The role of pharmaceutical grade titanium dioxide in preparations

The role of pharmaceutical grade titanium dioxide in the preparation is divided into short-wave region 190~280nm, medium-wave region 280~320nm, and long-wave band 320~400nm according to different wavelengths
.

The short-wave zone has the highest energy in ultraviolet light, but is blocked when passing through the ozone layer, so the harm to the human body is generally medium-wave and long-wave ultraviolet
.

Titanium dioxide's strong UV resistance 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 barrier to ultraviolet rays is mainly reflected and scattered, and it is effective
for both the medium and long-wave regions.

The sunscreen mechanism is simple to cover, which is a general physical sunscreen, and the sunscreen ability is weak; With the reduction of particle size, light can pass through the particle surface of titanium dioxide, and the reflection and scattering of ultraviolet rays in the long wave region are not obvious, but the absorption of ultraviolet rays in the medium wave region is significantly enhanced
.

Its sunscreen mechanism is to absorb ultraviolet rays, mainly absorbing ultraviolet rays
in the middle wave zone.

It can be seen that the sunscreen mechanism of titanium dioxide on different wavelengths of ultraviolet rays is different, and the barrier of ultraviolet rays in the long-wave region is mainly scattered, and the barrier to ultraviolet rays in the medium wave region is mainly absorbed
.

Nanoscale titanium dioxide due to its small particle size and large activity, it can reflect, scatter ultraviolet rays, and absorb ultraviolet rays, thus having a stronger ability to block ultraviolet rays
.

The absorption mechanism of titanium dioxide on ultraviolet rays may be: the electronic structure of nano titanium dioxide is composed of a conduction band formed by valence electron bands and empty orbitals, when it is irradiated by ultraviolet rays, the light with greater energy than its band gap (about 3.
2eV) is absorbed, so that the electrons of the valence band are excited to the conduction band, and the result is that the valence electron band lacks electrons and holes occur, forming an electron hole pair
that is easy to move and very active.

Such electron hole pairs, on the one hand, may recombine with each other when various redox reactions occur, releasing energy in the form of heat or fluorescence, on the other hand, they can be dissociated into free holes and free electrons that freely migrate to the lattice surface or other reaction sites in the lattice, and are immediately captured
by the surface group.

Normally, titanium dioxide will activate the surface water to produce surface hydroxyl groups to trap free holes, forming hydroxyl radicals, while free free electrons will soon combine with the absorbed oxygen to produce superoxide radicals, thus killing
the surrounding bacteria and viruses.

It can be seen that ultraviolet radiation, the degree of surface water activation and oxygen absorption rate are the three basic conditions
for the photoactivity of titanium dioxide.

It is precisely because nano titanium dioxide absorbs ultraviolet rays to produce free radicals, which will accelerate the aging of the skin and cause harm
to the skin.

Therefore, when using nano titanium dioxide as a sunscreen, it is necessary to start from weakening or eliminating 3 basic conditions to weaken or completely eliminate its photoactivity, thereby reducing its harmfulness