Salty Coronene Sorts Carbon Nanotubes

Taking advantage of charge-transfer interactions, scientists in India have developed a new method for separating metallic and semiconducting single-walled carbon nanotubes (J. Am. Chem. Soc., DOI: 10.1021/ja100190p). Both types of nanotubes are produced in SWNT synthesis, and finding a practical way to sort them is a major challenge nanotechnologists face in exploiting the materials. The separation process developed by C. N. R. Rao and coworkers at Jawaharlal Nehru Centre for Advanced Scientific Research, in Bangalore, takes advantage of π-π interactions between the nanotubes and the polycyclic aromatic compound potassium coronene tetra­carb­oxyl­ate. When the researchers mix a 10-mM solution of the coronene salt with a raw SWNT product mixture, the metallic tubes precipitate and the semiconducting tubes remain in solution. Both the concentration of the coronene solution and the interaction time are critical to sorting the nanotubes, the scientists point out. The method avoids cumbersome ultracentrifugation, which is used in a number of other SWNT-sorting methods, the researchers note, and the technique “is amenable for large-scale separation and can be used as a routine laboratory procedure.”