Science Concentrates POLLUTION
Burned organic matter captures ammonia Burned organic matter—so-called pyrogenic organic matter—retains ammonia by forming covalent bonds with the molecule at normal temperatures and pressures, according to a new study by former Cornell University graduate student Rachel Hestrin and coworkers (Nat. Commun. 2019, DOI: 10.1038/s41467-019-08401-z). The findings could have implications for the global nitrogen cycle and provide a new source of fertilizers. “We did not know that ammonia gas would adsorb to the extent we reported,” says Johannes Lehmann of Cornell University, who led the research. Under normal temperatures and pressures, the pyrogenic material, obtained by burning maple wood chips, retained more nitrogen by mass than is found in plants or most animal manures, Lehmann says.
When the researchers artificially weathered the pyrogenic matter by oxidizing it, the amount of trapped ammonia increased sixfold. More than half the nitrogen remained in the material via covalent bonds. Spectroscopic analysis revealed that about 10% of the covalent bonds involved nitrogen-containing heterocyclic compounds. The material could have practical uses for converting ammonia pollution into fertilizers. For example, ammonia-polluted effluents from farmlands or wastewater treatment plants could be passed through beds of biochar—burned plant material— before being discharged, says Michael Bird, a geochemist at James Cook University who studies biochar and was not involved in this study. “You end up discharging cleaner water and with an agricultural
Burning brush could be a source of pyrogenic material for capturing ammonia. product with carbon-sequestration potential, soil-improvement potential, and now a built-in source of fertilizer.” Previous work by others has shown that plants can take up nitrogen in biochar. Lehmann sees the material as a way to clean up agricultural waste. “I’m thinking of dairy manure lagoons or poultry barn floors,” he says. Poultry barns “pretty much stink of ammonia.” In addition, Lehmann says, the results suggest that pyrogenic organic matter may play a previously unappreciated role in the global nitrogen cycle by serving as a nitrogen sink. “Since nobody knew that it can happen, nobody even looked to see whether it’s happening,” Lehmann says.—CELIA ARNAUD
INORGANIC CHEMISTRY
Chelator selectively grabs uranium Bioinspired adsorbent soaks up uranium from seawater, leaving interfering ions behind which have a knack for latching onto The world’s oceans contain some 4 billion uranyl ions, the aqueous form of uranium. metric tons of dissolved uranium. That’s Nearly 20 years ago, the Japan Atomic roughly 1,000 times as much as all known Energy Agency (JAEA) confirmed that terrestrial sources combined, and enough amidoxime-functionalized polymers could to fuel the global nuclear power industry soak up uranium for centuries. But the oceans are reliably even under so vast, and uranium’s concenharsh marine conditration in seawater is tions. But that type so low—roughly 3 of adsorbent has not ppb—that extracting been implemented it remains a foron a large scale because it has midable challenge. a higher affinity for vanadium That task may have just become easier thanks to a new H2BHT than uranium. Separating the two ions raises production costs. adsorbent material based on a bioinAlexander S. Ivanov of Oak Ridge Naspired chelating agent (Nat. Commun. 2019 tional Laboratory, together with colleagues DOI: 10.1038/s41467-019-08758-1). there and at Lawrence Berkeley National Researchers have been looking for ways to extract uranium from seawater for more Laboratory and other institutions, may have come up with a solution. Using comthan 50 years. In the 1980s, surveys pointputational methods, the team identified a ed to amidoxime-type chelating agents,
6
C&EN | CEN.ACS.ORG | FEBRUARY 25, 2019
highly selective triazine chelator known as H2BHT that resembles iron-sequestering compounds found in bacteria and fungi. Starting with low-cost reagents, the team prepared fibers containing polyethylene and poly(acrylic acid), functionalized them with H2BHT (shown), and analyzed their performance as adsorbents. H2BHT exhibits little attraction for vanadium but has roughly the same affinity for uranyl ions as amidoxime-based adsorbents do. And in contrast to amidoxime adsorbents—which are tough to recycle because of the acid treatment needed to further purify the uranium they gather— the new adsorbent can be regenerated with mild carbonate solution and reused. JAEA’s Masashi Kaneko offers high praise for the study. H2BHT’s high selectivity and uranium uptake capacity, coupled with molecular insights from the team’s analyses, may lead to improved methods for recovering uranium from seawater, he says.—MITCH JACOBY
C R E D I T: S H UT T E RSTO CK ( BU R N I N G B RU S H ) ; A LEXA N D E R S . I VA N OV/O R N L (H 2 B H T )
C&EN Global Enterp 2019.97:6-6. Downloaded from pubs.acs.org by MACQUARIE UNIV on 02/26/19. For personal use only.
Material could turn nitrogen pollution into fertilizers
