Views: 0 Author: Site Editor Publish Time: 2021-06-25 Origin: Site
In the process of photocatalytic reaction of large-diameter spiral steel tube, the specific surface area, surface morphology and crystal plane structure of the material have a very important influence on the efficiency of photocatalytic reaction, because the photocatalytic reaction mainly occurs on the contact surface between the reactants and titanium dioxide. The effect of nanoscale titanium dioxide on photocatalytic efficiency is mainly reflected in three aspects.
Quantum size effect and small size effect of large diameter spiral steel tube caused by particle size reduction. With the decrease of particle size, the gap width between conduction band and valence band of TiO2 becomes wider, the absorption wavelength shifts blue, the required excitation wavelength becomes shorter, and the ability of the electrons and holes generated to undergo REDOX reaction becomes stronger. Second, with the decrease of the size of titanium dioxide, the diffusion time of photogenerated electrons and holes from the inside of titanium dioxide to the surface becomes shorter, which effectively reduces the probability of recombination of electrons and holes and improves the photocatalytic efficiency. Third, when the size of titanium dioxide is reduced, the specific surface area doubles.
On the one hand, a larger specific surface area will provide more reaction sites for photocatalytic reaction and improve the reaction efficiency: Larger specific surface area, on the other hand, also can enhance light absorption, improve the efficiency of photocatalytic reaction to play an active role with the development of nanometer composite technology, through the different preparation methods have been able to obtain different morphology and knot 枃 titanium dioxide nanoparticles to improve the efficiency of photocatalysis, such as preparation of different particle size of nanometer ball, nanorods, nanowires, nanotubes, On this basis, by increasing the area of a specific surface and constructing an ordered spatial structure, it plays a positive role in increasing the specific surface area of the material, improving the light absorption efficiency, separating electrons and holes. The following will focus on the sol-gel method, non-aqueous sol-gel method, hydrothermal method, solvothermal synthesis method, template method as the representative, the synthesis method of titanium dioxide nanomaterials 1. Sol-gel process Sol-gel process was originally used to prepare inorganic materials such as ceramics.
The typical sol-gel method is to hydrolyze inorganic metal salts or metallic organic compounds to form colloidal suspension or sol. After a period of reaction, a certain morphology is formed. After drying or heat treatment, the material with specific nanostructure can be formed. The sol-gel method has been widely used in the preparation of inorganic materials because of its good homogeneity and mild reaction conditions. Figure 1-5 shows TEM images of TO2 nanoparticles with different morphologies generated by the hydrolysis of TOR4 in the presence of tetramethylammonium hydroxide by sol-gel method. 27 Non-aqueous sol-gel method refers to the process of metal precursors, such as metal halides, reacting in non-aqueous conditions to form inorganic oxides. Because the reaction speed is relatively slow, it is easier to control the reaction process. With the assistance of surfactants, large-diameter spiral steel tubes with different nanostructures can be synthesized. For example, by controlling the reaction rate of isopropyl titanate and titanium tetrachloride in heptadecane, Trentler et al. were able TO produce anatase phase TO, nanoparticles 3 with different morphologies in the presence of surfactants. Hydrothermal method Hydrothermal method refers to a chemical reaction in a sealed pressure reaction vessel under high temperature and high pressure.
By controlling the temperature of the solution in the high-pressure reaction kettle, the reaction solvent forms a state similar to that of supercritical fluid under high pressure, so as to precipitate and grow crystals. Because the hydrothermal method does not require high equipment, the source of raw materials is relatively simple, and only needs to control the ratio of raw materials, different nanostructures can be formed through heating, so it has received extensive attention. At present, the nanostructures of titanium dioxide synthesized by hydrothermal synthesis mainly include nanoparticles, nanorods, nanowires, nanotubes and porous structures. Figure 1-7 shows TEM images of TO2 nanorods prepared by hydrothermal method. The length of the nanorods can be achieved by controlling different types of surfactants and solvents.