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

Nucléation et croissance de nanoparticules métalliques dans une matrice organique poreuse : application à la catalyse

Nanoparticles immobilized on a solid support are able to catalyse a wide range of reactions, and they offer advantages in the recycling and manipulation compared to homogeneous catalyst. In the present work, Preparation of such materials is described, and then their use in catalysis is checked. As support, we have chosen a microcellular polymer, known as polyHIPE, which is synthetised by polymerisation of high internal phase emulsion. As reactive part of the catalyst, we have generated palladium nanoparticles in-situ by an impregnation-reduction method. We have synthetised a wide range of Palladium/PolyHIPEs hybrid materials upon differents conditions and characterised them by techniques such as SEM, TEM, XPS and infra-red spectroscopy. We have tried to control particle sizes and dispersion state by a careful choice of the reactions parameters and/or a suitable matrix fonctionnalisation. To check the efficiency of our supports in catalysis, we have chosen a test reaction which is the Suzuki coupling reactions. We have found a strong dependance of the activity with the particles stabilization strenght, but also with the surface chemistry of the colloïds. Some of our supports offer a good activity, even compared to commercial and soluble catalysts, and also a satisfying reusability and selectivity. Those reactions have been extended to the less reactive non activated aryl chloride.Les nanoparticules supportées sur un support solide permettent de catalyser un grand nombre de réactions. Dans ce travail, nous nous sommes intéressé à la préparation du matériau, puis à son utilisation dans une réaction de catalyse. Le support utilisé est un polymère poreux insoluble de structure microcellulaire appelé polyHIPE, obtenu par la polymérisation d'une émulsion inverse concentrée. La partie réactive est apportée par la génération in situ de nanoparticules de palladium. Nous avons synthétisé une large gamme de matériaux hybrides palladium/polyHIPEs, puis nous les avons caractérisé par diverses techniques comme le MEB, le MET, l'XPS ou la spectroscopie infrarouge. Nous avons contrôlé la taille moyenne et l'état de dispersion des particules grâce au choix des conditions et/ou par une fonctionnalisation adéquate des supports. Nous avons choisi, pour tester l'efficacité en catalyse, de comparer nos supports sur la catalyse d'une réaction de couplage de type Suzuki-Miyaura. Nous avons mis en évidence une forte dépendance de l'activité avec la force de stabilisation des particules, ainsi qu'avec la chimie de surface des nanoparticules. Certains des catalyseurs préparés proposent une bonne activité par rapport aux catalyseurs commerciaux et même, dans un cas, par rapport à un catalyseur homogène. Deux études préliminaires proposent également des améliorations potentielles du support, pour la manipulation des catalyseurs (préparation sous forme de billes) ou leur utilisation dans des conditions de haute température (carbonisation)

Nucléation et croissance de nanoparticules métalliques dans une matrice organique poreuse : application à la catalyse

Les nanoparticules supportées sur un support solide permettent de catalyser un grand nombre de réactions. Dans ce travail, nous nous sommes intéressé à la préparation du matériau, puis à son utilisation dans une réaction de catalyse. Le support utilisé est un polymère poreux insoluble de structure microcellulaire appelé polyHIPE, obtenu par la polymérisation d'une émulsion inverse concentrée. La partie réactive est apportée par la génération in situ de nanoparticules de palladium. Nous avons synthétisé une large gamme de matériaux hybrides palladium/polyHIPEs, puis nous les avons caractérisé par diverses techniques comme le MEB, le MET, l'XPS ou la spectroscopie infrarouge. Nous avons contrôlé la taille moyenne et l'état de dispersion des particules grâce au choix des conditions et/ou par une fonctionnalisation adéquate des supports. Nous avons choisi, pour tester l'efficacité en catalyse, de comparer nos supports sur la catalyse d'une réaction de couplage de type Suzuki-Miyaura. Nous avons mis en évidence une forte dépendance de l'activité avec la force de stabilisation des particules, ainsi qu'avec la chimie de surface des nanoparticules. Certains des catalyseurs préparés proposent une bonne activité par rapport aux catalyseurs commerciaux et même, dans un cas, par rapport à un catalyseur homogène. Deux études préliminaires proposent également des améliorations potentielles du support, pour la manipulation des catalyseurs (préparation sous forme de billes) ou leur utilisation dans des conditions de haute température (carbonisation).Nanoparticles immobilized on a solid support are able to catalyse a wide range of reactions, and they offer advantages in the recycling and manipulation compared to homogeneous catalyst. In the present work, Preparation of such materials is described, and then their use in catalysis is checked. As support, we have chosen a microcellular polymer, known as polyHIPE, which is synthetised by polymerisation of high internal phase emulsion. As reactive part of the catalyst, we have generated palladium nanoparticles in-situ by an impregnation-reduction method. We have synthetised a wide range of Palladium/PolyHIPEs hybrid materials upon differents conditions and characterised them by techniques such as SEM, TEM, XPS and infra-red spectroscopy. We have tried to control particle sizes and dispersion state by a careful choice of the reactions parameters and/or a suitable matrix fonctionnalisation. To check the efficiency of our supports in catalysis, we have chosen a test reaction which is the Suzuki coupling reactions. We have found a strong dependance of the activity with the particles stabilization strenght, but also with the surface chemistry of the colloïds. Some of our supports offer a good activity, even compared to commercial and soluble catalysts, and also a satisfying reusability and selectivity. Those reactions have been extended to the less reactive non activated aryl chloride

Nucléation et croissance de nanoparticules métalliques dans une matrice organique poreuse (application à la catalyse)

Les nanoparticules supportées sur un support solide permettent de catalyser un grand nombre de réactions. Dans ce travail, nous nous sommes intéressé à la préparation du matériau, puis à son utilisation dans une réaction de catalyse. Le support utilisé est un polymère poreux insoluble de structure microcellulaire appelé polyHIPE, obtenu par la polymérisation d'une émulsion inverse concentrée. La partie réactive est apportée par la génération in situ de nanoparticules de palladium. Nous avons synthétisé une large gamme de matériaux hybrides palladium/polyHIPEs, puis nous avons caractérisé par diverses techniques comme le MEB, le MET, l'XPS ou la spectroscopie infrarouge. Nous avons contrôlé la taille moyenne et l'état de dispersion des particules grâce au choix des conditions et/ou par une fonctionnalisation adéquate des supports. Nous avons choisi, pour tester l'efficacité en catalyse, de comparer nos supports sur la catalyse d'une réaction de couplage de type Suzuki-Miyaura. Nous avons mis en évidence une forte dépendance de l'activité avec la force de stabilisation des particules, ainsi qu'avec la chimie de surface des nanoparticules. Certains des catalyseurs préparés proposent une bonne activité par rapport aux catalyseurs commerciaux et même, dans un cas, par rapport à un catalyseur homogène. Deux études préliminaires proposent également des améliorations potentielles du support, pour la manipulation des catalyseurs (préparation sous forme de billes) ou leur utilisation dans des conditions de haute température.BORDEAUX1-BU Sciences-Talence (335222101) / SudocMULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF

Long-term Stability of Graphene Based Nanofluids

International audienceLong-term stability of nanofluids remains quite challenging for graphene-based nanofluid preparation. This is however a crucial aspect for their use in heat transfer applications. In this study, we have used the derived Hummers’ method for graphene oxide preparation. Then, reduction of graphene oxide is realized in various conditions. Stability of nanofluids of graphene oxide and reduced graphene oxide are investigated. We show graphene oxide nanofluids suffer of rapid destabilization which dramatically reduces the thermal properties. Nanofluids prepared with reduced graphene oxide show an improved stability depending of the reduction conditions. NaBH4 is recommended compared to N2H4 for which impurities are introduced in the graphene structure and destabilization easily occurs

Rheological properties and surface tension of stable graphene oxide and reduced graphene oxide aqueous nanofluids

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A critical review on thermal conductivity enhancement of graphene-based nanofluids

International audienceNanofluids which consist of nanoparticles added to conventional fluids (or base fluids) are considered as promising heat transfer fluids. Compared to metal, metal oxide nanoparticles and carbon nanotubes, graphene with its extremely high intrinsic thermal conductivity became the best candidate to design nanofluids. Such nanofluids have the potential to be highly-efficient heat transfer fluid by reducing loss of heat and increasing cooling rates. Over the last ten years, graphene-based nanofluids have shown significant thermal conductivity enhancements, however due to the numerous and interlinked parameters to consider, optimisation of their efficiency is still challenging. The present review article analyses and discusses the reported thermal conductivity in term of performance with respect to the amount of the used graphene to develop the prepared nanofluids. The enhancement of thermal conductivity must meet the minimal graphene amount due to its production cost and because graphene nanoparticles induces high viscosity in the nanofluid leading to higher energy consumption for the heat transfer systems. Unprecedented in the literature, this work proposes a simple approach to quantitatively compare the enhancement of the thermal conductivity of the nanofluids. The thermal conductivity performance parameter introduced could be applied to all nanofluid families and may become a reference tool in the nanofluid community. Such tool will help to determine the optimal preparation conditions without compromising the superior thermal performances

Integrative chemistry toward the first spontaneous generation of gold nanoparticles within macrocellular polyHIPE supports (Au@polyHIPE) and their application to eosin reduction

Gold nanoparticles have been generated for the first time within open-cell macrocellular polyHIPE matrices, leading to new hybrid organic–inorganic catalytic supports labelled “Au@polyHIPE”. The overall synthesis can be realized with ease, as it is based on the spontaneous nucleation of gold nanoparticles. These new hybrid organic–inorganic materials have then been tested for heterogeneous catalysis, particularly for eosin Y reduction in the presence of NaBH4. In this reductive media the as-synthesized hybrid catalytic supports “Au@polyHIPE” exhibit a good activity. All the kinetic parameters are discussed in term of internal surface (porosity), external surface (shape), temperature and gold loading revealing a first order reaction

High-rate synthesis of graphene by a lower cost chemical vapor deposition route

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