▎ 摘　　要

A novel method for preparing high-quality graphene sheets by the liquid-phase exfoliation of expanded graphite (EG) in task-specific ionic liquids (TSILs) was developed. The used TSILs contain alkyl-3-methylimidazolium cations that have stronger intercalation in the expanded graphite and peroxydisulfate anions that oxidize the edge of the expanded graphite and facilitate the intercalation of the imidazole cation. Such coordinated attack of the anion oxidation and the cation intercalation resulted in sufficient exfoliation of EG and provides single- and few-layer graphene sheets with fewer defects, lateral extent of more than ten micrometers and higher optical transmittance. The nanocomposites comprising the prepared graphene sheets and P25 exhibit a higher photocatalytic activity for the photodegradation of methylene blue under UV-light.