More on the Science of UV/PCO DisinfectionUltraviolet (UV) light has been studied for disinfection of air and surfaces before 1950. In the 1980's two prominent researchers published a comprehensive report on the ability of UV to disinfect upper air currents, leading to valuable data for designing UV systems.
Commercial UV lamps emit light in the range of 185 nm and 400nm. The well known "germicidal" range of microorganisms is between 240-280 nm. With the sufficient UV energy emitted by the lamp, the photons penetrate the microorganisms and split their DNA to prevent their replication. This is considered "inactivation". However, with additional energy in the 185 to 400 nm range, they are destroyed since other life-sustaining portions of their cells absorb the light of the varying UV wavelengths.
Photocatalytic Oxidation (PCO) disinfection involves a semiconductor surface impregnated onto a filter type substrate. UV light (referred to as "hv" in the following chemical reactions) is located adjacent to the semiconductor material. UV light of 185-400 nm is sufficient to overcome the Eg of common semiconductors studied and promote transfer of electrons (e-CB) and holes (h+VB) as follows.
(Equation 1)
Oxygen of sufficient concentration in the fluid system scavenges the electrons (e-) to prevent electron-hole recombination and produces superoxide ions, while holes (h+) react with water molecules to form hydroxyl radicals (OH•).
(Equation 2)
(Equation 3)
Hydrogen peroxide is also formed and immediately converted to hydroxyl radicals (OH•) through the following chain of reactions.
(Equation 4)
(Equation 5)
(Equation 6)
Hydroxyl radicals are among the strongest oxidizing species, even much stronger than chlorine, ozone, and peroxide. They detach double carbon bonds to break down the constituents into single carbon bond intermediates, then into carbon dioxide and water. They act as very powerful disinfecting agents by oxidizing the cells of microorganisms, causing rupture and leakage of vital composition.