That’s the sentiment behind a device which uses solar energy to disinfect water.
The device is nanostructured and its size is approximately half that of a postage stamp. Harnessing the visible part of the solar spectrum, where half of the sun’s energy is stored, the device yields pure water much faster than traditional UV methods.
The device was created by stacking very thin molybdenum disulfide films on edge atop a rectangle of glass. Molybdenum disulfide is typically used as an industrial lubricant. However, a team of engineers were able to completely alter its properties by creating layers of molybdenum disulfide merely a few atoms thick.
As a result, it transformed from a lubricant into a photocatalyst. When the films are hit by incoming light, many of their electrons are scattered. Both the electrons, and the empty spaces left behind, are highly reactive.
The films’ thickness had to be specifically tailored to absorb the full range of visible sunlight. Furthermore, each film is topped with a thin layer of copper. This acts as a catalyst for creating reactive oxygen species, such as hydrogen peroxide. Hydrogen peroxide is a very common disinfectant, and so kills the bacteria in the surrounding water.
With sunlight as the instigator forming hydrogen peroxide (among other disinfectants), over 99.999 percent of the bacteria in the water were killed within 20 minutes. At the termination of the reaction, the disinfectants dissipated, with the final result being pure water.
In addition to purifying water quickly and effectively, these devices have the advantage of being primarily composed of molybdenum disulfide, which is inexpensive and easy to create. Furthermore, the device is able to absorb a much broader range of solar wavelengths than other commonly used photocatalysts.
Improving Water Purification
While this device has proven to be a powerful weapon against bacteria, it is unable to remove chemical pollutants from water. It has been tested on three strains of bacteria, though its creators predict that it will kill other strains and types of microbes as well.
That being said, the test environment was very idealized. The researchers tested the device on specific bacteria concentrations mixed with less than an ounce of water, which is unrealistic compared to the complicated mixtures of contaminants encountered outside the lab.
Regardless of its shortcomings, this device is a promising solution for dealing with microbial contaminations in drinking water.
The project was carried out by professor Alexandria Boehm and her team at the Stanford department of civil and environmental engineering.
For another example of engineers working to provide access to clean water, find out how graphene-based nanoscrolls could improve water purification.