Viscose-based activated carbon fibers (VACFs) were treated by a direct-current (DC) discharge plasma at different conditions. The surface functional groups of VACFs were modified to improve the adsorption and catalysis capacity for SO 2 and NO x . The surface properties of the untreated and treated VACFs which were modified in different feed gases (air, O 2 , N 2 and NH 3 ) were performed by scanning electron microscopy, BET, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR). The results show that after being treated with plasma, more particles appeared on the external surface of the VACFs and the surface became rougher, the average pore size decreased but the pore volume and the surface area decreased first and then increased. XPS revealed that DC discharge plasma can remarkably change the distribution of functional groups on the surface of VACFs. FTIR-ATR also indicated that more nitrogen atoms were introduced to the VACFs surface when the feed gas contained nitrogen atoms and N and O atoms were introduced to the surface of VACFs at the same time when the feed gas was air, but it did not happen in the feed gas of N 2 , or O 2 , or NH 3 . Discharge voltage and treatment time were important factors and for our experiment in the feed gas of nitrogen, the optimum modification conditions were 8 kV and 5 min, respectively. 

Viscose-based activated carbon fibers (VACFs) were treated by a dielectric-barrier discharge plasma under the feed gas of N2. The surface functional groups of VACFs were modified to improve the adsorption and catalysis capacity for SO2. The surface properties of the untreated and plasma-treated VACFs were diagnosed by SEM, BET, FTIR, and XPS, and the adsorption capacities of VACFs for SO2 were also compared and discussed. The results show that after the plasma treatment, the external surface of VACFs was etched and became rougher, while the surface area and the total pore volume decreased. FTIR and XPS revealed that nitrogen atoms were introduced onto the VACFs surface and the distribution of functional groups on the VACFs surface was changed remarkably. The adsorption characteristic of SO2 indicates that the plasmatreated VACFs have better adsorption capacity than the original VACFs due to the nitrogen functional groups and new functional groups formed in modification, which is beneficial to the adsorption of SO2.