Antonio Fonseca - Academia.edu (original) (raw)

Papers by Antonio Fonseca

Research paper thumbnail of Catalytic synthesis and purification of carbon nanotubes

Synthetic Metals, 1996

Carbon deposition on a catalyst surface during decomposition of different carbon-containing compo... more Carbon deposition on a catalyst surface during decomposition of different carbon-containing compounds can be used for the synthesis of carbon nanotubes of graphitic structure. Different supported transition metal oxides were found to be active in the production of these nanotubes. The selectivity of the catalytic method is significantly higher than that of either the arc discharge or the flame method. The experiments were carried out in a flow system, at 700 °C, with various acetylene/nitrogen feeds. Deposited carbon was investigated by transition electron microscopy. The best samples were selected for further investigation and for the synthesis of carbon nanotubes in large amounts. For the purification, different methods were utilized. Separation of nanotubes from the catalyst (support and metal particles) and from other carbon products (soot, fibres) can be carried out only by the combination of ultrasound and various chemical treatments.

Research paper thumbnail of Catalytic synthesis of carbon nanotubes over Co, Fe and Ni containing conventional and sol gel silica aluminas

Physical Chemistry Chemical Physics, 2000

... Conclusion. Results obtained for the catalytic synthesis of carbon nanotubes using Co or Fe s... more ... Conclusion. Results obtained for the catalytic synthesis of carbon nanotubes using Co or Fe supported on Al 2 O 3 –SiO 2 mixtures of different compositions show that all thecatalysts tested produce nanotubes with high activity and selectivity. ...

Research paper thumbnail of Imaging the Elastic Properties of Coiled Carbon Nanotubes with Atomic Force Microscopy

Physical Review Letters, 2000

Research paper thumbnail of Structural and electronic properties of bent carbon nanotubes

Chemical Physics Letters, 1995

Atomic models of two single joints connecting (a) (9, 0) to (5, 5) and (b) (10, 0) to (6, 6) nano... more Atomic models of two single joints connecting (a) (9, 0) to (5, 5) and (b) (10, 0) to (6, 6) nanotubes have been constructed and relaxed on the computer using a molecular-mechanics model. Each connection is based on a pair of diametrically opposed pentagon and heptagon which bend the structure. The electronic properties of these metal-metal and semiconductor-metal junctions are explored within a tight-binding description of the π bands of the carbon sp2 network.

Research paper thumbnail of Synthesis of single- and multi-wall carbon nanotubes over supported catalysts

Applied Physics A-materials Science & Processing, 1998

Research paper thumbnail of Control of the outer diameter of thin carbon nanotubes synthesized by catalytic decomposition of hydrocarbons

Chemical Physics Letters, 2000

Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo... more Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo, Co–V and Co–Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst.

Research paper thumbnail of Production of short carbon nanotubes with open tips by ball milling

Chemical Physics Letters, 2001

Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball... more Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball milled carbon nanotubes, synthesised by decomposition of acetylene on different types of supported metal catalysts, is ca. 0.8 μm. The cleavage was caused by the collision between one agate ball and the nanotube powder contained in an agate mortar.

Research paper thumbnail of Large-scale synthesis of single-wall carbon nanotubes by catalytic chemical vapor deposition (CCVD) method

Chemical Physics Letters, 2000

The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities ... more The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000°C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70–80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products.

Research paper thumbnail of A Generic Organometallic Approach toward Ultra-Strong Carbon Nanotube Polymer Composites

Journal of The American Chemical Society, 2004

Research paper thumbnail of Production of nanotubes by the catalytic decomposition of different carbon-containing compounds

Applied Catalysis A-general, 2000

Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing comp... more Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing compounds over supported transition metal catalysts. Besides acetylene, ethylene, propylene, acetone, n-pentane, methanol, toluene, and methane were tested and each resulted in carbon nanotube formation. The quality of as-made nanotubes was investigated by TEM and was found to be at least as good as obtained in acetylene decomposition. Ethylene and propylene showed somewhat lower reactivity in the buckytube formation with respect to acetylene, simultaneously suppressed formation of amorphous carbon on the outer surface was found.

Research paper thumbnail of The structure of acid treated sepiolites: small-angle X-ray scattering and multi MAS-NMR investigations

Applied Clay Science, 1999

Structural changes in the chain silicate sepiolite brought about by acid treatment were studied b... more Structural changes in the chain silicate sepiolite brought about by acid treatment were studied by X-ray diffraction, gas adsorption and MAS-NMR methods. It was established that as the amount of iron and aluminum extracted from the mineral is increased, the specific surface area of the sample is also increased (from 195.2 to 306.6 m2/g) and the originally microporous structure is transformed into a mesoporous one. The ion exchange capacity of sepiolite (0.486 mequ/g) may be completely eliminated by acid treatment. The changes in the surface fractal dimension Ds (from 2.35 to 2.03) and the correlation length lc (from 24.9 nm to 17.6 nm) were followed by SAXS measurements. and studies yield information on changes occurring in the structure of the mineral, i.e., on the arrangement of Si and Al atoms in the lattice. During acid treatment the clay structure is progressively transformed into amorphous silica–alumina.

Research paper thumbnail of Reinforcement of Polymers with Carbon Nanotubes:  The Role of Nanotube Surface Area

Research paper thumbnail of Respiratory toxicity of multi-wall carbon nanotubes

Toxicology and Applied Pharmacology, 2005

Carbon nanotubes focus the attention of many scientists because of their huge potential of indust... more Carbon nanotubes focus the attention of many scientists because of their huge potential of industrial applications, but there is a paucity of information on the toxicological properties of this material. The aim of this experimental study was to characterize the biological reactivity of purified multi-wall carbon nanotubes in the rat lung and in vitro. Multi-wall carbon nanotubes (CNT) or ground CNT were administered intratracheally (0.5, 2 or 5 mg) to Sprague–Dawley rats and we estimated lung persistence, inflammation and fibrosis biochemically and histologically. CNT and ground CNT were still present in the lung after 60 days (80% and 40% of the lowest dose) and both induced inflammatory and fibrotic reactions. At 2 months, pulmonary lesions induced by CNT were characterized by the formation of collagen-rich granulomas protruding in the bronchial lumen, in association with alveolitis in the surrounding tissues. These lesions were caused by the accumulation of large CNT agglomerates in the airways. Ground CNT were better dispersed in the lung parenchyma and also induced inflammatory and fibrotic responses. Both CNT and ground CNT stimulated the production of TNF-α in the lung of treated animals. In vitro, ground CNT induced the overproduction of TNF-α by macrophages. These results suggest that carbon nanotubes are potentially toxic to humans and that strict industrial hygiene measures should to be taken to limit exposure during their manipulation.

Research paper thumbnail of Influence of NaOH and KOH on the synthesis of MCM-22 and MCM-49 zeolites

Microporous and Mesoporous Materials, 2006

Research paper thumbnail of Study of silver species stabilized in different microporous zeolites

Microporous and Mesoporous Materials, 2013

ABSTRACT Electronic behavior of different structure zeolites containing silver species was studie... more ABSTRACT Electronic behavior of different structure zeolites containing silver species was studied by X-ray photoelectron spectroscopy (XPS). Three different microporous zeolite structures in sodium form, Mordonite (NaMOR), Faujasite (Nay) and Linde Type A (NaA) were loaded with silver (Ag) by ion exchange method. The characterization of materials was also performed by X-ray diffraction (XRD) and chemical analysis. The results indicate that silver was interchanged in the structure of the zeolites. From XRD data the introduction of silver in zeolites increases the average of the crystallite size. X-ray photoelectron spectroscopy measurements of silver zeolites were made and Auger parameters for different chemical states of silver have been derived based upon these measurements. XPS analysis confirms different oxidation states of silver species present in zeolite structures. (c) 2013 Elsevier Inc. All rights reserved.

Research paper thumbnail of Large scale production of short functionalized carbon nanotubes

Chemical Physics Letters, 2002

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of bal... more A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Research paper thumbnail of Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Physicochemical Aspects

Chemical Research in Toxicology, 2008

Experimental studies indicate that carbon nanotubes (CNTs) have the potential to induce adverse p... more Experimental studies indicate that carbon nanotubes (CNTs) have the potential to induce adverse pulmonary effects, including alveolitis, fibrosis, and genotoxicity in epithelial cells. Here, we explored the physicochemical determinants of these toxic responses with progressively and selectively modified CNTs: ground multiwall CNTs modified by heating at 600 degrees C (loss of oxygenated carbon functionalities and reduction of oxidized metals) or at 2400 degrees C (annealing of structural defects and elimination of metals) and by grinding the material that had been heated at 2400 degrees C before (introduction of structural defects in a metal-deprived framework). The CNTs were administered intratracheally (2 mg/rat) to Wistar rats to evaluate the short-term response (3 days) in bronchoalveolar lavage fluid (LDH, proteins, cellular infiltration, IL-1beta, and TNF-alpha). The long-term (60 days) lung response was assessed biochemically by measuring the lung hydroxyproline content and histologically. In vitro experiments were also performed on rat lung epithelial cells to assess the genotoxic potential of the modified CNTs with the cytokinesis block micronucleus assay. The results show that the acute pulmonary toxicity and the genotoxicity of CNT were reduced upon heating but restored upon grinding, indicating that the intrinsic toxicity of CNT is mainly mediated by the presence of defective sites in their carbon framework.

Research paper thumbnail of Reinforcement of polymers with carbon nanotubes. The role of an ordered polymer interfacial region. Experiment and modeling

Polymer, 2006

Significant increases in the Young's modulus of nanotube–polymer composites have been associated ... more Significant increases in the Young's modulus of nanotube–polymer composites have been associated with the formation of an ordered polymer layer coating the nanotubes. Polyvinyl alcohol (PVA) is known to display nanotube-induced ordering. It is used here as a model matrix to investigate how the polymer coating influences the mechanical reinforcement of the composite material. Young's modulus and calorimetry measurements were carried out on films of PVA-based composites reinforced with different types of nanotubes. An unmistakable correlation between polymer ordering and reinforcement was found. This is supported by the introduction of a model capable of establishing, on quantitative grounds, how the ordered phase affects the increase in the Young's modulus. Rather than acting as intrinsically stiffer reinforcing agents, our results suggest that the major role played by the nanotubes in improving the mechanical properties of composites is to nucleate an ordered polymer coating. It is the presence of this stiff ordered phase that dominates the reinforcement mechanism.

Research paper thumbnail of 13C n.m.r. quantitative analysis of catalyst carbon deposits

Fuel, 1996

ABSTRACT An assessment has been made of several techniques for the quantitative analysis of carbo... more ABSTRACT An assessment has been made of several techniques for the quantitative analysis of carbonaceous compounds by MAS 13C n.m.r. The best results were obtained using the proton gated decoupling pulse sequence coupled with depth pulses. Calibration was performed with external model compounds. From comparative studies using model compounds and samples of real catalyst carbon deposits (coke), it is concluded that only ∼ 50% of the carbon atoms in coke are ‘n.m.r.-visible’. The ‘invisible’ carbon atoms are either graphite-like or different kinds close to the paramagnetic centres, e.g. The Ni2+ species. This conclusion affects previous n.m.r. results and will make n.m.r. data collected in the future more reliable so that they can provide valuable support for other techniques used to characterize carbonaceous deposits. From the curves, the transverse relaxation rates of the different carbons of the cokes can be estimated. Even if the carbons in the coke are relaxed by the Haldor Topsøe TK551 catalyst and paramagnetic metals present in it, the transverse relaxation rates are higher for the aliphatic carbons than for the aromatic carbons.

Research paper thumbnail of Very short functionalized carbon nanotubes for membrane applications

Desalination, 2010

... Scopus (121). [8] N. Pierard, A. Fonseca, JF. Colomer, C. Bossuot, JM. Benoît, G. Van Tendelo... more ... Scopus (121). [8] N. Pierard, A. Fonseca, JF. Colomer, C. Bossuot, JM. Benoît, G. Van Tendeloo, JP. Pirard and JB Nagy, Carbon 42 (2004), p. 1691. Article | PDF (683 K) | View Record in Scopus | Cited By in Scopus (51). [9] Z ...

Research paper thumbnail of Catalytic synthesis and purification of carbon nanotubes

Synthetic Metals, 1996

Carbon deposition on a catalyst surface during decomposition of different carbon-containing compo... more Carbon deposition on a catalyst surface during decomposition of different carbon-containing compounds can be used for the synthesis of carbon nanotubes of graphitic structure. Different supported transition metal oxides were found to be active in the production of these nanotubes. The selectivity of the catalytic method is significantly higher than that of either the arc discharge or the flame method. The experiments were carried out in a flow system, at 700 °C, with various acetylene/nitrogen feeds. Deposited carbon was investigated by transition electron microscopy. The best samples were selected for further investigation and for the synthesis of carbon nanotubes in large amounts. For the purification, different methods were utilized. Separation of nanotubes from the catalyst (support and metal particles) and from other carbon products (soot, fibres) can be carried out only by the combination of ultrasound and various chemical treatments.

Research paper thumbnail of Catalytic synthesis of carbon nanotubes over Co, Fe and Ni containing conventional and sol gel silica aluminas

Physical Chemistry Chemical Physics, 2000

... Conclusion. Results obtained for the catalytic synthesis of carbon nanotubes using Co or Fe s... more ... Conclusion. Results obtained for the catalytic synthesis of carbon nanotubes using Co or Fe supported on Al 2 O 3 –SiO 2 mixtures of different compositions show that all thecatalysts tested produce nanotubes with high activity and selectivity. ...

Research paper thumbnail of Imaging the Elastic Properties of Coiled Carbon Nanotubes with Atomic Force Microscopy

Physical Review Letters, 2000

Research paper thumbnail of Structural and electronic properties of bent carbon nanotubes

Chemical Physics Letters, 1995

Atomic models of two single joints connecting (a) (9, 0) to (5, 5) and (b) (10, 0) to (6, 6) nano... more Atomic models of two single joints connecting (a) (9, 0) to (5, 5) and (b) (10, 0) to (6, 6) nanotubes have been constructed and relaxed on the computer using a molecular-mechanics model. Each connection is based on a pair of diametrically opposed pentagon and heptagon which bend the structure. The electronic properties of these metal-metal and semiconductor-metal junctions are explored within a tight-binding description of the π bands of the carbon sp2 network.

Research paper thumbnail of Synthesis of single- and multi-wall carbon nanotubes over supported catalysts

Applied Physics A-materials Science & Processing, 1998

Research paper thumbnail of Control of the outer diameter of thin carbon nanotubes synthesized by catalytic decomposition of hydrocarbons

Chemical Physics Letters, 2000

Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo... more Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo, Co–V and Co–Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst.

Research paper thumbnail of Production of short carbon nanotubes with open tips by ball milling

Chemical Physics Letters, 2001

Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball... more Short multi-wall carbon nanotubes can be obtained by ball milling. The average length of the ball milled carbon nanotubes, synthesised by decomposition of acetylene on different types of supported metal catalysts, is ca. 0.8 μm. The cleavage was caused by the collision between one agate ball and the nanotube powder contained in an agate mortar.

Research paper thumbnail of Large-scale synthesis of single-wall carbon nanotubes by catalytic chemical vapor deposition (CCVD) method

Chemical Physics Letters, 2000

The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities ... more The large-scale production of single-wall carbon nanotubes (SWNTs) is reported. Large quantities of SWNTs can be synthesised by catalytic decomposition of methane over well-dispersed metal particles supported on MgO at 1000°C. The thus produced SWNTs can be separated easily from the support by a simple acidic treatment to obtain a product with high yields (70–80%) of SWNTs. Because the typical synthesis time is 10 min, 1 g of SWNTs can be synthesised per day by this method. The SWNTs are characterized by high-resolution transmission electron microscopy and by Raman spectroscopy, showing the quality and the quantity of products.

Research paper thumbnail of A Generic Organometallic Approach toward Ultra-Strong Carbon Nanotube Polymer Composites

Journal of The American Chemical Society, 2004

Research paper thumbnail of Production of nanotubes by the catalytic decomposition of different carbon-containing compounds

Applied Catalysis A-general, 2000

Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing comp... more Carbon nanotubes were prepared in the catalytic decomposition of different carbon containing compounds over supported transition metal catalysts. Besides acetylene, ethylene, propylene, acetone, n-pentane, methanol, toluene, and methane were tested and each resulted in carbon nanotube formation. The quality of as-made nanotubes was investigated by TEM and was found to be at least as good as obtained in acetylene decomposition. Ethylene and propylene showed somewhat lower reactivity in the buckytube formation with respect to acetylene, simultaneously suppressed formation of amorphous carbon on the outer surface was found.

Research paper thumbnail of The structure of acid treated sepiolites: small-angle X-ray scattering and multi MAS-NMR investigations

Applied Clay Science, 1999

Structural changes in the chain silicate sepiolite brought about by acid treatment were studied b... more Structural changes in the chain silicate sepiolite brought about by acid treatment were studied by X-ray diffraction, gas adsorption and MAS-NMR methods. It was established that as the amount of iron and aluminum extracted from the mineral is increased, the specific surface area of the sample is also increased (from 195.2 to 306.6 m2/g) and the originally microporous structure is transformed into a mesoporous one. The ion exchange capacity of sepiolite (0.486 mequ/g) may be completely eliminated by acid treatment. The changes in the surface fractal dimension Ds (from 2.35 to 2.03) and the correlation length lc (from 24.9 nm to 17.6 nm) were followed by SAXS measurements. and studies yield information on changes occurring in the structure of the mineral, i.e., on the arrangement of Si and Al atoms in the lattice. During acid treatment the clay structure is progressively transformed into amorphous silica–alumina.

Research paper thumbnail of Reinforcement of Polymers with Carbon Nanotubes:  The Role of Nanotube Surface Area

Research paper thumbnail of Respiratory toxicity of multi-wall carbon nanotubes

Toxicology and Applied Pharmacology, 2005

Carbon nanotubes focus the attention of many scientists because of their huge potential of indust... more Carbon nanotubes focus the attention of many scientists because of their huge potential of industrial applications, but there is a paucity of information on the toxicological properties of this material. The aim of this experimental study was to characterize the biological reactivity of purified multi-wall carbon nanotubes in the rat lung and in vitro. Multi-wall carbon nanotubes (CNT) or ground CNT were administered intratracheally (0.5, 2 or 5 mg) to Sprague–Dawley rats and we estimated lung persistence, inflammation and fibrosis biochemically and histologically. CNT and ground CNT were still present in the lung after 60 days (80% and 40% of the lowest dose) and both induced inflammatory and fibrotic reactions. At 2 months, pulmonary lesions induced by CNT were characterized by the formation of collagen-rich granulomas protruding in the bronchial lumen, in association with alveolitis in the surrounding tissues. These lesions were caused by the accumulation of large CNT agglomerates in the airways. Ground CNT were better dispersed in the lung parenchyma and also induced inflammatory and fibrotic responses. Both CNT and ground CNT stimulated the production of TNF-α in the lung of treated animals. In vitro, ground CNT induced the overproduction of TNF-α by macrophages. These results suggest that carbon nanotubes are potentially toxic to humans and that strict industrial hygiene measures should to be taken to limit exposure during their manipulation.

Research paper thumbnail of Influence of NaOH and KOH on the synthesis of MCM-22 and MCM-49 zeolites

Microporous and Mesoporous Materials, 2006

Research paper thumbnail of Study of silver species stabilized in different microporous zeolites

Microporous and Mesoporous Materials, 2013

ABSTRACT Electronic behavior of different structure zeolites containing silver species was studie... more ABSTRACT Electronic behavior of different structure zeolites containing silver species was studied by X-ray photoelectron spectroscopy (XPS). Three different microporous zeolite structures in sodium form, Mordonite (NaMOR), Faujasite (Nay) and Linde Type A (NaA) were loaded with silver (Ag) by ion exchange method. The characterization of materials was also performed by X-ray diffraction (XRD) and chemical analysis. The results indicate that silver was interchanged in the structure of the zeolites. From XRD data the introduction of silver in zeolites increases the average of the crystallite size. X-ray photoelectron spectroscopy measurements of silver zeolites were made and Auger parameters for different chemical states of silver have been derived based upon these measurements. XPS analysis confirms different oxidation states of silver species present in zeolite structures. (c) 2013 Elsevier Inc. All rights reserved.

Research paper thumbnail of Large scale production of short functionalized carbon nanotubes

Chemical Physics Letters, 2002

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of bal... more A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Research paper thumbnail of Structural Defects Play a Major Role in the Acute Lung Toxicity of Multiwall Carbon Nanotubes: Physicochemical Aspects

Chemical Research in Toxicology, 2008

Experimental studies indicate that carbon nanotubes (CNTs) have the potential to induce adverse p... more Experimental studies indicate that carbon nanotubes (CNTs) have the potential to induce adverse pulmonary effects, including alveolitis, fibrosis, and genotoxicity in epithelial cells. Here, we explored the physicochemical determinants of these toxic responses with progressively and selectively modified CNTs: ground multiwall CNTs modified by heating at 600 degrees C (loss of oxygenated carbon functionalities and reduction of oxidized metals) or at 2400 degrees C (annealing of structural defects and elimination of metals) and by grinding the material that had been heated at 2400 degrees C before (introduction of structural defects in a metal-deprived framework). The CNTs were administered intratracheally (2 mg/rat) to Wistar rats to evaluate the short-term response (3 days) in bronchoalveolar lavage fluid (LDH, proteins, cellular infiltration, IL-1beta, and TNF-alpha). The long-term (60 days) lung response was assessed biochemically by measuring the lung hydroxyproline content and histologically. In vitro experiments were also performed on rat lung epithelial cells to assess the genotoxic potential of the modified CNTs with the cytokinesis block micronucleus assay. The results show that the acute pulmonary toxicity and the genotoxicity of CNT were reduced upon heating but restored upon grinding, indicating that the intrinsic toxicity of CNT is mainly mediated by the presence of defective sites in their carbon framework.

Research paper thumbnail of Reinforcement of polymers with carbon nanotubes. The role of an ordered polymer interfacial region. Experiment and modeling

Polymer, 2006

Significant increases in the Young's modulus of nanotube–polymer composites have been associated ... more Significant increases in the Young's modulus of nanotube–polymer composites have been associated with the formation of an ordered polymer layer coating the nanotubes. Polyvinyl alcohol (PVA) is known to display nanotube-induced ordering. It is used here as a model matrix to investigate how the polymer coating influences the mechanical reinforcement of the composite material. Young's modulus and calorimetry measurements were carried out on films of PVA-based composites reinforced with different types of nanotubes. An unmistakable correlation between polymer ordering and reinforcement was found. This is supported by the introduction of a model capable of establishing, on quantitative grounds, how the ordered phase affects the increase in the Young's modulus. Rather than acting as intrinsically stiffer reinforcing agents, our results suggest that the major role played by the nanotubes in improving the mechanical properties of composites is to nucleate an ordered polymer coating. It is the presence of this stiff ordered phase that dominates the reinforcement mechanism.

Research paper thumbnail of 13C n.m.r. quantitative analysis of catalyst carbon deposits

Fuel, 1996

ABSTRACT An assessment has been made of several techniques for the quantitative analysis of carbo... more ABSTRACT An assessment has been made of several techniques for the quantitative analysis of carbonaceous compounds by MAS 13C n.m.r. The best results were obtained using the proton gated decoupling pulse sequence coupled with depth pulses. Calibration was performed with external model compounds. From comparative studies using model compounds and samples of real catalyst carbon deposits (coke), it is concluded that only ∼ 50% of the carbon atoms in coke are ‘n.m.r.-visible’. The ‘invisible’ carbon atoms are either graphite-like or different kinds close to the paramagnetic centres, e.g. The Ni2+ species. This conclusion affects previous n.m.r. results and will make n.m.r. data collected in the future more reliable so that they can provide valuable support for other techniques used to characterize carbonaceous deposits. From the curves, the transverse relaxation rates of the different carbons of the cokes can be estimated. Even if the carbons in the coke are relaxed by the Haldor Topsøe TK551 catalyst and paramagnetic metals present in it, the transverse relaxation rates are higher for the aliphatic carbons than for the aromatic carbons.

Research paper thumbnail of Very short functionalized carbon nanotubes for membrane applications

Desalination, 2010

... Scopus (121). [8] N. Pierard, A. Fonseca, JF. Colomer, C. Bossuot, JM. Benoît, G. Van Tendelo... more ... Scopus (121). [8] N. Pierard, A. Fonseca, JF. Colomer, C. Bossuot, JM. Benoît, G. Van Tendeloo, JP. Pirard and JB Nagy, Carbon 42 (2004), p. 1691. Article | PDF (683 K) | View Record in Scopus | Cited By in Scopus (51). [9] Z ...