Gas-Phase Purification of Single-Wall Carbon Nanotubes

A gas-phase purification method for raw nanotube material has been developed which incorporates a chlorine, water, and hydrogen chloride gas mixture to remove unwanted carbon. The evolved gases can be easily monitored by infrared spectroscopy to follow the cleaning process. The quality of the final material was verified by SEM (scanning electron microscopy), TGA (thermogravimetric analysis), and UV−vis (ultraviolet and visible absorption spectroscopy). The yield of ∼15 wt % indicates a uniquely selective carbon surface chemistry that prevents etching of the nanotubes, which are generally more reactive due to their larger curvature. Although the technique's usefulness for large-scale purification was not determined, the ability to purify single-wall nanotubes by a gas-phase method has been demonstrated, and a mechanism proposed.