Mineralization of surfactant functionalized multi-walled carbon nanotubes (MWNTs) to prepare hydroxyapatite/MWNTs nanohybrid

Multi-walled carbon nanotubes (MWNTs) were well dispersed in water and functionalized by adding surface active agent (i.e., sodium dodecyl sulfate, SDS). Subsequently, biomimetic mineralization was carried out on the SDS functionalized MWNTs by using an alternate soaking process (ASP) in the Ca/P solutions. As-prepared samples were characterized by transmission electron microscope, infrared spectrum and X-ray diffraction. The results show that nano-HA crystals were formed on the SDS functionalized MWNTs and the mineralized MWNTs remained a dispersing state. As-prepared HA-MWNTs nanohybrid combining the osteconductive property of HA and the excellent mechanical property of MWNTs will provide a promising material for bone tissue engineering.     

Surface modification of multi-walled carbon nanotubes by O2 plasma

The surface modification of multi-walled carbon nanotubes (MWCNTs) by O₂ plasma was carried out in this study. In order to achieve a relatively homogeneous treatment of MWCNTs powder, a rotating barrel fixed between the two discharge electrodes was used. The effect of plasma treatment parameters, such as power, time, and positions of samples (inside and outside the barrel), on the morphology and structure of MWCNTs surface was systematically analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results showed that the direct discharge (outside the barrel) could result in not only a quick grafting of polar functional groups but also an easy damage of MWCNTs after longer time, particularly under intensive power. It was found that the surface of MWCNTs powder might be changed in three steps—expansion (loosed structure formed), peel off and oxidization with increasing of treatment time during the irradiation. In this way, a complete purification of MWCNTs powder could be finished within 30 min via plasma treatment. Our work suggested that plasma treatment could be a simple and nonpolluting method for a large scale purification of MWCNTs.     

Mild hydrothermal treatment to prepare highly dispersed multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) with improved dispersion property have been prepared by a mild and fast hydrothermal treatment. The hydrothermal process avoids using harsh oxidants and organic solvents, which is environmental friendly and greatly decreases the damage to intrinsic structure of MWCNTs. The modified MWCNTs were highly soluble in polar solvents such as water, ethanol and dimethylformamide. Morphological observation by TEM indicated that the diameter and inherent structure were well reserved in modified MWCNTs. X-ray photoelectron spectroscopy and Raman spectroscopy were used to quantify functional groups created on the MWCNT surface, and to determine rational parameters of hydrothermal process.     

Photoresponsive conductance switching of multi-walled carbon nanotubes bearing covalently linked spironaphthoxazine

Multi-walled carbon nanotubes functionalized with a photochromic spironaphthoxazines (MWCNTs-SPO) were synthesized by the reaction between the hydroxyl group of SPO and the carbonyl chloride groups on the surface of MWCNTs. The functional spirooxazine photochromic groups on the surface of MWCNTs were identified by the X-ray photoelectron spectroscopy. As a novel derivative of MWCNTs, photoresponsive conductance switching of the MWCNTs-SPO was demonstrated under a 365 nm UV light irradiation. A simple photoinduced resistance measurement following the cyclic irradiation of UV light shows a very reversible response. The effect of the electron injection in the SPO is rationalized in terms of the HOMO–LUMO energy levels of both spiro and merocyanine forms.     

Effect of oxyfluorination on gas sensing behavior of polyaniline-coated multi-walled carbon nanotubes

Polyaniline-coated multi-walled carbon nanotubes were prepared by in situ chemical polymerization method for the novel sensing materials of ammonia gas. The thickness of the polyaniline coatings was controlled by the oxyfluorination treatment on the multi-walled carbon nanotubes. The oxyfluorination with higher oxygen content produced the more hydrophilic functional groups on the surface of multi-walled carbon nanotubes. Both the resistivity change and the response time were significantly improved with high repeatability using the more hydrophilic multi-walled carbon nanotubes which were modified with oxyfluorination.     

Electrochemical and surface characterisation of gold nanoparticle decorated multi-walled carbon nanotubes

A novel type of gold nanoparticle/multi-walled carbon nanotube (AuNP/MWCNT) composite electrodes is presented. The electrochemical reduction of oxygen on these hybrid electrodes was studied using the rotating disk electrode (RDE) method. The AuNP/MWCNT nanocomposites were prepared by sputter deposition of gold in argon atmosphere on MWCNTs followed by heat-treatment of the catalyst at different temperatures. High-resolution scanning electron microscopy (HR-SEM), glancing incidence angle X-ray powder diffraction (GIXRD) and small-angle X-ray scattering (SAXS) techniques were employed to characterise the surface structure and morphology of catalyst materials. Au nanoparticles with diameter around 20 nm were dispersed at the tips and on the sidewalls of nanotubes. Electrochemical measurements were performed to demonstrate the electrocatalytic properties of the composite catalysts towards O₂ reduction in acid media. The successful preparation of AuNP/MWCNT nanocomposites by magnetron sputtering opens up the possibility of making an efficient dispersion of nanoparticles for electrocatalyst design.     

Comparative study on modification of multi-walled carbon nanotubes by a hydrophilic polymer with different approaches

The multi-walled carbon nanotubes (MWNTs) modified by a hydrophilic polymer were prepared with polymerization and blending approaches. The differences of both modified MWNTs were compared by Fourier transform infrared and Raman spectroscopies, thermogravimetric analysis and transmission electron microscopy. Chemical grafting reaction had occurred between MWNTs and polyvinyl pyrrolidone (PVP) after modification with polymerization and blending approaches. Polymerization modification can graft more PVP on the surface of MWNTs compared with blending modification. Polymerization modification of MWNTs belongs to the “grafting from” mechanism, while blending modification belongs to the “grafting to” mechanism. Modified MWNTs exhibit remarkable solubility in water, ethanol and dimethyl formamide.     

Comparative study of electrochemical capacitance of multi-walled carbon nanotubes before and after chopping

In the work, short multi-walled carbon nanotubes (S-CNTs) were synthesized by chopping conventional μm-long multi-walled carbon nanotubes (L-CNTs) under ultrasonication in H₂SO₄/HNO₃ mixed acids. A comparative electrochemical investigation performed in 6 M KOH solution demonstrated that a specific capacitance (SC) of ca. 14.6 μF cm⁻² was delivered by the S-CNTs with the specific surface area (SSA) of 207 m² g⁻¹, much larger than that of ca. 10.1 μF cm⁻² for the L-CNTs with the SSA of 223 m² g⁻¹, the reason for which was that S-CNTs with two open ends, due to good ion penetrability, provided more entrances for electrolyte ions to access the inner surface easily through their shorter inner pathway so as to enhance their SSA utilization and geometric SC. The surface structure disruption of S-CNTs, owing to ultrasonication and oxidation during chopping process, deteriorated their electronic conductivity and resulted in an inferior power property in contrast to L-CNTs.     

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H₂, H₂O, CO and O₂ and then imaged in the field electron emission microscope. Only the samples exposed to O₂ showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.     

Improving the surface properties of multi-walled carbon nanotubes after irradiation with gamma rays

The effects of gamma-irradiation on the modification of the surface and structure of multi-walled carbon nanotubes were studied. Gamma-irradiation affected the graphitization properties of functional groups, and decreased the diameter of multi-walled carbon nanotubes. The irradiated multi-walled carbon nanotubes with the absorbed dose of 100 kGy exhibited a larger specific surface area and microporous volume as compared with the other samples. The Raman spectroscopy and X-ray photoelectron spectroscopy showed that the interaction between the gamma-irradiation and the multi-walled carbon nanotubes with the absorbed dose of 150 kGy destroyed the nanostructure of carbons, leading to the formation of diamond-like structures and carbon oxides. In addition, gamma-irradiation with the absorbed dose of 100 kGy improved multi-walled carbon nanotubes graphitization and surface properties while at higher absorbed dose (150 kGy), it induced damaged structures (sp³ bonds and oxygen compositions).     

Effects of corona discharge on the surface structure, morphology and properties of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were modified by corona discharge and then heat treated in the air. The influences of corona discharge parameters such as treatment time and processing power were investigated. The results of energy dispersive X-ray analysis (EDX) and thermogravimetric analysis (TGA) indicated the introduction of oxygen-containing functional groups onto the surface of the MWCNTs after heat treatment. The water contact angle tests showed that the hydrophobicity of the MWCNTs was decreased to some extent. The static water contact angle was reduced from 146° to 122° when the time of the corona discharge treatment reached 3 min at the processing power of 200 W. The enhanced thermomechanical and mechanical properties of epoxy nanocomposites filled with the corona discharge treated MWCNTs were observed. The modified MWCNTs conferred better properties on the composites than the pristine MWCNTs because of the improved dispersion of MWCNTs in matrix and the enhanced interfacial interaction between the treated MWCNTs and epoxy.     

The effect of chemical treatment on the crystallinity of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were chemically treated using nitric acid solution for different time. Quantitative analysis of the crystallinity of the MWCNTs was performed by wide-angle X-ray diffraction (WAXD). The WAXD patterns were deconvoluted into the crystalline diffraction peaks and the amorphous scattering peaks. The introduction of a correction factor for the integrated peak intensity can enhance the computational accuracy of the crystallinity. With increasing the chemical treatment time, the crystallinity of MWCNTs first increases, and then decreases. When the chemical treatment time is equal to 2 h, the crystallinity of MWCNTs reaches the maximum of 85.9%. Moreover, the degree of order in the structures of chemically treated MWCNTs was further studied by thermogravimetric analysis (TGA) and high-resolution transmission electron microscopy (HRTEM). It was found that the external walls of chemically treated MWCNTs with high crystallinity consist of a series of perfectly continuous and straight graphite layers.     

Nanocomposites based on polymer blends: enhanced interfacial interactions in polycarbonate/ethylene-propylene copolymer blends with multi-walled carbon nanotubes

In this article, the phase separation in the melt blended polycarbonate (PC) and ethylene propylene copolymer (EPC) has been studied with dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Two glass transition temperatures on the tan δ curves were detected. This confirms the immiscibility of PC and EPC phases. Different content of multi-walled carbon nanotubes (MWCNTs) were added to the PC/EPC blends and the interfacial adhesion between MWCNTs and PC/EPC blend were shown using transmission electron microscopy (TEM). The MWCNTs were located in the PC phase and at the interfaces of PC and EPC phases. Moreover, the storage modulus (E′) of polymer blends was changed by the increasing content of EPC elastomer and MWCNTs. The value of E′ of PC decreased with an incorporation of EPC. While, along with an addition of MWCNTs in the PC/EPC blends an increase of E′ was visible. The strong interfacial interactions between the matrix and MWCNTs played the main role in increasing the values of the E′ of the nanocomposites.     

Individuals, grasses, and forests of single- and multi-walled carbon nanotubes grown by supported Co catalysts of different nominal thicknesses

The relationships among the nominal thickness of Co catalyst, the structure of the catalyst particles, and the structure of carbon nanotubes (CNTs) growing from the catalyst during chemical vapor deposition were investigated. Various morphologies of CNTs such as individuals, random networks parallel to the surface of the substrate (‘grasses’), and vertically aligned forests of single- and multi-walled carbon nanotubes were grown by only varying the nominal thickness of catalyst under the same reaction condition. These different morphologies at the same growth time were due to the different areal density rather than to the length of CNTs. With increasing nominal thickness of catalyst, the catalyst particles changed in diameter while their areal density remained relatively almost constant. The change in diameter possibly affected the number ratio of active catalyst particles to the whole particles, which in turn affected the areal density of CNTs and yielded the various morphologies. Longer growth time increased the CNT length, which caused further change in CNT morphologies from individuals to grasses and grasses to forests.     

A study on the electrical conductivity of multi-walled carbon nanotube aqueous solution

The electrical conductivity was investigated for multi-walled carbon nanotubes (MWNTs) dissolved in chloroform and toluene, respectively. The electrical conductivity remarkably increased with increase in the content of MWNTs, which is in accordance with Archie's equation . Furthermore, a hypothesis of the electronic transport process was proposed to explain the difference between the solution and the solid compound. In addition, the temperature dependence of the electrical conductivity shows that log σ vs. 1/T exist in a good linear relationship. The activation energy of the electrical conductivity decreased with increase in concentration and an inflexion was observed at 60 °C in MWNT/toluene solution.     

多壁碳纳米管光限幅特性的研究

用化学气相沉积法制备了多壁碳纳米管,并将其溶解在甲苯溶液中.用波长为1064nm的皮秒脉冲激光测量该样品的透过率,发现了非常明显的光限幅特性.当入射光强较小时,透射光强度随入射光强度的增大而增大,输出与输入为线性关系;随着入射光强的增大,透射光强增长的速度明显变慢,并逐渐趋于饱和.当入射光强度较小时,样品的透过率接近100%;而当入射光强为8GW/cm²时,非线性透过率达到30%.根据三光子吸收理论计算,理论拟合与实验结果非常符合,说明多壁碳纳米管的三光子吸收产生了光限幅效应.实验测 关键词： 多壁碳纳米管 光限幅 三光子吸收     

氢在多壁碳纳米管中的吸附储存

利用巨正则系综蒙特卡罗(GCMC)的方法模拟了氢在多壁碳纳米管中的吸附,氢气分子之间、氢气分子和碳原子之间的相互作用势能采用Lennard-Jones势能模型。模拟了不同结构参数(管内径、管壁数、管壁间距)的多壁碳纳米管在77K和298K下的吸附等温线,分析了多壁碳纳米管的管内径、管壁数以及管壁间距对吸附性能的影响。模拟结果表明:多壁碳纳米管的管壁数和管壁间距对吸附性能的影响较明显;管壁数越少,管壁间距越大,其吸附性能越好;多壁碳纳米管的管内径对其吸附性能的影响甚微。     

Preparation of highly dispersed Pt-SnOx nanoparticles supported on multi-walled carbon nanotubes for methanol oxidation

To maximize the utilization of catalysts and thereby reduce the high price, a new strategy was developed to prepare highly dispersed Pt-SnO_x nanoparticles supported on 8-Hydroxyquinoline (HQ) functionalized multi-walled carbon nanotubes (MWCNTs). HQ functionalized MWCNTs (HQ-MWCNTs) provide an ideal support for improving the utilization of platinum-based catalysts, and the introduction of SnO_x to the catalyst prevents the CO poisoning effectively. The as-prepared catalysts are characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It is found that the HQ functionalization process preserves the integrity and electronic structure of MWCNTs, and the resulting Pt-SnO_x particles are well dispersed on the HQ-MWCNTs with an average diameter of ca. 2.2 nm. Based on the electrochemical properties characterized by cyclic voltammetry and chronoamperometry, the Pt-SnO_x/HQ-MWCNTs catalyst displays better electrocatalytic activity and stability for the methanol oxidation. It is worth mentioning that the forward peak current density of Pt-SnO_x/HQ-MWCNTs catalyst is ca. 1.9 times of that of JM commercial 20% Pt/C catalyst, which makes it the preferable catalyst for direct methanol fuel cells.     

Electrochemical behavior of amino-modified multi-walled carbon nanotubes coordinated with cobalt porphyrin for the oxidation of nitric oxide

Cobalt (II) tetrakis (4-sulfonatophenyl) porphyrin (CoTPPS) was axially coordinated with amino-modified multi-walled carbon nanotubes (MWCNT) to form a MWCNT-CoTPPS hybrid. The hybrid was drop cast on the glassy carbon electrode (GCE) to obtain MWCNT-CoTPPS/GCE. The structure of the MWCNT-CoTPPS hybrid was characterized by field-emission transmission electron microscope. X-ray photoelectron spectroscopy was also conducted to characterize the MWCNT-CoTPPS hybrid. Cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry were used to evaluate the electrocatalytic activity of MWCNT-CoTPPS/GCE for the oxidation of nitric oxide (NO). The effects of potential scan rate, temperature and NaNO₂ concentration on the electrochemical oxidation of NO at the MWCNT-CoTPPS/GCE were studied in detail. The obtained MWCNT-CoTPPS/GCE demonstrated a potential application for detecting NO in aqueous solution.     

Successful incorporation of multi-walled carbon nanotubes in nickel electrodeposited coating by electrophoresis

A homogenous and adhesive multi-walled carbon nanotube (MWCNT) coating was electrophoretically deposited on stainless steel from an aqueous solution by applying high strength electric fields. Then, nickel was electrodeposited on MWCNT films. MWCNTs content in the composite coatings was reached to 12.5 wt% which was much higher than the content of MWCNTs in conventional nickel-MWCNT electrodeposited coatings. The hardness value of composite coatings significantly increased up to 870 Vickers which it was measured by both micro and nanohardness tests.