Designing nitrogen and phosphorus co-doped graphene quantum dots/g-C3N4 heterojunction composites to enhance visible and ultraviolet photocatalytic activity

Highlights: • We synthesized a new diatomic-doped graphene quantum dots, namely, nitrogen and phosphorus co-doped GQDs, and it exhibits high efficiency and stability in pollutant photodegradation. • Under visible and ultraviolet irradiation, NP-GQDs/g-C₃N₄ can rapidly decompose 97.5% and 96% Methyl Orange (MO) in 8 min and 120 min, respectively. • NP-GQDs/g-C₃N₄ exhibits high stability after repeated usage in MO degradation. • All the results demonstrate NP-GQDs/g-C₃N₄ is highly prospective in pollutant photodegradation. In metal-free g-C₃N₄ based materials, the rapid recombination of photoexcited carriers limits its photocatalytic activity. In this work, for the first time, we synthesized a new kind of diatomic-doped graphene quantum dots (GQDs), namely, nitrogen and phosphorus co-doped GQDs (NP-GQDs), and then loaded on g-C₃N₄ surface to obtain NP-GQDs/g-C₃N₄ composite photocatalyst. Under visible and ultraviolet irradiation, the MO photodegradation rate of NP-GQDs/g-C₃N₄ is as high as 97.5% and 96%, respectively, which was 1.71 and 1.85 times higher than that of pure g-C₃N₄. The remarkable enhancement of photodegradation activity is mainly attributed to the introduction of NP-GQDs could promote the formation, transportation and separation of photoexcited carriers. Furthermore, the photocatalyst exhibits outstanding recycle stability without a significant decrease in activity after three reused runs. This study provides a new understanding of the roles played by diatomic-doped graphene quantum dots in photocatalytic systems and provides a new prospect in developing highly efficient g-C₃N₄-based photocatalysts.