In these times of COVID-19, masks and disinfectant gel have increased awareness about safety and hygiene measures to avoid infections. It is in this scenario that incredible improvements appear in the sector and known technologies are reviewed and take on a new role, reaching new heights. One of the most innovative disinfection systems is the photocatalysis process, which in recent years has seemed to be efficient in removing organic components, from bacteria and fungi, to viruses, prions or even harmful particles or contaminating molecules. Photocatalytic disinfectants not only act when applied, but can continue to react for up to several months later.
Photocatalysis is the process of activation of mineral compounds by UV light from the sun (although they can also be activated by the light energy provided by low intensity artificial light). This quality of Titanium nanoparticles was discovered during the second half of the last century. Since then its mechanism and its applications have been studied. When these compounds from the group of semiconductor metals receive photons from a light source, they take energy in their valence shell. The energy excites an electron (e) - and will create a charged electron hole (h +). This change in its surface allows its interaction at a chemical level with water or oxygen molecules. The e- will reduce molecular oxygen creating superoxide anions. While h + will oxidize water molecules, dissociating them into their hydroxyl (OH), superoxide and hydrogen peroxide radicals. These reactive oxygen species (ROS) cause the inactivation and oxidation of infectious agents by breaking down matter. Turning out to be a powerful disinfectant that interacts with bacterial cell walls and virus coatings, altering their composition and undoing them.
To generate this electric potential capable of transforming water or molecular oxygen into reactive species, semiconductor metals are used. Among the most used in this type of technology we find Cadmium, Zinc, but the one that is giving the best results is undoubtedly Titanium, in the form of titanium dioxide (TiO2). In turn, the presence of other metals such as copper, silver or gold, zinc oxides or cadmium sulphides mixed with titanium oxides seem to improve photocatalysis. In fact, since the beginning of the pandemic, copper has been revalued as a material for hospitals because it has biocidal properties.
Studies on the biocidal capacity two months after their application of these compounds show that they are 100% effective against fungi and a wide variety of GRAM negative and GRAM positive bacteria (E. coli, Salmonella spp, Pseudomonas, Enterobacteria). In adenovirus type 5 (the most resistant because it lacks an envelope) it has been proven that it maintains an efficiency close to 85% after two months. A long list of viruses from different taxonomic groups (both DNA and RNA single or double stranded) have been inactivated by titanium oxide photocatalysis processes. For example: herpes group viruses, rotavirus A, poliovirus, or bacterial phage T4 and MS2.