▎ 摘　　要

The reaction of calcium carbide (CaC2) with water to produce acetylene is common in industrial production, but its side reaction, removal of calcium from CaC2 (also termed de-Ca) to fabricate highly graphitic carbon, is highly overlooked. Herein, we report the synthesis of highly crystalline few-layered graphene by controlling the reaction of tetragonal-phased CaC2 with water at room temperature (20-25 degrees C). The resulting carbon materials were revealed to be highly graphitic, with approximate to 3 nm thickness, containing >93 at% carbon. Raman spectroscopy evidenced their low defect content with a defect (D)/graphitization (G) ratio of approximate to 0.07. HRTEM further verified their high graphitization degree. A formation mechanism was proposed: the C-2(2-) dumbbells donate their electrons to nearby oxidative species, e.g. H+ in water, followed by topotactic cross-linking to form a conjugated sp(2)-carbon network. Furthermore, the capability of CaC2 reduction and re-assembly into graphitic carbon was clearly evidenced by reaction with Ag+ in non-aqueous solvent, which resulted in a larger quantity of graphene materials and small-sized Ag nanoparticles.