Synthesis of graphene nanoplatelets from peroxosulfate graphite intercalation compounds

Ultrasonic exfoliation of expanded graphite compound obtained by cold expansion of graphite intercalated with peroxodisulfuric acid was shown to allow the creation of graphene nanoplatelets with thickness of about 5 – 10 nm. The resulting graphene material contained surface oxide groups. The expanded graphite intercalation compound was exfoliated by ultrasound much easier than thermally expanded graphite. A mechanism for the cleavage of graphite to graphene nanoplatelets is proposed. It includes: (1) formation of ionic graphite compound intercalated with peroxodisulfate anions; (2) decomposition of intercalated peroxodisulfate anions with formation of active free radicals which (3) attach covalently to carbon atoms; (4) cleavage and expansion of the graphite crystal due to the thickening of the peripheral region of graphene layers and release of gaseous oxygen between graphene layers; (5) hydrolysis of the expanded graphite compound; and, finally, (6) ultrasonic breaking of graphene nanoplatelet agglomerates.