Metallic 1T-phase MoS₂ quantum dots/g-C₃N₄ heterojunctions for enhanced photocatalytic hydrogen evolution

Recently, molybdenum disulfide (MoS₂) has been regarded as an efficient non-precious-metal co-catalyst for photocatalytic hydrogen (H₂) evolution, however, its inherent low-density active site and poor electron transfer efficiency have essentially limited its photocatalytic properties. Here we report that 1T-MoS₂ quantum dots (QDs) can act as co-catalysts in assisting the photocatalytic H₂ evolution to form heterostructures with g-C₃N₄ nanosheets (denoted as 1T-MoS₂ QDs@g-C₃N₄). Benefiting from the abundance of exposed catalytic edge sites and the excellent intrinsic conductivity of 1T-MoS₂ QDs, an optimized 1T-MoS₂ QD@g-C₃N₄ composite (15 wt%) exhibits an extraordinary photocatalytic H₂ evolution rate of 1857 μmol h^-1 g^-1 under simulated solar light irradiation, apparently 37.9 times higher than that of pure g-C₃N₄ NSs (49 μmol h^-1 g^-1). Meanwhile, the 1T-MoS₂ QD@g-C₃N₄ composites exhibit a good stability in the cyclic runs for the photocatalytic H₂ production. The high efficient photocatalytic activity and stability of the 1T-MoS₂ QD@g-C₃N₄ composite is primarily attributed to the following reasons: (1) the introduction of 1T-MoS₂ QDs results in a stronger light absorption capability in comparison with pure g-C₃N₄; (2) the tiny particle size of 1T-MoS₂ QDs, in which edges and basal surface are catalytically active, provides a proliferated density of catalytically active sites; (3) 1T-MoS₂ 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-C₃N₄ NSs to 1T-MoS₂ 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 H₂ evolution. This work will provide new insight for the design and fabrication of smarter, cheaper and more robust artificial photocatalysts for photocatalytic H₂ evolution.