Facile synthesis of ultrathin g-C3N4 nanosheets modified with N-doped carbon dots: Enhanced photocatalytic hydrogen production activity and mechanism insight

In this study, nitrogen-doped carbon dots (NCDs) modified ultrathin carbon nitride (g-C3N4) nanosheets were synthesized by a simple secondary calcination method, which realizes efficient photocatalytic hydrogen production. The secondary calcination process can not only thermally exfoliate g-C3N4 into ultrathin nanosheets, but also uniformly anchor NCDs (∼3 nm) on the surface of g-C3N4. The photocatalytic results manifested that a very small amount of NCDs (0.5 wt%) loading on g-C3N4 could achieve a high photocatalytic hydrogen production rate (5.21 mmol g−1 h−1). The reasons for the enhanced photocatalytic activity were analyzed. The ultrathin g-C3N4 nanosheets facilitated the migration of photogenerated carriers. Moreover, NCDs/g-C3N4 exhibited enhanced visible light absorption owing to the up-conversion fluorescence effect of NCDs and the narrow band gap caused by the decoration of NCDs. Furthermore, NCDs as electron acceptors can promote carrier separation. This combination strategy provides a basis for the synthesis of inexpensive, metal-free, and efficient carbon-based photocatalysts.