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A. Q. Liu, H. Chen; Angew. Chem. Int. Ed. Engl., 2013, 52, 8570).
2 ethanol -H2 O Scheme 3 1-butanol >94% selectivity Scheme 4
first modified with citric acid to make them soluble in water (Scheme 5). After purification, these NPs are dispersed in water/2-propanol mixture (v/v=3:5). To align the NPs and simultaneous encapsulate them in silica, tetraethyl orthosilicate (TEOS) and ammonia are added to the solution and the reaction vessel immediately placed close to a magnet. After incubation overnight, the products are isolated and purified by means of centrifugation. The straight rigid single-line chains assembled from 40nm magnetic NPs, show immediate response to a common magnetic stir plate and can be easily recovered. Their small size turns out to be of great importance. The nano stir bars can be used for stirring inside extremely small droplets; they can remain suspended and stir all parts of the solution; they can be easily confined inside a droplet instead of being pulled out by an external magnetic field, they can stir effectively without breaking up the droplet, and finally, they can be easily fabricated in great numbers, allowing economic usage, easy dispensing, and effective stirring.
stabilised Fe3O4 Scheme 5
Controllable foam destruction Foams are commonly applied in the clean-up of chemical spills, where they are sprayed over large areas to prevent evaporation of volatile and harmful organic materials. While this demands stability, the foam then needs to be destabilised for transport due to its voluminous nature, often accomplished by the addition of an anti-foaming agent. The resulting liquid mixture can then be removed and the components recovered. A new approach for controlling foam stability using light irradiation has been
Scheme 6
In a typical synthesis, oleic acid NPs (d=40 nm) are
developed based on the simple and green surfactant, 12-hydroxystearic acid (12- HSA), derived from a sustainable, plant- based material (A-L. Fameau, S. Lam, O. D. Velev; Chem. Sci., 2013, doi: 10.1039/ C3SC51774H).
Like most surfactants, when shaken
in water, 12-HSA will form stable foam, which collapses at elevated temperatures (~45°C) (Scheme 6). Addition of carbon black and carbonyl iron particles further stabilises the foam. In addition to heat, the foam can be
destroyed by heat, UV light and magnetic fields. UV light makes the photosensitive carbon black particles generate heat, and application of a magnetic field which causes the carbonyl iron particles to move and distorting the foam structure, the net result of either being the foam’s collapse. Such multi-stimuli responsive systems could find applications in diverse industries requiring highly stable systems, which can be destroyed on-demand.
Visible sarin sensor
A new complex that could be used to develop simpler and more sensitive devices for the nerve agent, sarin (L. Ordronneau, A. Carella, M. Pohankab, J-P. Simonato; Chem. Commun., doi: 10.1039/C3CC45029E) (Scheme 7). Sarin’s use as a deadly weapon include a terrorist attack on Tokyo’s subway in 1995, an attack by Iraqi government forces on the town of Halabja in Southern Kurdistan in 1988 and in Syria in 2013. It is highly toxic, affecting muscle function, and at high doses it causes death by asphyxiation. Current detection methods are expensive and have low selectivity, or require complex equipment that is not portable. Sensors based on chemicals that visually respond to sarin would be very simple for untrained first responders to use at the site of an attack. The new sensor is based on a
Stirring dye in water droplets Chemistry&Industry • November 2013 55
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