12-03 :: March/April 2012
nanotimes News in Brief
come in more than a hundred different forms, and the composition of each variant determines the size of the cavity and thus the kinds of molecules and ions that can be retained, or excluded, within. As a result, zeolites can separate and sort chemical species: Added to a solution containing a mixture of ions, they can selectively retain only those ions that can fit within the pores. The authors are building on a series of studies that demonstrate how to assert control over the kinds of guests that zeolites will hold within their cavities. The team uses a stimulus that is seldom used to control cavity size: pressu- re. Working with natrolite, a natural zeolite with a 2:3:10 ratio of Al:Si:O in the framework, the team reported in Angewandte Chemie that they managed to coax trivalent Eu3+ ions to exchange with K+ ions within the material‘s nanoscale cavities. The immobilized ions were then trapped within after the pressure was removed.
“With natrolite, people have always said you can‘t get Eu3+ in there. But under pressure, you can,” said Thomas Vogt, one of the co-authors and a professor in the department of chemistry and bio- chemistry in the College of Arts and Sciences at the University of South Carolina.
The result is counter-intuitive in that the pressure – applied hydrostatically in a diamond-anvil cell and typically exceeding 1 GPa (more than 10,000 atm) – can cause the cavities within natrolite to expand in volume. This auxetic behavior essentially opens a window for larger ions to migrate within the pores, and then they remained trapped there after the pressure is released, said Vogt. The exchange of europium ions shows promise for nuclear waste processing. “The Eu3+ radius is 108.7 picometers,
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which is close to the 103 picometers of U4+,” Vogt said. “And we‘ve demonstrated we can exchange Eu3+ for K+ – the aliovalent exchange replaces 90% of the potassium.”
Prof. Yongjae Lee, Yongmoon Lee, Donghoon Seoung, Jun-Hyuk Im, Hee-Jung Hwang, Tae-Hyun Kim, Dr. Dan Liu, Dr. Zhenxian Liu, Dr. Seung Yeop Lee, Dr. Chi-Chang Kao, Prof. Dr. Thomas Vogt: Immobilization of Large, Aliovalent Cations in the Small-Pore Zeolite K-Natrolite by Means of Pressure, In: Angewandte Chemie Interna- tional Edition Early View, April 04, 2012, DOI:10.1002/ anie.201201045:
http://dx.doi.org/10.1002/anie.201201045
http://www.chem.sc.edu/people/facultyStaffDetails. asp?SID=616
Researcher at Johannes Kepler University (Aus- tria), University of Tokyo (Japan), Exploratory Research for Advanced Technology (ERATO, JST, Japan), Johannes Kepler University Linz demons- trate polymer-based photovoltaic devices on plastic foil substrates less than 2µm thick, with equal power conversion efficiency to their glass-based counterparts. They can reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight. The processing methods are standard. Martin Kaltenbrunner, Matthew S. White, Eric D. Głowacki, Tsuyoshi Sekitani, Takao Someya, Niyazi Ser- dar Sariciftci, Siegfried Bauer: Ultrathin and lightweight organic solar cells with high flexibility, In: Nature Com- munications, Vol. 3, April 03, 2012, Article number: 770, DOI:10.1038/ncomms1772:
http://dx.doi.org/10.1038/ncomms1772
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