The device, which looks like a tiny rectangle of black glass, can cleanse water faster because it taps into the visible part of the solar spectrum that contains 50 percent of the sun's energy. When you leave bottles out in the sun, you're depending on UV rays that only contain four percent of the sun's energy to annihilate germs. In the team's tests, it managed to destroy most of the germs in 25mL of water with a bacterial concentration of 1,000,000 per mL within 20 minutes. That's under a light source that only had visible light without UV, which means the process could be even faster under actual sunlight.
Stanford's creation has a layer of molybdenum disulfide, commonly used as a dry industrial lubricant, that's a few atoms thick. When that layer is hit by sunlight, many of its electrons fly out. Both those electrons and the holes they leave behind make chemical reactions possible. It also has a layer of copper that acts as a catalyst to trigger the reaction needed to produce hydrogen peroxide -- the disinfectant that does the actual work.
The researchers warn that while it could make lives easier, it's not capable of removing chemical pollutants. They also have to conduct more tests, because thus far, it's only been proven to kill three types of bacteria. To ensure people can actually use it in real life situations, the scientists still need to prove that it can clean overly contaminated water with a bigger variation of microorganisms.