▎ 摘　　要

Synthesis of graphene with scalable characteristics, quality, and quantity has drawn much attention because of its massive potential application. Herein, we introduce a facile and scalable synthesis of graphene by direct-reduction and hydrothermal methods. The direct-reduction method involved the reduction of graphene oxide using ascorbic acid at 60 degrees C, whereas the hydrothermal method was performed using the same precursor under high pressure and at 160 degrees C. The effects of the synthesis pathways on the graphene characteristics and quality were investigated through Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and gas sensing measurements. Results demonstrated that the hydrothermal method was effective for the fabrication of graphene with scalable quantity. Gas-sensing characteristics of the high-quality synthesized graphene were tested against NO2 and Cl-2 gases at different temperatures. The results demonstrated that the graphene sensors could detect the toxic oxidizing gases investigated with reasonable response and good response/ recovery characteristics, suggesting a great potential application in air pollution monitoring.