Electrochemical synthesis of nitrogen-doped graphene quantum dots and their photocatalytic hydrogen evolution application

A very simple electrochemical top-down procedure was employed to obtain pure graphene quantum dots (GQDs) in water and using only graphite as carbonaceous precursor. The graphitic structure of the GQDs has been clearly observed by high-resolution transmission electronic microscopy (HRTEM). Then, the synthesis of N-doped GQDs was allowed by the addition of ammonia in the solution. The nitrogen doping was plainly evidenced by X-ray photoelectron (XPS) and Raman spectroscopies. The role of the electrolytic solution employed during the synthesis has been also discussed. Finally, these N-doped and non-doped GQDs were further used to prepare hybrids by grafting them onto ZnO semi-conductors, and their photocatalytic properties towards water-splitting were investigated. Interestingly, a very important enhancement of the amount of dihydrogen produced was observed with N-doped GQDs, compared to ZnO alone or to hybrids prepared with non-doped GQDs.