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The sunscreen mechanism of titanium dioxide

wallpapers Industry 2020-07-21
According to the different wavelengths, ultraviolet rays are divided into short-wave regions 190-280nm, medium-wave regions 280-320nm, and long-wave regions 320-400nm. Ultraviolet rays in the short-wave area have the highest energy, but they are blocked when passing through the ozone layer. Therefore, the ultraviolet rays in the medium-wave and long-wave regions are generally harmful to the human body.
The intense UV resistance of titanium dioxide is due to its high refractive index and high photoactivity. Its anti-ultraviolet ability and its mechanism are related to its particle size: when the particle size is large, the UV blocking is mainly based on reflection and scattering. It is useful for both mid-wave and long-wave ultraviolet. The sun protection mechanism is a simple covering, which is general physical sun protection, and the sun protection ability is weak; as the particle size decreases, the light can pass through the particle surface of titanium dioxide, and the reflection and scattering of ultraviolet rays in the long-wavelength region are not visible, but the centering The absorption of ultraviolet rays in the wave zone is enhanced. Its sun protection mechanism is to absorb ultraviolet rays, mainly in the mid-wave region. It can be seen that the sun-protection device of titanium dioxide for different wavelengths of ultraviolet rays is different. The long-wave ultraviolet rays are mainly blocked by scattering, and the medium-wave ultraviolet rays are mostly stuck by absorption.

Due to its small particle size and high activity, nano-sized titanium dioxide can not only reflect and scatter ultraviolet rays but also absorb ultraviolet rays. It has a stronger blocking ability against ultraviolet rays.

The absorption mechanism of titanium dioxide to ultraviolet rays may be: the nanometer titanium dioxide's electronic structure is composed of a conduction band formed by a valence electron band and an empty orbit. When ultraviolet rays irradiate it, it has higher energy than its bandgap (about 3.2eV). The light is absorbed, and the electrons in the valence band are excited to the conduction band. As a result, the valence band lacks electrons and holes are generated, forming electron-hole pairs that are easy to move and are highly active. On the one hand, such electron-hole pairs can recombine with each other during various redox reactions, releasing heat or generating fluorescence.

On the other hand, they can be dissociated into the lattice and migrate freely to the lattice's surface. Or the free holes and free electrons in other reaction sites are immediately captured by the surface groups. Under normal circumstances, titanium dioxide will activate surface water to generate surface hydroxyl groups to achieve free holes and form hydroxyl radicals. Free electrons will quickly combine with absorbed oxygen to make superoxide radicals, killing surrounding bacteria and viruses. Dead. It can be seen that ultraviolet radiation, surface water activation degree, and oxygen absorption rate are the three necessary conditions for the photoactivity of titanium dioxide. It is precise because nano-titanium dioxide absorbs ultraviolet rays to generate free radicals, which will accelerate the skin's aging and cause harm to the surface. Therefore, when using nano-titanium dioxide as a sunscreen, the three necessary conditions should be reduced or eliminated to reduce or eliminate its photoactivity and reduce its harmfulness.

Trunnano is one of the largest titanium dioxide producers in the world. There are titanium dioxide powders and photocatalyst products in various particle sizes. If necessary, please contact Dr. Leo. Email: brad@ihpa.net.

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