Topotactic conversion of calcium carbide to highly crystalline few-layer graphene in water - Carbon4Energy

The reaction of calcium carbide (CaC2) with water to produce acetylene is common in industrial productions, but its side reaction, removal of calcium from CaC2 (also termed as de-Ca) to fabricate highly graphitic carbon is highly overlooked. Herein, we reported the synthesis of high-crystalline few-layered graphene by controlling the reaction of tetragonal-phased CaC2 with water at room temperature (20~25℃). The resultant carbon materials were revealed to be highly graphitic, in ~3 nm thick, containing >93 at.% carbon. Raman evidenced their low defect contents of ~0.07 defect (D)/graphitization(G) ratio. HRTEM further verified its high graphitization degree. A formation mechanism was proposed that the C_2^(2-) "dumbbells" donate their electrons to nearby oxidative species, e.g. H+ in water, followed by the topotactic cross-linking to form conjugated sp2-carbon network. Furthermore, the capability of CaC2 reducing and re-assembly into graphitic carbon was clearly evidenced by reacting with Ag+ in non-aqueous solvent, resulting in larger quantity of graphene materials as well as small-sized Ag nanoparticles.