The Experts below are selected from a list of 2214 Experts worldwide ranked by ideXlab platform
André Hamwi - One of the best experts on this subject based on the ideXlab platform.
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Enhanced concentration of dispersed Carbon Nanofibres in organic solvents through their functionalization by fluorination
Journal of Colloid and Interface Science, 2013Co-Authors: Nadiège Nomède-martyr, Elodie Disa, Katia Guérin, Marc Dubois, Lawrence Frezet, André HamwiAbstract:Abstract Covalent functionalization through pure molecular gaseous fluorination has been applied on Carbon Nanofibres. Nuclear magnetic resonance and thermal gravimetric analysis investigations have been performed on fluorinated Carbon Nanofibres in order to determine the chemical and thermal stability of the C–F bonding. The high covalency obtained allows no significant modification of the physicochemical nanostructure of fluorinated Carbon Nanofibres after sonification. Such modification of surface chemistry leads to a high increase in the limit concentration of dispersed Carbon Nanofibres in organic solvents without surfactant. An exciting maximum of 570 mg L−1 of fluorinated Nanofibres can be homogeneously dispersed in N-methylpyrrolidone, whereas 310 mg L−1 is the maximum for non-fluorinated Carbon Nanofibres. In order to understand such dispersibility differences, Hildebrand and Hansen solubility theory has been used.
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The effect of nanostructure on the thermal properties of fluorinated Carbon Nanofibres
Carbon, 2011Co-Authors: Elodie Disa, Katia Guérin, Marc Dubois, Francis Masin, Hayat Kharbache, André HamwiAbstract:Abstract Using thermogravimetic analysis in air, the thermal properties of fluorinated Carbon Nanofibres have been investigated. The fluorination level, the C–F bonding, the number of structural defects and the distribution of fluorine atoms in the Carbon matrix have been modified using three fluorination routes, (i) a direct process using a flux of pure molecular fluorine F 2 (dynamic process), (ii) a filling of a closed reactor by this reactive gas (static process) and (iii) controlled fluorination using the thermal decomposition of a solid fluorinating agent TbF 4 . At given fluorine contents, only the location of the fluorine atoms within the nanofibre changes the thermal stability, which can be increased up to 480 °C; such improvement is obtained when the fluorinated regions are located in the outer shell (tubes).
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New synthesis methods for fluorinated Carbon Nanofibres and applications
Journal of Fluorine Chemistry, 2010Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, André Hamwi, Francis Masin, L. Spinelle, Hayat Kharbache, Alexander P. Kharitonov, Jérôme Brunet, Christelle VarenneAbstract:Several new synthesis methods of fluorinated Carbon Nanofibres, such as controlled fluorination using fluorinating agent (TbF4 or XeF 2), or assisted fluorination under UV and gamma irradiation, are reviewed and compared with the direct fluorination using undiluted fluorine gas. The results highlight the different fluorinationmechanisms for the direct fluorination and the new methods. The other advantage of those alternative fluorination routes is the possibility to provide fine tuning of the fluorination level, i.e. from F/C atomic ratio close to zero, as a functionalization, to the unity (CF1) according to the required application, electrochemical or tribological. Two applications are described in this paper as a function of the fluorine content: protection against ozonation and use as solid lubricants. © 2010 Elsevier B.V. All rights reserved.
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Carbon Nanofibres fluorinated using tbf4 as fluorinating agent part i structural properties
Carbon, 2008Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, Ziad Fawal, Dimitri A Ivanov, Loic Vidal, André HamwiAbstract:Abstract Fluorination of Carbon Nanofibres (CNFs) under fluorine gas at 480 °C leads to high fluorine content but also to some partial exfoliation. In order to avoid such phenomenon, an alternative route has been performed at temperatures ranged between 420 and 500 °C using a fluorinating agent, i.e. terbium tetrafluoride. The structural properties of the fluorinated CNFs are discussed taking into account the data of 13 C solid state NMR, Raman spectroscopy, SEM, TEM and XRD. Whatever the fluorination temperature, a fluorinated phase of (CF) n structural type, is formed contrary to the direct process using F 2 gas for which a (C 2 F) n -type fluorinated phase appeared for fluorination temperatures lower than 450 °C. The progressive release of fluorine atoms from the thermal decomposition of TbF 4 allows an homogenous distribution of the fluorinated part into the CNFs matrix and the formation of a unique (CF) n type structure. Moreover, for high fluorination temperatures (480 and 500 °C), the fluorination leads to some Nanofibres breaking but in no way to exfoliation.
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Carbon Nanofibres fluorinated using TbF4 as fluorinating agent. Part II: Adsorption and electrochemical properties
Carbon, 2008Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, Francis Masin, Axel Houdayer, André HamwiAbstract:Abstract The adsorption and electrochemical properties of the Carbon Nanofibres fluorinated using TbF4 as fluorinating agent have been investigated by nitrogen measurements and galvanostatic discharge in primary lithium batteries, respectively. These properties are compared to those obtained for Carbon Nanofibres fluorinated by pure fluorine gas (direct fluorination). The amount of structural defects, the formed structural phase and the possible partial exfoliation have been investigated in order to understand the properties difference for the CNFs fluorinated by the two routes. Higher amounts of both dangling bonds and CF2, CF3 groups were registered by EPR and 19F NMR for CNFs fluorinated by direct route. Moreover, SEM study underlines the partial exfoliation, which occurred only during the direct fluorination at 480 °C. As a consequence, CNFs fluorinated by TbF4 develop the highest faradic yield for a use in primary lithium battery.
Katia Guérin - One of the best experts on this subject based on the ideXlab platform.
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Enhanced concentration of dispersed Carbon Nanofibres in organic solvents through their functionalization by fluorination
Journal of Colloid and Interface Science, 2013Co-Authors: Nadiège Nomède-martyr, Elodie Disa, Katia Guérin, Marc Dubois, Lawrence Frezet, André HamwiAbstract:Abstract Covalent functionalization through pure molecular gaseous fluorination has been applied on Carbon Nanofibres. Nuclear magnetic resonance and thermal gravimetric analysis investigations have been performed on fluorinated Carbon Nanofibres in order to determine the chemical and thermal stability of the C–F bonding. The high covalency obtained allows no significant modification of the physicochemical nanostructure of fluorinated Carbon Nanofibres after sonification. Such modification of surface chemistry leads to a high increase in the limit concentration of dispersed Carbon Nanofibres in organic solvents without surfactant. An exciting maximum of 570 mg L−1 of fluorinated Nanofibres can be homogeneously dispersed in N-methylpyrrolidone, whereas 310 mg L−1 is the maximum for non-fluorinated Carbon Nanofibres. In order to understand such dispersibility differences, Hildebrand and Hansen solubility theory has been used.
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The effect of nanostructure on the thermal properties of fluorinated Carbon Nanofibres
Carbon, 2011Co-Authors: Elodie Disa, Katia Guérin, Marc Dubois, Francis Masin, Hayat Kharbache, André HamwiAbstract:Abstract Using thermogravimetic analysis in air, the thermal properties of fluorinated Carbon Nanofibres have been investigated. The fluorination level, the C–F bonding, the number of structural defects and the distribution of fluorine atoms in the Carbon matrix have been modified using three fluorination routes, (i) a direct process using a flux of pure molecular fluorine F 2 (dynamic process), (ii) a filling of a closed reactor by this reactive gas (static process) and (iii) controlled fluorination using the thermal decomposition of a solid fluorinating agent TbF 4 . At given fluorine contents, only the location of the fluorine atoms within the nanofibre changes the thermal stability, which can be increased up to 480 °C; such improvement is obtained when the fluorinated regions are located in the outer shell (tubes).
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New synthesis methods for fluorinated Carbon Nanofibres and applications
Journal of Fluorine Chemistry, 2010Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, André Hamwi, Francis Masin, L. Spinelle, Hayat Kharbache, Alexander P. Kharitonov, Jérôme Brunet, Christelle VarenneAbstract:Several new synthesis methods of fluorinated Carbon Nanofibres, such as controlled fluorination using fluorinating agent (TbF4 or XeF 2), or assisted fluorination under UV and gamma irradiation, are reviewed and compared with the direct fluorination using undiluted fluorine gas. The results highlight the different fluorinationmechanisms for the direct fluorination and the new methods. The other advantage of those alternative fluorination routes is the possibility to provide fine tuning of the fluorination level, i.e. from F/C atomic ratio close to zero, as a functionalization, to the unity (CF1) according to the required application, electrochemical or tribological. Two applications are described in this paper as a function of the fluorine content: protection against ozonation and use as solid lubricants. © 2010 Elsevier B.V. All rights reserved.
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Carbon Nanofibres fluorinated using tbf4 as fluorinating agent part i structural properties
Carbon, 2008Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, Ziad Fawal, Dimitri A Ivanov, Loic Vidal, André HamwiAbstract:Abstract Fluorination of Carbon Nanofibres (CNFs) under fluorine gas at 480 °C leads to high fluorine content but also to some partial exfoliation. In order to avoid such phenomenon, an alternative route has been performed at temperatures ranged between 420 and 500 °C using a fluorinating agent, i.e. terbium tetrafluoride. The structural properties of the fluorinated CNFs are discussed taking into account the data of 13 C solid state NMR, Raman spectroscopy, SEM, TEM and XRD. Whatever the fluorination temperature, a fluorinated phase of (CF) n structural type, is formed contrary to the direct process using F 2 gas for which a (C 2 F) n -type fluorinated phase appeared for fluorination temperatures lower than 450 °C. The progressive release of fluorine atoms from the thermal decomposition of TbF 4 allows an homogenous distribution of the fluorinated part into the CNFs matrix and the formation of a unique (CF) n type structure. Moreover, for high fluorination temperatures (480 and 500 °C), the fluorination leads to some Nanofibres breaking but in no way to exfoliation.
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Carbon Nanofibres fluorinated using TbF4 as fluorinating agent. Part II: Adsorption and electrochemical properties
Carbon, 2008Co-Authors: W. Zhang, Katia Guérin, Marc Dubois, Francis Masin, Axel Houdayer, André HamwiAbstract:Abstract The adsorption and electrochemical properties of the Carbon Nanofibres fluorinated using TbF4 as fluorinating agent have been investigated by nitrogen measurements and galvanostatic discharge in primary lithium batteries, respectively. These properties are compared to those obtained for Carbon Nanofibres fluorinated by pure fluorine gas (direct fluorination). The amount of structural defects, the formed structural phase and the possible partial exfoliation have been investigated in order to understand the properties difference for the CNFs fluorinated by the two routes. Higher amounts of both dangling bonds and CF2, CF3 groups were registered by EPR and 19F NMR for CNFs fluorinated by direct route. Moreover, SEM study underlines the partial exfoliation, which occurred only during the direct fluorination at 480 °C. As a consequence, CNFs fluorinated by TbF4 develop the highest faradic yield for a use in primary lithium battery.
D.c. Koningsberger - One of the best experts on this subject based on the ideXlab platform.
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Preparation and Activity of Small Rhodium Metal Particles on Fishbone Carbon Nanofibres
Journal of Catalysis, 2002Co-Authors: T. G. Ros, Adrianus J. Van Dillen, John W. Geus, D.e. Keller, D.c. KoningsbergerAbstract:A number of different impregnation and ion-exchange procedures have been employed to synthesize very small rhodium metal particles on HNO3/H2SO4-oxidized fishbone Carbon Nanofibres. The surface-oxidation of the Nanofibres with HNO3/H2SO4 is a prerequisite for a good interaction between aqueous catalyst precursor solutions and the fibres. Depending upon the preparation technique applied and using 1 wt% rhodium metal loadings average particle sizes ranging from 1.1 to 2.1 nm were detected with XAFS spectroscopy. The rhodium metal particles are so small that metal–support interactions on Carbon Nanofibres can be investigated with XAFS spectroscopy. All catalysts are highly active in the liquid-phase hydrogenation of cyclohexene. No significant effect of particle size on the catalytic activity is observed, suggesting that other factors, such as clustering of the support particles in the liquid phase, are much more important.
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modification of Carbon Nanofibres for the immobilization of metal complexes a case study with rhodium and anthranilic acid
Chemistry: A European Journal, 2002Co-Authors: T. G. Ros, Adrianus J. Van Dillen, J W Geus, D.c. KoningsbergerAbstract:The immobilisation of the rhodium/anthranilic acid complex onto fishbone Carbon Nanofibres (CNFs) was executed by means of the following steps: 1) surface oxidation of the fibres, 2) conversion of the oxygen-containing surface groups into acid chloride groups, 3) attachment of anthranilic acid and 4) complexation of rhodium by the attached anthranilic acid. The immobilisation process was followed and the resulting surface species were characterised by IR, X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS), and by molecular modelling. Anthranilic acid bonds to the CNFs by an amide linkage to the carboxyl groups that are present after surface oxidation of the fibres. The immobilised anthranilic acid coordinates to rhodium through the nitrogen atom and the carboxyl group. The assynthesised RhIII complex itself is not active in the liquid-phase hydrogenation of cyclohexene. Reduction with sodium borohydride yields small particles (d = 1.5-2 nm) of rhodium metal that are highly active. The results indicate that different activation procedures for the immobilised Rh/anthranilic acid system should be applied, such as reduction with a milder reducing agent or direct complexation of the rhodium in the RhI state.
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Surface oxidation of Carbon Nanofibres
Chemistry - A European Journal, 2002Co-Authors: T. G. Ros, Adrianus J. Van Dillen, John W. Geus, D.c. KoningsbergerAbstract:Carbon Nanofibres of the fishbone and parallel types were sur- face-oxidised by several methods. The untreated and oxidised fibres were stud- ied with infrared spectroscopy, thermog- ravimetric analysis and X-ray photo- electron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen- containing surface groups. This treat- ment results not only in the formation of carboxy and carboxyic anhydride groups, but also in the generation of ether-type oxygen groups between graphitic layers that are puckered at their edges. The IR spectroscopic data clearly show that the formation of oxy- gen-containing surface groups occurs at defect sites on the Carbon Nanofibres and that oxidation proceeds via Carbonyl groups and other oxides to carboxy and carboxyic anhydride groups. Owing to the presence of defects, the two types of fibre have similar surface reactivities. With parallel Nanofibres, in contrast to fishbone fibres, the macroscopic struc- ture was severely affected by treatment with HNO3/H2SO4. The HNO3/H2SO4- treated fibres are highly wettable by
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surface oxidation of Carbon Nanofibres
Chemistry: A European Journal, 2002Co-Authors: T. G. Ros, Adrianus J. Van Dillen, John W. Geus, D.c. KoningsbergerAbstract:Carbon Nanofibres of the fishbone and parallel types were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation of carboxy and carboxyic anhydride groups, but also in the generation of ether-type oxygen groups between graphitic layers that are puckered at their edges. The IR spectroscopic data clearly show that the formation of oxygen-containing surface groups occurs at defect sites on the Carbon Nanofibres and that oxidation proceeds via Carbonyl groups and other oxides to carboxy and carboxyic anhydride groups. Owing to the presence of defects, the two types of fibre have similar surface reactivities. With parallel Nanofibres, in contrast to fishbone fibres, the macroscopic structure was severely affected by treatment with HNO(3)/H(2)SO(4). The HNO(3)/H(2)SO(4)-treated fibres are highly wettable by water.
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Surface Structure of Untreated Parallel and Fishbone Carbon Nanofibres: An Infrared Study
ChemPhysChem, 2002Co-Authors: T. G. Ros, Adrianus J. Van Dillen, John W. Geus, D.c. KoningsbergerAbstract:KEYWORDS:Carbon ¥Carbon Nanofibres ¥IR spectroscopy ¥nanostructures¥surface analysisCarbon Nanofibres (CNFs) that are obtained by catalytic decom-position of Carbon-containing gases over small metal particlesare a promising catalyst support material for liquid-phasereactions. The fibres are mechanically strong and can withstandthe forces executed on them by stirring the reaction medium.Furthermore, the skeins of fibres possess a mesoporous macro-structure, decreasing the chance of encountering diffusionlimitation during catalytic reactions in the liquid phase. Thestructure of the CNFs can be tuned by changing the growthconditions and their hydrophobicity can be altered by surfaceoxidation. Moreover, Carbon Nanofibres are very pure. No othertypes of Carbon, such as Carbon onions, fullerenes or amorphousCarbon, are formed and no heteroatoms such as sulfur areincorporated during synthesis. They are chemically inert and canbe used in strongly acidic or basic environments. Finally, whengrown in a fluidised bed reactor, Carbon Nanofibres can beobtained at low cost, making an application as catalyst supportmaterial possible.
Mario Culebras - One of the best experts on this subject based on the ideXlab platform.
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bio derived Carbon Nanofibres from lignin as high performance li ion anode materials
Chemsuschem, 2019Co-Authors: Maurice N Collins, Mario Culebras, Hugh Geaney, Anne Beaucamp, Prathviraj Upadhyaya, Eric Dalton, Kevin M RyanAbstract:Development of cost-effective and increasingly efficient sustainable materials for energy-storage devices, such Li-ion batteries, is of crucial future importance. Herein, the preparation of Carbon Nanofibres from biopolymer blends of lignin (byproduct from the paper and pulp industry) and polylactic acid (PLA) or a thermoplastic elastomeric polyurethane (TPU) is described. SEM analysis shows the evolving microstructural morphology after each processing step (electrospinning, stabilisation and Carbonisation). Importantly, it is possible to tailor the nanofibre porosity by utilising miscibility/immiscibility rules between lignin and the polymer additive (PLA/TPU). PLA blends (immiscible) generate porous structures whereas miscible lignin/TPU blends are solid when Carbonised. Electrodes produced from 50 % PLA blends have capacity values of 611 mAh g-1 after 500 charge/discharge cycles, the highest reported to date for sustainable electrodes for Li-ion batteries. Thus, this work will promote the development of lignocellulose waste materials as high-performance energy-storage materials.
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thermoelectric properties of electrospun Carbon Nanofibres derived from lignin
International Journal of Biological Macromolecules, 2019Co-Authors: Niall Dalton, Robert P Lynch, Maurice N Collins, Mario CulebrasAbstract:Abstract Developing sustainable and efficient thermoelectric materials is a challenge because the most common thermoelectric materials are based on rare elements such as bismuth and telluride. In this context, we have produced bio-based Carbon Nanofibres (CNFs) derived from mixtures of polyacrylonitrile and lignin using electrospinning. The addition of lignin (up to 70%) reduces the diameter of CNFs from 450 nm to 250 nm, increases sample flexibility, and promotes inter-fibre fusion. The crystalline structure of the CNFs was analysed by Raman spectroscopy. The electrical conductivity and the Seebeck coefficient were evaluated as function of the lignin content in the precursor and Carbonised equivalents. Finally, a conversion of p-type to n-type semiconducting behaviour was achieved with a hydrazine vapour treatment. We observe a maximum p-type power factor of 9.27 μW cm−1 K−2 for CNFs Carbonised at 900 °C with 70% lignin which is a 34.5-fold increase to the CNFs with 0% lignin. For the hydrazine treated samples, we observe a maximum n-type power factor of 10.2 μW cm−1 K−2 for the CNFs produced in the same way which is an 11.0-fold increase to the hydrazine-treated CNFs with 0% lignin.
Chuanwei Yan - One of the best experts on this subject based on the ideXlab platform.
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coupling effect between the structure and surface characteristics of electrospun Carbon Nanofibres on the electrochemical activity towards the vo2 vo2 redox couple
Physical Chemistry Chemical Physics, 2015Co-Authors: Guanjie Wei, Jianguo Liu, Zhenguo Gao, Zengfu Wei, Xinzhuang Fan, Chuanwei YanAbstract:In order to investigate the structure-function relationship of electrospun Carbon Nanofibres (ECNFs), polyacrylonitrile (PAN)-based electrospun Carbon webs (ECWs) have been developed, consisting of ECNFs Carbonized over the temperature range of 1000–1500 °C in a nitrogen atmosphere. The surface morphology, microstructure, composition, electrical conductivity and hydrophilicity of the ECNFs have been characterized. The electrochemical activity of the ECNFs towards the VO2+/VO2+ redox reaction has been measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is worth noting that the electrochemical performance of the ECNFs decreases firstly and then rises gradually with the increase in Carbonization temperature, and a Carbonization temperature of about 1300 °C is the turning point. This unusual phenomenon might be attributed to the coupling effect between the surface and structure characteristics of the ECNFs towards the VO2+/VO2+ redox couple. The surface composition plays a leading role in the electrochemical activity of ECNFs Carbonized over the temperature range of 1000–1300 °C; however, the edge planes of graphite crystallites which form during the high temperature range from 1300–1500 °C then become the dominant factor. Therefore, the electrochemical activity decreases with the reduction of functional groups on the surface from Carbonization at 1000–1300 °C, and then increases with the addition of the edge planes of graphite crystallites from Carbonization at 1300–1500 °C.
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electrospun Carbon Nanofibres as electrode materials toward vo2 vo2 redox couple for vanadium flow battery
Journal of Power Sources, 2013Co-Authors: Guanjie Wei, Jianguo Liu, Huan Zhao, Chuanwei YanAbstract:Abstract Polyacrylonitrile (PAN) Carbon Nanofibres with diameters of 100–200 nm have been developed by electrospinning and subsequent Carbonization process. The composition, structure, electrical conductivity, and electrochemical properties of the Carbon Nanofibres as electrode materials for vanadium flow battery (VFB) have been characterized. It is found that with the increasing of Carbonization temperature, the electrochemical activity of Carbon Nanofibres toward VO 2+ /VO 2 + redox couple is enhanced greatly. Particularly, the 1000 °C-Carbonized Nanofibres show excellent performance. The good behavior of the Nanofibres Carbonized at high temperature may attribute to the conversion of fibers inner-structure and the improvement of electrical conductivity. Compared with the traditional Carbon fibers (TCFs), electrospun Carbon Nanofibres (ECNFs) Carbonized at temperature of 1000 °C exhibit higher activity toward the vanadium reaction, presenting considerable potential for electrode application in VFB.