Spectroscopic Evidence of Carbon Nanotubes’ Metallic Character Loss Induced by Covalent Functionalization via Nitric Acid Purification

A detailed characterization of covalently functionalized HiPco single-walled carbon nanotubes (SWNTs) has been carried out using several physicochemical methods (thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Raman scattering). The chemical process, finally leading to SWNT?ester derivatives, starts from nitric acid purification of pristine SWNTs. Besides the efficiency of the functionalization, we show that a loss of metallic character of the carbon nanotubes is initiated by the nitric acid treatment of pristine SWNTs and is maintained in the final SWNT ester derivatives. A higher reactivity of the metallic tubes is also demonstrated

Synthesis and characterization of polymers for nonlinear optical applications

International audienceA difunctional NLO Azo-Dye chromophore has been synthesized and polymerization has been performed with a comonomer bearing a side-chain epoxy group. Deposition of the polymer on glass substrates was performed by spin-coating, resulting in uniform films up to 2 µm thickness. The orientation of the chromophore was performed under a " pin-to-plane " positive corona discharge followed by a heat-treatment in order to obtain reticulation of the films. Molecular orientation has been investigated using UV-Vis. and Raman spectroscopy. Poling of the films results in a decay of absorbency as well as in a blue shift of the spectrum. At the same time, the 1600 cm-1 band disappears from the Raman spectra, indicating orientation of the chromophores. Cross-linking has been studied by FTIR and all-optical poling and showed an improved stability of the electro-optic thin films

Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Bromination of double-walled carbon nanotubes (DWCNTs) was carried out using a saturated vapor of Br2 at room temperature with or without a pretreatment in bromine water. X-ray photoelectron spectroscopy revealed that ultrasound pretreatment modified the chemical state of bromine in the product. The binding energies of the Br 3d electrons in the pre-sonicated DWCNT sample were between those characteristic of the covalent C–Br bonds and the negatively charged Br2 molecules, observed when the pretreatment was not performed. Raman spectroscopy, however, clearly evidenced Br–Br vibrations in both brominated samples. Calculations of CNT–Br2 models within density functional theory were used to propose that the electronic state of a Br2 molecule depends on the adsorption site. The bromine molecules prefer to be located near edge hydroxyl groups, which acept the electron density from Br2. This increases the binding energy of Br 3d levels as compared to that for Br2 molecules in other adsorption sites

Fusions municipales au Québec, coopération intercommunale en France : deux approches convergentes ?

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Gold Nanoparticles as Probes for Nano-Raman Spectroscopy: Preliminary Experimental Results and Modeling

This paper presents an effective Tip-Enhanced Raman Spectrometer (TERS) in backscattering reflection configuration. It combines a tip-probe nanopositioning system with Raman spectroscope. Specific tips were processed by anchoring gold nanoparticles on the apex of tapered optical fibers, prepared by an improved chemical etching method. Hence, it is possible to expose a very small area of the sample (~20 nm2) to the very strong local electromagnetic field generated by the lightning rod effect. This experimental configuration was modelled and optimised using the finite element method, which takes into account electromagnetic effects as well as the plasmon resonance. Finally, TERS measurements on single-wall carbon nanotubes were successfully performed. These results confirm the high Raman scattering enhancement predicted by the modelling, induced by our new nano-Raman device

Mesoporous silica encapsulating Rh(0) colloids : structure and catalytic properties

International audienceColloidal metallic precursors have been used successfully to prepare new rhodium(0) supported mesoporous catalysts. The aqueous dispersion of Rh(0) previously synthesized was added either (i) to preformed mesoporous silica (MCM-41 or SBA-15) or (ii) to the gel mixture used for the solid synthesis. The different materials have been characterized by TEM, N2 adsorption-desorption, PXRD and elemental analysis. All the solids, especially those obtained by the direct route, reveal well-organized mesoporous structures. Their catalytic activity was investigated in the hydrogenation of aromatic ring (conversion of styrene into ethylcyclohexane) and was shown to be better in hexane than in ethanol. The solids prepared by impregnation of MCM-41 and SBA-15 with Rh(0) colloids (pathway (i)) afforded the best yields of ethylcyclohexane (up to 100% in hexane and 72% in ethanol, respectively)

Preferred attachment of fluorine near oxygen-containing groups on the surface of double-walled carbon nanotubes

Two samples of double-walled carbon nanotubes (DWCNTs), one with well-graphitized nanotube walls and another containing oxygen at outer nanotube surfaces, were fluorinated at room temperature using gaseous BrF3. The products were comprehensively studied using transmission electron microscopy, Raman scattering, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopies. The experimental data found twice the concentration of sidewall fluorine in the oxygenated DWCNTs. Quantum chemical modeling supported the experimental results revealing the preferable development of CF areas near the carbon atoms bonded with oxygen-containing groups. This observation demonstrates that tuning of the physical and chemical properties of carbon nanotubes can be achieved via the controlled co-modification by fluorine and oxygen functional groups