Basics of UV photo-oxidation

Photo-oxidation is an oxidation reaction triggered by light. UV light consists of electromagnetic waves, the energy content of which depends on the wavelength. The shorter the wavelength, the more energetic the radiation is.

A typical UV radiation source emits different wavelengths. If a pollutant molecule is to be cleaved directly by a radical chain reaction by means of UV radiation, then the binding energy of this molecule must ideally coincide with the energy of the photons emitted by the emitter. This reaction process is called photolysis.

These dissociation energies are known for almost all compounds and functional groups and are determined by the chemical bond types involved in the molecule.

In addition to photolysis, other effects can be used for pollutant degradation.

If radiation (H) is emitted by the UV emitter in the range of 185nm, these photons can dissociate oxygen. The atomic oxygen formed can form ozone (O₃) by reaction with other oxygen molecules from the ambient air or oxidize a pollutant molecule (R-R) directly and thus enhance the photolysis process. Existing water (H₂O) is also split by photons into hydroxyl radicals (OH), which also participate in the oxidation reaction with the pollutants.

The reactions triggered by this then proceed to complete oxidation if the irradiation time is long enough.