| Titanium dioxide is one kind of n-type semiconductors with a wide bandgap, covering the application fields of photocatalysis, gas sensors, photochemical synthesis, electrochromic, soalr cells and lithium-ion battery, etc. However, the problem is also obvious. Single TiO2 usually can not meet actual needs. Therefore, the development of TiO2 composites would be the mainstream of current and future in the research of TiO2. Meanwhile, as a new material, nanomaterials have a nature advantage in the applications used as function materials. It is also a hot issue how to prepare nano-TiO2 with special morphologies and large surface areas.The research of TiO2 composites in this paper mainly involved two fields, photocatalysis and gas sensors. It consists of material selection, preparation, characterization and theoretical analysis of phenomena in the experiments. The main contents are summarized as follows:1. Composite magnetic photocatalysts were prepared by a simple hydrolysis and hydrothermal method. Their structures can be described as (-Fe2O3@SiO2)n@TiO2 and n indicates that there are severalγ-Fe2O3@SiO2 cores distributing in TiO2 matrix. The composite materials exhibit superparamagnetic property and good magnetic response. Under the action of an external magnetic field, they can come together quickly and easily re-dispersed in solution by a slight shake. Their photocatalytic activity is close to the pure TiO2, degradating about 80% of the methylene within 80 min.2. TiO2 nanotube arrays prepared by anodic oxidation were used as substrates and then a layer of Ni was deposited on them by an electrochemical reduction method. Electrochemical curves showed that the TiO2 nanotube arrays have a wide work potential window (-0.7-1.0 V) in 0.1 M NaOH solutions. Under the potential of 0.6 V, the saturation current was only about 0.03μA. The electrochemical performances above make TiO2 nanotube arrays suitable as substrates for electrochemical biosensors. The composite biosensors can reach very high sensitivity (about 200μA mM-1 cm-2) in the detection of glucose with a detection limit of 4μM (S/N=3). In the experiments, as the oxidation potential increases, the linear detection range of glucose gradually widened. This is because the electro-oxidation of glucose is adsorption-controlled under low potentials while diffusion-controlled under high potentials. The latter is sensitivity to concentration while the former not. So, high potential is useful to get wide linear range. In addition, the selectivity of the composite biosensors needs further improvements.3. Chrysanthemum-like three-dimensional hierarchical TiO2 nanostructure was prepared by a simple hydrothermal method. The morphologies of products at different reaction time indicated that forming of the hierarchical structures was a corrosion-redeposition process. Morphologies of products formed by different reactants indicated that Ti powder, NaOH, H2O2 are all necessary. BET surface area of TiO2 hierarchical structures was about 64 m2g-1. Gas sensors fabricated by the hierarchical TiO2 have the greatest sensitivity (-6.4) upon exposure to 100 ppm ethanol vapor at 350℃. Response and recovery time is 12,9s, respectively. As the temperature increases, response and recovery time gradually shortened. Fast response and recovery time is due to the porous internal structure of the sensors, which is conducive to diffusion of gases. The change of sensitivity with temperature is not linear, but first increases and then decreases. There is a maximum value at 350℃. Oxygen is the oxidant of gas sensing reaction and the adsorption of O2 on TiO2 surface determines the sensitivity. The adsorption of O2 on TiO2 surface increases first and then decrease as the temperature increases. So, the sensitivity first increases and then decreased as the temperature increases.4. TiO2 nanowires were prepared by a hydrothermal method and then Pt nanoparticles were deposited on them by a chemical reduction method. Pt nanoparticles can enhance the photocatalytic activity of TiO2 nanowires obviously. This is due to the Schottky barrier forming between TiO2 and Pt naonoparticles, which leads to a fast transport of photogenerated electrons to Pt particles. This would decrease the electron-hole recombination. The modification of Pt for the improvement of photocatalytic activity of TiO2 has an optimum value, not the more the better. The experimental results showed that the photocatalytic activity of sample with Pt/Ti of 1:100 (atom ratio) was better than samples with 1:50 and 1:200. FTIR spectrum indicated that the catalytic activity of Pt could help to degradate organic pollutants completely.5. TiO2 nanocrystals were prepared by a hydrothermal method and used as the carrier of metal ions doping. The size of nanocrystals can be adjusted by changing the reaction time. Iron oleate and copper oleate were used as precursor for doping. The results indicated that Fe3+ and Cu2+ could be doped into TiO2 nanocrystals by the hydrothermal method. The absorption edge of doped TiO2 nanocrystals was extended to the visible region. As the doping level increases, the absorption intensity gradually increases. |
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