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

In this research, we present the systematic investigation of the effect of hydroxyl radical (HO) on the structure of multi-walled carbon nanotubes (MWNTs) via Fenton oxidation treatment in given conditions: molar ratio of hydrogen peroxide (H2O2) and ferrous ion (Fe2+) is approximately equal to 10 and pH value is controlled at 3 ± 0.5. Fenton oxidation process was followed and characterized by using Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The experimental results showed that the original graphene structure was disordered/destroyed by the newly generated oxygen-containing functional groups including OH, COOH and quinone groups, which were introduced while MWNTs was treated by Fenton reagents (Fe2+-H2O2). Moreover, two attackable routes for possible mechanism of interactions between HO and MWNTs were assumed by spectral changes and properties of reactive species, which were described as follows: (l) a preferred attack on defect sites existing in the purified MWNTs sample (2) a synchronous or succedent attack on unsaturated bonds of CC on the sidewalls of MWNTs by electrophilic addition reaction. The possible mechanism indicated that introduction of those functional groups into the structure of MWNTs could be regarded as the results of attacks of HO with double properties of oxidizability and electrophilic addition on defect sites and unsaturated bonds of CC in the MWNTs sample, which were consistent with spectral changes in infrared spectroscopy and Raman spectroscopy.