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Published online: 14 November 2007 | doi:10.1038/nchina.2007.237
Amphiphilic catalysts: Under the spotlight
Anne Pichon
Abstract
The dispersion of a surfactant catalyst at the interface of emulsion droplets is observed for the first time by direct imaging
Original article citation
et al. A direct imaging of amphiphilic catalysts assembled at the interface of emulsion droplets using fluorescence microscopy. Chem. Commun. doi: 10.1039/b713831h (2007).Introduction
© (2007) RSC
Under suitable conditions surfactants, which lower the interfacial tension between liquids, can enable two immiscible liquids to form a single phase called an emulsion. Can Li and co-workers at the Chinese Academy of Sciences in Dalian have synthesized a surfactant using a polyoxometalate (POM) substituted with europium1. The surfactant is bright red under photoexcitation at a wavelength of 615 nm owing to the strong charge transfer from oxygen to europium, and this characteristic was exploited to observe the surfactant dispersion directly using fluorescence microscopy.
The researchers assembled surfactant catalysts, formed by quaternary ammonium cations and POM anions, into emulsion droplets for the oxidation of organic molecules in aqueous media. Until this study, the dispersion of the catalysts at the interface of the two liquids had only been characterized by indirect methods.
Surfactants avoid the traditional diffusion problems associated with multiphasic systems. The catalyst, which was first entirely dissolved in water, assembled into circular domains when immiscible dodecane was added, showing the presence of the surfactant at the water–dodecane interface of the emulsion droplets.
When tested for the oxidation of five different alcohols into ketones, the surfactant catalyst showed excellent properties in emulsion, including 100% activity and selectivity in the oxidation of organic molecules and a turnover number (the number of substrates converted before de-activation) that is 25 times higher than that of biphasic systems.
The authors of this work are from:
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China.
Reference
- Gao, J. et al. A direct imaging of amphiphilic catalysts assembled at the interface of emulsion droplets using fluorescence microscopy. Chem. Commun. doi: 10.1039/b713831h (2007). | Article |
