NEXAFS光谱分析聚合物修饰的单壁碳纳米管

利用C1s、O1s、N1s近边X射线吸收精细结构(Near Edge X-Ray Absorption Fine Structure,NEXAFS)光谱对聚合物修饰的碳纳米管进行了分析,研究了氧化及偶联聚合物对碳纳米管结构的影响。氧化碳纳米管及十八胺修饰的、聚合物/十八胺双修饰的碳纳米管的NEXAFS光谱均出现了碳/氧K边π*(C=O)和σ*(C-O)共振峰;而十八胺修饰的、聚合物/十八胺双修饰的碳纳米管则出现了氮K边π*(N-C=O)和σ*(N1s)共振峰。分析表明,NEXAFS光谱可有效表征聚合物修饰的碳纳米管。     

Characterization of the chemical interaction between single-walled carbon nanotubes and titanium dioxide nanoparticles by thermogravimetric analyses and resonance Raman spectroscopy

Raman spectroscopy is a powerful technique that is used to characterize or observe alterations in the structure or properties of carbon nanotubes and its composites. This method can provide information about electronic changes or quantify them. We used Raman spectroscopy to study the chemical and electronic changes in a composite formed by titanium dioxide nanoparticles and single-walled carbon nanotubes. This composite was characterized by scanning electron microscopy to investigate the morphology and by thermogravimetric analyses to assess the thermal stability of the isolated carbon nanotubes as compared with the nanotubes by titanium dioxide nanoparticles. The Raman results showed that the modification of the nanotubes with the TiO₂ nanoparticles generates a new material with different structure of the nanotubes, resulting in a decrease in defects. The charge transfer from the TiO₂ nanoparticles to the nanotubes alters the electronic properties of both moieties in the hybrid material. The interaction between the nanotubes and nanoparticles decreases the CC bound order of the nanotubes and decreases their thermal stability.     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Simple and fast fluorimetric determination of the critical gel concentration of soft nanomaterials

Soft materials or gels are new interesting materials resulting from the combination of carbon nanotubes with ionic liquids. However, it should be noted that not all ionic liquid/carbon nanotubes combinations lead to the formation of gels. In fact, this requires using an optimum concentration of CNTs known as “critical gel concentration” (CGC) in the mixture. Up to now, this critical concentration has been determined by means of rheological measurements or by observing a change of a physical property in the new material such as density. On the basis of the high stability of gels in solvents, owing to the presence of carbon nanotubes, this paper reports for the first time a simple and fast method to determine the critical gel concentration for the formation of soft materials by means of fluorescence measurements. We have determined the critical gel concentration of four gels obtained by the combination of three different types of multi walled carbon nanotubes and one single walled carbon nanotubes with the ionic liquid 1-hexyl 3-methylimidazolium hexafluorophosphate. The main characteristics of carbon nanotubes and gels resulting of them were established by Raman spectroscopy. The proposed methodology is presented as an alternative to traditional complex rheological measurements.     

Investigation of the Orientation in Composite Fibers of Polycarbonate with Multiwalled Carbon Nanotubes by Raman Microscopy

The superior association of the inherent good mechanical and electrical properties makes carbon nanotubes (CNT) exceptionally interesting for the production of composite fibers of thermoplastic polymers with CNT. Alignment of the CNT in the polymer fiber is important for improved mechanical properties. Especially the production of fibers makes it necessary to get a controlled orientation and/or alignment of the CNT. We applied transmission electron microscopy (TEM) and polarized Raman microscopy to quantify multiwalled carbon nanotubes (MWNT) orientation, alignment and crystallinity in polycarbonate (PC). The evaluation of the Raman measurements provided an improved alignment orientation of the MWNT in the fibers with increasing take-up velocity during melt spinning and that the crystal structure of the MWNT is not changed through melt spinning.     

Spectroscopic Characteristics of Differently Produced Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWNTs) synthesized with different methods are investigated by using multiple characterization techniques, including Raman scattering, optical absorption, and X‐ray absorption near edge structure, along with X‐ray photoemission by following the total valence bands and C 1s core‐level spectra. Four different SWNT materials (produced by arc discharge, HiPco, laser ablation, and CoMoCat methods) contain nanotubes with diameters ranging from 0.7 to 2.8 nm. The diameter distribution and the composition of metallic and semiconducting tubes of the SWNT materials are strongly affected by the synthesis method. Similar sp² hybridization of carbon in the oxygenated SWNT structure can be found, but different surface functionalities are introduced while the tubes are processed. All the SWNTs demonstrate stronger plasmon resonance excitations and lower electron binding energy than graphite and multiwalled carbon nanotubes. These SWNT materials also exhibit different valence‐band X‐ray photoemission features, which are considerably affected by the nanotube diameter distribution and metallic/semiconducting composition.     

Preparation of micelle-encapsulated single-wall and multi-wall carbon nanotubes with amphiphilic hyperbranched polymer

The hyperbranched polyester (Boltorn^TM H20) was modified by maleic anhydride and then polystyrene (H20-MAh-PSt) to form amphiphilic micelles in water. The single-wall and multi-wall carbon nanotubes (SWCNTs and MWCNTs, respectively) were encapsulated in the formed micelles through non-covalent interactions. The formed structures were confirmed by FTIR, NMR, GPC, and XPS analysis. The dispersion and aggregation behaviors were observed by TEM and UV-vis and Raman spectroscopic analysis. The results showed that the dispersion performance of the obtained micelle-encapsulated carbon nanotubes in water was greatly improved compared to the pure carbon nanotubes. From the TEM observation, the individual SWCNT structure and the uniform polymer coating around the surface of SWCNT were seen after crosslinking. The Raman spectroscopic measurements also demonstrated that for the crosslinked samples, no effect occurred associated with concentration-dependent carbon nanotube aggregation.     

Pore characterization of assembly-structure controlled single wall carbon nanotube

Single wall carbon nanotube (SWCNT), which has bundle structure and entangled structure, was untangled and cut by sonication in hydrogen peroxide (H₂O₂) solution. The untangled state of SWCNT was examined by SEM, TEM, Raman spectroscopy and N₂ adsorption. It was confirmed that the surface area of sonicated nanotubes strongly depended on the sonication time. The BET specific surface area (SSA) of nanotubes sonicated for 3 h was maximum. The SSA decreased at 6 h or more of sonication time. These results indicated that the bundle structure was untangled and the cap of SWCNT was opened. Thus, N₂ molecules can access the most efficiently inside of the SWCNT sonicated for 3 h. On the contrary, the sonication treatment for 6 h or more decomposed the nanotubes to produce amorphous carbon, evidenced by TEM and SEM observation; the amorphous carbon blocked the open pore sites such as the internal pore spaces and interstitial pores.     

Hybrid Nanomaterial Architectures: Combining Layers of Carbon Nanowalls,Nanotubes, and Particles

The paper focuses on the integration in hybrid architectures of plasma produced nanomaterials. The routes for the fabrication of layered structures consisting of carbon nanowalls on carbon nanotubes (CNW/CNT), of carbon nanotubes on carbon nanowalls (CNT/CNW), and nanoparticles on carbon nanowalls (NP/CNW) are presented. The morphology and structure of the hybrid architectures were investigated by electron microscopy techniques. We show that higher substrate temperature promotes the formation of high mass hydrogenated carbon clusters which favors the dominance of CNW growth over that of CNT. On this basis, a procedure of obtaining CNT/CNW architectures by switching the growth regime via substrate temperature is described. The specific limitations or advantages concerning the control or the properties of the obtained architectures are discussed.     

Mechanical, electrical and spectroscopic investigations of carbon nanotube-reinforced elastomers

This paper reports investigations carried out on elastomeric matrices filled with multiwall carbon nanotubes. A comparison with carbon black-filled polymers is also made. The state of dispersion of the fillers in the polymer matrix is evaluated through transmission electron and atomic force microscopies. Stress–strain measurements of the composites demonstrate that carbon nanotubes bring significant improvements in the mechanical properties with regard to the pure polymer. Infrared and Raman spectroscopies are shown to bring molecular insights into the structure/property correlations. Electrical properties of the filled materials are also analyzed in order to determine the so-called percolation threshold and the insulator–conductor transition corresponding to the formation of an interconnected filler network throughout the matrix.     

电位质子滴定与NEXAFS和XPS表征功能化多壁碳纳米管比较(英文)

Since the discovery of carbon nanotubes (CNT), this material has been recognized as an attractive catalyst support. CNT must be functionalized before use as a catalyst support and typically this involves oxidation. However, the functional group distribution on the CNT is very complex mixture of groups and varies with oxidation agent used. Here a simple acid-base titration is introduced to characterize the oxygen functionalized CNT. By comparing characterization with near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for both at the C and O K-edges, it can be demonstrated that potentiometric proton titration can be a fast and quantitative analysis for Brnsted acid functional groups on CNT.     

Clusterization, electrophoretic deposition, and photoelectrochemical properties of fullerene-functionalized carbon nanotube composites

We have successfully developed a new methodology for the self-organization of C(60) molecules on the sidewall of carbon nanotubes for use in photoelectrochemical devices. Novel nanocarbon composites of fullerene (e.g., C(60)) and highly soluble, chemically functionalized single-walled carbon nanotubes (f-SWNT) have been prepared by the rapid injection of a poor solvent (e.g., acetonitrile) into a mixed solution of C(60) and f-SWNT in o-dichlorobenzene. Measurements by using scanning electron microscopy of cast samples revealed that the composites are categorized into three groups; i) f-SWNT bundles covered with layers of C(60) molecules, ii) round, large C(60) clusters (sizes of 500-1000 nm) containing f-SWNT, and iii) typical, round C(60) clusters (sizes of 150-250 nm). The electrophoretic deposition of the composites onto a nanostructured SnO(2) electrode yielded the hierarchical film with a gradient composition depending on the difference in the mobilities of C(60) and f-SWNT during the electrophoretic process. The composite film exhibited an incident photon-to-photocurrent efficiency as high as 18 % at lambda=400 nm under an applied potential of 0.05 V vs. SCE. The photocurrent generation efficiency is the highest value among carbon nanotube-based photoelectrochemical devices in which carbon nanotubes are deposited electrophoretically, electrostatically or covalently onto semiconducting electrodes. The highly aligned structure of C(60) molecules on f-SWNT can rationalize the efficient photocurrent generation. The results obtained here will provide valuable information on the design of carbon nanotube-based molecular devices.     

Synthesis of straight and helical carbon nanotubes from catalytic pyrolysis of polyethylene

Straight and helical carbon nanotubes with diameter from 20 to 60 nm have been synthesized through catalytic decomposition of polyethylene in autoclave at 700 °C. The X-ray power diffraction pattern indicates that the products are hexagonal graphite, and transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) images reveal the morphologies and structures of carbon nanotubes. The effects of reaction temperature, catalyst and maleated polypropylene on the growth of the carbon nanotubes were also discussed, and the growth mechanism of the CNTs was proposed. Pyrolysis of polyethylene is a promising green chemical method for economically producing carbon nanotubes.     

Evidence for, and an understanding of, the initial nucleation of carbon nanotubes produced by a floating catalyst method

An understanding of the growth mechanism of carbon nanotubes (CNTs) is very important for the control of their structures, which in turn will be the basis for their further theoretical studies and applications. On the basis of high-resolution transmission electron microscopy observations of the initial nucleation of CNTs, the following deductions are made: (1) the nucleation of single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) starts at a low-temperature zone in front of the reaction zone; (2) the addition of sulfur results in localized liquid zones on the surface of big catalyst particles as the initial nucleation sites; (3) a temperature gradient is necessary to realize the role of sulfur in the structure of CNTs; and (4) the shell number of CNTs can be changed at the nucleation and growth stages. On the basis of the above, a growth model for the formation of SWNTs and DWNTs is proposed, which might open up the possibility of controlling the structure of CNTs.     

Topology and electronic structure of nanotube junctions of tetrapod shape

We propose a series of carbon nanostructures in the shape of tetrapod as a kind of three-dimensional junction for carbon nanotubes. The tetrapod junctions are such open networks that are made of sp² carbon atoms only, have negative Gaussian curvature, and connect four nanotubes together. We define the structure of standard tetrapod junctions, the simplest one, that have 12 heptagons other than hexagons and have the T_d symmetry.Our tight-binding energy-band calculations for the standard tetrapod junctions of smaller sizes show that their electronic property mainly depends on one particular topological factor: the junctions having a carbon atom in the center of each triangular face of tetrahedron exhibit metallic band structure while the junctions having a benzene ring in the center of the faces are semiconductors. We also find that tetrapod junctions connecting (6,0) nanotubes exhibit a flat band near the Fermi energy in a particular momentum region. The origin of the flat band states can be figured out from the wavefunction distribution. We also show the possibility to extend the standard tetrapod junctions to some non-standard ones that can connect nanotubes of different kinds and/or radii.     

Melting behavior of water in cylindrical pores: carbon nanotubes and silica glasses

We report a study of the effects of confinement in multi-walled carbon nanotubes and mesoporous silica glasses (SBA-15) on the solid structure and melting of both H(2)O and D(2)O ice, using differential scanning calorimetry, dielectric relaxation spectroscopy, and neutron diffraction. Multi-walled nanotubes of 2.4, 3.9 and 10 nm are studied, and the SBA-15 studied has pores of mean diameter 3.9 nm; temperatures ranging from approximately 110 to 290 K were studied. We find that the melting point is depressed relative to the bulk water for all systems studied, with the depression being greater in the case of the silica mesopores. These results are shown to be consistent with molecular simulation studies of freezing in silica and carbon materials. The neutron diffraction data show that the cubic phase of ice is stabilized by the confinement in carbon nanotubes, as well as in silica mesopores, and persists up to temperatures of about 240 K, above which there is a transition to the hexagonal ice structure.     

气凝胶催化剂上甲烷裂解制备的碳纳米管结构特征

采用XRD、TGA、SEM、TEM、 Raman光谱等多种表征手段,考察了Al2O3气凝胶催化剂上甲烷裂解生长的碳纳米管的结构特征.制得的碳纳米管形态单一,为管径均匀、管壁光滑的中空纳米管,平均直径在10～20 nm.碳纳米管的比表面积较大,具有较强的抗氧化能力,其结构的长程有序度较石墨低.由碳纳米管的Raman光谱分析可知,碳纳米管存在碳层缺陷和无定形碳.当反应温度升高或甲烷浓度下降时,碳纳米管石墨化程度逐渐提高.     

Modification of the surface of carbon fibers with multi-walled carbon nanotubes and its effect on mechanical characteristics of composites with epoxy resin

Effect of the catalyst composition on the structure of nanotubes layers obtained on the surface of carbon nanofibers was studied. We found the preliminary functionalization of the surface of carbon fibers to affect the coating uniformity and the thickness of synthesized nanotube layer. We determined the optimal surface concentration of the catalyst (Fe–Co) which provides uniform layer of nanotubes on the surface of carbon fibers. The effect of modification of the surface of carbon fibers with multi-walled carbon nanotubes on the mechanical properties of carbon fiber–epoxy resin composites was examined. The modification of the carbon fibers with multi-walled carbon nanotubes were shown to increase the flexural modulus and the flexural strength.     

Single carbon nanotube optical spectroscopy.

This Minireview discusses novel insights into the electronic structure of carbon nanotubes obtained using single-molecule fluorescence spectroscopy. Fluorescence spectra from single nanotubes are well described by a single, Lorentzian lineshape. Nanotubes with identical structures fluoresce with different energies due to local electronic perturbations. Carbon nanotube fluorescence unexpectedly does not-show any intensity or spectral fluctuations at 300 K The lack of intensity blinking or bleaching demonstrates that carbon nanotubes have the potential to provide a stable, single-molecule infrared photon source, allowing for the exciting possibility of applications in quantum optics and biophotonics.     

Nitrogen-doped carbon nanotubes: growth, mechanism and structure

Nitrogen-doped bamboo-structured carbon nanotubes have been successfully grown using a series of cobalt/molybdenum catalysts. The morphology and structure of the nanotubes were analysed by transmission electron microscopy and Raman spectroscopy. The level of nitrogen doping, as determined by X-ray photoelectron spectroscopy, was found to range between 0.5 to 2.5 at.%. The growth of bamboo-structured nanotubes in the presence of nitrogen, in preference to single-walled and multi-walled nanotubes, was due to the greater binding energy of nitrogen for cobalt in the catalyst compared to the binding strength of carbon to cobalt, as determined by density functional theory.