Nanometre-thin films can harvest natural light and use it to rapidly disinfect water.
Sunlight offers a useful means of purifying water, particularly in countries that lack reliable energy sources. Ultraviolet light is widely used to kill microbes, but accounts for only 4% of the solar spectrum. Yi Cui and his colleagues at Stanford University in California have developed a film — comprising vertically aligned layers of molybdenum disulfide — that captures visible light, taking advantage of about 50% of the total solar energy. Light causes the films to generate reactive oxygen molecules, which kill water-borne pathogens.
Placing the film in water containing Escherichia coli and exposing it to light led to near-total disinfection in 20 minutes. Previous systems needed 30 to 60 minutes.
Nature Nanotechnol. http://dx.doi.org/10.1038/nnano.2016.138 (2016)