Photocatalysis is defined as "the acceleration of the speed of a photoreaction in the presence of a catalyst". A catalyst neither changes nor is consumed by the chemical reaction.
There are numerous published studies on the use of titanium dioxide as a photocatalyst for the decomposition of organic compounds: as a result of exposure to light, the titanium dioxide produces Reactive Oxygen Species (RSO), which react with the organic substances, producing non-toxic inorganic substances.
The absorption by the titanium dioxide of Ultraviolet radiation (UV radiation) coming from the sun or from an artificial light source (fluorescent lamps) generates pairs of electrons and holes (electron-hole pairs). The whole (positive) of the titanium dioxide breaks up the water molecules into hydrogen ions and / hydroxyl radicals. The electron (negative) reacts with the oxygen molecules to form superoxide ions. This cycle, which continues as long as the photocatalyst is illuminated, is the general mechanism of the photocatalytic reaction of titanium dioxide.
It is exactly the formation of Reactive Oxygen Species that has the bactericidal and virucidal effect: most of the studies in fact lead to the same conclusion: that the hydroxyl radical is the main species involved in bactericidal and virucidal photocatalysis.
The hydroxyl radicals with an extremely short duration must be generated in the vicinity of the membrane so that they are able to oxidise some components. The extremely short life time and the fact that they are produced on a surface make them harmless to people.
The most powerful advanced oxidation systems are based on the generation of hydroxyl radicals, which are extremely powerful oxidising agents. Because of its strong oxidative capacity, photocatalytic oxidation can effectively sanitise, deodorise and purify air, water and various surfaces.
Photocatalysis not only kills the bacteria cells, but decomposes them. It has been verified that titanium dioxide is more effective than any other antibacterial agent, because the photocatalytic reaction occurs even when there are cells covering the surface and the multiplication of bacteria is active. In addition, the endotoxin resulting from the death of the cell is decomposed by photocatalytic action. The titanium dioxide does not deteriorate and shows long term antibacterial and virucidal effects.
In general, sanitation by means of titanium dioxide is 3 times more effective than that obtained with chlorine, and 1.5 times more effective than that obtained with ozone.