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

Quantum correlations and quantum fisher information of two qubits in the presence of the time-dependent coupling effect

In this paper, we consider two separate Jaynes–Cummings (JC) nodes with a nonidentical qubit-field system in the presence of dissipation terms. We reveal the influence of the time variation of the coupling terms on some important measures when the qubits are immersed in a vacuum. The density matrix for the two qubits initially in Bell states are obtained. The dynamical behavior of the quantum discord (QD), classical correlation (CC), qubit-qubit entanglement, and quantum Fisher information (QFI) is investigated. We explore the relationship among QD, CC, qubit-qubit entanglement, and QFI in the absence and presence of the dissipation effect during the time evolution. Furthermore, we show the main optimal conditions for obtaining a high level of correlation and coherence between the two qubits. © 2020, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature

De l’interêt du dichlore pour une élimination hautement sélective des impuretés métalliques et carbonées des nanotubes de carbone

Since their discovery, carbon nanomaterials such as carbon nanotubes (CNTs) and graphene have raised a great interest in the scientific community. Indeed, they are impressive materials thanks to their unique and remarkable properties: nanometric size and lightness, high chemical stability due to their all-carbon structure, high specific surface area. However, after their synthesis, available CNT samples contain impurities (metallic catalyst residues and carbonaceous). These unwanted particles hinder exploitation of the properties of the CNTs and thus prevent the scale-up transfer. This is the reason why a post-synthesis purification treatment is required. Existing standard methods are often too aggressive, time-consuming because of the multi steps involved and they lead to low sample yields. In this work, we have developed an alternative purification approach. The combination of two reactants in gas phase (chlorine and dioxygen) allowed us to propose an original method consisting of a one-pot treatment. Thanks to this simple technique, we were able to substantially enhance the removal selectivity of both metallic based and carbonaceous impurities while preserving CNT quality; the sample yields obtained with our method are indeed high. In addition to its simplicity and efficiency, this method is versatile since it has been successfully applied to various types of CNTs. Finally, these works have a significant social-economic impact and in terms of innovation because these purified CNTs can be used for sustainable development. The prepared CNT-based nanofluids have the potential to be utilized as heat transfer fluid in solar panels. We have also shown that these carbon nanomaterials, once being functionalized, had a high interest in green synthesis methods, in particular in enzymatic biocatalysis.Les nanomatériaux carbonés tels que les nanotubes de carbone (CNTs) et le graphène, suscitent un engouement certain dans toute la communauté scientifique depuis leur découverte. En effet, leur taille nanométrique et leur structure unique leur confèrent de nombreuses propriétés jusqu'alors inégalées par les matériaux connus. Grâce à leur nature « tout-carbone », ils sont stables chimiquement, possèdent une bonne tenue mécanique et une surface spécifique élevée. Cependant les échantillons produits et disponibles pour développer des applications contiennent inévitablement des impuretés (de nature métallique et carbonée). Ces dernières gênent considérablement l’exploitation des propriétés des CNTs et le transfert technologique vers les applications potentielles. Un traitement de purification post-synthèse de ces nanoparticules s’avère donc indispensable. Des méthodes de purification existent mais ne sont pas satisfaisantes puisqu’elles sont multi-étapes, chronophages, complexes et à faible rendement. Ce travail de thèse avait pour objectif de développer une méthode alternative de purification des CNTs. L’utilisation d’un couplage de gaz réactionnels (le dichlore et le dioxygène) a permis de proposer une approche originale qui requiert un seul traitement et qui permet d’augmenter substantiellement la sélectivité d’élimination des impuretés tout en préservant les CNTs. Les rendements obtenus par cette méthode sont donc élevés. En plus de sa simplicité et de son efficacité, ce traitement a l’énorme avantage de convenir à plusieurs types d’échantillons de CNTs. Enfin, ces travaux ont un fort impact en termes socio-économique et d’innovation puisque ces nanoparticules sont au service du développement durable. Les échantillons de CNTs purifiés obtenus ont notamment été testés pour la production de nanofluides pour des applications de transfert thermique dans les panneaux solaires. Nous avons également montré que ces nanomatériaux, une fois fonctionnalisés, présentaient un intérêt certain dans les procédés de synthèse verts, notamment en bio-catalyse enzymatique

Chlorine for a high selective elimination of metallic and carbonaceous impurities from carbon nanotubes

Les nanomatériaux carbonés tels que les nanotubes de carbone (CNTs) et le graphène, suscitent un engouement certain dans toute la communauté scientifique depuis leur découverte. En effet, leur taille nanométrique et leur structure unique leur confèrent de nombreuses propriétés jusqu'alors inégalées par les matériaux connus. Grâce à leur nature « tout-carbone », ils sont stables chimiquement, possèdent une bonne tenue mécanique et une surface spécifique élevée. Cependant les échantillons produits et disponibles pour développer des applications contiennent inévitablement des impuretés (de nature métallique et carbonée). Ces dernières gênent considérablement l’exploitation des propriétés des CNTs et le transfert technologique vers les applications potentielles. Un traitement de purification post-synthèse de ces nanoparticules s’avère donc indispensable. Des méthodes de purification existent mais ne sont pas satisfaisantes puisqu’elles sont multi-étapes, chronophages, complexes et à faible rendement. Ce travail de thèse avait pour objectif de développer une méthode alternative de purification des CNTs. L’utilisation d’un couplage de gaz réactionnels (le dichlore et le dioxygène) a permis de proposer une approche originale qui requiert un seul traitement et qui permet d’augmenter substantiellement la sélectivité d’élimination des impuretés tout en préservant les CNTs. Les rendements obtenus par cette méthode sont donc élevés. En plus de sa simplicité et de son efficacité, ce traitement a l’énorme avantage de convenir à plusieurs types d’échantillons de CNTs. Enfin, ces travaux ont un fort impact en termes socio-économique et d’innovation puisque ces nanoparticules sont au service du développement durable. Les échantillons de CNTs purifiés obtenus ont notamment été testés pour la production de nanofluides pour des applications de transfert thermique dans les panneaux solaires. Nous avons également montré que ces nanomatériaux, une fois fonctionnalisés, présentaient un intérêt certain dans les procédés de synthèse verts, notamment en bio-catalyse enzymatique.Since their discovery, carbon nanomaterials such as carbon nanotubes (CNTs) and graphene have raised a great interest in the scientific community. Indeed, they are impressive materials thanks to their unique and remarkable properties: nanometric size and lightness, high chemical stability due to their all-carbon structure, high specific surface area. However, after their synthesis, available CNT samples contain impurities (metallic catalyst residues and carbonaceous). These unwanted particles hinder exploitation of the properties of the CNTs and thus prevent the scale-up transfer. This is the reason why a post-synthesis purification treatment is required. Existing standard methods are often too aggressive, time-consuming because of the multi steps involved and they lead to low sample yields. In this work, we have developed an alternative purification approach. The combination of two reactants in gas phase (chlorine and dioxygen) allowed us to propose an original method consisting of a one-pot treatment. Thanks to this simple technique, we were able to substantially enhance the removal selectivity of both metallic based and carbonaceous impurities while preserving CNT quality; the sample yields obtained with our method are indeed high. In addition to its simplicity and efficiency, this method is versatile since it has been successfully applied to various types of CNTs. Finally, these works have a significant social-economic impact and in terms of innovation because these purified CNTs can be used for sustainable development. The prepared CNT-based nanofluids have the potential to be utilized as heat transfer fluid in solar panels. We have also shown that these carbon nanomaterials, once being functionalized, had a high interest in green synthesis methods, in particular in enzymatic biocatalysis

Dynamic viscosity of purified MWCNT water and water-propylene glycol-based nanofluids

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Graphene-based nanofluids: structural quality of graphene vs. dispersion quality

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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)

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Dynamic Viscosity of Purified Multi-Walled Carbon Nanotubes Water and Water-Propylene Glycol-Based Nanofluids

International audienceWe report in this study the experimental investigation of the dynamic viscosity of purified multi-walled carbon nanotubes (MWCNT) water and water-propylene glycol-based nanofluids in the temperature range 10-80 degrees C. Four weight concentrations of MWCNTs are considered, between 0.005 and 0.1 wt.%. Triton X-100, a common nonionic surfactant, is used to disperse the nanotubes and stabilize the nanofluids as evidenced by optical characterization. Purified and non-damaged MWCNTs are used for nanofluid preparation by the two-step method. MWCNT characterization is deeply investigated from a set of complementary techniques such as thermogravimetric analysis, transmission electron microscopy, and Raman spectroscopy. The studied nanofluids behave as Newtonian fluids for low nanotube content while a shear-thinning behavior is noticed for higher concentration. Finally, the viscosity enhancement of nanofluids with MWCNT loading is compared to the modified Maron-Pierce model considering the presence of aggregates and their size obtained from optical observations

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

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