▎ 摘　　要

As a metal-free catalyst, nitrogen-doped graphene (N-doped graphene) has considerable attention in recent years. A simple and easy preparation method for its mass-producion is desired. The single-step one-pot preparation method, using graphite and ammonium solution via ultrasonic irradiation, is one of the candidates for the mass -production method. In this study, we investigated the effects of ultrasonic frequencies on the preparation of N -doped graphene using graphite and ammonium solution. Ultrasonic wave with frequencies of 485 kHz, 1.64 MHz, and 2.5 MHz were applied and the chemical bonding structures of three samples were analyzed using X-ray electron spectroscopy (XPS) and Raman spectroscopy. Additionally, the morphologies of the samples were observed using scanning electron microscope (SEM) and atomic force microscope (AFM). XPS and Raman analysis indicated the formation of pyridinic-N bonding configuration and the generation of defects in graphite networks owing to the sonication process. The highest nitrogen concentration N/C was obtained in the sample prepared using frequency of 1.64 MHz. The physical impact of the ultrasonic wave at 1.64 MHz to graphite is considered low in comparison with that of the waves at 485 kHz and 2.5 MHz. Moreover, the sample exposed to the ultrasound frequency of 485 kHz reduced in size and exhibited low nitrogen concentration in comparison with other samples.