Temperature dependence of exciton recombination in semiconducting single-wall carbon nanotubes

We study the excitonic recombination dynamics in an ensemble of (9,4) semiconducting single-wall carbon nanotubes by high-sensitivity time-resolved photoluminescence experiments. Measurements from cryogenic to room temperature allow us to identify two main contributions to the recombination dynamics. The initial fast decay is temperature independent and is attributed to the presence of small residual bundles that create external nonradiative relaxation channels. The slow component shows a strong temperature dependence and is dominated by nonradiative processes down to 40 K. We propose a quantitative phenomenological modeling of the variations of the integrated photoluminescence intensity over the whole temperature range. We show that the luminescence properties of carbon nanotubes at room temperature are not affected by the dark/bright excitonic state coupling.     

New strategy for label-free and time-resolved luminescent assay of protein: conjugate Eu3+ complex and aptamer-wrapped carbon nanotubes

We report here a carbon nanotube-based approach for label-free and time-resolved luminescent assay of lysozyme (LYS) by engineering an antilysozyme aptamer and luminescent europium(III) (Eu(3+)) complex. The sensing mechanism of the approach is based on the exceptional quenching capability of carbon nanotubes for the proximate luminescent Eu(3+) complex and different propensities of single-stranded DNA and the DNA/protein complex to adsorb on carbon nanotubes. The luminescence of a mixture of chlorosulfonylated tetradentate β-diketone-Eu(3+) and the antilysozyme aptamer was efficiently quenched by single-walled carbon nanotubes (SWNTs) unless the aptamer interacted with LYS. Due to the highly specific recognition ability of the aptamer for the target and the powerful quenching property of SWNTs for luminescence regents, this proposed approach has a good selectivity and high sensitivity for LYS. In the optimum conditions described, >700-fold signal enhancement was achieved for micromolar LYS, and a limit of detection as low as 0.9 nM was obtained, which is about 60-fold lower than those of commonly used fluorescent aptamer sensors. Moreover, due to the much longer lifetime of the Eu(3+) luminescence than those of the ubiquitous endogenous fluorescent components, the time-resolved luminescence technique could be conveniently used for application in complicated biological samples. LYS concentrations in human urine were thus detected using time-resolved luminescence measurement with satisfactory recoveries of 95-98%.     

Structural and proactive safety aspects of oxidation debris from multiwalled carbon nanotubes

The removal of oxidation debris from the oxidized carbon nanotube surface with a NaOH treatment is a key step for an effective functionalization and quality improvement of the carbon nanotube samples. In this work, we show via infrared spectroscopy and ultrahigh resolution and accuracy mass spectrometry that oxidation debris obtained from HNO(3)-treated multiwalled carbon nanotubes is a complex mixture of highly condensed aromatic oxygenated carbonaceous fragments. We have also evaluated their cytotoxicity by using BALB/c 3T3 mouse fibroblasts and HaCaT human keratinocytes as models. By knowing the negative aspects of dissolved organic carbon (DOC) to the water quality, we have demonstrated the removal of these carbon nanotube residues from the NaOH solution (wastewater) by using aluminium sulphate, which is a standard coagulant agent used in conventional drinking water purification and wastewater treatment plants. Our results contribute to elucidate the structural and proactive safety aspects of oxidation debris from oxidized carbon nanotubes towards a greener nanotechnology.     

纳米镍颗粒填充碳纳米管的制备与磁性能

采用自制的实验装置, 通过阳极弧放电等离子体技术成功制备了Ni纳米颗粒填充的碳纳米管, 利用高分辨透射电子显微镜(HRTEM)、 XRD、 TEM、 X射线能量色散分析谱仪(XEDS)和振动样品磁强计(VSM)等测试手段对样品的化学成分、 形态、 微观结构和磁性能进行了表征。实验结果表明, 采用本文中实验方法能获得大量被纳米金属颗粒填充的碳纳米管, 其内部填充物为面心立方(FCC)结构的纳米Ni颗粒, 外围薄层为石墨碳层。碳纳米管的外径为30~40 nm, 壁厚5~8 nm, 内部填充的纳米颗粒呈球形和椭球形, 粒径均匀, 在管腔内不连续分布。产物具有顺磁特性, 矫顽力是78 Oe, 饱和磁化强度是33 enu/g。     

Doping and phonon renormalization in carbon nanotubes

We show that the Raman frequency associated with the vibrational mode at approximately 1,580 cm(-1) (the G mode) in both metallic and semiconducting carbon nanotubes shifts in response to changes in the charge density induced by an external gate field. These changes in the Raman spectra provide us with a powerful tool for probing local doping in carbon nanotubes in electronic device structures, or charge carrier densities induced by environmental interactions, on a length scale determined by the light diffraction limit. The G mode shifts to higher frequency and narrows in linewidth in metallic carbon nanotubes at large fields. This behaviour is analogous to that observed recently in graphene. In semiconducting carbon nanotubes, on the other hand, induced changes in the charge density only shift the phonon frequency, but do not affect its linewidth. These spectral changes are quantitatively explained by a model that involves the renormalization of the carbon nanotube phonon energy by the electron-phonon interaction as the carrier density in the carbon nanotube is changed.     

Synthesis and electronic properties of ferrocene-filled double-walled carbon nanotubes

Double-walled carbon nanotubes (DWNTs) are filled with ferrocene molecules by a vapour diffusion method for the first time. The as-synthesized ferrocene-filled DWNTs are characterized by transmission electron microscopy (TEM), energy-dispersive x-ray spectrometry (EDX) and Raman spectroscopy. Electronic properties of double-walled carbon nanotubes (DWNTs) filled with ferrocene molecules are studied by fabricating them as the channels of field-effect transistor (FET) devices. Our results reveal that electronic properties of ferrocene-filled DWNTs are greatly modified due to the charge transfer between ferrocene molecules and DWNTs. In addition, after ferrocene molecules are decomposed inside DWNTs, electronic properties of DWNTs exhibit a further change due to Fe encapsulation, and unipolar n-type semiconducting DWNTs are consequently obtained.     

Biodegradation of single-walled carbon nanotubes through enzymatic catalysis

We show here the biodegradation of single-walled carbon nanotubes through natural, enzymatic catalysis. By incubating nanotubes with a natural horseradish peroxidase (HRP) and low concentrations of H2O2 (approximately 40 microM) at 4 degrees C over 12 weeks under static conditions, we show the increased degradation of nanotube structure. This reaction was monitored via multiple characterization methods, including transmission electron microscopy (TEM), dynamic light scattering (DLS), gel electrophoresis, mass spectrometry, and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy. These results mark a promising possibility for carbon nanotubes to be degraded by HRP in environmentally relevant settings. This is also tempting for future studies involving biotechnological and natural (plant peroxidases) ways for degradation of carbon nanotubes in the environment.     

Direct synthesis of Y-junction carbon nanotubes by microwave-assisted pyrolysis of methane

Both Y-junction carbon nanotubes and individual carbon nanotubes were synthesized without any additive catalyst by microwave decomposition of methane. Detailed microstructures of as-synthesized products have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The results show that these Y-junction CNTs possess an internal bamboo-shaped structure, and some three dimensional multi-terminal junctions are also observed on CNTs. As gas flow rate decreased to 15 sccm, only individual nanotubes could be obtained. A possible mechanism is proposed for the synthesis of the Y-junction carbon nanotubes on these observations. This technique may also have great potential in making other nano-structured carbon materials on a large scale and at low cost.     

Label-free imaging of semiconducting and metallic carbon nanotubes in cells and mice using transient absorption microscopy

As interest in the potential biomedical applications of carbon nanotubes increases, there is a need for methods that can image nanotubes in live cells, tissues and animals. Although techniques such as Raman, photoacoustic and near-infrared photoluminescence imaging have been used to visualize nanotubes in biological environments, these techniques are limited because nanotubes provide only weak photoluminescence and low Raman scattering and it remains difficult to image both semiconducting and metallic nanotubes at the same time. Here, we show that transient absorption microscopy offers a label-free method to image both semiconducting and metallic single-walled carbon nanotubes in vitro and in vivo, in real time, with submicrometre resolution. By using appropriate near-infrared excitation wavelengths, we detect strong transient absorption signals with opposite phases from semiconducting and metallic nanotubes. Our method separates background signals generated by red blood cells and this allows us to follow the movement of both types of nanotubes inside cells and in the blood circulation and organs of mice without any significant damaging effects.     

定向纳米碳管表面有机和无机膜的制备

在AAO ( 阳极氧化铝 ) 模板上的定向纳米碳管表面制备了有机和无机膜。一种是采用真空蒸镀的方法沉积酞菁铜 ( CuPc ) 有机膜,另一种是用电沉积的方法在碳管表面沉积钴金属膜。对所镀的膜层进行了扫描电镜和透射电镜观察,结果表明:在纳米碳管表面获得了均匀的有机和无机涂层。它们的区别是蒸镀方法使纳米碳管背面不能获得涂层,而电镀方法能在整根纳米碳管上获得均匀涂层。      

Synthesis of single-walled carbon nanotubes (C-SWNTs) with a plasma torch: a parametric study

In this study, we examine, in detail, the synthesis of single wall carbon nanotubes (C-SWNTs) with a plasma torch, using molecular sources for both carbon and catalyst (typically a carbon-containing gas such as ethylene and ferrocene for the metal catalyst). A comparison of the results obtained by Raman spectroscopy, using two different excitation wavelengths, permitted us to evaluate the importance of certain experimental parameters affecting the quality of the samples; these include the growth temperature of the nanotubes, and the temperature gradient between the flame and the oven. We have found that our method provides results that are qualitatively similar to those obtained using arc and laser techniques: C-SWNTs mixed with catalyst nanoparticles and amorphous carbon. Although the yields of C-SWNTs in the experiments reported here are somewhat lower than other approaches, our method avoids the inconveniences related to the solid phase of the initial material. Observations from scanning electron micrographs (SEM) and transmission electron micrographs (TEM) suggest that the mechanisms involved in the synthesis of the C-SWNTs by our plasma torch are similar to these latter techniques. An industrial-scale process based on a plasma torch could produce large amounts of C-SWNTs with good efficiency, since the present set-up produces continuously 1.5 g/h of deposit while using only 1 kW of power.     

In situ nucleation of carbon nanotubes by the injection of carbon atoms into metal particles

The synthesis of carbon nanotubes (CNTs) of desired chiralities and diameters is one of the most important challenges in nanotube science and achieving such selectivity may require a detailed understanding of their growth mechanism. We report the formation of CNTs in an entirely condensed phase process that allows us, for the first time, to monitor the nucleation of a nanotube on the spherical surface of a metal particle. When multiwalled CNTs containing metal particle cores are irradiated with an electron beam, carbon from graphitic shells surrounding the metal particles is ingested into the body of the particle and subsequently emerges as single-walled nanotubes (SWNTs) or multiwalled nanotubes (MWNTs) inside the host nanotubes. These observations, at atomic resolution in an electron microscope, show that there is direct bonding between the tubes and the metal surface from which the tubes sprout and can be readily explained by bulk diffusion of carbon through the body of catalytic particles, with no evidence of surface diffusion.     

氢气流量对碳纳米管生长的影响

采用等离子体增强化学气相沉积技术,以C2H2、H2和N2为反应气体,制备出碳纳米管薄膜。利用扫描电镜和拉曼光谱仪对其进行表征。结果表明:氢气流量对碳纳米管薄膜的生长起着重要作用,获得分布均匀、密度适中、杂质缺陷少的碳纳米管的最佳氢气流量为30 sccm。     

化学气相沉积法合成碳纳米管及其导电性能研究

以二甲硫醚为碳源前驱体,Co/MgO为催化剂,采用化学气相沉积法生长出碳纳米管及Y形碳纳米管,此法稳定性及重现性较好.通过扫描电子显微镜、透射电子显微镜、拉曼光谱及X射线衍射对产品形态和结构进行了分析和表征,结果表明,所制备的碳纳米管形态较规整、纯度较高,具有较好的石墨微晶结构;导电性能测试结果显示,Y形碳纳米管各分支均呈现出典型的金属性导电性能.     

Controlled multistep purification of single-walled carbon nanotubes

A controlled and scalable multistep purification method has been developed to remove iron impurity and nonnanotube carbon materials from raw single-walled carbon nanotubes (SWNTs) produced in the HiPco (high-pressure CO) process. In this study, iron nanoparticles, coated by carbon, are exposed and oxidized by multiple step oxidation at increasing temperatures. To avoid catalytic oxidation by iron oxide of carbon nanotubes, the exposed and oxidized iron oxide is deactivated by reaction with C(2)H(2)F(4) or SF(6). The iron fluorides are removed by a Soxhlet extraction with a 6 M HCl solution. The purity and quality of each sample were determined by thermogravimetric analysis (TGA), Raman spectrometry, ultraviolet-visible-near-IR (UV-vis-near-IR) spectrometry, fluorescence spectrometry, and transmission electron microscope (TEM) spectroscopy. The purity and yield of SWNTs are improved due to reduced catalytic activity of the iron oxide. Greater iron oxide removal also resulted from oxidation at higher temperatures.     

Dispersion study of long and aligned multi-walled carbon nanotubes in water

Dispersion of nanotubes is a crucial step for many applications. The properties of the final nanotube-based material are strongly dependent on the quality of nanotube suspensions. In this study, long and aligned multi-walled carbon nanotubes obtained by catalytic chemical vapour deposition were dispersed in water with different dispersing agents using high intensity ultrasounds. Among different additives, we selected sodium dodecyl sulfate (SDS) as dispersing agent to prepare suspensions of nanotubes. UV-Visible spectrometry method was used to measure the influence of dispersion parameters (power and duration of sonication) on dispersion state and suspension stability. Therefore, we demonstrated that, even if high intensity ultra-sounds are breaking nanotubes, it is possible to obtain stable water-based suspensions containing MWNTs which exhibit length up to 20 microm.     

Carbon nanotubes as assisted matrix for laser desorption/ionization time-of-flight mass spectrometry

Analysis of low molecular weight compounds with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been developed by using carbon nanotubes obtained from coal by arc discharge as the matrix. The carbon nanotube matrix functions as substrate to trap analytes of peptides, organic compounds, and beta-cyclodextrin deposited on its surface. It has been found that carbon nanotubes can transfer energy to the analyte under laser irradiation, which makes analytes well desorbed/ionized, and the interference of intrinsic matrix ions can be eliminated. At the same time, the fragmentation of the analyte can be avoided. A good sensitivity and excellent reproducibility of the spectrum signals are achieved. It is believed that this work not only will open a new field for applications of carbon nanotubes, but also will offer a new technique for high-speed analysis of low molecular weight compounds in areas such as metabolism research and characterization of natural products.     

纳米碳管/环氧树脂复合材料的制备及力学性能

报道了利用催化裂解法制备的纳米碳管合成环氧树脂复合材料的技术及工艺条件。利用透射电子显微镜(TEM)对制备的复合材料进行观察表征;通过拉伸及压缩实验对纳米碳管/环氧树脂复合材料的力学性能进行了测试。实验结果表明:纳米碳管的加入可以明显地改变环氧树脂基体材料的力学性能。      

Enhancement of β phase crystals formation with the use of nanofillers in PVDF films and fibres

Nanoclay and carbon nanotubes (CNT) have been in focus recently as means of enhancing β phase crystals formation in poly(vinylidene fluoride)(PVDF). Dominantly, the so-far work has been carried out on films/thin sheets filled with nanoclay. It has been found, mainly from combined XRD and DSC data, that nanoclay influences the PVDF structure, and particularly the β phase crystals formation is enhanced. Results published by various groups are in fairly good agreement. There are no results for nanoclay filled melt-spun PVDF fibres.The influence of CNT on PVDF structure has been less studied. XRD data indicating an enhancing role of multi-wall carbon nanotubes (MWNT) on β phase crystals formation in solution compounded PVDF films are available. Published results for MWNT/PVDF films are not in good agreement. The only study into single-wall carbon nanotube (SWNT)/PVDF has been made on electrospun nanofibres.We explore above findings towards melt-spun nanofilled PVDF fibres. We present new results obtained by us for melt-spun PVDF fibres containing non-functionalized and amino-functionalized double-wall carbon nanotubes (DWNT). The key finding is that amino-DWNT can influence the β to α polymorphic balance.     

Novel vapor phase reactions for the synthesis and modification of carbon nanotubes and inorganic nanowires

Several vapor phase methods have been developed for the preparation and modification of carbon nanotubes and inorganic nanowires. Thus, nebulized spray pyrolysis has been employed for the synthesis of carbon nanotubes and metal nanowires. Multi-walled carbon nanotubes (MWNTs) with fairly uniform diameters and aligned nanotube bundles have been obtained by nebulized spray pyrolysis using solutions of organometallics such as ferrocene in hydrocarbon solvents. Single-crystalline nanowires of zinc, cadmium, cobalt, and lead are obtained by the decomposition of metal acetates. By reacting acid-treated carbon nanotubes with vapors of metal halides, followed by reaction with water and calcination chemically-bonded oxide layers can be obtained on the nanotubes. A similar procedure has been employed to prepare chemically-bonded oxide layers on Al2O3, ZnO, and silicon nanowires by the reaction of the metal halides with the surface hydroxyl groups present on these nanowire surfaces.