Graphene Quantum Dots Prepared from Graphene Hydrogels Basing on Hydrothermal Method

Graphene quantum dots (GQDs) is one of the derivatives of graphene. Due to the unique spin, electronic and optical properties, GQDs has attracted much attention. Graphene is a famous 2D and zero-bandgap material, and its size can be controlled to be from several micrometers to 30 inches. In principle, the bandgap of graphene can be tuned by varying its size. GQDs, less than 20 nm, can be considered as ultra-small fragments of graphene. The bandgap of small GQDs widens due to the quantum confinement effect. GQDs become semiconductors, which makes GQDs suitable for various fields such as optoelectronic devices, sensors and bio-imaging.

Herein, we report a novel method to prepare graphene quantum dots (GQDs) from graphene hydrogels. Various methods of synthesizing GQDs have been reported, such as hydrothermal synthesis, solvothermal, electrochemical methods, microwave technology and the bottom-up method. In our study, graphene hydrogels were prepared using a hydrothermal technique. By immersion of the hydrogels in low-polarity organic solvents, GQDs were released from the hydrogels. This method did not require additional treatments such as the centrifugation, filtration and dialysis in the general hydrothermal process. These GQDs have the strongest emission at ~347 nm.