Faster water filter is Stanford, SLAC team’s latest creation
Providing clean water is one of the most pressing challenges in the developing world. It takes expensive infrastructure to purify a municipal water supply, hours of household labor to boil or chemically treat impure water, or even longer to put water in a plastic bottle and wait for the sun’s ultraviolet rays to disinfect it.
Now, researchers at Stanford and the SLAC National Accelerator Laboratory have developed a nanostructured water filter half the size of a postage stamp that can disinfect water in minutes by harnessing more of the sun’s power to trigger microbe-killing chemical reactions.
In lab tests, the little filter dropped into about an ounce of water killed more than 99.999 percent of bacteria in 20 minutes without further human effort.
“We just dropped it into the water and put everything under the sun, and the sun did all the work,” Chong Liu, lead author of the report in in Nature Nanotechnology, told SLAC. Liu is a postdoctoral researcher in the laboratory of Stanford associate professor of materials science and engineering Yi Cui, an investigator with the Stanford Institute for Materials and Energy Sciences at SLAC (SIMES).
The device exploits how the properties of its material change when milled at nanoscale. It’s made with molybdenum disulfide, a common industrial lubricant. When fabricated into ridges just a few atoms thick, topped with copper and exposed to light, molybdenum disulfide triggers the formation of hydrogen peroxide and other chemicals that kill bacteria.
By reacting to visible light — 50 percent of the sun’s energy — rather than just the 4 percent of solar energy that is ultraviolet rays, the new filter works many times faster than other solar purification methods. Because it is made of inexpensive materials, its creators believe it holds promise for the developing world.
As a graduate student in Cui’s lab in 2015, Liu worked on a similar project to create a low-cost, highly efficient air filter from nanospun polyacrylonitrile (PAN), a material commonly used to make surgical gloves. Spun at nanoscale, PAN develops properties that attract and trap particles of a size most dangerous to human lungs.
These are only two of the many innovations Cui’s lab has developed to apply nanotechnology to environmental challenges. Since 2010, members of the group have published more than 30 papers each year on concepts ranging from pollution filters to renewable energy to ultra-efficient batteries.
Next steps for the water filter are to lab-test it on more bacteria and on viruses, and then to field-test it in naturally polluted water, including in developing countries.
“Nanotechnology is bringing very exciting opportunities – new ideas, new materials, new devices, new mechanisms for treating water,” Cui told Stanford Engineering. “This has become some of the key research guiding my group.”