Photoelectrochemical reactions of electrodes modified with composites between conjugated polymer or ruthenium complex and single-walled carbon nanotubes

Composite materials between conjugated polymer; poly[2-methoxy-5-(2'-ethylhexyloxy)-1.4-phenylene vinylene] (MEHPPV), or ruthenium(II)-tris(2,2'-bipyridine) (Ru(bpy)₃²⁺)-poly(sodium 4-styrenesulfonate) (PSS) complex and single-walled carbon nanotubes (SWNTs) were fabricated using polymer wrapping method. Formation of SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was confirmed by absorption and fluorescence spectra, and AFM images. Electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite was prepared by casting from DMF solution of SWNT/MEHPPV or aqueous solution of SWNT/PSS/Ru(bpy)₃²⁺. The electrode modified with SWNT/MEHPPV or SWNT/PSS/Ru(bpy)₃²⁺ composite showed photocurrent response due to photoexcitation of MEHPPV or Ru(bpy)₃²⁺. The photocurrents are ascribed to photoinduced electron-transfer reaction from excited state of MEHPPV or Ru(bpy)₃²⁺ to SWNT.     

Selective adsorption of cations on single-walled carbon nanotubes: A density functional theory study

The selective adsorption of cation on single-walled carbon nanotubes (SWNTs) is systemically studied by using density functional theory calculations. It is found that the adsorption energy of cations on SWNTs depends on the concentration of cations and the diameter and the electronic structure of SWNTs. The binding strength of on each SWNT increases monotonically as the concentration of decreases, undergoing a change from endothermic to exothermic reaction. Generally speaking, the binding of on SWNTs becomes weaker as the diameter increases. In the medium-diameter region (9 < d < 11 Å), prefers to interact with metallic SWNTs (m-SWNTs) rather than semiconducting SWNTs (s-SWNTs) at the same concentration of . In the small-diameter region (d < 9 Å), the binding of is nearly independent of metallicity, but it is stronger than that of on the medium-diameter s-SWNTs. In the large-diameter region (d > 11 Å), the dependence of adsorption on the electronic structure is complicated, but the binding of is weaker than that on the medium-diameter s-SWNTs. Our results are in agreement with the experimental report that the small-diameter m- and s-SWNTs and the medium-diameter m-SWNTs are etched away by while the medium-diameter s-SWNTs and the large-diameter m- and s-SWNTs are intact.     

Buffered internal stresses in diamond-like carbon films reinforced with single-walled carbon nanotubes

Diamond-like carbon (DLC) films reinforced with single-walled carbon nanotubes (SWCNTs) were fabricated by sputter-deposition of DLC onto a few monolayers of spray-coated SWCNTs on glass substrates. The thickness-averaged internal stress was reduced by 1.5 GPa by incorporation of SWCNTs into 10-nm-thick DLC films. Stress analysis indicates that the internal stress is reduced by 1.8 GPa at the SWCNT-DLC nanocomposite layer and decreases exponentially as a function of film thickness. Microscopy reveals significant cracking and delamination in 150-nm-thick DLC films, while the SWCNT-reinforced films remain essentially intact. The results demonstrate that SWCNTs in DLC films influence the early stage of DLC film growth and act as an effective stress-buffering layer near the boundary between the film and substrate.     

The Influence of Cs Adsorption on Field Electron Emission from Single-Walled Carbon Nanotube Layers

The influence of Cs adsorption on field emission characteristics of single-walled carbon nanotube (SWNT) layers has been investigated. It has been found that Cs adsorption onto SWNT tips not only decreases the work function of SWNTs with the corresponding increase of the emission current, but also causes the additional increasing of the emission current in tens times without the decrease of the work function. We attribute the second effect to the appearance of local surface states associated with Cs, that increase the transparency of the surface potential barrier.     

Ho/Ni作为催化剂合成单壁碳纳米管

利用直流电弧等离子体方法，以Ho／Ni作为催化剂合成了单壁碳纳米管，借助扫描电子显微镜、拉曼光谱和热重分析方法对所合成的单壁碳纳米管的形貌、结构以及含量进行了表征。电镜观察以及热重分析表明，收集到的大量网状物中单壁碳纳米管含量较高；不同激发波长拉曼测量表明碳纳米管直径分布比较集中，在1．35nm～1．69nm范围，且直径为1．5nm的碳纳米管占多数；与Ce／Ni等作为催化剂合成的单壁碳纳米管的直径分布不同。研究结果表明，Ho／Ni对于合成单壁碳纳米管具有很好的催化效果且影响管径分布，元素Ho对单壁碳纳米管的形成起到了重要的作用。     

DNA biosensor by self-assembly of carbon nanotubes and DNA to detect riboflavin

The fabrication of biosensors via self-assembly of single-walled carbon nanotubes (SWNTs) and DNA on a platinum electrode was presented in this paper. The carboxylic SWNTs were assembled on an amine-modified platinum electrode surface and followed by the assembly of NH₂-DNA with the carboxyl-amine coupling. The decorated surface was characterized by Field Emission Electron Microscopy (FEG-SEM) and electrochemical experiments, which showed that the reaction of DNA–SWNTs biosensor was quasi-reversible. The mechanism of DNA and riboflavin (VB₂) was studied by cyclic voltammetry and UV–Vis spectroscopy. The fabricated SWNTs-reinforced biosensor exhibits high sensitivity and low detection limit for the tested VB₂ compared to the reported methods.     

Thermo-mechanical vibration of a single-walled carbon nanotube embedded in an elastic medium based on nonlocal elasticity theory

A single-elastic beam model has been developed to analyze the thermal vibration of single-walled carbon nanotubes (SWCNT) based on thermal elasticity mechanics, and nonlocal elasticity theory. The nonlocal elasticity takes into account the effect of small size into the formulation. Further, the SWCNT is assumed to be embedded in an elastic medium. A Winkler-type elastic foundation is employed to model the interaction of the SWCNT and the surrounding elastic medium. Differential quadrature method is being utilized and numerical solutions for thermal-vibration response of SWCNT is obtained. Influence of nonlocal small scale effects, temperature change, Winkler constant and vibration modes of the CNT on the frequency are investigated. The present study shows that for low temperature changes, the difference between local frequency and nonlocal frequency is comparatively high. With embedded CNT, for soft elastic medium and larger scale coefficients (e₀a) the nonlocal frequencies are comparatively lower. The nonlocal model-frequencies are always found smaller than the local model-frequencies at all temperature changes considered.     

Nonlocal anisotropic elastic shell model for vibrations of single-walled carbon nanotubes with arbitrary chirality

A nonlocal anisotropic elastic shell model is developed to study the effect of small scale on shell-like vibration of single-walled carbon nanotubes (SWCNTs) with arbitrary chirality. Anisotropic elastic shell model is reformulated using the nonlocal differential constitutive relations of Eringen. The equations of motion are derived and analytical solution for the vibration of anisotropic SWCNTs is presented by using the Flügge shell theory and complex method. The suggested model is justified by a good agreement between the results given by the present model and available data in literature. Furthermore, the model is used to elucidate the effect of small scale on the vibration of zigzag, armchair and chiral SWCNTs. Our results show that small scale is essential for vibration of SWCNTs when the axial wave-length is not extremely long. Moreover, the results show that local model substantially overestimates vibrational frequencies of almost all modes.     

Effect of nucleases on the cellular internalization of fluorescent labeled DNA-functionalized single-walled carbon nanotubes

Nuclease effects on the cell internalization of single-walled carbon nanotubes (SWNTs) functionalized with fluorescent-labeled DNA in serum containing cell growth media were examined. When Cy3-labeled DNA-functionalized SWNT conjugates (Cy3DNA-SWNTs) were incubated with HeLa cells in a fatal bovine serum (FBS) medium, a high fl uorescence intensity was obtained from the cells, indicative for the high level inclusion of Cy3DNA-SWNTs. However, the fluorescence intensity was remarkably reduced if Cy3DNA-SWNTs were incubated with cells in the FBS-free medium. Further systematic control experiments revealed that Cy3 dye molecules were released from Cy3DNA-SWNT conjugates by nuclease, and the free Cy3 dyes penetrate into HeLa cell with high efficiency. Although the actual amounts of SWNTs internalized in the cells were almost identical for both cells incubated in the FBS-present and FBS-absent media according to the Raman measurements, one should be cautious to determine the degree of SWNT internalization based on the fluorescence intensities especially when the coloring dye molecules were linked to oligonucleotides in nuclease containing media. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Properties of well aligned SWNT modified poly (methyl methacrylate) nanocomposites

The PMMA/SWNT composites with good uniformity, dispersion and alignment of SWNT were fabricated in a stretching process. The semidried mixture was stretched along one direction at a draw ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The TEM and SEM observation demonstrated that SWNT in the PMMA/SWNT composite tend to align in the stretching direction. The electrical conductivity and the mechanical properties of composite rise with the increase of SWNT concentration, composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The TGA revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

用于制备优质单壁碳纳米管管束的MgO负载Fe3O4纳米粒子的合成

采用沉淀方法制备了直径分布狭窄的均匀Fe3O4纳米颗粒.Fe3O4纳粒形体几近一致,平均粒径为10.33 nm±2.99 nm(平均粒径±标准偏差).在超声作用下将MgO纳米颗粒分散在一定量Fe3O4纳米颗粒的水溶液中获得MgO负载Fe3O4的纳米颗粒.以甲烷为碳源,Fe3O4/MgO为催化剂,经化学气相沉积,在Fe3O4纳粒上制得了大量直径近乎均匀的单壁碳纳米管(SWCNTs)束.TEM显示:SWCNTs的平均直径1.22rm.热重分析显示:样品在400℃～600℃温度区间失重量约19％.拉曼光谱显示:SWCNTs的ID/IG的强度比为0.03,表明采用Fe3O4/MgO催化剂可制得高石墨化程度的单壁碳纳米管.     

Moderate temperature synthesis of single-walled carbon nanotubes on alumina supported nickel oxide catalyst

A simple nickel oxide catalyst has been developed in synthesizing single-walled carbon nanotubes (SWNTs) at moderate temperature. The catalyst used in the experiment was without a preceding reduction in hydrogen flow. The synthesis of SWNTs was performed at a temperature of 700 °C, which represents a moderate reaction temperature. The presence of SWNTs on the catalyst was confirmed by transmission electron microscope (TEM) and Raman spectroscope. The Raman spectrum shows a strong intensity at the radial breathing mode, indicating that the occurrence of SWNTs was dominant. Raman data further reveals that the synthesized SWNTs had the diameters in the range from 0.58 to 2.02 nm.     

Investigation of temperature effect on the mechanical properties of single-walled carbon nanotubes

A temperature-related higher-order gradient continuum theory is proposed for predicting the mechanical properties of single-walled carbon nanotubes (SWCNTs) at various temperatures. It is found that the axial elastic moduli of zigzag (21, 0), armchair (12, 12) and chiral (15, 9) SWCNTs with similar radii approach 0.7 TPa when T = 0 K, but decline slightly on different slopes. These results indicate that the temperature effect influences the axial Young moduli of zigzag SWCNTs less than those of the other types. Moreover, the parameters λ₁ and λ₂ corresponding to the uniform longitudinal and circumferential stretches at different temperatures are also examined, and the results show that with an increasing temperature, all SWCNTs are stretched in the longitudinal direction, while in the circumferential direction, only the zigzag SWCNTs are stretched, whereas the others are compressed.     

Tailoring the diameter of single-walled carbon nanotubes for optical applications

Single-walled carbon nanotubes (SWCNTs) with specific diameters are required for various applications particularly in electronics and photonics, since the diameter is an essential characteristic determining their electronic and optical properties. In this work, the selective growth of SWCNTs with a certain mean diameter is achieved by the addition of appropriate amounts of CO₂ mixed with the carbon source (CO) into the aerosol (floating catalyst) chemical vapor deposition reactor. The noticeable shift of the peaks in the absorption spectra reveals that the mean diameters of the as-deposited SWCNTs are efficiently altered from 1.2 to 1.9 nm with increasing CO₂ concentration. It is believed that CO₂ acts as an etching agent and can selectively etch small diameter tubes due to their highly curved carbon surfaces. Polymer-free as-deposited SWCNT films with the desired diameters are used as saturable absorbers after stamping onto a highly reflecting Ag-mirror using a simple dry-transfer technique. Sub-picosecond mode-locked fiber laser operations at ∼1.56 μm and ∼2 μm are demonstrated, showing improvements in the performance after the optimization of the SWCNT properties.      

An efficient numerical method for analyzing the thermal effects on the vibration of embedded single-walled carbon nanotubes based on the nonlocal shell model

Employing the variational differential quadrature (VDQ) method, the effects of initial thermal loading on the vibrational behavior of embedded single-walled carbon nanotubes (SWCNTs) based on the nonlocal shell model are studied. According to the first-order shear deformation theory and considering Eringen's nonlocal elasticity theory, the energy functionality of the system is presented and discretized using the VDQ method. The effects of thermal loading and elastic foundation are simultaneously taken into account. The use of the numerical discretization technique in the context of variational formulation reduces the order of differentiation in the governing equations and consequently improves the convergence rate. The accuracy of the present model is first checked by comparison with molecular dynamics simulation results and those of other methods. The effects of involved parameters are then investigated on the fundamental frequencies of thermally preloaded embedded SWCNTs. The results imply that the thermal loading has a significant effect on the vibration analysis of embedded SWCNTs.     

纳米碳管／聚酰亚胺复合材料制备与性能研究

利用纳米碳管的N甲基吡咯烷酮分散液，通过改变纳米碳管表面的性质和薄膜的制备条件，成功地制备了一系列均匀的纳米碳管，聚酰亚胺薄膜。研究结果表明，添加酰氯化后的纳米碳管到聚酰亚胺中可以改善聚酰亚胺的拉伸性能，而对聚酰亚胺的热稳定性和光学性质没有明显的影响。当添加1．0％的纳米碳管时，与纯PI相比复合材料的弹性模量增加了25．6％，拉伸强度增加了31．0％，断裂伸长率增加了7．6％。     

Investigation of the thermo-mechanical properties of single-walled carbon nanotubes based on the temperature-related higher order Cauchy-Born rule

In the present study, a nanoscale quasi-continuum constitutive model for predicting the thermal-mechanical properties of single-walled carbon nanotubes (SWCNTs) and graphene sheet is established based on the interatomic potential and the temperature-related higher order Cauchy-Born rule. Helmholtz free energy is used as the corresponding thermodynamic potential. It is a function of some temperature-dependent lattice parameters that can be determined through an energy minimization process. As an application of the proposed quasi-continuum model, temperature dependency and curvature effect of the specific heat, the coefficient of thermal expansion (CTE) and the Young’s modulus of SWCNTs are investigated systematically. Numerical results obtained show the effectiveness of the proposed constitutive model.