Flame CVD Preparation Of Nitrogen-doped Nano-titania And Its Photocatalytic And Electrochemical Properties

hotocatalysis nanomaterials have very broad application prospects in the field of environmental pollution,solar energy and self-cleaning etc, which attracted great interest of researchers to explore their configuration, property and application. Among them with titanium dioxide (TiO₂) as a representative of the photocatalyst become the research hotspot of photocatalysis due to its low cost, strong chemical stability, non-toxic, no secondary pollution etc. However, the band-gap of TiO₂ is 3.2eV and it absorbs very small ultraviolet part accounting for only 5% of solar light, thus the efficiency of TiO₂ utilizing sunlight is very limited. An effective approach to shifting the optical response of TiO₂ from the ultraviolet to the visible spectral range by doping TiO₂ has become the research emphases in recent years.Doping nonmetal atoms causes many researchers attention because of its good visible response. Nitrogen doped TiO₂ has been proved to be a good method for narrowing the band gap energy of TiO₂. In this thesis, the flame chemical vapor deposition (FCVD) method is used to produce TiO₂ nanoparticles using ammonia gas as nitrogen source, TiCl₄ as the precursor of TiO₂, the oxidation of titanium tetrachloride (TiCl₄) in propane/air turbulent flame. FCVD process has advantages of high industrialization, fast reaction rate, low energy consumption, easy mass production and the reagents without any further post treatment. Samples are investigated by XRD, TEM, UV-vis, XPS etc, using dye as target of pollutants, evaluating the photocatalytic activity of self-made photocatalysts under the irradiation of ultraviolet and visible light, also its application in biological sensors. The content can be divided into three parts as follows:(1) Compare the relevant properties of nitrogen doped nanoparticles which were prepared by FCVD method (one step synthesis) and FCVD/high-temperature calcination method (two steps synthesis). The content of rutile phase plays an important role in the photocatalytic activity. It suggested that it has a positive effect on the catalytic when the content of rutile is around 40%; XRD results show that with the increase of temperature, the content of rutile also increases, thus 450C is considered to be the best temperature. The results were characterized by UV-vis absorption spectroscopy and investigated by element analysis, suggesting that N-doped TiO₂ nanoparticles direct prepared by the CVD method have high absorbance and more amount of nitrogen doping under the same flow rate of ammonia.(2) The content of nitrogen doped TiO₂ influences photocatalytic activity of photocatalyst under visible light directly. TiO₂ nanoparticles with different content of nitrogen were prepared by FCVD method when adjusting the flow rate of ammonia, and degradated of Rhodamine B under UV/visble light. These results suggested that a new absorption band for all N doping powders could be observed in the visible range from 400 to 500 nm but the undoped TiO₂. With the increase of N doped into TiO₂, the response of the samples to visible light also increases, the main reason is that doped N atoms narrowed the band gap of TiO₂. The photocatalytic efficiency of nitrogen doped TiO₂ can reach 75.16% for the degradation of Rhodamine B under visible light, while the catalytic efficiency of commercial P-25 has only 22.91%.(3) The biosensor based on the immobilization of horseradish peroxidase(HRP) and titanium dioxide nanoparticles (TiO₂) on glassy carbon electrode was explored. The entrapped HRP in nano- structure was characterized by UV-vis absorption spectroscopy and investigated by cyclic voltammetry. These results suggested that the absorbed HRP retain its bioactivity and realize direct electron transfer due to the improved biocompatibility and conductivity of TiO₂. The biosensor displayed good bioelectrocatalytic ability toward the reduction of H₂O₂, and the linear calibration was obtained in the range from2.0×10^-6 to 1.5×10^-5 mmol L-1 with a detection limit of 2.0×10^-7 mmol L-1 (at the ratio of signal to noise, S/N=3). The apparent Michaelis-Meten constant ( ) was estimated to be 0.0452 mmol L-1.