Almost 20% of the world’s population has no access to electricity, according to the International Energy Agency. Without electricity, people in developing regions can’t run modern-day sanitation and sterilization devices needed to prevent the spread of infectious diseases.
To address this problem, a research team led by Naomi J. Halas of Rice University has engineered a portable sterilization apparatus—an autoclave—that generates steam by using sunlight and metallic nanoparticles (Proc. Natl. Acad. USA 2013, DOI: 10.1073/pnas.1310131110). The autoclave makes enough steam to raise the temperature and keep it at 132 °C for at least five minutes. That’s enough time to make water drinkable, sterilize a physician’s surgical equipment, or sanitize the contents of a portable toilet.
Last year, the Rice University researchers demonstrated how gold-coated silica nanoparticles dispersed in water can directly convert solar energy into steam (C&EN, Nov. 26, 2012, page 9). When focused sunlight hits the particles, they heat rapidly and vaporize the surrounding liquid. “This starts happening instantaneously,” says Rice’s Oara Neumann, lead author of the studies. When it does, there’s a visible “explosion” of steam bubbles at the surface.
Moving on to a practical application for the heating effect, the Rice team constructed a device that collects sunlight via a solar dish, focuses the light into a nanoparticle-containing vessel, and pushes the steam produced into a treatment container.
Using this setup, the researchers killed all the bacteria in a sample of simulated human waste with just a five-minute steam treatment.
Neumann declined to estimate how much the autoclave might cost if it were mass produced. But she points out that the gold nanoparticles are reusable and would be one of the least expensive components of the device. “I’ve been working with the same batch for at least three years,” she says.
Developing the autoclave is no small feat, says Christopher Ackerson, a chemist at Colorado State University. “Reducing fundamental science to real-world practice, as they have mostly accomplished here, is impressive.”