Metallic 1T-phase MoS quantum dots/g-CN heterojunctions for enhanced photocatalytic hydrogen evolution.

Recently, molybdenum disulfide (MoS) has been regarded as an efficient non-precious-metal co-catalyst for photocatalytic hydrogen (H) evolution, however, its inherent low-density active site and poor electron transfer efficiency have essentially limited its photocatalytic properties. Here we report that 1T-MoS quantum dots (QDs) can act as co-catalysts in assisting the photocatalytic H evolution to form heterostructures with g-CN nanosheets (denoted as 1T-MoS QDs@g-CN). Benefiting from the abundance of exposed catalytic edge sites and the excellent intrinsic conductivity of 1T-MoS QDs, an optimized 1T-MoS QD@g-CN composite (15 wt%) exhibits an extraordinary photocatalytic H evolution rate of 1857 μmol h g under simulated solar light irradiation, apparently 37.9 times higher than that of pure g-CN NSs (49 μmol h g). Meanwhile, the 1T-MoS QD@g-CN composites exhibit a good stability in the cyclic runs for the photocatalytic H production. The high efficient photocatalytic activity and stability of the 1T-MoS QD@g-CN composite is primarily attributed to the following reasons: (1) the introduction of 1T-MoS QDs results in a stronger light absorption capability in comparison with pure g-CN; (2) the tiny particle size of 1T-MoS QDs, in which edges and basal surface are catalytically active, provides a proliferated density of catalytically active sites; (3) 1T-MoS QD co-catalysts with metallic characteristics could act as efficient electron acceptors, which builds up a highly efficient pathway for photo-generated electrons from the CB of g-CN NSs to 1T-MoS and thus realizes rapid spatial charge separation. The improved light harvesting ability, increased catalytically active sites, as well as increased separation of charge carriers could be responsible for the improved photocatalytic H evolution. This work will provide new insight for the design and fabrication of smarter, cheaper and more robust artificial photocatalysts for photocatalytic H evolution.