An American study has revealed that a new visible light photocatalyst destroys bacteria and viruses, even in the dark.
The technique, developed by University of Illinois scientists, is based upon a new catalyst and can help to purify drinking water, sanitize surgical instruments and remove unwanted fingerprints from delicate electrical and optical apparatus.
Jian Ku Shang, a professor of materials science and engineering at the U. of I, said: "The new catalyst also has a unique catalytic memory effect that continues to kill deadly pathogens for up to 24 hours after the light is turned off."
Shang's team has earlier created a catalytic material, which worked with visible light instead of the ultraviolet light required by other catalysts. This development, made by doping a titanium-oxide matrix with nitrogen, meant the disinfection process could be initiated with sunlight or standard indoor lighting.
Shang said: "When visible light strikes this catalyst, electron-hole pairs are produced in the matrix.
"Many of these electrons and holes quickly recombine, however, severely limiting the effectiveness of the catalyst."
Aiming to enhance the efficiency of the catalyst, Shang and his colleagues at the U. of I. and at the Chinese Academy of Sciences added palladium nanoparticles to the matrix.
The palladium nanoparticles lock in the electrons, enabling the holes to react with water to produce oxidizing agents, primarily hydroxyl radicals, which kill bacteria and viruses.
When the light is turned off, the palladium nanoparticles slowly release the trapped electrons, which then react with water to produce additional oxidizing agents.
Shang said: "In a sense, the material remembers that it was radiated with light... This 'memory effect' can last up to 24 hours."
Although, the disinfection is not as efficient in the dark as it is in visible light, it allows for the continuous operation of a catalytic disinfection system driven by solar or other visible light illumination.
The study has appeared in the Journal of Materials Chemistry and is also available on the journal's Web site.