INTRODUCTION

Pure carbon exists in nature in the form of diamond and graphite. Besides graphite and diamond several allotropes of carbon has been developed or discovered. Carbon nanotubes (CNTs) are one such allotropes of carbon in which hexagonally oriented carbon atoms (graphite sheets) roll up to make a tubular or cylindrical structure. These nanotubes are characterized by diameters of the order of nanometers and lengths up to few microns. These structures were first reported by Ijima in 1991 who discovered multi walled carbon nanotubes (MWCNTs) by arc-discharge method. Nanotubes can be classified into single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs) depending on the number of cylindrical carbon walls. CNTs are also characterized by a vector called chiral vector that indicates how the carbon atoms are rolled up. Since their discovery, a tremendous amount of research has been done to study different optical, mechanical, electrical and thermal properties of CNTs and how they can put into application. Several techniques of CNT synthesis and carbon growth mechanisms for its mass production have also been studied extensively. Several synthetic strategies like arc discharge, laser ablation, chemical vapor deposition (CVD), pyrolysis, flame synthesis have been successfully developed. Among these synthesis processes, arc discharge, laser ablation and CVD methods are commonly used for mass production of CNTs and nanotube blended materials. Despite a huge progress in CNT research over the years, we are still unable to produce CNTs of well-defined properties in large quantities by a cost-effective technique. The root cause of this problem is the lack of proper understanding of the CNT growth mechanism. This study will mainly cover the various applications of CNTs in energy sector.