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

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.