Photocatalysis has been shown by numerous researches to kill a wide range of organisms, including Gram-negative and Gram-positive bacteria, including endospores, fungi, algae, protozoa, and viruses, as well as to inactivate prions and destroy microbial toxins.
During the photocatalytic process promoted by UV radiation, oxygen radicals and monoatomic and triatomic oxygen molecules are developed, which become the promoters of antibacterial action, leading initially to the leakage of cellular contents, then to cell lysis and eventually by the complete mineralization of the organism.
Photocatalysis, to put it better then, not only kills bacterial cells but also decomposes them because the killing mechanism acts by degrading the cell wall and cytoplasmic membrane.
Killing is most efficient when there is close contact between organisms, and the catalyst used for photocatalysis is titanium dioxide.
Titanium dioxide performs better 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, activating on the surface and bypassing the biofilm created by the bacteria. It proves effective where traditional chemical sanitizers perform less well. In addition, the endotoxin resulting from cell death is decomposed due to the photocatalytic action.
Among catalysts, therefore, titanium dioxide is particularly suitable because it does not degrade and shows a long-term antibacterial and virucidal effect. In general, disinfection by titanium dioxide is 3 times more effective than disinfection by chlorine, and 1.5 times of ozone.
The ability to sanitize air by reducing bacterial load has led to the development of several commercial products.
Major applications include those related to surface sanitization, which are applied in spray or liquid form, and filters for air purification.
Its use in air filtration, which has grown significantly with the pandemic, is particularly effective and because it allows multiple results to be achieved with a single solution:
- Reduction of bacterial load (viruses, bacteria, molds, pollens etc)
- Substantial pollution abatement, as effective against volatile organic compounds (a category into which most pollutants in the air fall);
- Longer filter life, which is self-cleaning as a result of photocatalysis.
For further study, see Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity (National Library of Medicine) and Photocatalytic oxidation of TiO2.
