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Manipulation and purification of multi-walled carbon nanotubes

Carbon nanotubes (CNTs) consist of one or more rolled-up sheets of graphitic structure. Some preparative methods produce single-walled cylinders, others give tubes with several nested cylinders arranged concentrically (multiwalled carbon nanotubes, or MWCNTs). Electrically, they can behave as semiconductors or metals, as also predicted theoretically. The wide range of conductivity should permit a purification and fractionation of the tubes by means of the force exerted on them in an electric field. We describe micro-scale concentration and orientation of MWCNTs, and also their characterisation using Raman spectroscopy. This is used to monitor their purification using medium-scale apparatus incorporating a flow cell.