New strategies for the synthesis and characterization of nanotubes and nanowires

Abstract

Carbon nanotubes and nanowires constitute an important class of nanomaterials and are excellent models to study the relationship between electrical transport, optical and other properties with dimensionality and size confinement. Chapter 1 presents a brief overview of the synthesis, properties and potential applications of carbon nanotubes as well as nanowires. The use of nebulized spray pyrolysis for the synthesis of carbon nanotubes is outlined in Chapter 2. Multi-walled carbon nanotubes (MWNTs) with fairly uniform diameters and ahgned MWNT bundles have been obtained by using solutions of organometallics such as ferrocene in hydrocarbon solvents. Well-graphitized MWNTs were obtained with a solution of ferrocene in xylene. Single-walled nanotubes (SWNTs) were obtained when cobaltocene or nickelocene is used along with toluene. Fe(C0)5 in mixture with acetylene also yielded aligned MWNT bundles. The procedure described can be scaled up for large-scale production. Chapter 3 discusses the purification of single-walled carbon nanotubes (SWNTs) and MWNTs by hydrogen treatment. The method involves acid washing followed by hydrogen treatment around 1000 °C. While acid washing dissolves the metal particles, the hydrogen treatment removes amorphous carbon as well as the carbon coating on the metal nanoparticles. The high quality of the nanotubes obtained after purification has been verified by electron microscopy, X-ray diffraction and spectroscopic methods. Chapter 4 discusses a new method based on nebulized spray pyrolysis for the preparation of nanowires of metals. The method, involving the decomposition of the metal acetate precursor for the synthesis of zinc, cadmium and lead nanowires. The nanowires are obtained in copious quantities and are single-crystalhne. Oxidation of metal nanowires gives one-dimensional oxidic nanostructures. In the case of zinc metal, tubular ZnO is obtained. Chapter 5 deals with polyaniline (PANI)- carbon nanotubes composites. Composites of PANI have been prepared with pristine multi-walled and single-walled nanotubes as well as nanotubes subjected to acid treatment and subsequent reaction with thionyl chloride. The composites have been characterized by various techniques, including X-ray diffraction, electron microscopy as well as infrared and Raman spectroscopy. Electrical resistivities of the PANI-nanotube composites have been measured and compared with those of the nanotubes and PANI.