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Portable Solar Device Generates Sanitizing Steam

Autoclave that uses gold-coated nanoparticles to rapidly boil water may help curb the spread of infectious diseases in developing regions

by Lauren K. Wolf
December 23, 2013 | A version of this story appeared in Volume 91, Issue 51

Almost 20% of the world’s population has no access to electricity, according to the International Energy Agency. And without electricity, people in developing regions can’t run modern-day sanitation and sterilization equipment needed to prevent the spread of infectious diseases. This year, a research team led by Naomi J. Halas of Rice University addressed this deficit by engineering a portable sterilization apparatus—an autoclave—that generates steam by using sunlight and metallic nanoparticles (C&EN, July 15, page 8; Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1310131110). The autoclave is capable of generating steam that can reach 132 °C and remain at that temperature for at least five minutes. That’s enough time to make water drinkable, sterilize surgical equipment, or sanitize the contents of a portable toilet. Halas and her team originally demonstrated how gold-coated silica nanoparticles dispersed in water can directly convert solar energy into steam last year (C&EN, Nov. 26, 2012, page 9). When focused sunlight hits the particles, they heat rapidly and vaporize the surrounding liquid. At that point, says Rice’s Oara Neumann, lead author of the studies, there’s a visible “explosion” of steam bubbles at the water’s surface. The researchers gave this phenomenon a practical application this year by building the autoclave. The device collects sunlight via a solar dish, focuses the light into a nanoparticle-containing vessel, and pushes the steam produced into a treatment container. Using the setup, the researchers can kill all of the bacteria in a sample of simulated human waste with just a five-minute steam treatment. The team is now optimizing the autoclave to improve its efficiency.


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