NEWS OF THE WEEK
FLAWED OIL-SPILL TESTS DETECTION: Methods may miss
about half of oil chemicals
F
OR DECADES, scientists studying oil spills have
relied on the same methods to detect oil compounds. Unfortunately, these techniques miss an entire class of chemicals that have yet to be identified and that could account for about half of the total oil in some samples, according to research presented in January at the Gulf of Mexico Oil Spill & Ecosystem Science Conference, in New Orleans. Studying these overlooked chemicals may improve scientists’ understanding of oil toxicity and could explain the fate of some of the oil released in the 2010 Deepwater Horizon spill, the researchers say. Since the 1980s, researchers have relied mostly on gas chromatography to hunt for about 150 different oil chemicals, mainly alkanes and COAST GUAR D
Crews clean up oil from the Deepwater Horizon spill on a Louisiana beach in 2010.
NEW COLORS FOR SILICON LIGHTEMITTING DIODES DISPLAYS: Devices could be alternative
to ones using toxic metals
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UANTUM DOTS, semiconducting inorganic
nanocrystals, have unique properties, such as the ability to emit pure colors, that could make them ideal as the basis for light-emitting diodes in computers and television displays. Unfortunately, quantum dot LEDs often rely on toxic heavy metals such as cadmium to emit light. Now, researchers report new colors of LEDs that use silicon quantum dots. Silicon could be a less toxic alternative, but scientists have struggled to fabricate silicon-based devices that glow in colors across the visible spectrum. Current silicon LEDs emit only red and near-infrared light. That’s because researchers haven’t controlled the NANO LETT.
Silicon quantum dots glow different colors depending on the size of the nanocrystals.
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aromatics. Christopher M. Reddy of Woods Hole Oceanographic Institution and colleagues ran an experiment to determine whether the method was missing anything. First, the scientists measured the amount of all oilrelated chemicals in sand samples collected during the Deepwater Horizon spill. Then they ran the samples through a gas chromatograph to measure the amount of the chemicals a spill scientist normally looks for. Reddy’s team found that the chemicals identified in the standard tests make up only about 50% of the total oil in the samples. Through elemental analysis, the researchers determined that the other substances are oxidized oil compounds. Reddy says that the standard tests don’t catch these molecules because gas chromatography doesn’t readily detect highly oxidized chemicals. These oxidized compounds could account for some of the “missing” oil from the Deepwater Horizon spill, Reddy says. Other possible explanations include oil buried in ocean bottom sediments or broken down by microbes. Government and academic scientists could explain the fate of only about 75% of the oil released into the Gulf of Mexico. Reddy’s team published some of their results in 2012 (Environ. Sci. Technol., DOI: 10.1021/es3015138). Edward B. Overton of Louisiana State University thinks more research is needed before deeming the oxidized compounds significant in terms of environmental impact.—MARK SCHROPE, special to C&EN
sizes of the silicon quantum dots in their devices, say Uli Lemmer of Karlsruhe Institute of Technology, in Germany, and Geoffrey A. Ozin of the University of Toronto. To control the sizes of the nanocrystals, Lemmer, Ozin, and their colleagues report separating quantum dots by ultracentrifugation, a technique often used to isolate biomolecules. After synthesizing silicon quantum dots by a previously reported method, the team spun a solution of 1- to 3-nm-diameter nanocrystals in a high-speed centrifuge. The spinning separated the quantum dots into 30 groups; within each group, particles had the same size. The researchers then took crystals of the same size and fabricated LEDs by spreading a layer of the quantum dots between two electrodes. The wavelength of light emitted by the LEDs increased with the size of the quantum dots. For instance, LEDs with 1.3-nmdiameter particles glowed yellow, while devices with 1.8-nm crystals glowed red (Nano Lett., DOI: 10.1021/ nl3038689). Lemmer and Ozin say they next need to improve the devices’ efficiency at converting electricity into light. Russell J. Holmes of the University of Minnesota, Twin Cities, thinks sorting quantum dots by size will be crucial if silicon quantum dot LEDs are to gain widespread application. But he says the ultimate challenge for scientists will be producing green and blue devices, which require synthesis of small silicon quantum dots.—PRACHI PATEL, special to C&EN
FEBRUARY 4, 2013
