Preparation, Modification And Their Application Research On Photoelectrochemical Performance Of Titania Nanofilm

Titanium dioxide as a new type of semiconductor catalytic function material has excellent UV-shielding effect, good chemical stability, non-toxic, high oxidation and good photoelectrochemical?PEC? properties, which has been widely applied in environment protection, sensitization solar battery and hydrogen sensor, water splitting, dielectric materials,and other fields. With the constant innovation of nanomaterials preparation technology, all kinds of low dimensional TiO₂ materials, such as nanoparticles, nanowires, nanotubes and nanorods have been synthesized. TiO₂ nanoparticles is easy to reunite, difficult to recycle.Highly ordered TiO₂ nanoarray prepared into thin film, not only can make up for the inadequacy of nanoparticles, but also can be used as photoelectrochemical electrodes for sensing detection.In this thesis, different morphologies of TiO₂ nano-film composed of nanoparticles,nanotubes and nanorods array were synthesised. By X-ray diffraction?XRD?, field emission scanning electron microscopy?FESEM? and transmission electron microscopy?TEM? test techniques, the effects of different reaction conditions on the morphology, crystal structure and photocatalytic, PEC performances were studied. In order to broaden visible light response range, TiO₂ nano-film were modified with Ag quantum dots, narrow band semiconductor CdS,alkali metal ions and graphene. Their PEC properties and applications in sensing field were also studied. Main contents as follows:?1? TiO₂ nanoparticles, three-dimensional network and TiO₂ nanorods array were prepared by alkali treatment hydrothermal method and hydrogen peroxide oxidation method.The photoconversion efficiency of TiO₂ nanorods array film can reach to 2.69% and applied to chemical oxygen demand?COD? determination. Under the optimizing conditions, the sensorcan respond linearly to the COD of glucose solution in the range of 0.5 to 200 mg/L, the lowest limit of detection was 0.15 mg/L and the sensitivity was 0.9987×10-4A/?mg/L?.?2? TiO₂ nanorods array were modified with Ag quantum dots and CdS. The photoconversion efficiency of Ag/TiO₂ nanorods array film with Ag quantum dots size of about 5 to 15 nm can reach to 8.55%. The experimental results showed that the sensor exhibited linear response for H2O2 in the range of 2.5mM to 22.5mM under the optimized testing condition with detection limit 1.2mM. CdS/TiO₂ nanorods array had good PEC property and its photoconversion efficiency can reach to 9.5%.?3? After TiO₂ nanorods array combined with narrow band gap semiconductor CdS and grapheme?G?, its PEC properties were discussed. Graphene with excellent conductivity increased photoelectronic transmission speed and AC impedance dropped to about 50?,achieving great PEC performance. However, CdS/G/TiO₂ showed the best PEC property only under high potential at 0.85 V.?4? The effect of alkali metal ions and K⁺/Ag doped TiO₂ nanorods array on PEC properties was studied. K⁺, Na⁺were successfully doped into TiO₂ crystal lattice through impregnation method. The interface charge transfer resistance of K⁺/TiO₂ was smaller than Na⁺/TiO₂ electrode. Besides, the PEC performance of co-doped with K⁺and Ag was worse than K⁺/TiO₂. Through analysis of Mott-Schottky curve, the inversion layer would appear under negative voltage and its band structure transformed from n-type to p-type and would revert to the n-type when potential of solution was higher than semiconductorunder.?5? HF thermal oxidation method was used to prepare TiO₂ nanosheets of mixed crystal structure. The impact of HF concentration and temperature on the morphology and PEC property were studied. The result showed that only when HF concentration was 0.4wt%,mixed crystal structure TiO₂ nanosheets could be synthesized. When the temperature reached700?, the maximum light absorption range was extended to 420 nm, with photoconversion efficiency of 0.35% and photocurrent density of 0.1mA/cm2.