Comparative study on different carbon nanotube materials in terms of transparent conductive coatings

We compared conductive transparent carbon nanotube coatings on glass substrates made of differently produced single-wall (SWNT), double-wall, and multiwall carbon nanotubes. The airbrushing approach and the vacuum filtration method were utilized for the fabrication of carbon nanotube films. The optoelectronic performance of the carbon nanotube film was found to strongly depend on many effects including the ratio of metallic-to-semiconducting tubes, dispersion, length, diameter, chirality, wall number, structural defects, and the properties of substrates. The electronic transportability and optical properties of the SWNT network can be significantly altered by chemical doping with thionyl chloride. Hall effect measurements revealed that all of these thin carbon nanotube films are of p-type probably due to the acid reflux-based purification and atmospheric impurities. The competition between variable-range hoping and fluctuation-assisted tunneling in the functionized carbon nanotube system could lead to a crossover behavior in the temperature dependence of the network resistance.     

Comparative measures of single-wall carbon nanotube dispersion

Model composites of DNA-wrapped single-wall carbon nanotubes in poly(acrylic acid) are used to evaluate metrics of nanotube dispersion. By varying the pH of the precursor solutions, we introduce a controlled deviation from ideal behavior. On the basis of small-angle neutron scattering, changes in near-infrared fluorescence intensity are strongly correlated with dispersion, while optical absorption spectroscopy and resonant Raman scattering are less definitive. Our results represent the first systematic comparison of currently accepted measures of nanotube dispersion.     

Novel hybrid materials consisting of regioregular poly(3-octylthiophene)s covalently attached to single-wall carbon nanotubes

Facile routes for the synthesis of hybrid materials consisting of regioregular poly(3-octylthiophene)s covalently attached to single-wall carbon nanotubes are presented for the first time. These materials are easily processable using common organic solvents, and at the same time combine the properties of regioregular poly(3-alkylthiophene)s with those of single-wall carbon nanotubes. Moreover, studies of the properties of these materials have provided strong evidence for an electron transfer from the regioregular poly(3-octylthiophene) to the single-wall carbon nanotube.     

Structural and reactivity properties of finite length cap-ended single-wall carbon nanotubes

The reaction of C2 with growing single-wall carbon nanotubes of different chiralities is investigated using density functional theory. It is found that the energy of the frontier orbitals for (5,5) and (6,6) armchair carbon nanotubes exhibits periodic behavior with an increasing number of carbon atoms in the nanotube. Such periodic behavior induces oscillations in the reaction energy released by adsorption of C2 to the nanotube open edge. In contrast, the energy of the frontier orbitals of the (6,5) chiral tube remains constant as the number of C atoms increases, and the same stability is observed in the adsorption energy. It is suggested that this may be one of the reasons for the low percent of armchair single-wall carbon nanotubes found in the experimental synthesis.     

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.     

Selective adsorption of proteins on single-wall carbon nanotubes by using a protective surfactant

The dispersion of highly hydrophobic carbon materials such as carbon nanotubes in biological media is a challenging issue. Indeed, the nonspecific adsorption of proteins occurs readily when the nanotubes are introduced in biological media; therefore, a methodology to control adsorption is in high demand. To address this issue, we developed a bifunctional linker derived from pyrene that selectively enables or prevents the adsorption of proteins on single-wall carbon nanotubes (SWNTs). We demonstrated that it is possible to decrease or completely suppress the adsorption of proteins on the nanotube sidewall by using proper functionalization (either covalent or noncovalent). By subsequently activating the functional groups on the nanotube derivatives, protein adsorption can be recovered and, therefore, controlled. Our approach is simple, straightforward, and potentially suitable for other biomolecules that contain thio or amino groups available for coupling.     

Persistence length control of the polyelectrolyte layer-by-layer self-assembly on carbon nanotubes

We have studied layer-by-layer polyelectrolyte self-assembly on pristine individual single-wall carbon nanotubes as a function of solution ionic strength. We report the existence of an ionic strength threshold for the deposition, below which the majority of nanotubes remain uncoated. Once the ionic strength reaches the threshold value, the majority of the individual nanotubes become coated with polyelectrolytes. Our results indicate that the self-assembly process likely involves wrapping of polymer chains around nanotubes and that the polymer chain's ability to bend in order to accommodate the nanotube curvature is one of the critical parameters controlling layer-by-layer electrostatic self-assembly on these one-dimensional templates.     

水溶性羟基化单壁碳纳米管与人血清白蛋白之间的相互作用研究

利用荧光光谱、UV吸收光谱、同步荧光光谱和透射电子显微镜等技术较为系统地研究了水溶性羟基化单壁碳纳米管与人血清白蛋白(HSA)的相互作用. 实验发现, 这种羟基化单壁碳纳米管可以明显猝灭HSA的内源荧光, 且猝灭效应随碳纳米管浓度增大而增强. 同时, HSA对水溶性羟基化单壁碳纳米管起到一定的分散和稳定作用. 同步荧光光谱表明, 二者之间的相互作用可导致HSA的构象发生变化, HSA的色氨酸残基荧光信号发生2 nm的红移, 表明色氨酸残基周围微环境的极性降低.     

Length-dependent optical effects in single-wall carbon nanotubes

Among the novel chemical and physical attributes of single-wall carbon nanotubes (SWCNTs), the optical properties are perhaps the most compelling. Although much is known about how such characteristics depend on nanotube chirality and diameter, relatively little is known about how the optical response depends on length, the next most obvious and fundamental nanotube trait. We show here that the intrinsic optical response of single-wall carbon nanotubes exhibits a strong dependence on nanotube length, and we offer a simple explanation that relates this behavior to the localization of a bound exciton along the length of a nanotube. The results presented here suggest that, for a given volume fraction, the longest nanotubes display significantly enhanced absorption, near-infrared fluorescence, and Raman scattering, which has important practical implications for potential applications that seek to exploit the unique optical characteristics of SWCNTs.     

Enthalpy and entropy effects in hydrogen adsorption on carbon nanotubes

Interaction energies and entropies associated with hydrogen adsorption on the inner and outer surfaces of zigzag single-wall carbon nanotubes (SWCNT) of various diameters are analyzed by means of molecular mechanics, density functional theory, and ab initio calculations. For a single molecule the strongest interaction, which is 3.5 greater than that with the planar graphite sheet, is found inside a (8,0) nanotube. Adsorption on the outer surfaces is weaker than that on graphite. Due to the steric considerations, both processes are accompanied by an extremely strong decline in entropy. Absence of specific adsorption sites and weak attractive interaction between hydrogen molecules within carbon nanotubes results in their close packing at low temperatures. Using the calculated geometric and thermodynamic parameters in Langmuir isotherms we predict the adsorption capacity of SWCNTs at room temperature to be smaller than 1 wt % even at 100 bar.     

Single-wall carbon nanotube interaction with gases: sample contaminants and environmental monitoring

Here, we show that residual contaminants in purified single-wall carbon nanotube bundles may be responsible for the reported sensitivity of the electronic and transport properties to oxygen. Removal of these contaminants makes the electronic spectra insensitive to O(2), CO, H(2)O, and N(2), while a strong sensitivity to NO(2), SO(2), and NH(3) is observed, confirming the possible application of single-wall nanotubes as powerful sensors capable of measuring environmentally significant levels of toxic gases.     

脉冲激光溅射下固液界面生长的碳纳米管及其机理初探

以脉冲激光束直接溅射浸在水中的单质碳样品，发现在固液界而也能产生碳纳米管．实验还发现碳纳米管的形成与样品的结构有密切的关联：石墨的层状结构越完整，碳纳米管的形成越容易，而且石墨层而相对于激光束的取向也会显著地影响碳纳米管的生成．通过对实验结果的分析，探讨了激光液相溅射产生碳纳米管的机理，认为激光溅射产生的碳蒸气被水束缚在固液的界而内，而完整的晶而使碳蒸气在界而内的分布具有准二维的性质，为碳纳米管的生长提供了较为理想的环境．     

脉冲激光溅射下固液界面生长的碳纳米管及其机理初探

以脉冲激光束直接溅射浸在水中的单质碳样品，发现在固液界面也能产生的碳纳米管，实验还发现碳纳米管的形成与样品的结构有密切的关联：石墨的层状结构越完整，碳纳米管的形成越容易，而且石墨层面相对于激光束的取向也会显著地影响碳的生成。     

Aqueous dispersion, surface thiolation, and direct self-assembly of carbon nanotubes on gold

We report the efficient aqueous dispersion of pristine HiPco single-walled carbon nanotubes (SWNTs) with ionic liquid (IL)-based surfactants 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), the thiolation of nanotube sidewalls with 2, and the controlled self-assembly of positively charged SWNT-1,2 composites on gold. Optical absorption spectra and resonance Raman (RR) data of obtained aqueous SWNT-1,2 dispersions are consistent with debundled and noncovalently functionalized nanotubes whose electronic properties have not been disturbed. Additionally, the dispersion of pristine nanotube material with surfactants 1 and 2 leads to a high degree of purification from carbonaceous particles. The chiralities of the 14 smallest semiconducting HiPco SWNTs in resonance with Raman excitation at 1064 nm (1.165 eV) were determined in SWNT-2 aqueous dispersion using UV-vis-NIR and RR spectra. X-ray photoelectron spectroscopy (XPS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopy of SWNT-2 submonolayers on gold verified the encapsulation of individualized SWNTs with IL surfactants, the cleavage of S-S disulfide bonds formed in aqueous SWNT-2 suspensions, and the direct chemisorption of the SWNT-2 composite on bare gold via the Au-S bond. Aqueous dispersions of SWNTs with IL-based surfactants add biofunctionality to carbon nanotubes by imparting the positive surface charge necessary for interactions with cell membranes. Our technique, which purifies pristine nanotube material and produces water-soluble, positively charged nanotubes with pendent surface-active thiol groups, may also be translated to other carbon nanotubes and carbon nanostructures. Self-assembled, positively charged submonolayers of SWNTs can be further used for applications in cell biology and sensor technology.     

用羟基磷灰石和单壁碳纳米管制备葡萄糖传感器的研究

在滴涂法制得单壁碳纳米管(SWNTs)修饰电极的基础上,采用电化学方法沉积纳米羟基磷灰石(HA)涂层,进而利用分子组装技术将葡萄糖氧化酶(GOD)固定到该电极上,制得的修饰电极的循环伏安测量结果表明,GOD发生了直接的电子传递.GOD-HA-SWNTs/GC修饰电极对不同浓度的葡萄糖呈现两个良好的线性响应范围,有望开发...     

Thermogravimetric analysis of synthesis variation effects on CVD generated multiwalled carbon nanotubes

Changes in the thermogravimetrically determined oxidation behaviors of CVD-grown multiwalled carbon nanotubes with varying synthesis conditions are examined. Catalyst type and synthesis temperature are found to have a measurable impact upon nanotube stability, suggesting differing levels of crystalline perfection in the resulting nanotubes. The results provide evidence showing the catalytic effects of nanotube catalyst particles and their oxides upon the oxidation of nanotube carbon and graphite. The significance of thermogravimetric analysis as a characterization tool for carbon nanotubes is discussed.     

Dimensional changes as a function of charge injection in single-walled carbon nanotubes

Motivated by the central importance of charge-induced dimensional changes for carbon nanotube electromechanical actuators, we here predict changes in nanotube length and diameter as a function of charge injection for armchair and zigzag nanotubes having different diameters. Density functional theory with periodic boundary conditions is used, which we show provides results consistent with experimental observations for intercalated graphites. Strain-versus-charge relationships are predicted from dimensional changes calculated with a uniform background charge ("jellium") for representing the counterions. These jellium calculations are consistent with presented calculations that include specific counterions for intercalated graphite, showing that hybridization between the ions and the graphite sheets is unimportant. The charge-strain relationships calculated with the jellium approximation for graphite and isolated single-walled nanotubes are asymmetric with respect to the sign of charge transfer. The dependence of nanotube strain on charge approaches that for a graphite sheet for intermediate-sized metallic nanotubes and for larger diameter semiconducting nanotubes. However, the strain-charge curves strongly depend on nanotube type when the nanotube diameter is small. This reflects both the dependence of the frontier orbitals for the semiconducting nanotubes on the nanotube type and the pi-sigma mixing when the nanotube diameter is small.     

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.     

CVD growth of N-doped carbon nanotubes on silicon substrates and its mechanism

In the present study, we report the chemical vapor deposition (CVD) of nitrogen-doped (N-doped) aligned carbon nanotubes on a silicon (Si) substrate using ferrocene (Fe(C5H5)2) as catalyst and acetonitrile (CH3CN) as the carbon source. The effect of experimental conditions such as temperature, gaseous environment, and substrates on the structure and morphology of N-doped carbon nanotubes arrays is reported. From XPS and EELS data, it was found that the nitrogen content of the nanotubes could be determined over a wide range, from 1.9% to 12%, by adding the addition of hydrogen (H2) to the reaction system. It was also shown by SEM that N-doped carbon nanotube arrays could be produced on Si and SiO2 substrates at suitable temperatures, although at different growth rates. Using these concentrations, it was possible to produce three-dimensional (3D) carbon nanotubes architectures on predetermined Si/SiO2 patterns. The mechanism underlying the effect of nitrogen containing carbon sources on nanotube formation was explored using X-ray photoelectron spectroscopy (XPS).     

Self-assembled carbon nanotubes on gold: polarization-modulated infrared reflection-absorption spectroscopy, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy study

Recently we reported noncovalent functionalization of nanotubes in an aqueous medium with ionic liquid-based surfactants, 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), resulting in positively charged single-wall carbon nanotube (SWNT)-1,2 composites. Thiolation of SWNTs with 2 provides their self-assembly on gold as well as templating gold nanoparticles on SWNT sidewalls via a covalent -S-Au bond. In this investigation, we studied the electronic structure, intermolecular interactions, and packing within noncovalently thiolated SWNTs and also nanotube alignment in the bulk of SWNT-2 dried droplets and self-assembled submonolayers (SAMs) on gold by high-resolution X-ray photoemission spectroscopy (HRXPS), C K-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). HRXPS data confirmed the noncovalent nature of interactions within the nanocomposite of thiolated nanotubes. In PM-IRRAS spectra of SWNT SAMs on gold, the IR-active vibrational SWNT modes have been observed and identified. According to PM-IRRAS data, the hydrocarbon chains of 2 are oriented with less tilt angle to the bare gold normal in a SAM deposited from an SWNT-2 dispersion than those of 1 deposited from an SWNT-1 dispersion on the mercaptoethanesulfonic acid-primed gold. For both the dried SWNT-2 bulk and the SWNT-2 SAM on gold, the C K-edge NEXAFS spectra revealed the presence of CH-pi interactions between hydrocarbon chains of 2 and the pi electronic nanotube structure due to the highly resolved vibronic fine structure of carbon 1s --> R*/sigma*C-H series of states in the alkyl chain of 2. For the SWNT-2 bulk, the observed splitting and upshift of the SWNT pi* orbitals in the NEXAFS spectrum indicated the presence of pi-pi interactions. In the NEXAFS spectrum of the SWNT-2 SAM on gold, the upshifted values of the photon energy for R*/sigma*C-H transitions indicated close contact of 2 with nanotubes and with a gold surface. The angle-dependent NEXAFS for the SWNT-2 bulk showed that most of the molecules of 2 are aligned along the nanotubes, which are self-organized with orientation parallel to the substrate plane, whereas the NEXAFS for the SWNT-2 SAM revealed a more normal orientation of functionality 2 on gold compared with that in the SWNT-2 bulk.