▎ 摘　　要

We reveal the origins of surface groups on pristine and defective graphene after oxidation with potassium permanganate in aqueous solution. Density functional theory calculations show that the hydroxyl group that is first introduced onto graphene via hydrolysis of permanganate ester plays an important role in the oxidative cutting of graphene. Our results demonstrate that oxidative unzipping of defect-free graphene will occur from the edge and the inner plane simultaneously in terms of comparable maximum barrier heights along these two reaction routes. Divacancy on the defective graphene may accelerate the etching process when the hydroxyl group is introduced at the defect edge. Different from the previous unzipping mechanisms producing graphene flakes with only zigzag edges, our new mechanism involves hydroxyl and both sides of the graphene sheet, which allows richer edge states after oxidative cutting that agree with experimental observations. The detailed molecular insight into the mechanisms for graphene oxidation and fragmentation will be valuable for developing an effective means for graphene manipulation and interpretation of the long-puzzling graphene oxide structure.