A device half the size of a postage stamp can kill 99.99% of bacteria in water in just 20 minutes

When dropped into the water, it quickly disinfects it with the help of sunlight

When dropped into the water, it quickly disinfects it with the help of sunlight

One way to disinfect contaminated water is to expose it to sunlight, in order for the ultraviolet rays to kill the microbes. But as these carry only 4 % of the sun’s total energy, this method takes up to 48 hours to complete. Now, an innovative nanostructured device has been created by researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University, which disinfects water much faster than the UV method. This is because it also makes use of the visible part of the solar spectrum that contains 50% of the sun’s energy. Their work was published in mid-August in the journal Nature Nanotechnology. “Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work,” said Chong Liu, lead author of the report.

The device’s coating is made of molybdenum disulfide (often used as an industrial lubricant), which operates as a photocatalyst: when hit by incoming light, many of its electrons leave their usual positions, and both the electrons and the “holes” they leave behind are eager to take part in chemical reactions. These reactions generate hydrogen peroxide and other disinfectants that kill 99.999 % of bacteria in just 20 minutes. Viewed under a microscope, the surface of the device resembles a fingerprint.

The promising news that could make the technology viable for the market is that molybdenum disulfide is cheap to produce. However, more research needs to be done, as only three strains of bacteria have been tested so far. Moreover, the coating has only been tested on specific concentrations of bacteria (diluted samples), not on actual contaminated water, and is also not currently effective against chemical pollutants.

Image credits:C. Liu et al., Nature Nanotechnology

Source: SLAC National Accelerator Laboratory