlled for the TiO2 thin films could be achieved more precisely by adjusting the duration of the intermediate heat treatment. The photocatalytic measurements indicated that, the branched TiO2 nanowires, which were synthesized by an intermediate heat treatment at 260℃ for 1 h and follows by sulfuric acid (pH=2.0) treatment at 80℃ for 72 h, possessed the best performance in photocatalytic degradations of aqueous sulfosalicylic acid.2. Metal-ion doped TiO2 thin films. By adding soluble metal sulfates into the H2SO4 solution, metal-ion doping of TiO2 was realized simultaneously with the morphology transformation of titanate nanowires. Uniformly metal-ion doping was confirmed by XPS and EDS analysis. The conversion of the titanate was significantly accelerated by the additive of metal sulfates in the H2SO4 solution. The major resultant phase for the doped TiO2 was anatase. For the Fe3+ doping, the size of the nanoflowers decreased with the increasing doping concentration and branched nanowires were also achieved by using a relatively high concentration of Fe3+. For the W6+ doping, anatase TiO2 nanoparticles were grown on top of nanowires. The titanate nanowires were completely converted to anatase TiO2 nanoparticles under a high concentration of W6+. The Ni2+ doping didn’t affect the nanowire morphology of the TiO2 films. Remarkable red shifts in the absorption range were observed for all the metal-ion doped TiO2 films. The metal-ion doping in the current investigation achieved slightly improved efficiency for the nanostructured TiO2 films to assist photocatalytic degradations of rhodamine B in water. |
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