Oxidative treatment of multi-wall carbon nanotubes with oxygen dielectric barrier discharge plasma

The surface chemical properties and morphology changes that occurred on carbon nanotubes after modification by oxygen dielectric barrier discharge (DBD) at atmospheric pressure were investigated by dispersion test, XPS, FTIR, Raman, SEM and nitrogen adsorption. The effects of plasma treatment parameter, such as discharge power and treatment time, have been conducted. At the power of 15 W following 40 min exposure to the discharge, the surface atomic oxygen percentage could increase from 1.90% to 7.47%. Meanwhile, the surface area increased from 125 m2/g to 156 m2/g and the total volume from 0.309 cm3/g to 0.358 cm3/g. The possible mechanism is drawn for the modification process. Firstly, the plasma would attack on the defect site, transformed the sp2-hybridized carbons in nanotubes framework into sp3-hybridization and introduce the oxygen-containing functional groups including OH, COOH groups within 10 min. Furthermore, the hydroxyl groups could be further oxidized to form carboxyl groups. Moreover, the COOH groups were further oxidized to CO2 and H2O under excessive exposure time causing the decrease of the amount of oxygen atom. This investigation may be a simple and nonpolluting method for the modification of MWCNTs.