Effect of hydroxyl radical on the surface and structure of multi-walled carbon nanotubes

After purification pretreatment by thermal oxidation and concentrated HCl, multi-walled carbon nanotubes (MWNTs) was treated with Fenton's reagents and concentrated H2SO4/HNO3 mixture, respectively. The results of FTIR spectra showed that hydroxyl groups and carbonyl groups could be brought into the MWNTs after Fenton chemical treatment. However, both carbonyl groups and carboxylic groups could be produced at broken sites when MWNTs was treated by concentrated H2SO4/HNO3 mixture. According to formation mechanisms of hydroxyl radical, the conditions of Fenton treatment were controlled: molar ratio of H2O2 and Fe2+ was 10 or so, pH was at around 3 under acidic condition. In addition, we discussed the probable mechanisms of reaction between hydroxyl radical and MWNTs by IR spectral changes before and after Fenton treatment. The probable mechanisms indicated that existence of hydroxyl groups and carbonyl groups could be viewed as outcome of addition and oxidation reaction of electrophilic hydroxyl radical on unsaturated bonds on the sidewalls of MWNTs.