Chemi- vs physisorption in the radical functionalization of single-walled carbon nanotubes under microwaves

The effect of microwaves on the functionalization of single-walled carbon nanotubes (SWNTs) by the diazonium method was studied. The usage of a new approach led to the identification of the strength of the interaction (physical or chemical) between the functional groups and the carbon nanotube surface. Moreover, the nature (chemical formula) of the adsorbed/grafted functional groups was determined. According to thermogravimetric analysis coupled with mass spectrometry and Raman spectroscopy, the optimal functionalization level was reached after 5 min of reaction. Prolonged reaction times can lead to undesired reactions such as defunctionalization, solvent addition and polymerization of the grafted functions. The strength (chemi- vs physisorption) of the bonds between the grafted functional groups and the SWNTs is discussed showing the occurrence of physical adsorption as a consequence of defunctionalization after 15 min of reaction under microwaves. Several chemical mechanisms of grafting could be identified, and it was possible to distinguish conditions leading to the desired chemical grafting from those leading to undesired reactions such as physisorption and polymerization

Dramatic enhancement of double-walled carbon nanotube quality through a one-pot tunable purification method.

The purification process we propose is a one-pot gas-phase treatment; the CNT powder is simply submitted to a chlorine/oxygen atmosphere at around 1000 °C for 2 h. By varying the oxygen content in an excess of chlorine, the conditions were optimized in order to efficiently remove both metal (catalyst) and carbon impurities from DWCNT samples. Even if a high amount of sample is lost under the oxidative conditions used, a selective elimination of the carbon impurities obviously occurs and a metal impurity removal yield of 99% is obtained from thermogravimetry. Based on a multi-technique approach, we show that the purified DWCNTs are of high structural quality without any surface functionalization. This improvement of the wall quality through the chlorine/oxygen action is seen in particular with a division by 15 of the D over G band intensity of the Raman spectra. Among the existing procedures, the advantages of our purification method are indisputably its simplicity, low time-consuming and high efficiency combined with an enhanced quality of the purified CNTs. Such quasi-pure DWCNTs have high interest since they offer a unique opportunity to study the intrinsic properties and effects of the nanotubes themselves

Protecting Carbon Nanotubes from Oxidation for Selective Carbon Impurity Elimination

Purity of carbon nanotubes (CNTs) is essential to avoid a dramatic decrease in their performances. In addition to metallic impurities, carbonaceous impurities have been shown to be responsible for pronounced effects. However, they are highly difficult to be selectively removed from CNT samples because of the similar chemical reactivity of these two kinds of carbon species. The existing purification methods often lead to high CNT consumption (>90 wt %). The proposed method consists of a one-pot gas-phase treatment combining chlorine and oxygen. The CNT powder maintained in a chlorine stream is submitted to oxygen at moderate temperature [350 and 500 °C for single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs), respectively], and the thermal treatment is then pursued at 900–1000 °C under chlorine alone. Our work reveals that this approach is able to significantly improve the selectivity of elimination of carbonaceous impurities. Thanks to the proposed purification treatment, only 19 and 11 wt % of carbon species (mainly carbon impurities) are lost for DWCNTs and SWCNTs, respectively. The mechanism proposed involves a protective effect by grafting of chlorine favored to the CNT walls. Because our simple one-pot purification method is also versatile and scalable, it opens new perspectives for CNT applications in high-added value fields

Entretien : La prose ou la lisibilité du hors-cadre chez Jean-Marie Gleize

Cher Jean-Marie Je ne vais pas tant t’interroger sur prose en proses, sur post-poésie, littéralité, littérature documentaire, dont il a déjà été beaucoup question à ton sujet. À Lyon tu enseignes, tu fondes des revues, tu animes des lieux, de jeunes écrivains que tu as contribué à former intensifient, radicalisent ces décloisonnements que tu avais commencé de théoriser, et qui ont été fertiles, le sont. Voilà, je te propose quelque chose : je vais développer cinq questions et puis tu répondra..

Dispersion of Graphene in Water for Heat Dissipation Applications

International audienc

Graphene-based nanofluids for heat transfer applications

International audienc

Graphene for Water-Based Nanofluid Preparation: Effect of Chemical Modifications on Dispersion and Stability

International audienceGraphene, whatever its number of layers, is recognized for heat and thermal transfer ability. As it is widely known to be highly hydrophobic, its use in water-based nanofluid development requires first to improve both their dispersion and stability properties. Here, we have investigated several ways to chemically modify the surface properties of multi-layer graphene in order to increase their hydrophilic character. Chemical reactivity of graphene was deeply analyzed based on a multi-scale characterization using TEM, Raman spectroscopy and TGA-MS coupled technique. By optimizing and combining both covalent and non-covalent functionalization, stable graphene-based nanofluids under static conditions could be prepared with a straightforward approach. Moreover, we have investigated their flowing behavior. Contrary to graphene nanosheets strongly attacked by HNO3, under a gentler oxidation treatment using KMnO4, stability is well preserved under flowing conditions. Such high-stability nanofluids could help toward the practical use of graphene-based dispersions as heat transfer fluid in flowing systems

Surface tension of functionalized MWCNT-based nanofluids in water and commercial propylene-glycol mixture

International audienceNanofluids which consist of the addition of nanoparticles in a base fluid are envisaged for a large domain of applications. For many of them, the surface tension (ST) behavior of the prepared nanofluids is a key parameter to exploit their thermophysical properties. Due to their remarkable properties, carbon nanotubes (CNTs) are commonly used to develop nanofluids. However, the evolution of the ST of CNT-based nanofluids is still far from being understood and predictable. In the present work, two base fluids were used: water and a commercial mixture of propylene-glycol/water (around 40:60 wt%). The impact of the used multi-walled CNT (MWCNT) addition, MWCNT concentration (0.001 and 0.1 wt%) and temperature variation (273.15–333.15 K) on the density and ST evolution for the two kinds of CNT-based nanofluids is studied. The chemically modified MWCNTs are assumed to bear both localized hydrophilic areas due to grafted functional groups and remaining hydrophobic surfaces. The found difference in ST behavior between the two types of nanofluids is explained in light with the involved interfaces in each nanofluid. ST evolution is found to strongly depend on the CNT surface properties

Development of chemical treatments to improve processability of carbon nanomaterials(carbon nanotubes and graphene)

International audienc

Magnetism for understanding catalyst analysis of purified carbon nanotubes

International audienceThe precise quantification of catalyst residues in purified carbon nanotubes is often a major issue in view of any fundamental and/or applicative studies. More importantly, since the best CNTs are successfully grown with magnetic catalysts, their quantification becomes strictly necessary to better understand intrinsic properties of CNT. For these reasons, we have deeply analyzed the catalyst content remained in nickel-yttrium arc-discharge single walled carbon nanotubes purified by both a chlorine-gas phase and a standard acid-based treatment. The study focuses on Ni analysis which has been investigated by transmission electron microscopy, X-ray diffraction, thermogravimetry analysis, and magnetic measurements. In the case of the acid-based treatment, all quantifications result in a decrease of the nanocrystallized Ni by a factor of two. In the case of the halogen gas treatment, analysis and quantification of Ni content is less straightforward: a huge difference appears between X-ray diffraction and thermogravimetry results. Thanks to magnetic measurements, this disagreement is explained by the presence of ions, belonging to NiCl2 formed during the Cl-based purification process. In particular, NiCl2 compound appears under different magnetic/crystalline phases: paramagnetic or diamagnetic, or well intercalated in between carbon sheets with an ordered magnetic phase at low temperature