Carbon quantum dots (CQDs) and Co(dmgH)(2)PyCl synergistically promote photocatalytic hydrogen evolution over hexagonal ZnIn2S4

CQDs/ZnIn2S4 nanocomposites (CQDs stands for carbon quantum dot) prepared by a microwave method in the presence of performed CQDs were impregnated with Co(dmgH)(2)PyCl (dmgH = dimethylglyoxime, Py = pyridine) to form ternary Co(dmgH)(2)PyCl/CQDs/ZnIn2S4 nanocomposites (Co/CQDs/ZnIn2S4). The photocatalytic performance for hydrogen evolution in the presence of TEOA as a sacrificial agent over the asobtained Co/CQDs/ZnIn2S4 under visible light was investigated. It was found that ternary Co/CQDs/ZnIn2S4 show significantly superior photocatalytic activity for hydrogen evolution than both Co(dmgH)(2)PyCl/ZnIn2S4 and CQDs/ZnIn2S4. An optimum activity was realized over Co/CQDs/ZnIn2S4 with the loading amount of 5.0 wt % CQDs and 1.0 wt% Co(dmgH)(2)PyCl, in which 703.9 mu mol of hydrogen was evolved in 8 h. The superior photocatalytic activity for hydrogen evolution over ternary Co/CQDs/ZnIn2S4 can be ascribed to the synergistic effect played by CQDs and Co(dmgH)(2)PyCl, in which CQDs acts as a mediator to promote the transfer of the photogenerated electrons to Co(dmgH)(2)PyCl, the hydrogen evolution cocatalyst. This work provides some guidance for the design of noble metal free photocatalysts for hydrogen generation and highlights the potential of using CQDs to promote the charge transfer in semiconductor-based photocatalysis.