In addition to the traditional disinfecting agents such as metal ions and biocides, photocatalytic surfaces are being developed and tested for usage in the context of self-disinfecting materials. Photocatalytic materials work by transferring the energy of light, such as sunlight or artificial light, to the surrounding oxygen. Reactive oxygen species (ROS) are generated and kill more than 99% of the microbes on the surface. Currently, there are several photocatalytic additives in use, such as titanium dioxide (TiO2) or zinc oxide (ZnO). Other bio-photocatalysts, such as specific pigments, are being explored and are on their way to market entry as an environmentally friendly, non-metallic, non-chemical and non-toxic disinfection alternative.
One of the big advantages of photocatalytic coatings is the broad range of possible applications and – in comparison to the metal based systems – the good activity under dry conditions. They can be found in all kinds of paints, plastics, ceramics, electronic components along with food and cosmetics. The disinfecting effect of photocatalytic surfaces against well-known bacteria such as the intestinal E.coli and viruses such as influenza have already been scientifically proven. Photocatalysis reacts unspecifically. These are positive news regarding the effectiveness against a broad range of microorganisms and viruses but might become a disadvantage when considering potential reactions with the binding material in the coating or the surface material. That is why detailed testing has to be conducted for every single field of application before commercialization, as toxic intermediates can be formed by reactions with additional chemicals present in the environment such as the air, the surface or binding material. The higher reactivity of the oxygen species can also affect plastic surfaces in the long term. Finally, as photocatalytic additives need sunlight or artificial light to be effective against microorganisms, the human body is also exposed to the UV light. UVA rays enter the tissue of skin and eyes and can cause high damage.