A solar-powered water disinfection device is described in a paper published online this week in Nature Nanotechnology. The device is made from nanometre-thin films of molybdenum sulfide (MoS2) and can rapidly kill bacteria in water using visible light.

Although ultraviolet (UV) light can directly kill bacteria, it makes up just 4% of the Sun's energy, meaning that devices utilizing UV light to disinfect water are slow (requiring up to 48 hours of exposure time). Yi Cui and colleagues have created a device that can harvest the whole spectrum of visible light (about 50% of solar energy) by using vertically aligned MoS2 films that have the necessary electronic properties to absorb the light. This allows the MoS2 films to generate reactive oxygen species, which rapidly kill the bacteria (Escherichia coli and Enterococcus faecalis).

They find that the disinfection can be sped up further by adding a copper layer, which acts as a catalyst, on the surface of the MoS2 films, giving clean water (better than 99.999% disinfection) in only 20 minutes. The authors conclude that the promising performance of their system shows great potential for the visible-light inactivation of a range of pathogens, such as bacteria and viruses, in water.