In this paper, a new and efficient way to oxidize and functionalize the multi-walled carbon nanotubes (MWNTs) has been developed by using a combination of ultraviolet (UV) irradiation and Fenton oxidation process, namely UV/Fenton oxidation treatment. Comparing with conventionally individual Fenton oxidation treatment of MWNTs, UV/Fenton combined treatment improved the etching rates and efficiencies and hence reduced the time for surface modification of MWNTs, which was proved to be an effective method in etching and functionalizing CNTs. The formation of new functional groups, structural changes and thermal stability during oxidation period were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and could be clarified by thermogravimetric analysis (TGA), which showed that it was under UV irradiation conditions that MWNTs could be rapidly functionalized with hydroxyl, carbonyl and carboxyl groups in the presence of Fenton reagents, originating from the increase in the gross HO• concentration and the existent synergetic effect when using UV irradiation combing with Fenton oxidation process. Introduction of such new oxygen-containing functional groups was attributed to attacks of HO• on defect sites and unsaturated bonds of C=C in the MWNTs sample, which should play an important role in accounting for the FTIR and Raman spectral changes.multi-walled carbon nanotubes (MWNTs), functionalization, UV/Fenton combined oxidation treatment As a consequence of their superior physicochemical properties and large potential applications, carbon nanotubes (CNTs) have opened new frontiers in the field of nanotechnology and nanoscience [1][2][3] . However, graphite and similar graphene including CNTs are well known to be chemically quite inert and insoluble in most organic and aqueous solvents, which limit their solution-based manipulation and processability, greatly hindering their wide application in practical work. So recently the modification or functionalization of CNTs has attracted great attention, primarily to improve their solubility and dispersibility in various solvents especially in aqueous solutions. Several ways of dispersion and solubilization have been explored and can be roughly divided into two approaches. One is noncovalent functionalization of CNTs with surfactants, polymers and biological macromolecules, where the mechanism of dispersion is based on adsorption, wrapping, π-stacking and hydrophobic/ π-π interactions [4][5][6][7][8][9] ; the other to render CNTs soluble and dispersible is convalent attachment of organic functional groups, which can be referred to as convalent functionalization. Two main strategies are currently used to attach functional groups onto CNTs. In the first case, the required functional groups are attached directly onto CNTs by using 1,3-dipolar cycloaddition, Birch reduction, and reactions with nitrenes, radicals and carbenes, etc. [10][11][12][13][14] . In the second one, a simple bridgehead func-
