NEWS OF THE WEEK
SOLAR-POWERED SANITATION This mobile autoclave focuses sunlight into a vessel above its solar dish to generate steam.
SUSTAINABILITY: Portable device
COURTESY OF OARA NEUMANN
uses sunlight and gold-coated nanoparticles to generate steam
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LMOST 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 dem-
SHAKING UP THE FRACKING DEBATE
Earthquakes near hydraulic fracturing wastewater injection wells may be affected by powerful, distant earthquakes, a new study finds.
GEOLOGY: Distant earthquakes can loosen faults near gas extraction sites
SHUTTERSTOCK
ARTHQUAKES NEAR hydraulic fracturing and
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waste-fluid injection wells in the central U.S. may be being triggered by massive earthquakes thousands of miles away, according to a new study (Science 2013, DOI: 10.1126/science.1238948). The study notes the recent rise in the U.S. of small to midsized earthquakes. It points to a relationship between that rise and the increased deep underground injection of large amounts of water and wastewater for hydraulic fracturing, or fracking, for natural gas and oil. The researchers looked at past earthquake recordings near three U.S. hydraulic fracturing injection sites. They found that pressure in faults at these sites was already approaching critical levels when major earthquakes occurred far away. The distant earthquakes triggered a rise in frequency and intensity of local tremors, the scientists report. “The injected fluids are driving the faults to their tipping point,” explains lead author Nicholas J. van der Elst, a researcher at Columbia University LamontDoherty Earth Observatory. “The remote triggering by CEN.ACS.ORG
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onstrated 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 realworld practice, as they have mostly accomplished here, is impressive.”—LAUREN WOLF
big earthquakes is an indication that the area is critically stressed.” The study points to a magnitude 8.8 quake in Chile in 2010 that sent surface waves rippling across the planet. Sixteen hours later, the powerful quake triggered a magnitude 4.1 earthquake near Prague, Okla., site of several injection wells, the study says. Over the years, swarms of quakes have affected Prague as well as injection-well sites in Colorado and Texas, the researchers say. Probably the largest quake associated with wastewater injection—a magnitude 5.7 tremor—occurred in Prague in 2011. That quake destroyed 14 homes and injured two people. William L. Ellsworth, a seismologist with the U.S. Geological Survey, wrote a review of the current study. He tells C&EN that although there is rapid growth in the worldwide use of fracturing technologies and an increase in earthquake activity, the exact relationship between the two remains unclear. Understanding that relationship better is the next research target, he says. The research has practical consequences, he adds. Building codes near fracturing and injection sites might need to be modified if scientists could specify risk changes, for instance. “We are sort of in ambulance-chasing mode right now,” Ellsworth says. “Earthquakes happen, and we rush to understand them. We’d be far better off if we had data about the conditions of Earth and the impact of industrial activities before and during their operations.”—JEFF JOHNSON
JULY 15, 2013
