Preparation, Characterization And Visible Light-activated Photocatalytic Properties Of A Series Of Titanium Dioxide-based Composited Photocatalysts

In recent years, photocatalysis technology is developing rapidly. Organic or inorganic contaminants can be degraded into harmless materials in the presence of photocatalysts using solar energy with mild reaction conditions and simple equipment. As a commonly used photocatalyst, TiO₂ is widely employed in the degradation of organic contaminants, disinfection, sterilization, self-cleaning and other fields due to its high catalytic activity, good chemical stability, non-toxicity, cheapness and abundance, etc. However, T1O₂ is an n-type semiconductor with a wide band gap (3.2 eV for anatase and 3.0 eV for rutile), so it can be only excited by ultraviolet light under solar irradiation, which greatly limits the TiO₂ photocatalytic technology to practical applications. In order to extend the optical response of TiO₂ to visible light region, various approaches were conducted to modify TiO₂, including noble metal deposition, semiconductor compositing, ion doping, photosensitization and surface reduction treatment. Researchers have been developed visible-light responsive photocatalysts, using a variety of modification techniques to make titanium dioxide be visible-light activated, but there is rare photocatalyst that can completely break down pollutants at present, and thus development of visible light responsive photocatalyst has very important practical significance.In this thesis, a series of TiO₂-based nanocomposite photocatalysts were prepared, and these photocatalysts were expected to show an enhancement in photo-degradation efficiency under visible light illumination.1. Anatase TiO₂ nanotubes were prepared by hydrothermal synthesis method and hydrogen peroxide treatment. AgCl nanoparticles were then loaded onto the TiO₂ nanotube by a precipitation reaction, and some of the AgCl particles were reduced to Ag particles under halogen tungsten lamp irradiation. This gave a visible light SPR photocatalyst of Ag@AgCl/TiO₂ nanotubes that exhibited high photocatalytic activity, which was due to its large adsorption capacity, wide visible light response due to the SPR effect, fast separation of photogenerated electron-hole pairs, and strong oxidizing ability of Cl0 generated by combining Cl ions with photoexcited holes. Methyl blue dye was thoroughly decolorized within one hour in the presence of this photocatalyst under visible light irradiation. In addition, the photocatalyst was stable after recycling the photocatalytic reaction five times.2. TiO₂ sol was prepared by sol-gel method, and graphene oxide was prepared by Hummer method firstly. Then TiO₂ sol was reacted with graphene oxide by hydrothermal synthesis, forming TiO₂Grephene nanocomposite. Ag nanoparticles were then loaded on the TiO₂G nanocomposite, getting a visible light photocatalyst of Ag/TiO₂G. Photocatalytic experiments demonstrated that the methylene blue can be strongly adsorped the photocatalyst of Ag/TiO₂/G and be decolorized under the visible light irradiation. The enhanced photocatalytic activity was associated with the big specific surface area and stronger electron mobility of graphene, as well as the broad absorption wavelength due to the surface plasmon resonance effect of Ag nanoparticles.3. Anatase TiO₂ nanotubes were obtained by hydrothermal synthesis method and hydrogen peroxide treatment. Semiconductor PbS quantum dots were then assembled on TiO₂ nanotubes with thioglycolic acid, obtaining PbS quantum dot-sensitized TiO₂ nanotubes photocatalysts. The effects of the concentration of thioglycolic acid and the stirring time on the photocatalytic efficiency were explored. Experimental results showed that when the concentration of thioglycolic acid was 0.6 mol/L and stirred 5 minutes, the photocatalsts have better photocatalytic activity.