Fractionation of multiwalled carbon nanotubes by cascade membrane microfiltration

Multiwalled carbon nanotubes were purified and size-separated by a multiste p! microfiltration process through a sequence of track-etched polycarbonate membranes of various pore sizes in both dead-ended and crossflow mode. For this cascade microfiltration, the electric are derived raw multiwalled sam ples were suspended in an aqueous solution of sodium dodecyl sulfate in dei onized water. By examining the deposits on the membrane surfaces and in the permeate suspensions with scanning electron microscopy and atomic force mi croscopy, the nanotube fractionation was confirmed and analyzed. These scan ning techniques showed that the components of the crude sample, which inclu ded carbon nanotubes, polyhedral nanoparticles, and large aggregates, were separated from each other during the filtration. In addition, fractionation of the multiwalled carbon nanotubes according to length was possible.