In this paper, an efficient and low-cost method was developed for producing isolated 2D MoN nanosheets via Na2CO3-assisted nitridation and exfoliation of natural 2H-MoS2 by NH3 at 700-800 degrees C. It was found that, in the presence of Na2CO3, the nitridation of MoS2 with NH3 was a topochemical transformation. After heat treatment the mixture of MoS2 and Na2CO3 in NH3 at 700-800 degrees C, layered MoN with intercalated Na2S was obtained. Na2CO3 can dramatically promote the topochemical nitridation and exfoliation of MoS2 in NH3. At 750 degrees C, the time for complete nitridation of (commercial) MoS2 can be shortened to 2 hours, which is much shorter than 40 hours in the case without the addition of Na2CO3 as reported in the previous literature. After acid-washing, the intercalated Na2S was removed, and the generated H2S promoted the further separation of the MoN nanosheets. Finally, dispersed high crystalline 2D MoN nanosheets with thickness of a few nanometers were successfully produced. This method may be also applicable for the production of other 2D nitrides or carbides by nitridation or carbonization of various transition metal dichalcogenides (TMDs) with the assistance of sulfur-fixed agent.