Conducting Interface for Efficient Growth of Vertically Aligned Carbon Nanotubes: Towards Nano-Engineered Carbon Composite

International audienceVertically aligned carbon nanotubes (VACNT) are manufactured nanomaterials with excellent properties and great potential for numerous applications. Recently, research has intensified toward achieving VACNT synthesis on different planar and non-planar substrates of various natures, mainly dependent on the user-defined application. Indeed, VACNT growth has to be adjusted and optimized according to the substrate nature and shape to reach the requirements for the application envisaged. To date, different substrates have been decorated with VACNT, involving the use of diffusion barrier layers (DBLs) that are often insulating, such as SiO2 or Al2O3. These commonly used DBLs limit the conducting and other vital physico-chemical properties of the final nanomaterial composite. One interesting route to improve the contact resistance of VACNT on a substrate surface and the deficient composite properties is the development of semi-/conducting interlayers. The present review summarizes different methods and techniques for the deposition of suitable conducting interfaces and controlled growth of VACNT on diverse flat and 3-D fibrous substrates. Apart from exhibiting a catalytic efficiency, the DBL can generate a conducting and adhesive interface involving performance enhancements in VACNT composites. The abilities of different conducting interlayers are compared for VACNT growth and subsequent composite properties. A conducting interface is also emphasized for the synthesis of VACNT on carbonaceous substrates in order to produce cost-effective and high-performance nano-engineered carbon composites

Nitrogen and Oxygen doped Vertically Aligned Carbon Nanotubes (VACNT) for high-energy ultracapacitors

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Critical role of the acetylene content and Fe/C ratio on the thickness and density of vertically aligned carbon nanotubes grown at low temperature by a one-step catalytic chemical vapor deposition process

International audienceThe present work explores the role of the carbon source content and the Fe/C ratio on the synthesis of vertically aligned carbon nanotubes (VACNTs) by one-step aerosol-assisted CCVD operated at a medium temperature (615 °C) on aluminum substrates. The main objective was to overcome the limitations of VACNT growth, constituting a drawback for applications requiring thick VACNTs. By using acetylene as carbon feedstock and ferrocene as a catalyst precursor, we demonstrate that when acetylene content is reduced to 1.5 vol%, it is possible to grow VACNT carpets up to 700 µm thick while maintaining constant VACNT growth for a long duration (up to 160 min). The carbon conversion yield is significantly improved when the acetylene content reaches 1.5 vol%. The Al surface roughness also influences VACNT growth. An optimum Fe/C ratio of 0.8 wt.% coupled with a low acetylene content gives the highest growth rate (5.4 µm/min) ever reported for a thermal aerosol-assisted CCVD process operated at such a low temperature. The CNT number density can be controlled by varying the Fe/C ratio, enabling high density growth (e.g., 1.3 × 10$^{11}$ CNT/cm$^2$)

High-Energy Ultracapacitors based on Nitrogen and Oxygen Doped Vertically Aligned Nanotubes (VACNT)

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Functionalized carbon nanotubes as sensitive layers for BTEX sensing

International audienceThe BTEX (benzene, toluene, ethylbenzene and xylene) volatile organic compounds constitute an important class of indoor air pollutants. Human exposure to these compounds can cause serious damages on human health due to their carcinogenic nature. Therefore, it is a priority to detect such pollutants. Carbon nanotubes (CNTs) have received considerable interest over the last decade as new sensing materials due to their high specific surface area and their electronic properties. For instance, several groups have already demonstrated their outstanding abilities by studying the changes of CNT electrical properties upon gas exposure1,2,3. In this context, the objective of our work is to develop chemical sensors based on carbon nanotubes to detect BTEX compounds and especially benzene and toluene. Carbon nanotubes used for sensing devices are synthesized using catalytic chemical vapour deposition (CCVD) process4, which provides multi-walled carbon nanotubes (MWCNTs) with an outer diameter around 40 nm. The raw MWCNTs are then annealed at 2000°C under argon atmosphere and, eventually, functionalized to increase sensing selectivity. In this study, the detection performances of simply annealed CNT and functionalized ones are both studied.Hence, functional groups with a high affinity towards the selected target, i.e. benzene or toluene, were grafted at the surface. First, as carboxylic groups are known for BTEX adsorption by π-π stacking interactions (Figure 1.A)5, a simple acid treatment with HCl and HNO3 was performed to obtain –COOH groups on the surface. Second, in order to increase beneficial interactions with BTEX, several poly(phenylene) coatings bearing carboxylic groups were investigated for BTEX detection (Figure 1.B). The principle is based on BTEX interaction by π-π stacking with the aromatics and carboxylic groups of the coating.The functionalisation process with poly(phenylene) coatings is derived from the diazonium salt chemistry6. 4-carboxyphenyldiazonium chloride was synthesized in situ from the 4-aminobenzoic acid and sodium nitrite. The synthesis was performed in HCl solution and ascorbic acid was used as reducing agent. Such coatings were characterized on gold substrates and on CNT by XPS, FTIR and contact angle measurements. First tests demonstrate that simply annealed CNT–based sensors are able to detect benzene at concentrations in the tenth of ppb range which is appropriate for indoor air qualification. The functionalized CNT-based sensors are now to be compared to annealed CNT-based sensors in order to determine their performance abilit

Functionalized carbon nanotubes as sensitive layers for BTEX sensing

International audienceThe BTEX (benzene, toluene, ethylbenzene and xylene) volatile organic compounds constitute an important class of indoor air pollutants. Human exposure to these compounds can cause serious damages on human health due to their carcinogenic nature. Therefore, it is a priority to detect such pollutants. Carbon nanotubes (CNTs) have received considerable interest over the last decade as new sensing materials due to their high specific surface area and their electronic properties. For instance, several groups have already demonstrated their outstanding abilities by studying the changes of CNT electrical properties upon gas exposure1,2,3. In this context, the objective of our work is to develop chemical sensors based on carbon nanotubes to detect BTEX compounds and especially benzene and toluene. Carbon nanotubes used for sensing devices are synthesized using catalytic chemical vapour deposition (CCVD) process4, which provides multi-walled carbon nanotubes (MWCNTs) with an outer diameter around 40 nm. The raw MWCNTs are then annealed at 2000°C under argon atmosphere and, eventually, functionalized to increase sensing selectivity. In this study, the detection performances of simply annealed CNT and functionalized ones are both studied.Hence, functional groups with a high affinity towards the selected target, i.e. benzene or toluene, were grafted at the surface. First, as carboxylic groups are known for BTEX adsorption by π-π stacking interactions (Figure 1.A)5, a simple acid treatment with HCl and HNO3 was performed to obtain –COOH groups on the surface. Second, in order to increase beneficial interactions with BTEX, several poly(phenylene) coatings bearing carboxylic groups were investigated for BTEX detection (Figure 1.B). The principle is based on BTEX interaction by π-π stacking with the aromatics and carboxylic groups of the coating.The functionalisation process with poly(phenylene) coatings is derived from the diazonium salt chemistry6. 4-carboxyphenyldiazonium chloride was synthesized in situ from the 4-aminobenzoic acid and sodium nitrite. The synthesis was performed in HCl solution and ascorbic acid was used as reducing agent. Such coatings were characterized on gold substrates and on CNT by XPS, FTIR and contact angle measurements. First tests demonstrate that simply annealed CNT–based sensors are able to detect benzene at concentrations in the tenth of ppb range which is appropriate for indoor air qualification. The functionalized CNT-based sensors are now to be compared to annealed CNT-based sensors in order to determine their performance abilit

Analysis of the continuous feeding of catalyst particles during the growth of vertically aligned carbon nanotubes by aerosol-assisted CCVD

International audienceAerosol-assisted catalytic chemical vapor deposition (AACCVD) is a powerful one-step process to produce vertically aligned carbon nanotubes (VACNTs), characterized by the continuous supply of the catalyst precursor (metallocene). The behavior of catalyst species all along the synthesis is essential for the continuous growth of VACNTs. It is there investigated through detailed observations and elemental analyses at scales of VACNT carpets and of individual CNTs. Our approach is based on two complementary experiments: quenching of the sample cooling, and sequential injection of two distinct metallocenes. Metal-based nanoparticles nucleated in the gas-phase during the whole synthesis duration are shown to diffuse in between the growing VACNTs from the top of the CNT carpet towards the substrate. They are much smaller than the catalyst particles formed on the substrate in the initial steps of the process and evidences are given that they continuously feed these catalyst particles at the VACNT roots. Particularly, the electron energy-loss spectroscopy (EELS) analyses of metal-based segments found into a single CNT show that the second injected metal is very gradually incorporated in the particle initially formed from the metal firstly injected. The feeding of the catalyst particles by the nanoparticles continuously nucleated in the gas-phase is therefore an essential feature of the base-growth of CNTs by AACCVD

A comparative study of high density Vertically Aligned Carbon Nanotubes grown onto different grades of aluminum – Application to supercapacitors

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Poly(3-methylThiophene)/Vertically Aligned Carbon Nanotubes/Aluminium Nanocomposites Electrodes: Synthesis Electrochemical Characterizations and Devices

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Electropolymerized Poly(3-methylthiophene) onto high density Vertically Aligned Carbon Nanotubes directly grown on Aluminum Substrates

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