Efficient visible-light photocatalytic activity by band alignment in mesoporous ternary polyoxometalate–Ag2S–CdS semiconductors

Abstract

Porous multicomponent semiconductor materials show improved photocatalytic performance due to the large and accessible pore surface area and high charge separation efficiency. Here we report the synthesis of well-ordered porous polyoxometalate (POM)–Ag₂S–CdS hybrid mesostructures featuring a controllable composition and high photocatalytic activity via a two-step hard-templating and topotactic ion-exchange chemical process. Ag₂S compounds and polyoxometalate cluster anions with different reduction potentials, such as PW₁₂O₄₀³⁻, SiW₁₂O₄₀⁴⁻ and PMo₁₂O₄₀³⁻, were employed as electron acceptors in these ternary heterojunction photocatalysts. Characterization by small-angle X-ray scattering, X-ray diffraction, transmission electron microscopy and N₂ physisorption measurements showed hexagonal arrays of POM–Ag₂S–CdS hybrid nanorods with large internal BET surface areas and uniform mesopores. The Keggin structure of the incorporated POM clusters was also verified by elemental X-ray spectroscopy microanalysis, infrared and diffuse-reflectance ultraviolet-visible spectroscopy. These new porous materials were implemented as visible-light-driven photocatalysts, displaying exceptional high activity in aerobic oxidation of various para-substituted benzyl alcohols to the corresponding carbonyl compounds. Our experiments show that the spatial separation of photogenerated electrons and holes at CdS through the potential gradient along the CdS–Ag₂S–POM interfaces is responsible for the increased photocatalytic activity.