Cd1−xZnxS supported on SBA-16 as photocatalysts for water splitting under visible light: Influence of Zn concentration

Cd_1−xZn_xS solid solutions (x = 0.05–0.3) supported on mesoporous silica SBA-16 substrate with 3D cubic structure were investigated for hydrogen production from water splitting under visible light. The influence of Zn concentration (x) in the Cd_1−xZn_xS solid solution and support morphology were investigated. The bare SBA-16 substrate was synthetized by the hydrothermal method whereas the Cd_1−xZn_xS photocatalysts were prepared by coprecipitation of metal sulfides from aqueous solutions of Cd²⁺ and Zn²⁺ using Na₂S as precipitating agent. An attempt has been made to determine the photocatalyst structures using several techniques including elemental analysis, N₂ adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS) and Raman spectroscopy. Surface characterization of the samples by XPS indicates that Cd_1−xZn_xS nanoparticles are unevenly distributed on both external surface and within the pore network. An increase of the band gap energy with increasing Zn loading up to x = 0.2 in the Cd_1−xZn_xS solid solution was observed. As a consequence, H₂ evolution increases gradually with an increase of the Zn loading in the photocatalysts from 0.05 to 0.2 wt% being the Cd_0.8Zn_0.2S/SBA-16 system the most active among the catalysts studied. The highest activity of this photocatalyst was explained in terms not only of its large band gap energy but also by the enhancement of the interaction between the particles of solid solution and the SBA-16 substrate.