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Menlo Park: SLAC and Stanford scientists advance water purification technology

 

Take a bottle of water contaminated by certain types of bacteria, drop into the water a new and inexpensive nanotechnology device about half the size of a postage stamp and resembling a piece of black glass, and set the bottle in the sunlight. In 20 minutes, the bacteria will be dead and the water will be clean, according to an announcement from the SLAC National Accelerator Laboratory in Menlo Park and Stanford University.

Tests show the device killing three specific strains of bacteria in water prepared in a lab, not the "complex stews of contaminants found in the real world," but there's reason to think that it would be fatal to other types of bacteria and microbes, including viruses, SLAC said.

The device could supersede traditional techniques of water decontamination, including boiling, which requires fuel, or placing containers of contaminated water in sunlight to allow the ultraviolet light to kill the bacteria, which takes six to 48 hours, scientists say.

The device employs walls of molybdenum disulfide a few atoms thick, topped by a thin layer of copper and arranged like a labyrinth on a small black rectangle of glass.

Sunlight falling on ultra-thin layers of molybdenum disulfide causes its electrons to migrate, scientists say. The result: electrically charged particles that leave behind electrically charged holes. With copper present as a catalyst, the situation favors chemical reactions, they say, including a reaction that creates hydrogen peroxide, a common disinfectant.

"Molybdenum disulfide is cheap and easy to make – an important consideration when making devices for widespread use in developing countries," said Yi Cui, an associate professor and investigator at Stanford and SLAC. "It also absorbs a much broader range of solar wavelengths than traditional photocatalysts."

"It's very exciting to see that by just designing a material you can achieve a good performance. It really works," said Chong Liu, a postdoctoral researcher and lead author of the report. She is also working on a project to develop air filters to defeat smog. "Our intention is to solve environmental pollution problems so people can live better."

Funding for the project comes from the U. S. Department of Energy through the Stanford Institute for Materials and Energy Sciences at SLAC, and done in collaboration with Stanford's Department of Civil and Environmental Engineering.

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