Effect of Pd-modification on photocatalytic H₂ evolution over Cd_0.8Zn_0.2S/SiO₂ from glycerol solution

A series of Pd/Cd_0.8Zn_0.2S/SiO₂ photocatalysts were prepared by incipient wet impregnation. The catalysts were characterized by XRD, H₂-TPR, XPS, and UV-vis DRS and used in the photocatalytic evolution of H₂ from glycerol and water mixture; the effects of Pd loading on the surface structure, photo absorption and H₂ evolution rate were investigated. The results showed that the chemical interaction between ZnS and CdS results in the formation of Cd_0.8Zn_0.2S solid solution on the surface of SiO₂; after the modification with Pd, the light absorption region of Cd_0.8Zn_0.2S/SiO₂ is expanded and the photo absorption efficiency is enhanced obviously. The loading of Pd exhibits significant influence on the rate of photocatalytic H₂ evolution; over 0.5%Pd/Cd_0.8Zn_0.2S/SiO₂ with a Pd loading of 0.5%, the maximum hydrogen production rates under UV light irradiation and under solar-simulated light irradiation reach 831 μmol·h^-1 and 153 μmol·h^-1, respectively, which are almost 4 times and 2 times higher than those obtained over unmodified Cd_0.8Zn_0.2S/SiO₂ under UV and solar-simulated light irradiation, respectively. The superior photocatalytic performance of Pd/Cd_0.8Zn_0.2S/SiO₂ can be partly related with the improvement of photo absorption, the enhancement in chemisorption and activation of H₂O and the increase in separation efficiency of photo induced electron-hole arising from the Pd modification.