Hydrochlorination of acetylene using supported bimetallic Au-based catalysts

A detailed study of the hydrochlorination of acetylene and higher alkynes using a supported gold catalyst is described and discussed. A series of reactions using sequential exposure of the catalysts to C2H2 and HCl demonstrate that exposure to HCl prior to reaction of C2H2/HCl leads to enhanced activity whereas exposure to C2H2 leads to deactivation. The reaction of higher alkynes is affected by steric factors with the trend in activity being: acetylene (ca. 40 % conversion)>> hex-1-yne (10%)>phenylacetylene (7 %) > hex-2-yne (2 %) under standard reaction conditions. Using 1H-NMR spectroscopy we have found that for hex-1-yne and phenyl acetylene the anti-Markovnikov product is formed by anti addition of HCl. However, the Markovnikov products are equivalent for syn- and antiaddition of HCl, and hence we investigated the reaction using deuterated substrates and confirmed the products are formed by the anti addition of HCl. The reaction mechanism is discussed in detail

Microscopic investigation of single-wall carbon nanotube uptake by Daphnia magna

The objectives of this study were to determine the extent of absorption of functionalized single-wall carbon nanotubes (SWCNTs) across the gut epithelial cells in Daphnia magna. Several microscopic techniques were utilized, including micro-Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM) and selective area diffraction (SAD). In an effort to examine the variation in uptake due to surface properties, four groups of differently functionalized SWCNTs were used: hydroxylated (OH-SWCNTs), silicon dioxide (SiO₂-SWCNTs), poly aminobenzenesulfonic acid (PABS-SWCNTs) and polyethylene glycol (PEG-SWCNTs). Raman spectroscopy was able to detect OH-SWCNTs within the gut, but lacked the spatial resolution that is needed to identify lower concentrations of SWCNTs that may have been absorbed by body tissues. Initially, low-magnification imaging of exposed D. magna sections in the TEM revealed several features, which suggested absorption of SWCNTs. However, subsequent analysis with additional techniques (HRTEM, X-ray energy-dispersive spectroscopy and SAD) indicated that these features were either artifacts produced via the specimen staining process or consisted of non-graphitic, organic structures. This latter observation emphasizes the inherent difficulty in resolving SWCNTs embedded within a complex, organic matrix, as well as the care with which imaging results must be interpreted and supplemented with other, more analytical techniques.Keywords: Nanomaterials, Electron microscopy, Absorptio

Size-Dependent Structural Distortions in One-Dimensional Nanostructures

No abstract.Keywords: Composites, Inorganic synthesis, Chalcogenides, Binary nanoparticle superlattices, Stability, Misfit layer compounds, Nanomaterials, Nonodisperse nanocrystals, Nanocrystal superlattices, Gold, Organization, Shape, Hybrid material

Overgrowth of rhodium on gold nanorods

[Image: see text] This study focuses on the deposition and growth mode of rhodium (Rh) on gold (Au) seed nanorods (NRs). Using a combination of scanning transmission electron microscopy imaging, energy-dispersive X-ray spectroscopy, and UV–visible absorption spectroscopy, we show that Rh deposition results in an uneven overlayer morphology on the Au NR seeds, with a tendency for Rh deposition to occur preferentially on the Au NR ends. The results suggest that complex and kinetically driven metal–metal interactions take place in this system

Qualitative Multiplatform Microanalysis of Individual Heterogeneous Atmospheric Particles from High-Volume Air Samples

High-resolution microscopic analysis of individual atmospheric particles can be difficult, because the filters upon which particles are captured are often not suitable as substrates for microscopic analysis. Described here is a multiplatform approach for microscopically assessing chemical and optical properties of individual heterogeneous urban dust particles captured on fibrous filters during high-volume air sampling. First, particles embedded in fibrous filters are transferred to polished silicon or germanium wafers with electrostatically assisted high-speed centrifugation. Particles are clustered in an array of deposit areas, which allows for easily locating the same particle with different microscopy instruments. Second, particles with light-absorbing and/or light-scattering behavior are identified for further study from bright-field and dark-field light-microscopy modes, respectively. Third, particles identified from light microscopy are compositionally mapped at high definition with field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Fourth, compositionally mapped particles are further analyzed with focused ion-beam (FIB) tomography, whereby a series of thin slices from a particle are imaged, and the resulting image stack is used to construct a three-dimensional model of the particle. Finally, particle chemistry is assessed over two distinct regions of a thin FIB slice of a particle with energy-filtered transmission electron microscopy (TEM) and electron energy-loss spectroscopy associated with scanning transmission electron microscopy (STEM)