High graphite N content in nitrogen-doped graphene as an efficient metal-free catalyst for reduction of nitroarenes in water

Four kinds of nitrogen-doped graphene (NG) as metal-free catalysts are synthesized by a one-step hydro thermal reaction and thermal treatment using graphene oxide and urea as precursors. It is found that the reduction of nitroarenes can be catalyzed by using a low NG loading and a small amount of NaBH4 in water with high yield. The type of nitrogen species in NG has an important effect on the reduction reaction. The NG catalyst containing the most graphite N shows the highest catalytic activity during reduction of nitroarenes, which demonstrates that the graphite N of NG plays a key role in impelling this reaction. The reaction mechanism is proven by GC-MS experiments, and DFT calculations reveal the reasons for the graphite N showing better catalytic activity. It is worth noting that no dehalogenation phenomenon occurs during the reduction process for halogen-substituted nitroarenes in contrast to conventional metal catalysts. In addition, the NG catalyst can be simply recycled and efficiently used for eight consecutive runs with no significant decrease in activity.