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An Investigation on Preparation and Application of High Quality Multi-walled Carbon Nanotubes

Author: ZhaoJiang
Tutor: ZhangYaFei
School: Shanghai Jiaotong University
Course: Microelectronics and Solid State Electronics
Keywords: MWCNTs DWCNTs Arc discharge Low pressure air Field emission CNTs/Cu composite
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Type: PhD thesis
Year: 2013
Downloads: 494
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Abstract

Carbon nanotubes (CNTs) have potential applications in different fileds, includingnanoelectronic devices, composite materials, and sensors, etc., due to their uniquestructure and good physical and chemical properties. At present, the main industrialgrowth of CNTs is chemical vapor deposition (CVD) method. However, CVD CNTs havevery disordered structures and a high content of defects including vacancies, danglingbonds, edges and dislocations, as a result of the idiosyncrasy of CVD conditions at lowtemperature. These have seriously restricted their excellent performance. The othersynthesis methods are always high cost, time-consuming, and low yield, which can notsatisfy the practical application. Therefore, to explore the large scale and low costpreparation of high quality and low defect CNTs has very important practical significance.This dissertation is mainly focused on the large scale synthesis of multi-walled carbonnanotubes (MWCNTs) with high quality and low defect and their application. The mainresults are as follows:1. A rapid high-temperature annealing technique has been developed, demonstrating agreat potential for defects reduction and structural enhancement of CVD MWCNTs. Highresolution TEM, Raman spectra, TGA and electrical resistivity measurement of nanotubepowders have been employed in order to evaluate the rapid high temperature annealingeffects. Moreover, a novel, simple, and effective method has been developed to cut theconventional long and entangled MWCNTs. The cutting process was carried out by theinteractive collision of CNTs with the silicon carbide particles adhered on the abrasivepapers. After cutting, the lengths of the most CNTs are200–300nm.2. The development of preparing straight MWCNTs on a large scale is demonstratedusing direct current arc discharge in low pressure air. The process is time-saving,economical and non-hazardous. It is found the optimum conditions for the highest yield of MWCNTs. Base on the detailed investigation on the internal organization of cathodedeposit, the growth process of MWCNTs by arc discharge method in low pressure air isdepicted. The semi-continuous and continuous initial productions of MWCNTs areachieved by the modification of arc discharge equipment. And the production processesare introduced in detail.3. Double-walled carbon nanotubes (DWCNTs) have been effectively synthesized byarc discharge in low pressure air using a mixture of Fe catalyst and FeS promoter.Compared with conventional arc methods, this method is easier to implement withoutusing expensive high purity gas sources. And it also simplifies the preparation processbecause of the absence of pre-vacuum. This method is expected to be low-cost, largeproduction preparation of DWCNTs. The optimum conditions for the preparation ofDWCNTs are investigated. DWCNT purification is employed by combining method usingwet selection in magnetic field, oxidation in air, treatment in hydrochloric acid andcentrifugation, which can effectively remove the impurities in samples, such as amorphouscarbon, metal catalyst particles and graphite particles, etc.. After purification, the purity ofDWCNTs is more than90wt.%, which is the foundation for the future to carry outresearch on DWCNTs. Finally, the possible growth mechanism of DWCNTs using Fe–FeS catalyst by arc discharge is given.4. Field emission tests of MWCNTs and DWCNTs prepared in low pressure air by arcdischarge are carried out, respectively. For MWCNTs, the field emission performances ofMWCNTs in black core region of cathode deposits before and after burning at750oC for30min in air have been investigated detailedly. The results indicate that simple burningcan improve dramatically the field emission properties. For DWCNTs, a tip structuralDWCNT film has been successfully fabricated by a mixing process of electrophoresis,electroplating and electrocorrosion. The field emission properties of tip structuralnanotube film is significantly increased compared with DWCNT film fabricated byelectrophoresis. The mixing process is not complicated, does not require expensive equipments and facilities, and not subject to special conditions, which provide a simpleand effective way to improve the contact between CNTs and substrate. Based on the fieldemission results, tip structural DWCNT film is superior for field emission, which can beapplied as field emission flat panel displays and cold electron sources in display devices.5. In order to prepare CNTs/Cu composite materials, radio frequency (RF) magnetronsputtering, substrate-enhanced electroless deposition (SEED) and molecular-level mixingare used. A composite material based on Cu nanoparticles with good crystallinitydeposited uniformly on the arc-prepared MWCNTs has been developed by RF magnetronsputtering. The CNTs/Cu composite prepared by SEED process shows that Cunanoparticles deposited on the surface of MWCNTs are cube shape, and are connectedtogether in series. The CNTs/Cu composite powders prepared by molecular-level mixingprocess show that nanotubes are implanted or through Cu nanosphere. The electronicstructure of Cu atom adsorbed on a single-walled carbon nanotube (SWCNT/Cu) isstudied by the First Principles calculations. Based on the experimental results andtheoretical calculations, we propose an electron conductive model of CNT/Cu composite,that is the high concentration of electrons provided by Cu flows in CNTs with the highmobility electronic structure, forming the conductivity enhancement mechanism. A sort ofnon-enzymatic electrochemical sensor is fabricated based on a composite of Cunanoparticles and arc-synthesized MWCNTs by using SEED method for detecting glucose.It exhibits excellent sensitivity, good specifity and high stability.

An Investigation on Preparation and Application of High Quality Multi-walled Carbon Nanotubes

Abstract

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