A sonoelectrochemical method has been successfully developed for the preparation of graphene nanosheet (GN)-supported graphene quantum dots (GN/GQDs) whereby sodium n-octyl sulfate intercalates into the interlayer spaces of a graphite working electrode under the combined effect of an applied potential and acoustic vibration power (640 W). GNs containing only pores can be prepared by lengthening the carbon chain of sodium n-alkyl sulfate (SCxS, x = 10, 12, and 14). Raman and X-ray photoelectron spectroscopic analyses and electrochemical analysis show that the densities of the structural defects on the GN/GQDs and different GNs and their responding activities for H2O2 reduction are dependent on the carbon chain length of SCxS. These GN/GQDs have been used as non-enzymatic sensors for the determination of H2O2. (c) 2017 Elsevier Ltd. All rights reserved.