At least 2 billion people worldwide routinely drink water contaminated with disease-causing microbes. Now, scientists at Stanford University and SLAC National Accelerator Laboratory have invented a low-cost, recyclable powder that kills thousands of waterborne bacteria per second when exposed to ordinary sunlight.
The discovery of this ultrafast disinfectant could be a significant advance for nearly 30 percent of the world’s population with no access to safe drinking water, according to the Stanford and SLAC team. Their results are published in a May 18 study in Nature Water.
Conventional water-treatment technologies include chemicals, which can produce toxic byproducts, and ultraviolet light, which takes a relatively long time to disinfect and requires a source of electricity.
The new disinfectant developed at Stanford is a harmless metallic powder that works by absorbing both UV and high-energy visible light from the sun. The powder consists of nano-size flakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide.
After absorbing photons from the sun, the molybdenum sulfide/copper catalyst performs like a semiconductor/metal junction, enabling the photons to dislodge electrons. The freed electrons then react with the surrounding water, generating hydrogen peroxide and hydroxyl radicals – one of the most biologically destructive forms of oxygen. The newly formed chemicals quickly kill the bacteria by seriously damaging their cell membranes.
“We stirred the powder into the contaminated water,” said co-lead author Bofei Liu, a former MSE postdoc. “Then we carried out the disinfection test on the Stanford campus in real sunlight, and within 60 seconds no live bacteria were detected.”
The powdery nanoflakes can move around quickly, make physical contact with a lot of bacteria and kill them fast, he added. The chemical byproducts generated by sunlight also dissipate quickly.
The nontoxic powder is also recyclable. Iron oxide enables the nanoflakes to be removed from water with an ordinary magnet. In the study, the researchers used magnetism to collect the same powder 30 times to treat 30 different samples of contaminated water.
According to news.stanford.edu