▎ 摘　　要

Nitrogen functionalization of graphene enables it to be used for catalysis and targeted adsorption of biomolecules in both the solid state and in suspension. Thus, we sought to characterize the functional groups and suspension charge behavior of nitrogen-doped graphene (NDG) prepared in the absence of hydrazine, a highly toxic reagent. The hydrothermal reaction of graphite oxide (GO) with ammonia was shown to effectively remove oxygen and to restore the graphitic framework within the resulting NDG sheets. The enhanced graphitic character of the NDG materials was verified using X-ray photoelectron spectroscopy, thermogravimetic analysis, and electrical conductivity measurements. With six hours of reaction time (sample NDG-6), up to 9.6 wt % (7.1 atomic %) of nitrogen could be introduced into the graphene. All the NDG materials exhibited excellent dispersibility in water allowing their surface charge to be probed by measuring zeta potential (zeta) as a function of suspension pH. The NDG-6 material could hold surface charge ranging from zeta = -50 mV to zeta = +20 mV, which is, to the best of our knowledge, the widest range of surface charges measured on a colloidal graphene material.