A little device developed by researchers at Stanford can purify water of nearly all bacteria in just 20 minutes. Water purification on a large scale is accomplished in one of two main ways, chlorine addition or UV radiation. Ozone can also be used, but it is less common in the treatment processes. This small black device attracts a wide array of the sun's rays to purify water using UV radiation in an incredibly short amount of time. Visible light in the sun's rays attract molybdenum disulfide on the small device's coating with then jumpstarts chemical reaction to purify the water, according to Science Alert.
[Image Source: SLAC]
"Solar energy is readily available in most climates and can be used for water purification. However, solar disinfection of drinking water mostly relies on ultraviolet light, which represents only 4% of the total solar energy, and this leads to a slow treatment speed. Therefore, the development of new materials that can harvest visible light for water disinfection, and so speed up solar water purification, is highly desirable." ~ Nature
From this chemical reaction, hydrogen peroxide is generated which then begins working to kill bacteria and germs suspended in the water. Below, you can take a look at a diagram demonstrating further how exactly this process takes visible light and disinfects water.
[Image Source: SLAC]
"Here we show that few-layered vertically aligned MoS2 (FLV-MoS2) films can be used to harvest the whole spectrum of visible light (∼50% of solar energy) and achieve highly efficient water disinfection. The bandgap of MoS2 was increased from 1.3 to 1.55 eV by decreasing the domain size, which allowed the FLV-MoS2 to generate reactive oxygen species (ROS) for bacterial inactivation in the water." ~ Nature
A device like this is a big deal when it comes to affordable water treatment. UV purification can be used on water on a smaller scale, but it would require people to leave the infected water in direct sunlight for 48 hours. This new process takes advantage of visible light from the sun to purify water much faster. So far, the device has only been proven on a small number of bacteria, but the results are promising to treatment as a whole.