Haut PDF Functionalized double-walled carbon nanotubes for integrated gas sensors

Functionalized double-walled carbon nanotubes for integrated gas sensors

Functionalized double-walled carbon nanotubes for integrated gas sensors

Acknowledgement Time, like water in Canal du Midi, flow quietly but so f ast. And now my life as a doctoral student has come to an end. First and foremost I am sincerely and gratefully appreci- ate my supervisors, Professors Christophe Vieu and Emmanuel Flahaut. You are excellent mentor for me. It is a pleasure and honor to be your Ph.D. student. I would like to thank you for guiding me, helping me and encouraging me in the scientific world. You are rigorous researcher but also very friendly friends. Working with you was a time under pressure but cheerful. It is precious experience and memory for my career and life. I would also like to thank my team colleagues, Emmanuelle Trevisiol, Christophe Thibault, Frank Carcenac, Alin Cerf, Laurrent Malaquin, Etienne Dague, Aude Dele- gard, Julie Foncy, Hélène Cayon, Maxime Sahun, Alejandro Kayum Jimenez Zenteno, Aurore Esteve, Emma Desvignes, and Angelo Accardo, and colleagues from other teams, Adrian Laborde, Matthieu Joly, Benjamin Reig, and my colleagues from CIRIMAT lab, Jean-Fran çois Guillet, Thomas Lorne, Pierre Lonchambon and Chunyang Nie. Thank you all for giving help to my work and my life in France. I also want to thank my friends who are not involved in my lab-life, Jinhui Wang, Yayu Huang, Longqi Lang, Xu Yang. Thank you for having banquets and treval and sports time with me. It helped me release pressure of work. I also want to thank my friend, Yue Zhao, who is far away in China but keeps in touch with me and support me like a brother.
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Chlorinated holey double-walled carbon nanotubes for relative humidity sensor

Chlorinated holey double-walled carbon nanotubes for relative humidity sensor

Humidity sensors are important in industry, medicine, research, and many everyday life applications. Theoretical calculations pre dict a weak interaction of water molecules with a perfect CNT surface [12]. The adsorbed H 2 O molecule polarizes a SWCNT without any noticeable transfer of electron density between the components [13]. However, changes in the electrical conductivity of CNTs depending on environmental humidity were detected experimentally [14]. The reason for this is mainly the functionali zation of the CNTs during puri fication procedures, and the adsorption of water between junctions in the networks of CNTs. Puri fication of CNTs using mineral acids produces oxygen containing groups, which interact with water via the hydrogen bonds [15]. This may signi ficantly influence the electrical response of CNTs in case they contain a low amount of defects. Actually, the characterization of a network of puri fied arc produced SWCNTs revealed a crossover from decreasing to increasing conductance versus H 2 O concentration in the surrounding atmosphere [16]. Interestingly, the DWCNTs did not exhibit such a behavior [17]. A large electrical hysteresis measured for a single DWCNT in wet and dry air was assigned to the inter wall interactions. These in teractions cause p doping of the outer nanotube, thus increasing its ability to adsorb H2O molecules.
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Tailoring of Double‐Walled Carbon Nanotubes for Formaldehyde Sensing through Encapsulation of Selected Materials

Tailoring of Double‐Walled Carbon Nanotubes for Formaldehyde Sensing through Encapsulation of Selected Materials

if n-type conduction is the dominant transport mechanism or a decrease in resistance (response) when p-type conduction is the dominant mechanism (see schematic illustration in Figure 6). As it has already been established that iodine induces p-type doping of SWNTs, creating charge carriers in the SWNTs walls and as a result, the semiconducting SWNTs become metallic, whereas metallic SWNTs become even more metallic due to increased density of carriers (holes). [25] The same effect was evi- denced in iodine-doped DWNTs, [20,27,28] it is, therefore, logical to assume that zinc iodide filling results in p-type doping of DWNTs, which explains the decrease in response. The increase in response observed for un filled DWNTs when formaldehyde was introduced can be explained as follows: un filled DWNTs are composed of a mixture of semiconducting and metallic DWNTs with the latter being predominant, and hence, the dominating conduction is due to electrons (n-type). This assumption is plausible due to the presence of 80% DWNTs in the sample as well as their wide diameter distribution. The same sensing mechanism is applicable for the zinc acetate- filled DWNTs, implying that zinc acetate filling enhances n-type conduction probably due to high density of elec- trons from the encapsulated zinc. An elementary analysis from EDX in Table 1 showed that zinc acetate- filled DWNTs have 2.5% more zinc by mass compared with zinc iodide- filled DWNTs, which might explain why this effect of zinc is not observed in zinc iodide- filled DWNTs as iodine dominates. 3.3. Gas Response in Synthetic Air Atmosphere
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A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

useful for the characterization of CNTs to evidence the variation of the intensity of the D band (frequency at ~ 1350 cm "1 ) to the G band (frequency at ~ 1590 cm "1 ), and therefore the defect density on the nanotubes. More precisely, the D band is associated to the func- tional groups and defects generated by both the initial acidic treatment and the functionalization. Hence, the progressive varia- tion of this band can suggest that the tubes are undergoing morphological modifications, as a result of the biodegrading action [14] . In particular, in the case of MWCNTs, although they already exhibit an intense D band as compared to DWCNTs, the biodegra- dation process in the presence of hydrogen peroxide creates more defects on the nanotubes, giving rise to an increase of this char- acteristic band. We have reported Raman spectra normalized to the G band because absolute values should be normalized on the vol- ume of homogenous samples, which are very difficult to obtain. Therefore, the Raman spectra allow the monitoring of the qualita- tive evolution of defects on the nanotubes up to complete disap- pearance of the signal if total CNT degradation is achieved (see Figures in Supporting Information) [14,17] . In Table 2 we have summarized the I D /I G values for the CNTs (entry 1e9), obtained
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A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

[14] . Contrary to the previous report, the results suggested that the biodegradation reduce the length of the tubes, creating a higher amount of defects on their walls, rather than exfoliating their external surface. In addition, Zhang et al. demonstrated the ability of some bacteria to degrade acid-treated MWCNTs under environ- mentally relevant conditions, leading to a decrease of their envi- ronmental persistence [18] . Very recently, we have demonstrated that specific functional molecules linked to CNTs can enhance the catalytic activity of HRP towards the degradation of multi-walled CNTs [24] . Coumarin derivatives and catechol were covalently conjugated to oxidized MWCNTs (ox-MWCNTs). These molecules are efficient reducing substrates for HRP. In addition, catechol is also a strong redox mediator of HRP as it favors electron transfer and prevents the enzyme inactivation. Other studies have evi- denced the persistence and degradation of CNTs in vitro and in vivo. Sato et al. have shown the long-term biopersistence of tangled ox- MWCNTs in vivo, demonstrating their potential use as biological implantable materials [25] . In that study, ox-MWCNTs were implanted into rat subcutaneous tissues. Two years after the im- plantation, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy were used to assess if the nanotubes did undergo structural changes. Large agglomerates of
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Effect of the fluorination technique on the surface-fluorination patterning of double-walled carbon nanotubes

Effect of the fluorination technique on the surface-fluorination patterning of double-walled carbon nanotubes

The higher fluorination loading, obtained through an increase of the synthesis temperature, creates defects in the DWCNT sur- face and introduces fluorine onto the inner shell too [4]. Although fluorinated CNTs are generally expected to be insu- lating, one-dimensional structures with a conducting shell surrounded by an insulating layer from the fluorinated carbon could find potential application in nanoelectronics and gas sensing [5]. The ability to change the functional composition of the outer shell would significantly extend the areas of possible DWCNT applications. For example, quantum-chemical calcula- tions predict that the conductivity of fluorinated CNTs changes from semiconducting to metallic depending on surface distribu- tion of fluorine atoms [6]. Furthermore, the energy of a C–F bond decreases with reduction of fluorine content in CNTs [7], which should promote nucleophilic substitution reactions, leading to new derivatives [8,9]. Fluorinated CNTs have a potential in chromatographic separations of various halo- genated compounds owing to an optimal combination of hydro- phobic properties and specific polar interactions [10]. The promises of the fluorinated CNTs may be fully realized only when the fluorine atoms would be controllably attached to the nanotube surface and the search of the appropriate ways for that is one of the key points in this scientific field at present [11]. There are several ways to fluorinate CNTs, the most common being fluorination using F 2 gas [12], CF 4 plasma [13], and BrF 3 vapor [14]. For all of these methods, the parameters preserving the tubular structure of the nanotubes after the fluorination have been determined. The high thermal stability of F 2 means
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Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Br2 molecules are weakly bonded with a SWCNT surface and un occupied bromine states form a band above the Fermi level of the na notube [ 10 ). These states overlap with carbon bands when Br 2 mole cules are intercalated into SWCNT ropes [ 11 ). In practice, bromination can assist in the purification of CNTs from the synthesis by products [ 12 ) and the separation of metallic and semiconducting SWCNTs [ 13 ). The use of bromine functionalized SWCNTs as efficient gas chemir esistor sensors [ 14 ) has also been demonstrated.
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Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

Effect of ultrasound pretreatment on bromination of double-walled carbon nanotubes

STO 3 G level gave a bond length of 2.297 Å, which well agrees with the experimental value of 2.289 Å for gas phase Br 2 [ 31 ]. An outer DWCNT wall was modeled by a fragment of armchair (9,9) CNT with a length of ca. 22.2 Å, where the edges were terminated by hydrogen and oxygen containing groups. The diameter of this CNT is 12.3 Å and this value is minimal for the outer shells of the studied DWCNTs as determined from the HRTEM analysis [ 27 ]. Geometry op timizations were performed with default convergence criteria. The ab sence of imaginary frequencies indicated that the obtained structures corresponded to the local minima on potential energy surfaces. 3. Results and discussion
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Experimental determination of microwave attenuation and electrical permittivity of double-walled carbon nanotubes

Experimental determination of microwave attenuation and electrical permittivity of double-walled carbon nanotubes

Centre Interuniversitaire de Recherche et d'Ingénierie des Matériaux, UMR CNRS 5085, Université Paul Sabatier, 31062 Toulouse, France The attenuation and the electrical permittivity of the double-walled carbon nanotubes (DWCNTs) were determined in the frequency range of 1–65 GHz. A micromachined coplanar waveguide transmission line supported on a Si membrane with a thickness of 1.4 µm was filled with a mixture of DWCNTs. The propagation constants were then determined from the S parameter measurements. The DWCNTs mixture behaves like a dielectric in the range of 1–65 GHz with moderate losses and an abrupt change of the effective permittivity that is very useful for gas sensor detection.
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Effect of the fluorination technique on the surface-fluorination patterning of double-walled carbon nanotubes

Effect of the fluorination technique on the surface-fluorination patterning of double-walled carbon nanotubes

The higher fluorination loading, obtained through an increase of the synthesis temperature, creates defects in the DWCNT sur- face and introduces fluorine onto the inner shell too [4]. Although fluorinated CNTs are generally expected to be insu- lating, one-dimensional structures with a conducting shell surrounded by an insulating layer from the fluorinated carbon could find potential application in nanoelectronics and gas sensing [5]. The ability to change the functional composition of the outer shell would significantly extend the areas of possible DWCNT applications. For example, quantum-chemical calcula- tions predict that the conductivity of fluorinated CNTs changes from semiconducting to metallic depending on surface distribu- tion of fluorine atoms [6]. Furthermore, the energy of a C–F bond decreases with reduction of fluorine content in CNTs [7], which should promote nucleophilic substitution reactions, leading to new derivatives [8,9]. Fluorinated CNTs have a potential in chromatographic separations of various halo- genated compounds owing to an optimal combination of hydro- phobic properties and specific polar interactions [10]. The promises of the fluorinated CNTs may be fully realized only when the fluorine atoms would be controllably attached to the nanotube surface and the search of the appropriate ways for that is one of the key points in this scientific field at present [11]. There are several ways to fluorinate CNTs, the most common being fluorination using F 2 gas [12], CF 4 plasma [13], and BrF 3 vapor [14]. For all of these methods, the parameters preserving the tubular structure of the nanotubes after the fluorination have been determined. The high thermal stability of F 2 means
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AFM imaging of functionalized double-walled carbon nanotubes

AFM imaging of functionalized double-walled carbon nanotubes

2.2. Non-covalent functionalization of DWNTs with BSA Purified DWNTs and BSA (Roche) were mixed with ultra-pure water with a concentration of 0.25 and 1.0 mg/ml, respectively. The mixture was sonicated for 45 min (Bandelin Sonoplus GM70 at 20% power) under cooling in an ice bath. The procedure resulted in a stable black suspension. The DWNT BSA suspension was then filtered in centrifugation cartridges with ultrafiltration membranes (nanosep, 300 kD cutoff) at around 5500g (Eppendorf Centrifuge 5417C) and washed 5 times with ultra-pure water to remove excess BSA. After re-suspension in ultra-pure water the concentration of DWNTs was estimated to be 0.05–0.1 mg/ml due to loss of material at the sidewall of the filtration device and the filter membrane. The suspension was stored at 4 1C until further usage within the next 2–3 days.
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Design of double-walled carbon nanotubes for biomedical applications

Design of double-walled carbon nanotubes for biomedical applications

than for the positive control DharmaFECT–siRNA survivin . protein regulates apoptosis and controls cell proliferation and is expressed highly in most human tumours and foetal tissue, but is completely absent in terminally differentiated cells. The successful delivery of siRNA to target specific genes in mammalian model organisms has been achieved using a variety of methods, including liposomes, cationic lipids, polymers and nanoparticles. However, systemic toxicity remains a great concern with most of these delivery options. Thus, there is an ever-growing need to enhance the available tools that can lead to effective and safe gene delivery. The functionalized oxDWNTs developed in this work present an alternative with reasonable biocompatibility, which can simultaneously serve as an imaging agent due to their unique Raman signature within biological environments (figure 3 ). DWNTs have an important advantage over SWNTs, for which any structural damage disrupts their mapping and progression over time. Furthermore, as we have shown in previous studies, they are released from the cells within 24 h after having fulfilled their task and do not accumulate within cells [ 20 ]. In this study we investigated whether oxDWNT–RNA causes any changes in the cell biochemistry within this time frame, which they did not (figure 4 ). This is in good agreement with a previous study of our group, which has shown that oxDWNT–RNA did not cause phosphorylation of mitogen-activate protein kinases (MAPKs), which are markers for induced cellular stress [ 19 ]. In addition, we have also previously investigated the effect of oxDWNTs on cell viability after 96 h incubation by a MTT cytotoxicity assay and found no dose-dependent toxicity, although an overall drop of cell viability of about 5–15% was observed, possibly due to inhibition of cell proliferation or decreased cell adhesion [ 17 ]. Overall, this indicates that oxDWNT–RNA does not have a deleterious effect on cells during their passage, although long-term effects remain to be investigated.
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Design of double-walled carbon nanotubes for biomedical applications

Design of double-walled carbon nanotubes for biomedical applications

3. Results oxDWNTs were found to consist of single or small bundles of shorter nanotubes (200–2000 nm length, 296 nm ± 123 nm on average as determined by AFM and phase-analysis light scattering (PALS) [ 17 ]). TEM analysis (figure S1 in the supporting information available at stacks.iop.org/Nano/ 23/365102/mmedia ) confirmed the Poly(Lys:Phe) coating of Poly(Lys:Phe)-wrapped oxDWNTs. Analysis by Raman spectroscopy revealed distinct peaks characteristic of DWNTs (figure 3 a): the radial breathing modes (RBMs) at 150, 200, 230 and 260 cm −1 (correlating with diameters of 0.9, 1.1, 1.2 and 1.58 nm [ 18 ]), as well as the D-band (1350 cm −1 ), G-band (1590 cm −1 ), and the 2D-band (2600 cm −1 ), which can be clearly observed in the spectrum. Figure 3 (b) shows a Raman map of the RBM in a mammalian cell, which has previously been exposed to oxDWNT–RNA. A strong, locally confined Raman signal was detected within the whole cell, confirming successful DWNT uptake and possible localization within endosomes, as also reported in previous work by our group, which has looked at the intracellular distribution of functionalized DWNTs in greater detail [ 19 ,
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Large-Diameter Single-Wall Carbon Nanotubes Formed Alongside Small-Diameter Double-Walled Carbon Nanotubes

Large-Diameter Single-Wall Carbon Nanotubes Formed Alongside Small-Diameter Double-Walled Carbon Nanotubes

solar cells depends signi ficantly on the type of CNTs, i.e., SWCNT-based cells show better performance under visible light illumination, whereas DWCNT-based solar cells exhibit high performance under infrared illumination. 12 Therefore, there is a strong need for the selective synthesis of DWCNTs over SWCNTs and MWCNTS. Although they are sometimes considered as intermediate between SWCNTs and MWCNTs, DWCNTs are much closer to SWCNTs, notably regarding the formation mechanisms. DWCNTs can be prepared by the appropriate treatments of SWCNTs that contain fullerene peapods, 13,14 but the extent of filling of the outer tube by the inner one is limited, and produced quantities are low. Catalytic chemical vapor deposition routes, where a carbonaceous gas is decomposed over nanoparticles, o ffers a better degree of control and higher yields. 15 It is well established that the number of graphene layers formed on the catalyst nanoparticles in the early stages of the CNT nucleation controls the number of walls formed. 16,17 It has been estimated that there is a threshold, around 5 nm, in the length of a SWCNT, beyond which it can grow very long. 18 As long as this critical length is not reached, a second carbon cap sometimes called yarmulke 16,19 can form underneath the first, spaced by roughly the interlayer spacing of graphite and forcing it to lift up by forming a tube whose open end remains chemisorbed to the catalytic particle, until at some point the simultaneous growth of the two walls starts. In suitable conditions, tubes with three walls are formed too. Puri fication methods 20,21 are e fficient to selectively eliminate the SWCNTs and poorly organized carbon species from the samples, but they are tedious and tend to generate a unacceptably high weight loss. Thus, DWCNTs are produced alongside SWCNTs and fine- tuning the experimental conditions allows one to make DWCNTs the major product. 19,22−31 Results have been reported regarding the in fluence of the synthesis parameters such as catalytic material composition, 32−36 catalyst particle size, 24,37−43 carbon source flow rate, 44−46 and temperature. 22−24,45 Con flict- ing results are reported, which is possibly due in part to the fact that the many experimental parameters are not independent. Moreover, some works rather deal with the control of the outer diameter, and, although there is a clear correlation with the number of walls in the case of MWCNTs, 47 it is not so for CNTs with less than about four walls. Nevertheless, the accepted requirements for the formation of DWCNTs preferentially to SWCNTs appear to be a larger catalyst particle and/or an increased carbon supply. 35,36 In earlier works, 23,27,31,34,48−54 we proposed and developed a CNT synthesis route involving the reduction in H 2 −CH 4 (or C 2 H 4 ) gas atmosphere of an Al 2 O 3 −
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Comparative micro-Raman spectroscopy study of tellurium-filled
double-walled carbon nanotubes

Comparative micro-Raman spectroscopy study of tellurium-filled double-walled carbon nanotubes

nent. Given the fact that the detected nanotubes have to be in resonance with the incident radiation, 共1.58 eV兲 we can con- clude that there is an energy increase in the corresponding interband optical transition in DWNT in comparison to the SWNT. This increase results in an upshift of the RBM mode of the CNT as compared to the corresponding RBM mode of a SWNT with the same diameter 共1.05 nm兲. Similar reason- ing can be applied for the assignment of the 170, 200-210, and 254 cm −1 components. Theoretical justification for the RBM mode upshift is found in calculations performed for breathinglike phonon modes in double-walled 12 , 13 and multiwalled 14 carbon nanotubes. The calculations indicate frequency upshift in comparison to the RBM position of a single nanotube with a given diameter due to carbon shell interaction. Low temperature high resolution Raman studies confirmed the frequency upshift of the RBM modes for both inner and outer CNTs up to 12 cm −1 . 15
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Chemical functionalization of Xanthan gum for the dispersion of double-walled carbon nanotubes in water

Chemical functionalization of Xanthan gum for the dispersion of double-walled carbon nanotubes in water

ing MWCNTs dispersions, one type of non-covalent function- alization has received considerable attention involving biocompatible polymers (gum arabic and carboxymethylcelu- lose) to investigate their ecotoxicity on the amphibian larvae [46] . Also, Roman et al. [47] have demonstrated that amino acids can adsorb through non-covalent interactions with CNTs through favorable adsorption pathways. Biopolymers, such as polysaccharides with a good toxicological profile, bring both steric repulsion and better stabilization (as thick- eners) of the aqueous phase behavior of these colloids. Besides being renewable, the unique structure of polysaccha- rides offers many interesting properties like hydrophilicity, biocompatibility, biodegradability (at least in the original state), stereoregularity, multichirality, and polyfunctionality, i.e. reactive functional groups (mainly OH–, NH–, and COOH– moieties) that can be modified by various chemical reactions [48] . Therefore, in the general context to achieve the stabiliza- tion of double-walled carbon nanotubes (DWCNTs) dispersion in aqueous media, we focused on the synthesis of hydropho- bically modified polysaccharide. We first propose the hypoth- esis that the benzene ring can interact strongly with CNTs yielding a homogeneous dispersion. Thus, among water-solu- ble biopolymers, Xanthan gum (Xan), a microbial biopolymer produced by the Xanthomonas campestris with a high molecu- lar weight ( Fig. 1 ) [49,50] seems a promising candidate.
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Polyethylene / single walled carbon nanotubes nanocomposites

Polyethylene / single walled carbon nanotubes nanocomposites

/ La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur. Access and use of [r]

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Chemical functionalization of Xanthan gum for the dispersion of double-walled carbon nanotubes in water

Chemical functionalization of Xanthan gum for the dispersion of double-walled carbon nanotubes in water

Most available experimental methods to disperse CNTs in common solvents or polymers require using surfactants [15,16] . Recent reports suggest the use of ionic surfactants with high HLB (Hydrophilic-Lyphophilic Balance) for disper- sion and stabilization of CNTs in water. There is no preferred ionic one when organic solvents have to be used [14] . As a starting point in understanding CNTs dispersion in water and organic media, several parameters must be known, such as the nature of the surfactant, its concentration and type of interactions in the stabilized phase [17] . Previous works show no clear conclusion on the dispersive efficiency of either anionic or cationic surfactants [17,18] . Therefore, knowing the surface charge of CNTs is absolutely required to under- stand the adsorption mechanism with ionic surfactants and to predict colloidal stability of CNTs suspensions. Zeta poten- tial analysis seems a useful tool to achieve this task. Thus, Jiang et al. [19] have shown that the surface of multi-walled carbon nanotubes (MWCNTs) in aqueous media is negatively charged. However, to shed some understanding on the behav- ior of single-walled carbon nanotubes (SWCNTs), Ausman et al. [20] have shown that highly polar solvents such as dimethylformamide (DMF), methylpyrrolidine (MP) and hex- amethylphosphoramide (HMPA) are rather efficient to prop- erly wet SWCNTs. Islam et al. [21] have obtained a stable dispersion in aqueous media of SWCNTs using dodecyl(tri- methyl)azanium bromide. Anionic surfactants such as so- dium dodecyl sulfate (SDS) [19,22–29] and dodecyl-benzene sodium sulfonate (NaDDBS) [30–32] have been widely used due to charge repulsion to limit the agglomeration tendency of CNTs [17] . Therefore, the former approach and the main driving force for surfactant-stabilized CNTs dispersions, the p–p stacking interaction [33–35] between the benzene ring and the CNTs surface, is believed to significantly increase the binding of surfactant molecules onto CNTs
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Structural Properties of Double-Walled Carbon Nanotubes Driven by Mechanical Interlayer Coupling

Structural Properties of Double-Walled Carbon Nanotubes Driven by Mechanical Interlayer Coupling

parameters corresponding to favored con figurations as discussed in Figure 4 . However, the relaxed structure presents important distortions and a lot of defects preventing a complete determination of its chirality. Despite that, our simulations emphasize that strain e ffects on the inner tube exist, leading to forbidden structures, as observed experimentally. In the case of a (12,0)@(18,0) DWNT, the system contains 720 atoms for a tube length close to 24 Å. The same conclusions can be drawn with stronger evidence due to the small interlayer distance, which increases the e ffects (see Figure 7 b). As an example, the diameter of the inner tube varies from 9.5 to 6.5 Å, in agreement with HRTEM observations of defected tubes where
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Synthesis of superparamagnetic iron(III) oxide nanowires in double-walled carbon nanotubes

Synthesis of superparamagnetic iron(III) oxide nanowires in double-walled carbon nanotubes

is equal to zero (no hysteresis) for temperatures above T Bw . In agreement with 57 Fe Mo¨ssbauer spectroscopy and magnetic measurements data, the reduction of FeI 2 in hydrogen was probably directly followed by oxidation, leading to superparamagnetic iron( III ) oxide crystallized nanowires (supported by HRTEM observations) forming chain-like structures inside DWNT (the exact nature of those structures, wires or particles, is under investigation).

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