Safe and damage-less dry-purification of carbon nanotubes using FeCl3 vapor

The FeCl3-vapor treatment was proposed and developed for the purification of carbon nanotubes (CNTs). The FeCl3-vapor treatment combined with vacuum heating at 1000 °C efficiently removed various catalysts (Fe, Ni, Y, Mg, and Al) from single-wall and multi-wall CNTs. No damage was found in the purified CNTs with retained/enhanced G-band to D-band intensity ratios in Raman spectroscopy and elevated combustion temperatures in thermogravimetric analysis. Even if vapors of metal chlorides leak, they show low vapor pressure at ambient temperature and turn solid, significantly reducing the hazard. A safe and damage-less dry-purification method will promote various practical applications of CNTs.