Photocatalysis is the process by which chemicals, bacteria, viruses or dust micro particles are broken down by a photocatalyst and light radiation. Many substances decompose naturally and spontaneously by the action of light, photocatalysts are substances that speed up this process.
Photocatalysis is therefore a process of chemical decomposition of substances in the presence of a photocatalyst and light radiation. It is based in principle on photolysis, the natural decomposition of some substances by the action of light, accelerated by the presence of a photocatalyst. If a material with photocatalytic properties is exposed to light from a suitable wavelength, its surface is activated and a characteristic reaction is triggered. The primary free electron-hole pair and the hydroxyl radicals secondary to the contact of the excited photocatalyst molecule and the water vapor decompose the organic and inorganic substances present.
Substances decomposable by photocatalysis include, for example:. nitrogen oxides, sulfur oxides, carbon monoxide, ozone, ammonia, hydrogen sulfide, chlorinated hydrocarbons, dioxins, chlorobenzene, chlorophenol, simple hydrocarbons, aromatic hydrocarbons (benzene, phenol, toluene, ethylbenzene), pesticides, etc. viruses, fungi or micro-dust particles. The final product is usually common and stable compounds. The specific industrial applications of the photocatalysis principle may differ mainly in the type of the catalyst. Titanium dioxide, which is activated by UV radiation, is most often used.
The use of photocatalysis is done in two basic areas:
- self-cleaning - thanks to photocatalysis, the surface of the material is resistant to the development of organic impurities and thus retains its original appearance and colour for a long time
- Cleaning the surrounding media - polluted air or water allows you to suppress some of the adverse effects of human activity, for example air pollution in densely populated areas.
The two areas of use are very closely related - these are actually only two somewhat different consequences of the same reaction. In the case of self-cleaning, however, the emphasis is on decomposition of solids adhering to the surface of the material, while in the case cleaning the surrounding media, the ability to decompose a particular substanceconsidered undesirable near the surface.