One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1−xS nanocrystal photocatalysts in a S2−/SO32− system

Abstract

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H₂-production reaction are highly required for improving its photocatalytic H₂-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H₂-evolution reaction of Cd_xZn_1−xS solid–solution photocatalysts in a sulfur-rich S²⁻/SO₃²⁻ solution. Here, the suspensible Cd_xZn_1−xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn²⁺/Cd²⁺ mixing ions in a sulfur-rich Na₂S–Na₂SO₃ solution, and the resultant Cd_xZn_1−xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S²⁻/SO₃²⁻ on the surface of these Cd_xZn_1−xS nanocrystals. It is found that the bandgap structure of Cd_xZn_1−xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd²⁺/Zn²⁺ molar ratio. The photocatalytic experimental results suggested that the suspensible Cd_xZn_1−xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H₂-production performance, and the suspensible Cd_0.6Zn_0.4S nanocrystals exhibit the highest photocatalytic H₂-generation performance of 717.19 μmol h⁻¹, a value higher than that of the sole CdS (320.99 μmol h⁻¹) and ZnS (5.89 μmol h⁻¹) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S²⁻ active site-mediated mechanism accounted for the high H₂-production activity of the suspensible Cd_xZn_1−xS nanocrystals, namely the numerous adsorbed S²⁻ ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible Cd_xZn_1−xS nanocrystals, but also serve as effective H⁺-capturing active sites to accelerate the interfacial H₂-production reaction. Meanwhile, an optimum bandgap structure of suspensible Cd_xZn_1−xS nanocrystals is also extremely required for promoting the photocatalytic H₂-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.