MICROSCOPY
Technique pinpoints active sites on surfaces University of California, Berkeley. Bandarenka and coworkers used the technique to identify reactive sites on electrodes while the surfaces catalyzed hydrogen-evolution and oxygen-reduction is about an order of magnitude better than Many industrial processes use solid catreactions in solution. They found that catSECM’s. alysts to accelerate chemical reactions in alytic activity is stronger at step edges than The ultimate goal is atomic resolution— gases or liquids. The activity of these heton plateaus of a terraced Pt surface. still about two orders of magnitude away. erogeneous catalysts often varies considerWhat makes the technique work is that But the new technique goes well beyond ably from site to site across their surfaces. electron-tunneling current between an STM earlier approaches in its ability to identify If scientists were able to identify highly tip and a nearby surface spot varies considsite activity precisely, comments heterogereactive sites precisely, they could improve erably with reaction activity. As a reaction the catalysts by redesigning them to include neous catalysis expert Alexis T. Bell of the occurs, localized surface variations, such more of those sites. as molecular adsorption and desorption, Aliaksandr S. Bandarenka and cocause noise changes in the electron-tunworkers at the Technical University neling current. The researchers identify of Munich have now devised a scanand measure activity differences by ning tunneling microscopy (STM) monitoring these changes. technique that identifies surface Hans Niemantsverdriet, director of activity variations during reactions the catalysis and surface science firm at higher spatial precision than has Syngaschem, says the work “is truly been possible before (Nature 2017, remarkable and a significant step forDOI: 10.1038/nature23661). Scanning ward in making catalytic sites visible” electrochemical microscopy (SECM), and wonders if it can also be extended which Allen J. Bard and coworkers at An STM instrument measures high electronto gas-phase reactions, in which noise the University of Texas developed, can tunneling signal noise at step edges (yellow) than on terraced Pt surface (blue) as it catalyzes water variations would be smaller.—STU also map surface activity, but the new STM technique’s 1- to 2-nm resolution splitting (red = oxygen, white = hydrogen). BORMAN
Scanning microscopy detects activity with unprecedented resolution while reactions occur
POLLUTION
Probiotic-treated trees clean up a carcinogen C R E D I T: NAT UR E ( ST M) ; JO H N FR E EM A N / IN TR I N SYX TEC H N O LO GI ES ( TR E ES)
Symbiotic bacteria help poplars strip trichloroethylene from groundwater Poplar trees inoculated with bacteria could help remediate sites contaminated with the carcinogen trichloroethylene (TCE), a new study shows (Environ. Sci. Technol. 2017, DOI: 10.1021/acs.est.7b01504). TCE contaminates the soil or water of more than 1,000 Superfund sites around the U.S., posing an expensive cleanup problem, says Sharon L. Doty of the University of Washington. Plants can be used to soak up a variety of pollutants—a method called phytoremediation—and introducing symbiotic, pollutant-destroying bacteria to the plants has shown even more promise in lab tests. Several years ago, Doty and her colleagues discovered a strain of Enterobacter in a hybrid poplar (Populus deltoides crossed with Populus nigra) that completely degrades TCE into chloride ions and carbon dioxide. The researchers found that they could successfully inoculate
other poplar trees by soaking tree cuttings in a solution containing the microbe. In collaboration with several environmental engineering firms, the researchers decided to test the fast-growing trees and the microbes at a Superfund study area in California contaminated with TCE. The team planted about 400 tree cuttings, half treated with the microbe and half with a control solution. Over three years, the researchers tracked the trees’ growth, and then tested groundwater at the end of the experiment. TCE concentrations upstream of the trees were about 300 µg/L, whereas downstream they were below EPA’s drinking water limit of 5 µg/L. The poplars treated with the microbe grew faster and visibly larger than the control trees. “It’s a really simple way to get rid of an important carcinogen,” Doty says. Om Parkash Dhankher, a phytoremediation expert at the University of Massa-
Poplar trees grow at a test site contaminated with trichloroethylene. The rows of larger trees have been given microbes and are growing faster than the poplars with no microbes. chusetts, Amherst, says it’s exciting that Doty’s team has shown that the method works in the real world. “This is a very cheap and green, clean technology,” he says.—DEIRDRE LOCKWOOD, special to
C&EN SEPTEMBER 11, 2017 | CEN.ACS.ORG | C&EN
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