There are two main crystalline habits of titanium dioxide: anatase and rutile. The physical properties of titanium dioxide: fine particles; the appearance of products is white loose powder. It has anti-ultraviolet, antibacterial, self-cleaning and anti-aging properties. Titanium dioxide products can be used in cosmetics, functional fibers, plastics, ink, coatings, oil paint, fine ceramics and other fields.
Here is a detailed introduction to the functions of titanium dioxide.
Titanium dioxide can absorb, reflect and scatter ultraviolet rays, and visible light can pass through it. Titanium dioxide is a physical shielding ultraviolet protective agent with excellent performance and great development prospect.
The anti-ultraviolet mechanism of titanium dioxide is as follows:
The strong ultraviolet resistance of titanium dioxide benefits from its high refractive index and high photoactivity. The ultraviolet resistance and its mechanism are related to the particle size: When the particle size is large, the main barriers to ultraviolet rays are reflection and scattering, and they are effective for ultraviolet rays in medium and long wavelength regions. The mechanism of sunscreen is simple covering, which belongs to the general physical sunscreen, and the sunscreen ability is weak; with the decrease of particle size, the light can pass through the particle surface of nano titanium dioxide, and the reflection and scattering of ultraviolet rays in long wavelength region is not obvious, but the absorption of ultraviolet rays in medium wavelength region is obviously enhanced. The sunscreen mechanism of TiO2 is to absorb ultraviolet rays, and it mainly absorbs ultraviolet rays in the medium wavelength region.
It can be seen that different TiO2 absorption spectra lead to different sunscreen mechanisms. Scattering is the main barrier to ultraviolet rays in long wavelength region, while absorption is the main sunscreen mechanism for ultraviolet rays in medium wavelength region. Compared with other organic sunscreen agents, titanium dioxide has the characteristics of non-toxicity, stable performance and good effect.
The TiO2 band gap refers to that the electronic structure of titanium dioxide is characterized by a TiO2-filled valence band and an empty conduction band. In the system of water and air, if nano TiO2 is exposed to sunlight, especially ultraviolet rays, the electrons can be excited from the valence band to the conduction band when the electron energy reaches or exceeds the band gap energy. At the same time, corresponding holes are generated in the valence band, that is, electrons and electron-hole pairs are formed.
Under the action of electric field, electrons separate from holes and migrate to different positions on the surface of particles for a series of reactions. The electrons absorb the oxygen dissolved on the surface of TiO2 and captured electrons to form O2. The superoxide anion radicals generated react with most organic compounds (oxidation). At the same time, the superoxide anion radicals can react with organic substances in bacteria to produce CO2 and H2O; while the holes will oxidize the OH and H2O adsorbed on the surface of TiO2 into OH. OH has strong oxidation ability, which enable OH to attack unsaturated bonds of organic substances or extract H atoms to produce new free radicals, trigger chain reaction and eventually cause bacterial decomposition.
Titanium dioxide has the properties of semiconductors. TiO2 electrical conductivity increases rapidly with the increase of temperature, and it is also very sensitive to hypoxia. The dielectric constant and semiconductor properties of rutile titanium dioxide are very important to electronic industry, because they can be used to produce ceramic capacitors and other electronic components.