Structural evolution of alkaline earth metal stannates MSnO3 (M = Ca, Sr, and Ba) photocatalysts for hydrogen production

Abstract

The alkaline earth metal stannates MSnO₃ (M = Ca, Sr, and Ba) photocatalysts with different morphologies are successfully prepared by hydrothermal method and their photocatalytic activities are evaluated by photocatalytic reforming of ethanol/water solution to hydrogen. All of the as-prepared samples are characterized in detail by X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance (UV-vis DRS), N₂ physical adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) before and after the photocatalytic hydrogen production to illustrate the effect of the photoreaction on the surface structure, and thus to make the photocatalysis clear. The results reveal that the greatest photocorrosion occurs on the surface of CaSnO₃, SrSnO₃, and BaSnO₃ samples. And the formed surface species have great influence on H₂ production from ethanol/water solution. The photocatalytic reaction can transform CaSnO₃ into CaSn(OH)₆, producing CaSn(OH)₆/CaSnO₃ composite where the photogenerated charges can be more efficiently separated and transferred, consequently enhancing the hydrogen evolution. As for SrSnO₃, the photocorrosion can cause the formation of Sn²⁺ self-doped SrSnO₃ nanoparticles on the surface to increase the hydrogen production efficiency. Unlike CaSnO₃ and SrSnO₃, the photocatalytic activity of BaSnO₃ is gradually decreased due to the conversion of BaSnO₃ to BaCO₃. As expected, the H₂ evolution rate decreased in the order of CaSnO₃ > SrSnO₃ > BaSnO₃ under UV light irradiation. It is well demonstrated in the present work that CaSnO₃ is a potential photocatalyst for the photocatalytic reforming of ethanol/water solution to hydrogen.