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Semiconductor quantum dots are extremely interesting photosensitizers for the development of solar hydrogen generation. However, most efficient quantum dots prepared with toxic heavy metal of Cd were limited by high toxicity and poor absorbance in visible and near-infrared regions. Herein we achieve effective composition regulation of (AgIn) x Zn 2(1−x) S 2 that provides bandgap-tunable quantum dots, leading to the development of high efficiency quantum dots photosensitizer with low toxicity for solar H 2 generation in a three-component system in combination with a molecular cobalt catalyst and ascorbic acid as the sacrificial reagent. The composition of (AgIn) x Zn 2(1−x) S 2 quantum dots can be continuously tuned from x = 0 (ZnS) at one end to x = 1 (AgInS 2 ) at the other end, resulting in the corresponding bandgap being modulated gradually from 3.55 eV to 1.80 eV. The effect of bandgap on photocatalytic performance of (AgIn) x Zn 2(1−x) S 2 quantum dots was investigated, and the results show that a balance between the light absorption capacity and the driving force decided by the bandgap in the (AgIn) 0.5 ZnS 2 quantum dots leads to the highest efficiency of visible light driven H 2 generation. A high apparent quantum yeild of 8.2% under monochromatic irradiation at 450 nm is obtained for this photocatalytic system. This efficiency is the best performance to date for solar H 2 generation system based on Cd-free quantum dots. It is believed that this bandgap-tunable (AgIn) x Zn 2(1−x) S 2 quantum dots would have great potential as durable and lowly toxic photosensitizers to replace commonly-used Cd-based and molecular dyes for highly-efficient solar H 2 generation. [ABSTRACT FROM AUTHOR]

Exploiting photocatalysts with characteristics of cost effectiveness, environmental friendliness, visible light response, high reactivity and good durability is a great challenge for solar H 2 generation. Here, we synthesis of MoS 2 -graphene composite as a highly-efficient cocatalyst to enhance the photocatalytic activity of ZnIn 2 S 4 under visible light irradiation. Through the optimizing of each composition proportion, the hierarchical MoS 2 -graphene/ZnIn 2 S 4 photocatalyst shows the highest H 2 evolution rate of 4169 μmol h −1 g −1 under visible light irradiation in presence of Na 2 S and Na 2 SO 3 as sacrificial reagents when the content of MoS 2 -graphene is 1.2 wt% and the weight ratio of MoS 2 to graphene is 10:1, which is almost 22.8 times higher than that of pure ZnIn 2 S 4 . More importantly, the ternary MoS 2 -graphene/ZnIn 2 S 4 composite exhibits much higher photocatalytic activity than Pt-loaded ZnIn 2 S 4 photocatalyst, suggesting that the MoS 2 -graphene composite can act as a more efficient cocatalyst than the commonly used Pt metal. The superior catalytic activity of MoS 2 -graphene cocatalyst can be assigned to the positive synergistic effect between MoS 2 and graphene, which act as a hydrogen evolution reaction catalyst and an electron transport bridge, respectively. The effective charge transfer from ZnIn 2 S 4 to MoS 2 through graphene is demonstrated by the significant enhancement of photocurrent responses in MoS 2 -graphene/ZnIn 2 S 4 composite photoelectrodes. [ABSTRACT FROM AUTHOR]