Synthesis of carbon nanomaterials based on graphene quantum dots and improving their surface properties via chemical modification

Graphene quantum dots (GQDs) have attracted increasing attention due to their unique properties such as high water solubility, photoluminescence activity, good biocompatibility, physical, chemical and electrical properties which makes them appropriate candidates for use in a variety of bio-applications, sensors and photocatalysts. The objective of this study is synthesis of GQDs and improving their surface properties via chemical modification.Here, urea and citric acid as carbon precursor were used.  Citric acid was self-assembled into graphene framework via hydrothermal method at 160 °C for 4 h.  Then, the synthesized GQDs were carbonized and chemically activated by KOH treatment. The surface area and pore structures of GQDs were analyzed by nitrogen adsorption/desorption isotherms. The results showed that the specific surface area of carbonized-activated graphene quantum dots (CA-GQDs) have been increased from 0.06 to 1204.0 m2/g and pore structures have been enhanced significantly. The XRD pattern of GQDs confirmed the basic structure of graphite layer. The TEM images indicated the unique morphology of GQDs and the sizes of GQDs  were less than 5 nm. Thus, our applied method is an effective approach in the formation of GQDs with large BET surface area and narrow pore structures which reveals their potential applicability in biomedical field.