Carbon Nanotubes from Coal

Abstract

Materials that pack in the form of small rod shapes are of technological interest since they can exhibit considerable strength. In the past decade we have seen an enormous level of activity in nanostructured materials, in particular relating to carbon nanotubes which are closed elongated structures of pure carbon. They have application in nanoelectronics as conductors, semiconductors and as transistors. Carbon nanotubes can also be used for hydrogen storage. In our laboratory we have made efforts to synthesise these materials from sources other than graphite and in particular coal. The work complements a similar program in synthesising fullerenes from coal. Because coal is a molecular solid, and graphite is a lattice solid, there are distinct differences in processing mechanisms between the two materials. Unlike graphite, coal has weak bonds, and hence can proceed through a mechanism that does not involve single carbon units. Thus the products can differ from those of graphite. Nanotubes come in a variety of types that include multi walled and single walled forms. Each form can have a variety of diameters or can arise from different ways of rolling the graphite sheet from which they derive. They are called armchair, chiral and zig zag. Additives such as naphthalene and cobalt can affect the nature of the product formed. The presence of other elements in coal produces a different type of nanotube distribution. Both iron and sulphur are important. Coal also produces other products such as microfilaments and polycyclic hydrocarbons.