Compared with heavy metal catalysts, persulfate (PS) activated with metal-free catalyst for controlling organic pollutants is more economic, environment-friendly and safe to human health. In this study, one type of nitrogen-doped carbon (NNC) material was evaluated to catalyze PS for the oxidation of Direct Red 23 (DR23). The results indicate that NNC could efficiently catalyze PS for degradation of DR23 and the reaction can be described by pseudo-first-order kinetics. Key factors affecting the reaction were tested, including the PS concentration, NNC dosage, and pH. DR23 degrading rate increased remarkably with the increase of the PS concentration and NNC dosage. The degradation was favored at low pH. A competitive radical experiment was conducted to evaluate the PS activation mechanism. The result indicates that the activation followed the non radical mechanism, which was different with the most PS advanced oxidation processes (AOPs). NNC can be effectively recovered. XPS results indicate that Pyridinic-N and G-N played a critical role in the catalytic oxidation of DR23. Byproduct analysis revealed that DR23 was completely degraded in the PS/NNC system. (C) 2017 Elsevier B.V. All rights reserved.