Aqueous electromigration of single-walled carbon nanotubes and co-electromigration with copper ions

The electromigration behaviour of raw and acid purified single walled carbon nanotubes (SWCNTs) in dilute aqueous systems (0.0034 mg mL^-1), in the absence of surfactant, with the addition of either 0.85 M acetic acid or 0.1 M CuSO₄, was evaluated using a 2-inch copper cathode and either a 2-inch copper or 0.5-inch platinum anode. The results showed that the electromigration of raw SWCNTs (with a high catalyst residue) in the presence of CuSO₄ resulted in the formation of a Cu-SWCNT composite material at the cathode. In contrast, acid purified SWCNTs were observed to diffuse to a copper anode, creating fibrillated agglomerates with "rice-grain"-like morphologies. Upon acidification with acetic acid (or addition of CuSO₄) the direction of electromigration reversed towards the cathode as a result of coordination of Cu²⁺ to the functional groups on the SWCNT overcoming the inherent negative charge of the acid purified SWCNTs. The result was the co-deposition of SWCNTs and Cu metal on the cathode. Addition of 0.005 M EDTA sequesters some of the Cu²⁺ and resulted in the separation of metal decorated SWCNTs to the cathode and un-decorated SWCNTs to the anode. The resulting SWCNT and Cu/SWCNT deposits were characterized by Raman spectroscopy, XPS, SEM, EDS, and TEM.