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)Zn2(1-x)S2 quantum dots can be continuously tuned from x=0 (ZnS) at one end to x=1 (AgInS2) 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)Zn2(1-x)S2 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)ZnS2 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)Zn2(1-x)S2 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. (C) 2016 Elsevier B.V. All rights reserved.