Synergistic effect of oxygen and nitrogen functionalities for graphene-based quantum dots used in photocatalytic H₂ production from water decomposition

Surface intact nitrogen-doped graphene oxide quantum dots (iNGO-QDs), which are based on the abundant elements C, H, O, and N, exhibit outstanding photocatalytic performance in H₂ production through water decomposition. In this study, we synthesize the iNGO-QDs by thermally treating graphene oxide sheets in NH₃ with subsequent ultrasonic exfoliation. The iNGO-QDs exhibit sizes of 2 to 6nm and consist of approximately 3 graphitic layers. Nitrogen doping in QD synthesis repairs the vacancy-type defects of GO and introduces n-type conductivity to compensate for the unbalanced charges on p-type GO, thereby suppressing leaks of photogenerated charges. Coexistence of p- and n-domains in the iNGO-QDs may form photochemical diodes to facilitate charge separation. Under visible light illumination, the iNGO-QDs steadily catalyze the production of H₂ from an aqueous solution containing triethanolamine. When deposited with Pt as the cocatalyst, the iNGO-QDs exhibit high activity in H₂ generation at an apparent quantum yield of 12.8% under monochromatic light (420nm) irradiation. The high activity of the iNGO-QDs can be attributed to the synergistic effect of the oxygen and nitrogen functionalities in facilitating charge separation and transfer.