▎ 摘　　要

A facile way to synthesize multilayer nitrogen-doped graphene (NG) from amorphous activated carbon (AC) without metal catalyst was successfully developed via ammonia-assisted hydrothermal method at 200 degrees C. The method's crucial advantage relied on harnessing unique ammonia hydrothermal mechanisms to change the amorphous carbon into multilayer graphene and provide an energy-save and metal-free approach. The NG products were consisted of 2-10 graphitic layers, which could form highly conductive network for electrodes. The hydrothermal process could trigger the reduction of oxygenates on the base unit (graphite nanocrystallites) of amorphous carbon by ammonia, leading to growth of basic units to multi-layer graphene. Compared with the traditional preparation via high temperature and pressure processing or catalytic graphitization by transition metals, the as-prepared multilayer graphene via metal-free and "green" method in a relative mild condition represented a high surface area and pore volume. The NG was used as electrode material of supercapacitors and showed high capacitance retention. (C) 2019 Elsevier Ltd. All rights reserved.