▎ 摘　　要

Nitrogen-doped graphene (NG) with different nitrogen levels was synthesized by using a simple hydrothermal method. Graphite oxide (GO), prepared by the modified Hummers method, served as the raw material, and urea served as both the reducing reagent and dopant. The variation in structures and morphologies indicates the successful incorporation of nitrogen in graphene. Urea can accelerate the reduction in GO. The optical properties also vary with the doping level, as verified by Raman analysis, and the intensity ratio (I-D/I-G) of the D to G Raman modes changes with increasing nitrogen doping level because of defects induced by doping. The relationship between the qualities of urea and the crystallite size of the as-produced NG was also studied in detail.