©  Copyright 2013 Increased use of carbon nanotubes in consumer and industrial products have scientists asking about  the implications of CNTs in our environment. Many end product applications include polymer  composites, drug delivery systems, coatings and films, military applications, electronics, cosmetics,  healthcare, among others.  CNTs are desirable for many applications because of their high surface area to weight ratio. They are  lightweight and highly elastic compared to carbon fibers, and deliver higher surface area for increased  chemical interaction in its specific application.  There are two types of CNTs, Single-walled CNT and Multi-walled CNT which are briefly described in  the following section.   Single-walled CNT Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length  that can be many millions of times longer. The structure of a SWNT can be conceptualized by  wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder. The way the  graphene sheet is wrapped is represented by a pair of indices. Single-walled nanotubes are an  important variety of carbon nanotube because they exhibit electric properties that are not shared by  the multi-walled carbon nanotube (MWCNTs) variants. The most basic building block of these  systems is the electric wire, and SWNTs can be excellent conductors. One useful application of  SWNTs is in the development of the first intramolecular field effect transistors (FET). Production of  the first intramolecular logic gate using SWNT FETs has recently become possible as well. Single-  walled nanotubes are still very expensive to produce, around $1500 per gram as of 2000.Several  suppliers offer as-produced arc discharge SWNTs for ~$50–100 per gram as of 2007 .  Chemical Engineering & Gas Processing