Photo via mckaysavage via Flickr CC
Sounds a little contradictory, but research coming from Jian-Ku Shang, professor of materials science and engineering at the University of Illinois, Urbana-Champaign, and his team have come up with a photocatalyst that disinfects water with sunlight or artificial light, and will keep on disinfecting even after the lights go out. It promises to be an effective solution for unsafe water in developing countries - or anywhere. Currently, we can use UV light to kill bacteria in water, but the scientists at University of Illinois have built upon this ability, using nanotechnology to create a photocatalyst that can use visible light, rather than UV light, to accomplish the same task. The research was published in the Journal of Materials Chemistry.
Working within wavelengths of 400 and 550 nanometers, the photocatalyst is made of titanium oxide fibers mixed with nitrogen so that the fibers will absorb visible light, and nanoparticles of palladium to maximize the efficiency of disinfection. By being able to utilize more visible light, and not just a sliver of the spectrum, the photocatalyst becomes a simple solar-powered and even artificial light-powered solution for safe drinking water.
According to Technology Review, "Shang and his colleagues tested the photocatalyst by placing it in a solution containing a high concentration of E. coli bacteria and then shining a halogen desk lamp on the solution for varying lengths of time. After an hour, the concentration of bacteria dropped from 10 million cells per liter to just one cell per 10,000 liters."
But the kicker is that it keeps disinfecting for up to 10 hours after the lights go out, which means water can be disinfected even over night. The photocatalyst was shown to kill bacteria for as long as 24 hours after losing its light source.
The photocatalyst can be a solution for developing countries where water quality is low, used in conjunction with purifiers that remove particles from the water so that safe, clean, pure water is available for everyone The scientists also imagine that it could provide mass disinfection by being incorporated into systems that expose water to light as it travels through pipes. The primary question we have, though, is what is left in the water after disinfection occurs - something we didn't see addressed in the available information about the new material.
The Journal of Materials Chemistry states,"Shang says that he hopes to study the charge transfer process in more detail, so that he can optimise the efficiency of the individual charge transfer steps. He indicates that the solar driven materials could have many environmental antimicrobial systems. In particular, he says that it could be a cheaper and more environmentally-friendly alternative to water disinfection by chlorination, which produces harmful disinfection by-products."