Photocatalytic Hydrogen Production on Cd1-xZnxS Solid Solutions under Visible Light: Influence of Thermal Treatment

Cd1-xZnxS solid solutions have been prepared by employing different thermal treatments (He flow from 773 to 1073 K and static vacuum at 1073 K). The photocatalysts were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), N-2 adsorption isotherms, X-ray diffraction (XRD), UV-vis absorption spectra, and X-ray photoelectron spectroscopy (XPS) techniques and tested in the production of hydrogen from aqueous solutions containing S2-/SO32- as sacrificial agents under visible light irradiation. Structure, morphology, composition, and visible light absorption capacity of the Cd1-xZnxS solid solutions were found to be strongly dependent on the postsynthesis thermal treatments. The samples treated under He flow presented Cd loss with the temperature rise that implies formation of defects in the crystalline structure of the solid solutions. The increase in the extent of the structural defects of the Cd1-xZnxS solid solutions with the annealing temperature rise is related with a progressive decrease in their capacity to produce hydrogen. A significant improvement of the photoactivity was obtained for the solid solution derived from the treatment under static vacuum. The improvement in activity is related to the formation of Cd1-xZnxS solid solutions with higher crystallinity and less thermal Cd sublimation that inhibits the formation of structural defects and thus improves the effective utilization of the e(-)/hole energy carriers.