A metal-free catalytic system combining oxidized carbon nanotubes (oCNTs) and ionic liquids (ILs) is pre- sented for the oxidation of aromatic thiophene compounds with H 2 O 2 as an oxidant. The oCNTs exhibit impressively high activity and stability in the system, which show an even better performance than those of some reported metal catalysts. The ILs are proved to have indispensable influence on the enhanced catalytic performance of the oCNTs. Detailed characterization by TG-MS and XPS demonstrates that the carbonyl groups are the active sites for the oxidation process, which is further supported by the deactiva- tion and the model catalysts experiments. The quantitative analysis of different oxygen groups in oCNTs could be achieved by an isothermal temperature programmed TG-MS method. The concentration of car- bonyl groups is 1.46 mmol per 1 g oCNTs and the turnover frequency of oCNTs could also be obtained (10.7 h ? 1 in the presence of OmimPF 6 ). H 2 O 2 decomposition experiments combined with the EPR results reveal that the presence of OmimPF 6 can avoid the intermediate HO ? to form O 2 and then improve the catalytic performance of oCNTs for the oxidation of dibenzothiophene.