Green and facile approach to synthesis of well-dispersed nitrogen-doped graphene without using surfactant or stabilizer with potential application for oxygen reduction reaction

A simple and green chemistry approach to synthesizing well-dispersed nitrogen-doped (N-doped) reduced graphene oxide (rGO) sheets through the hydrothermal reduction of graphene oxide was demonstrated. The UV–vis and Raman results illustrated the reduction of graphene oxide (GO) through a hydrothermal process. The X-ray photoelectron spectroscopy (XPS) results confirmed that nitrogen atoms had been doped in the reduced graphene oxide structure during the hydrothermal process in the presence of ammonia. The effects of the probe-sonication and pH of the GO solution before the hydrothermal treatment on the nitrogen doping, graphene nanosheet size, and its dispersibility were investigated. Zetasizer measurement and atomic force microscopy (AFM) images showed a high surface charge for the sample prepared under optimum conditions, with an average sheet size of 100 nm and a thickness of 1.1 nm, which enabled the nitrogen-doped graphene nanosheets to be well-dispersed and stable in water, with a concentration of up to 1 mg mL⁻¹. The stability of the product was measured in terms of the rGO concentration as a function of the sediment time using a UV–vis spectrophotometer for 49 consecutive days.