Nano Focus: Electrified nanostructures enable low-cost water sterilization
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icles are core−multishell nanoparticles with an average diameter of 12.2 nm ± 0.3 nm. A representative particle has a core region of about 3.3 nm, a 1.8-nm thick (on average) first shell, and a 10-nm thick (on average) second shell. As an interesting case, one of these particles was actually a multicore–multishell particle containing two cores with single-shell encapsulated together in a δ΄-Al3Li second shell. According to the researchers, this is a demonstration of the limitation of control over nanoscale features with this technique, but also an unexpected new architecture possible with this solid-state synthesis technique representing a minor but measureable subpopulation. Vickers microhardness tests show an increase in microhardness from 725 ± 10 MPa after the first aging step, when the core–
Nano Focus Electrified nanostructures enable low-cost water sterilization
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aterborne bacterial diseases represent a major global problem killing over two million people worldwide annually, mostly children in developing countries. Conventional filters used to prevent such diseases are made from membranes but clogging of such devices is a common problem. A new strategy for deactivating bacteria by incorporating antibacterial silver nanowires (Ag NWs) in a carbon nanotube (CNT)-coated cotton fiber matrix has now been demonstrated. The material is mechanically robust, electrically conductive, and uses a very small amount of current to inactivate bacteria, while the open structure allows for high volume water filtration. The work led by Y. Cui and S. Heilshorn at Stanford University was published in the September 8th issue of Nano Letters (DOI: 10.1021/ nl101944e; p. 3628). Three components with different functionalities spanning three length scales formed the filter: (1) inexpensive
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MRS BULLETIN
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VOLUME 35 • NOVEMBER 2010
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Schematic of the filtration device showing the three components used and the testing technique used for evaluation. NWs is nanowires and CNT is carbon nanotube. Reproduced with permission from Nano Lett. 10 (9) (2010) DOI: 10.1021/nl101944e; p. 3628. © 2010 American Chemical Society.
cotton cloth formed the structural backbone, (2) Ag NWs (diameters of 40−100 nm, up to 10 µm long) with antibacterial properties formed a secondary mesh, and (3) carbon nanotubes formed a conductive coating on the cotton fibers. The final material (Ag NW/CNT cotton) was shaped into a cylindrical filter (4 mm diameter, 2.5 mm length) and placed in the stem of a glass funnel. Water was poured
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single-shell nanoparticles are present, to 960 ± 20 MPa after the second aging, when core−multishell nanoparticles are also present providing evidence that the more complex multishell architecture has an advantage over core–single-shell particles. The researchers said that this solidstate synthesis technique should be generally applicable to a range of alloys. Key considerations are (1) choice of alloying elements, relative diffusivities, and solubilities, and (2) choice of aging temperatures, which signi
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