| Nano-titanium dioxide(nano-Ti O2) is one of the most important photocatalysts, which has been widely used in environmental treatment, water splitting into hydrogen, solar cells, gas sensors, and so on. Recently, the research of constructing the special architecture and morphology of nano-Ti O2 has been increasing steadily. Especially, in order to meet the need of separation and recycling in the practical environmental treatment, the study on immobilized Ti O2 nanocomposites(monolithic catalyst) has been more and more attractive, and attracted a great deal of attention from researchers at home and abroad. In the thesis, the immobilized one-dimensional Ti O2 nanomaterials, such as, Ti O2 nanobelts(NBs), Ti O2 nanotubes(NTs) and Ti O2 nanorods(NRs), have been synthesized using Ti sheet as titanium source and substrate by hydrothermal synthesis and anodic oxidation method. Nanocomposite catalysts with visible-light performance have been prepared via noble metal deposition, semiconductor compositing and Ti3+ doping. The structure and morphology of nanocomposite were characterized by FE-SEM, XRD, TEM, UV-Vis/DRS, respectively. The photoelectrochemical properties and photocatalytic activity were detailedly studied. Main contents are as follows:(1) The immobilized Ti O2 NBs grown on Ti metal sheet surface were synthesized in alkaline media by improved thermal method, and then Ag I/Ti O2 NBs nanocomposite photocatalyst were prepared by impregnation precipitation method. The size of Ti O2 NBs reached to between several tens to one hundred nanometers in width and extended to tens of microns in length. Non-oriented and crisscrossed nanobelts with high porosity formed the curled network structure. The loadings and dispersion of Ag I nanoparticles(NPs) on the surface of Ti O2 could be controlled by impregnation times. Under the optimum impregnation of three times, Ag I NPs with a size of 5~8 nm in diameter were supported on Ti O2 NBs uniformly. Ag I/Ti O2 composite catalyst not only maintained the light absorption in the ultraviolet region, but also broadened the absorption edge to visible region(approximately 450 nm). Under visible light irradiation, the photocurrent density of Ag I/Ti O2 composite photocatalyst was 6 times that of pure Ti O2 NBs, and the photo-degradation efficiency for AO-II was up to 86% for 100 minutes. After repeated use four times, the photo-degradation efficiency remained 70%, suggesting that composite catalyst has a good photocatalytic activity and reusability under visible light irradiation. The results of photocatalytic mechanism showed that the main active species is ?O2-, the energy band between Ag I and Ti O2 is matching. The formed heterostructure makes the photogenerated electrons-hole pairs to separate and transfer effectively, resulting in the enhanced visible-light photoactivity, and restrains the photo-decomposition of Ag I, resulting in the improved stability.(2) The immobilized anatase Ti O2 NTs were prepared via anodic oxidation under 25 V DC voltage for 2h, using Ti sheet as titanium source and substrate, and glycerol containing F- as electrolyte. And then Ag/Ti O2 NTs plasma composite catalyst was prepared by lowtemperature polyol-assisted reduction method. The prepared Ti O2 NTs were highly ordered with 100 nm of length and around 10 nm of wall thickness. Ag NPs with average size of around 8nm were uniformly dispersed on the outer and inner surface of the Ti O2 NTs. The localized plasmon resonance peak of Ag NPs appeared at a wavelength of 410 nm, resulting in that the photocurrent density of Ag/Ti O2 NTs composite catalyst was 15 times higher than that of pure Ti O2 NTs. The result of EIS proved that the electron mobility on Ag/Ti O2 NTs surface significantly was enhanced, and the separation and transfer of photogenerated electron-hole pairs were promoted efficiently. Under visible light irradiation, the photodegradation efficiency for AO-II was up to 40% for 2 h, which was 6.7 times that of pure Ti O2 NTs. Under 0.2 V bias, the photocatalytic efficiency increased to 60%.(3) Using the immobilized Ti O2 NTs prepared via anodic oxidation as reactant and substrate, Bi2Ti2O7/Ti O2 nanocomposite catalysts were successfully prepared by hydrothermal method without any template. The electron microscopy analysis showed that the loaded Bi2Ti2O7 with octahedral structure and average particle size of about 200 nm, partially embedded into the Ti O2 NTs. The loadings of Bi2Ti2O7 on the surface of Ti O2 could be controlled by the concentration of precursor. The crystal phase and chemical valence state of Bi2Ti2O7/Ti O2 photocatalyst were confirmed by XRD and XPS. The spectra analysis showed that Bi2Ti2O7/Ti O2 catalyst had a enhanced the optical absorption in the visible light spectrum and an effective separation of photoinduced electron-hole pairs. Under visible light irradiation, the photocurrent density of BTO/Ti O2-2 composite reached to 9.2 μA/cm2, which was 6.5 times that of pure Ti O2NTs; the photo-degradation efficiency for AO-II reached 60% for 5h. After repeated use four times, the photo-degradation efficiency remained 52%, suggesting that composite catalyst has a good photocatalytic activity and reusability under visible light irradiation.(4) Under optimum reaction conditions of HCl concentration of 0.5M, reaction temperature of 220 oC and reaction time of 12 h, the immobilized Ti3+ doped rutile Ti O2 NRs were prepared by one-step hydrothermal method on the Ti sheet. The prepared sample was consisted of vertically aligned Ti O2 NRs with pyramid structure and width ranging from 50 to 250 nm and length of ca. 600 nm. The prepared catalyst was thermally treated in different atmospheres(Ar, Air, H2). The results showed that the catalyst treated in H2 atmospheres had highest photocurrent density due to the more Ti3+ produced by H2. The catalyst treated in Ar atmospheres had higher photocurrent density than that in air atmospheres. The reason for this difference might be the sample prepared by hydrothermal method contained Ti3+ species, which was strengthened by Ar thermal treatment, and oxidized into Ti4+ by air thermal treatment. Finally, the N2H4 reduction method was designed to further improve the photoelectrochemical properties of Ti3+/Ti O2 NRs. |
PDF Full Text Request