铬酸及硝酸混合液处理以增强碳纳米管场发射

为了修饰碳纳米管(CNTs)的表面型态及改变碳纳米管的表面结构, 进一步增强碳纳米管的场发射特性, 使用铬酸及硝酸的混合溶液对碳纳米管进行后处理. 采用SEM、TEM、Raman 和EDS测试手段对样品的形貌、表面成份组成和微观结构特征进行了表征. 场发射(FE)的数据显示, 经过铬酸及硝酸的混合溶液处理20 min的碳纳米管场发射电流比未经任何处理的碳纳米管场发射电流明显增加一个数量级以上, 场发射电流增强的主要原因为样品上的碳纳米管的表面型态的改变, 造成碳纳米管场发射增强因子茁的增大. 与单独使用硝酸溶液后处理比较, 使用铬酸及硝酸的混合溶液对碳纳米管进行后处理可以得到较高的场发射电流及较低的起始电场. 铬酸及硝酸的混合溶液处理方法能经济且有效增强碳纳米管的场发射特性.     

纳米三氧化钨修饰碳纳米管载铂催化剂对甲醇氧化的电催化性能

采用表面修饰技术将碳纳米管(CNT)表面羧基化, 通过羧基将钨离子基团修饰到碳纳米管的外表面, 再通过高温焙烧处理将钨离子基团氧化成WO₃, 成功合成了纳米WO₃/CNT复合物, 进一步还原Pt 的前驱体而得到Pt-WO₃/CNT复合催化剂. 采用X射线粉末衍射(XRD)和透射电镜(TEM)对样品的形貌和晶型结构进行了表征, 结果表明, Pt纳米粒子为面心立方晶体结构, 均匀地分布在WO₃修饰的碳纳米管表面. 采用循环伏安(CV)和计时电流法研究了在酸性溶液中Pt-WO₃/CNT催化剂对甲醇的电催化氧化活性, 结果表明WO₃修饰的碳纳米管载铂催化剂比用混酸处理的碳纳米管载铂催化剂对甲醇呈现出更高的电催化氧化活性和更好的稳定性.     

Prussian Blue/Multiwalled Carbon Nanotube Hybrids: Synthesis,Assembly and Electrochemical Behavior

Prussian blue/carbon nanotube (PB/CNT) hybrids with excellent dispersibility in aqueous solutions were synthesized by adding CNTs to an acidic solution of Fe³⁺, [Fe(CN)₆]^3? and KCl. Fourier transform infrared spectroscopy, UV‐vis absorption spectroscopy and scanning electron microscopy were employed to confirm the formation of PB/CNT hybrids. The PB nanoparticles formed on the CNT surfaces exhibit a narrow size distribution and an average size of 40 nm. The present results demonstrate that the selective reduction of Fe³⁺ to Fe²⁺ by CNTs is the key step for PB/CNT hybrid formation. The subsequent fabrication of the PB/CNT hybrid films was achieved by layer‐by‐layer technique. The thus‐prepared PB/CNT hybrid films exhibit electrocatalytic activity towards H₂O₂ reduction.     

NiO/CNTs derived from metal-organic frameworks as superior anode material for lithium-ion batteries

In this work, porous NiO microspheres interconnected by carbon nanotubes (NiO/CNTs) were successfully fabricated by the pyrolysis of nickel metal-organic framework precursors with CNTs and evaluated as anode materials for lithium-ion batteries (LIBs). The structures, morphologies, and electrochemical performances of the samples were characterized by X-ray diffraction, N₂ adsorption-desorption, field emission scanning electron microscopy, cyclic voltammetry, galvanostatic charge/discharge tests, and electrochemical impedance spectroscopy, respectively. The results show that the introduction of CNTs can improve the lithium-ion storage performance of NiO/CNT composites. Especially, NiO/CNTs-10 exhibits the highest reversible capacity of 812 mAh g^?1 at 100 mA g^?1 after 100 cycles. Even cycled at 2 A g^?1, it still maintains a stable capacity of 502 mAh g^?1 after 300 cycles. The excellent electrochemical performance of NiO/CNT composites should be attributed to the formation of 3D conductive network structure with porous NiO microspheres linked by CNTs, which benefits the electron transfer ability and the buffering of the volume expansion during the cycling process.     

Effects of CNT‐film Pretreatment on the Characteristics of NiCo2O4/CNT Core‐shell Hybrids as Electrode Material for Electrochemistry Capacitor

NiCo₂O₄/CNT nanocomposite films were fabricated by in‐situ growing ultrafine NiCo₂O₄ nanoparticles on acid‐modified carbon nanotube (CNT) films. The effects of CNT‐film pretreatment were investigated thoroughly by various characterization outfits including Fourier Transform Infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, RTS‐9 four‐point probes resistivity measurement system, X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and CHI660D electrochemical workstation. These results suggested that carbon nanotubes were uniformly wrapped by NiCo₂O₄ nanoparticles forming a hierarchical core‐shell structure. And the crystallinity, conductivity of the CNTs and detail structure (both morphology and size) of the NiCo₂O₄ nanoparticles varied with prolonged acid treatment time which resulted in increased functional groups and defects on CNT films and further affected the electrochemical properties. The composite film composed of the CNT film pretreated by mixed acid for 12 h exhibited excellent electrochemical properties: 828 F/g at 1 A/g and 656 F/g at 20 A/g, and maintained over 99 % of its capacitance after 3000 cycles of charge/discharge at 5 A/g. Acid treatment for either too long or too short is detrimental to the electrochemical properties of the composite films. Such work should be of fundamental importance for tailoring electrochemical properties by elaborate design of acid treatment on CNTs.     

Effects of pH on electrocatalytic activity of functionalized carbon nanotubes

In this study, we modified carbon nanotubes (CNTs) by grafting with poly(ethylene glycol) (PEG) using the “grafting to” method. The PEG-grafted CNT (CNT-g-PEG) was cast on indium tin oxide (ITO) electrode to investigate the electrocatalytic activity of CNT to the redox reactions of the Fe(CN)₆^3−/4−as a probe using cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic activity of CNT was correlated with CNT dispersion in the cast film on ITO as a function of pH of aqueous solution from which the film was cast. The CNT dispersions in aqueous solutions of different pH and in the cast films were examined by visual observation and zeta potential, scanning electron microscopy and transmission electron microscopy, respectively. At a pH in the range of 3–11 at which ITO electrode was modified, two functionalized CNT (fCNT and CNT-g-PEG) were both found to electrocatalyze the redox reactions of the Fe(CN)₆^3−/4−probe and the PEG grafts in CNT-g-PEG could help CNT adhere to the electrode to obtain durable modified electrode. The more uniform CNT dispersions in aqueous solutions and in the cast films appeared to have greater electrocatalytic acitivity.     

CNTs表面改性与TiO2-CNTs异质结光催化性能

碳纳米管(CNTs)混酸(H₂SO₄/HNO₃, 体积比为3:1)超声辅助纯化及氧化植入活性基团－COOH, 进一步借助其转化为酰氯基团, 分别于CNTs 表面共价嫁接亲水性赖氨酸及亲脂性正十八胺基团, 赋予赖氨酸表面改性CNTs 显著水溶(6.85 mg·mL-1)和十八胺表面改性CNTs 显著醇溶(10.15 mg·mL^-1)性能. 运用低温水热法以亲水性CNTs 复合TiO₂, 溶胶-凝胶法以亲脂性CNTs 复合TiO₂, 观察到复合催化剂光催化性能随CNTs 溶剂分散性能增加而明显提升. 运用傅里叶变换红外(FTIR)、激光拉曼、X射线衍射(XRD)、Brunauer-Emmett-Teller 低温氮气吸附、透射电镜(TEM)及X光电子能谱(XPS)等手段表征, 系统探讨CNTs 的表面改性机制及CNTs 溶解分散性能与复合催化剂的光活性的关联. 认为表面改性CNTs 借助Ti－O－C键合促进其与纳米TiO₂的异质结合, 从而充分利用CNTs的大比表面积及电荷传输性能促进催化剂的污染物光催化降解.     

Controlled surface functionalization of carbon nanotubes by nitric acid vapors generated from sub‐azeotropic solution

Controlled surface modification of nanocarbons is crucial for their use in applications. The paper deals with the functionalization of carbon nanotubes (CNTs) with HNO₃ vapors. Sub‐azeotropic HNO₃ + H₂O + Mg(NO₃)₂ solution is used for the generation of nitric acid vapors. Because this approach allows tuning the HNO₃ concentration in the vapor phase, the effect of its variation on the surface chemistry and structural properties of the CNTs is investigated. A combination of analytical techniques is applied to evaluate oxidation extent of the CNT surface, selectivity towards the formation of carboxyl groups compared with other oxygenated functionalities, and CNT integrity. The comparison with liquid‐phase functionalization in H₂SO₄ + HNO₃ mixture (1 : 3–3 : 1 v/v), conventionally utilized for oxidizing CNTs, shows that vapor‐phase functionalization affords greater surface oxygen uptakes and higher selectivity towards the formation of carboxyl groups, with smaller tube damage; more importantly, it evidences that, regardless of the method and conditions chosen, the selectivity towards carboxyl groups increases linearly with the surface oxygen concentration. The presented results prove that the product of HNO₃ concentration in the vapor‐phase (25–93 wt%) and vapor‐phase functionalization duration (0.5–5 h) controls the surface oxygen concentration. A simple rate model is proposed to account for its increase. Copyright © 2015 John Wiley & Sons, Ltd.     

Cu2O/CNTs复合材料的制备及其光催化性能

以乙二醇为还原剂,采用溶剂热法在混酸(V_(H_2SO_4)/V_(HNO_3)=3∶1)超声处理的碳纳米管(CNTs)表面负载氧化亚铜(Cu_2O),通过改变CNTs的含量制备出球形Cu_2O/CNTs复合材料。采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)、扫描电镜(SEM)、能谱分析(EDS)、N_2吸附-脱附、紫外-可见光漫反射(DRS)、有机总碳量(TOC)等对Cu_2O/CNTs进行表征;研究CNTs含量对Cu_2O/CNTs复合材料的结构、形貌、比表面积与孔径、光吸收特性的影响;结合光催化机理讨论CNTs对Cu_2O/CNTs光催化性能的影响。结果表明,当CNTs含量为0.2 g时,Cu_2O/CNTs的光催化性能最佳,在可见光照射60 min后,对甲基橙的降解率达到92.1%。     

Bulk synthesis of linear carbon chains confined inside single-wall carbon nanotubes by vacuum discharge

Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm.     

Low‐Temperature Growth of Carbon Nanotubes Catalyzed by Sodium‐Based Ingredients

Synthesis of low‐dimensional carbon nanomaterials such as carbon nanotubes (CNTs) is a key driver for achieving advances in energy storage, computing, and multifunctional composites, among other applications. Here, we report high‐yield thermal chemical vapor deposition (CVD) synthesis of CNTs catalyzed by reagent‐grade common sodium‐containing compounds, including NaCl, NaHCO₃, Na₂CO₃, and NaOH, found in table salt, baking soda, and detergents, respectively. Coupled with an oxidative dehydrogenation reaction to crack acetylene at reduced temperatures, Na‐based nanoparticles have been observed to catalyze CNT growth at temperatures below 400 °C. Ex situ and in situ transmission electron microscopy (TEM) reveal unique CNT morphologies and growth characteristics, including a vaporizing Na catalyst phenomenon that we leverage to create CNTs without residual catalyst particles for applications that require metal‐free CNTs. Na is shown to synthesize CNTs on numerous substrates, and as the first alkali group metal catalyst demonstrated for CNT growth, holds great promise for expanding the understanding of nanocarbon synthesis.     

Quantitative analysis of electron field-emission characteristics of individual carbon nanotubes: the importance of the tip structure

Electron field-emission measurements on individual carbon nanotubes (CNTs) were performed inside the transmission electron microscope (TEM). The field-emission characteristics of CNTs with different tip structures were compared, and their field conversion factor and emission area were studied systematically. It was found that the field-emission characteristics of a CNT depend sensitively on its tip structure, and in particular an opened CNT was shown to be superior to a capped CNT. High-resolution TEM observations revealed that the tip of an opened CNT may, in general, be regarded as being composed of irregular shaped graphitic sheets, and these graphitic sheets have been found to improve dramatically the field-emission characteristics, but the sharp edge may result in larger error in the calculated emission area. The influence of uncertainty in the work function of the CNTs on the field conversion factor and emission area calculation was also investigated.     

Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy

Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red–orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO₄/HNO₃ and H₂SO₄/HNO₃ mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.     

High-sensitivity matrix-assisted laser desorption/ionization Fourier transform mass spectrometry analyses of small carbohydrates and amino acids using oxidized carbon nanotubes prepared by chemical vapor deposition as matrix

In matrix-assisted laser desorption/ionization (MALDI) Fourier transform mass spectrometry (FTMS) analyses of small oligosaccharides and amino acids, high sensitivities for oligosaccharides (10 fmol) were obtained by introducing oxidized carbon nanotubes (CNTs) with short and open-end structure as valuable matrix. The CNTs were deposited in porous anodic alumina (PAA) templates by chemical vapor deposition. Transmission electron microscopy (TEM) images show that those CNTs include low levels of amorphous carbon. Thus, the background interference signals generally caused by amorphous carbon powder in CNTs can be reduced effectively. Experiments also confirmed that the FTMS signal intensity of CNTs prepared in PAA template is much lower than that of commercial multi-wall carbon nanotubes (MCNTs). Moreover, the purified process for CNTs with mixed acid (H₂SO₄ and HNO₃) also contributed to the minimization of background. Intense signals corresponding to alkali cation adduct of neutral carbohydrates and amino acids have been acquired. In addition, reliable quantitative analyses for urine and corn root were also achieved successfully. The present work will open a new way to the application of oxidized CNTs as an effective matrix in MALDI MS research.     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

Observation of curling effects in tubular and planar graphene-like structures by pyrolysis of ferrocene/dichlorobenzene mixtures

In this work, we investigate the morphological and structural properties of carbon nanostructures fabricated by means of chemical vapor deposition (CVD) methods in the presence of controlled quantities of Cl-containing precursor and ferrocene. We report the observation of a structural transition from tubular-like carbon nanotube (CNT) morphology into planar few-layers graphite in experiments involving the pyrolysis of ferrocene and dichlorobenzene mixtures. An unusual intermediate curling-like mechanism in the walls of the as-grown CNTs is found when intermediate quantities of dichlorobenzene are used. This unusual phenomenon vanishes for high quantities of dichlorobenzene, where the nucleation of planar few-layers graphene-like structures directly connected to micrometer-scale Fe₃C particles is found. Such morphological variation is investigated by means of both scanning electron microscopy (SEM) and transmission electron microscopy (TEM), whereas the structural variation of the obtained structures is analyzed through X-ray diffraction and Raman spectroscopy techniques.     

A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)n films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O2; as a result, they are more attractive compared to (CNT/polyelectrolyte)n and (NP/polyelectrolyte)n films because of their multifunctionality.     

Controllable preparation and properties of composite materials based on ceria nanoparticles and carbon nanotubes

We report a method to prepare composites based on carbon nanotubes (CNTs) and CeO₂ nanoparticles (NPs). The CeO₂ NPs were attached to CNTs by hydrothermal treatment of Ce(OH)₄/CNT mixture in NaOH solution at 180 °C. It was found that larger CeO₂ NPs were formed in the presence of CNTs. Grain size of CeO₂ NPs in the composites can be reduced when NaNO₃ was added in the hydrothermal process. Electrochemical characterizations have shown that the composites possess a specific capacity between those of CNTs and CNTs mechanically mixed with CeO₂. These CeO₂/CNT composites could serve as promising anode materials for Li-ion batteries.     

复合碳纳米管增强纳米Ag2CO3的可见光催化活性和稳定性

在二甲基甲酰胺溶液中, 通过简单的沉淀法制备了纳米Ag₂CO₃和碳纳米管(CNT)的复合物. 用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电镜(SEM)和紫外-可见(UV-Vis)漫反射光谱(DRS)表征了所制备的Ag₂CO₃/CNT复合物, 通过在可见光下降解甲基橙(MO)检测了样品的光催化活性. 结果表明, 纳米Ag₂CO₃颗粒与CNT结合良好. CNT的含量为1.5% (w)的Ag₂CO₃/1.5% CNT复合物活性最高, 经过60 min 的降解, 甲基橙的降解率达到93%. 与纯相纳米Ag₂CO₃比较, CNT的加入还提高了Ag₂CO₃的稳定性, 经过三次循环降解, Ag₂CO₃/1.5% CNT复合物还能降解81%的甲基橙, 而纳米Ag₂CO₃只能降解59.5%的甲基橙. 其活性和稳定性提高的原因是由于CNT的高导电性, 它不仅促进了电子-空穴对的分离, 还能快速转移产生的光生电子.     

三维碳微米管/碳纳米管复合结构的制备及在超级电容器中的应用

利用天然生物质杨絮特殊的管状结构通过简单的高温碳化法制备出碳微米管(CMTs). 将所得到的碳微米管作为基底, 采用化学气相沉积法制备出三维结构的碳微米管/碳纳米管(CNTs)复合材料. 利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)光谱仪、拉曼光谱仪对其进行了详细分析. 通过两电极测试体系对其超级电容性能进行测试, 碳微米管/碳纳米管复合电极在1 mol·L^-1Li₂SO₄电解液中的比电容值可达77 F·g^-1, 远大于碳微米管的比电容值(23 F·g^-1).