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- 2010 (4) (entfernen)
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- Ionic liquid (2)
- Core shell (1)
- Gold nanoparticle (1)
- Hybrid materials (1)
- Ionic liquid templating (1)
- Iron carbide (1)
- Nanosilver (1)
Nanosilver is increasingly used in optics, medicine and analytical chemistry. We recently reported on the synthesis and properties of novel peptide-coated chiral nanosilver [1] using a small hexapeptide based on the amino acids CKK. In a continuation of our previous work, we use the peptides to catalyse TEOS hydrolysis in order to form a dense silica layer shell around a single nanoparticle, preventing chemical etching, allowing their inclusion in other inorganics, and making them biocompatible. Because of mild reaction conditions, the peptide integrity is ensured, as the chiral information which is contained in the nanoparticle. Moreover, these novel core-shell structures remain well-dispersed and are biocompatible. The possibility of further processing (creation of metamaterials etc.) is also in the focus of our interest.
Ionic liquids (ILs) have attracted tremendous interest in the recent past for their potential in many chemical fields. The current report explores the effects of a set of ILs based on the 1-ethyl-3-methyl-imidazolium cation and different anions on the formation of gold nanoparticles. X-Ray diffraction finds face-centered cubic gold in all cases, but transmission electron microscopy (TEM) shows that there are distinct differences in particle formation and stabilization with the ethyl sulfate (ES), trifluoromethanesulfonate (TfO) and methanesulfonate (MS) anions. With the MS anion, nanoparticles with diameters between 5 and 7 nm form, which increasingly aggregate at higher reaction temperatures. With TfO, also small 5 to 7 nm particles form, but only at low temperatures. Above ca. 160 °C, large, ill-defined and aggregated particles form. With ES, polydisperse samples form at all temperatures except 160 °C. In this case the nanoparticles appear often surrounded by an IL film, which appears to stabilize individual, ca. 15 to 20 nm particles. Dynamic light scattering and UV/Vis spectroscopy further show that in suspension the particles are, much like seen in the TEM, more strongly aggregated with higher reaction temperatures. In summary, the results suggest that there are very specific IL-gold interactions that are responsible for the formation of gold particles with an IL-specific shape, size, and aggregation behavior.
Dispersions of Fe3C nanoparticles in several ionic liquids (ILs) have been investigated. The ILs are based on 1-ethyl-3-methylimidazolium [Emim] and 1-butyl-3-methylimidazolium [Bmim] cations. Anions are ethylsulfate [ES], methanesulfonate [MS], trifluoromethylsulfonate (triflate) [TfO], tetrafluoroborate [BF4], dicyanamide [N(CN)2], and thiocyanate [SCN]. Among the ILs studied, [Emim][SCN] and [Emim][N(CN)2] stand out because only in these ILs have stable and transparent nanoparticle dispersions been obtained. All other ILs lead to blackish, slightly turbid dispersions or to completely nontransparent suspensions, which often contain undispersed sediment. UV/vis spectroscopy, transmission electron microscopy, and X-ray scattering suggest that the reason for the stabilization of the Fe3C nanoparticles in [Emim][SCN] is the leaching of traces of iron from the particles (without affecting the crystal structure of the Fe3C particles). The resulting particle surface is thus carbon-rich, which presumably favors the stabilization of the particles. A similar explanation can be postulated for [Emim][N(CN)2], with the dicyanamide anion also being a good ligand for iron.