Synthesis, Functionalization and Application of Few-Walled Carbon Nanotubes

Abstract

Few-walled carbon nanotubes (FWNTs) have 2 to 3 layers of sidewalls with diameters ranging from 3 to 8 nm and length around tens of micrometers; they are unique MWNTs with perfect graphitization structure as in single walled carbon nanotubes (SWNTs). Double-walled carbon nanotubes (DWNTs) are special type of FWNTs which are considered as the intermediate between SWNTs and MWNTs, respectively. Many of the applications proposed for DWNTs require the precise control of their diameters. In this dissertation we describe a simple, scalable approach for the selective synthesis of high-quality DWNTs by carbon monoxide chemical vapor deposition (CO-CVD) method. The inner-tube diameter distribution measured by HRTEM is about 0.7~1.1nm. The structural correlation and optical properties of high quality DWNTs were also exploited. To further exploit the excellent properties of FWNTs, it is necessary to functionalize them and make well dispersed solution. FWNTs have been chemically functionalized via efficient ultrasound-mediated dissolving metal method and ultrasound-mediated oxidation method. Such methods can be generalized towards other types of CNTs and the chemically functionalized CNTs are highly soluble in various organic solvents and aqueous solution respectively.The reported fluorescence from inner shells of double-walled carbon nanotubes (DWCNTs) is an intriguing and potentially useful property. A combination of bulk and single-molecule methods was used to study the spectroscopy, chemical quenching, mechanical rigidity, density, and TEM structures of the near-IR emitters in DWCNT samples. It is found that DWCNT inner shell fluorescence is weaker than SWCNT fluorescence by a factor of at least 10,000. The near-IR emission from DWCNT samples actually arises from SWCNT impurities.Compared to SWNTs and MWNTs, the thin FWNTs are believed to have extraordinary mechanical properties. The mechanical properties of composite films (CNTs/PVA) have been investigated. It is observed that the Young's modulus of composite films with only 0.2wt % functionalized FWNTs shows a remarkable reinforcement. In addition, the Young's modulus increased steadily with the increased concentration of FWNTs. In order to tackle the problem of the poor conductivity of the metal oxides, we have designed a ternary nanocomposite film composed of metal oxide (MnO2), functionalized FWNTs and conducting polymer (CP). Each component in the MnO2/CNT/CP film provides unique and critical function to achieve optimized electrochemical properties. It turned out that the electrodes exhibited excellent electrochemical properties.