Jining Xie

Functionalization of carbon nanotubes by potassium permanganate assisted with phase transfer catalyst

An improved process is presented to functionalize carbon nanotubes by potassium permanganate with the help of phase transfer catalyst (PTC). The PTC helps to extract potassium permanganate from the solid phase to an organic solvent phase and improves the efficiency of nanotube oxidation. The higher reaction efficiency as well as mild reaction conditions leads to a higher yield of functional nanotube preparation. X-ray photoelectron spectroscopy confirms the functional groups attached to the nanotube surface. A preliminary comparison is given of the potassium permanganate oxidation of nanotubes with and without PTC. This method is believed to be a potential economic method for large-scale functional nanotube preparation.

A novel nanocomposite from multiwalled carbon nanotubes functionalized with a conducting polymer

A nanocomposite of a multiwalled carbon nanotube and polythiophene was prepared by functionalizing the nanotube surface with a polythiophene, poly[3-(2-hydroxyethyl)-2,5-thienylene], containing pendant hydroxyl groups. The composite was characterized by IR, high resolution TEM and conductivity measurements. The poly[3-(2-hydroxyethyl)-2,5-thienylene] (PHET) was synthesized by the oxidation polymerization of 2-(3-thienylethanol) using FeCl3 and CHCl3. Multiwalled carbon nanotubes were synthesized by a microwave CVD method and oxidized with potassium permanganate using a phase transfer catalyst in mild conditions. The COOH groups formed on the nanotube surface were converted to COCl using thionyl chloride and it was then condensed with the polythiophene at high temperature in anhydrous DMF. High resolution TEM images showed that the functionalization provided a firm coating of the conducting polymer on nanotube walls. This nanocomposite with PHET grafted to CNT showed higher conductivity than a nanocomposite of PHET and CNT in the same percentage weight composition prepared by ultrasonic mixing of the two. Such a material was designed and synthesized with a view to electronic and sensor applications.

Passive wireless sensors using electrical transition of carbon nanotube junctions in polymer matrix

This paper presents the design and development of a passive wireless sensor for the detection of bio-hazard materials and vapors using chemiresistive thin films. Composite polymer thin film with functionalized carbon nanotubes (f-CNT) and polymethylmethacrylate (PMMA) is employed as a sensing material. It is investigated that resistance change is determined with the concentration of dichloromethane vapors diffused into composite thin film, due to electrical transition from direct contact to tunneling in carbon nanotube nanojunctions. The chemiresistive film is integrated into a passive wireless system which works based on the change in phase of the reflected RF signal. Measurement results of sensors in a wireless sensing system show a large differential phase shift, which can be utilized for remote monitoring of bio-hazard vapors in real time.

Large-scale synthesis of multi-walled carbon nanotubes by microwave CVD

Carbon nanotubes (CNTs) are an interesting class of nanostructures which can be thought of as arising from the folding of a layer of graphite (a graphene sheet) to form a hollow cylinder composed of carbon hexagons. However, practical applications are still limited by the intricate process of synthesis and the inability of present day methods to provide large-scale production of CNTs. Moreover, high-quality nanotubes with functionalization capability with polymers are desired for polymer microelectromechanical systems (MEMS), nanodvices and BioMEMS. In this paper, an innovative CVD approach using microwave energy was developed for the large-scale production of multi-wall carbon nanotubes (MWNTs). Straight and helical CNTs were obtained when acetylene created by a microwave field was decomposed over the cobalt catalyst at 700 °C. Scanning electron microscopy of microwave-driven MWNTs revealed their homogenous nature. High-resolution electron microscopy showed that typically the MWNT has 26 layers. The average diameter of the tubes observed was 20-30 nm. Electron microscope observations showed a higher yield of nanotubes obtained from microwave CVD than the thermal filament CVD method.

Development and characterization of micro-coil carbon fibers by a microwave CVD system

Nano- and micro-coiled carbon fibers find applications in electronic devices, electromagnetic absorbers and filters. Smart devices can be conceived using tunable films on these fibers and tunable host materials. A new method of producing helical carbon fibers with dimensions in the order of less than a micrometer has been developed using microwaves. The microwave CVD system presented here eliminates the use of the toxic impurity gas, which is required in the conventional method. Both methods involve gas phase reactions over a substrate seeded with an appropriate catalyst. Micro-coiled carbon fiber (MCCF) was grown by the catalytic pyrolysis of acetylene on a silicon carbide substrate on which nickel metal powder was dispersed as a catalyst. Various factors, for example flow rate of the gas, particle size of the catalyst, effect of reaction temperature and time, were studied in order to understand the growth of the microwave synthesis of MCCF. MCCFs were also synthesized by a conventional method in the presence of thiophene as an impurity gas so that a comparison can be made with the materials obtained by the microwave system. The morphology of the final products were investigated by scanning electron microscopy. The carbon products obtained by traditional and microwave methods were investigated with the help of x-ray diffraction. The effect of various reaction conditions on the morphological development of a MCCF were examined in detail. Furthermore, a brief study was made on the microwave absorbing property of the MCCF.

Chemical bonding of multiwalled carbon nanotubes to SU-8 via ultrasonic irradiation

Multiwalled carbon nanotubes (CNT) were functionalized by oxidation with potassium permanganate using a phase transfer catalyst in mild conditions. SU-8 reacted with functional groups, such as –OH and –COOH, of the functionalized carbon nanotubes by opening epoxide groups with the help of surfactants. Ultrasonic irradiation has been employed to prepare SU-8/CNT nanocomposites, using multiple effects such as dispersion, initiation, and activation. The influence of factors such as acidity, reaction temperature, and the nanotube concentration were investigated. The final product is a dark uniform solution. This new UV-curable polymer is expected to have applications in UV coating and microstereolithography for microelectromechanical systems (MEMS) devices.

Catalytic chemical vapor deposition synthesis and electron microscopy observation of coiled carbon nanotubes

Coiled carbon nanotubes exhibit excellent mechanical and electrical properties because of the combination of coil morphology and properties of nanotubes. They could have potential novel applications in nanocomposites and nano-electronic devices as well as nano-electromechanical systems. In this work, synthesis of regularly coiled carbon nanotubes is presented. It involves pyrolysis of hydrocarbon gas over metal/support catalyst by both thermal filament and microwave catalytic chemical vapor deposition methods. Scanning electron microscopy and transmission electron microscopy were performed to observe the coil morphology and nanostructure of coiled nanotubes. The growth mechanism and structural and electrical properties of coiled carbon nanotubes are also discussed.

Synthesis of carbon nanocoils by microwave CVD

The carbon nanocoil is an interesting kind of nanomaterial, which is expected to have various novel applications in microelectronics, microelectromechanical systems (MEMS) and bioMEMS due to its nanosize coil morphology. Carbon nanocoils were synthesized by catalytic pyrolysis of acetylene over 2.2–3.0 µm Ni particles at 600°C in a microwave chemical vapour deposition (CVD) system. Microwave CVD derived nanocoils are rather uniform with an average coil diameter of 110–170 nm, fibre diameter of 80–120 nm and pitch of around 130–200 nm. The effects of reaction temperature, the size of Ni catalyst and the flow rate of acetylene were examined. Additionally, the growth mechanism of carbon nanocoils was studied. It was found that two individual carbon nanocoils extrude from the same Ni particle in the same direction as straight fibres at the beginning and then bend to grow into nanocoils in opposite directions.

A new synthetic route to enhance polyaniline assembly on carbon nanotubes in tubular composites

In tubular nanocomposites prepared from carbon nanotubes and polyaniline, carbon nanotubes can improve the structural ordering, compactness, delocalization of charges and carrier mobility. Such properties are very much critical in the case of organic semiconducting materials for electronics applications. In this paper we describe the synthesis of a nanotubular composite of polyaniline and carbon nanotube using p-phenylenediamine functionalized multiwalled carbon nanotubes. This functionalization helped to disperse the nanotubes well in acidic solution. The in situ polymerization of aniline in the presence of these well dispersed nanotubes gave rise to a new tubular composite of carbon nanotubes having a uniform encapsulation of doped polyaniline. It also improved the structural order, molecular packing and delocalization of the charges in the material.

Soluble functionalized carbon nanotube/poly(vinyl alcohol) nanocomposite as the electrode for glucose sensing

Carbon nanotubes exhibit excellent properties which make them a good candidate as the electrode material for bioapplications. A soluble functionalized carbon nanotube/poly(vinyl alcohol) nanocomposite was synthesized via esterification reactions. The obtained nanocomposite exhibits significantly improved electrical conductivity. Nanocomposite-based electrodes were prepared by a thick film technique and their performances were electrochemically characterized. After enzyme immobilization, they can be used as biosensors for glucose detection. Preliminary results show these nanotube composite-based electrodes exhibit good electrochemical performance for glucose detection. Comparison was also made between graphite and nanocomposite-based electrodes.