Hydrothermal synthesis of CdS/CdLa ₂S ₄ heterostructures for efficient visible-light-driven photocatalytic hydrogen production

Large-scale hydrogen production through water splitting using photocatalysts with solar energy can potentially produce clean fuel from renewable resources. In this work, photocatalytic hydrogen evolution with a high efficiency was achieved using CdS nanocrystal decorated CdLa ₂S ₄ microspheres (CdS/CdLa ₂S ₄) successfully prepared by a two-step hydrothermal process. The obtained CdS/CdLa ₂S ₄ composite was characterized by X-ray diffraction (XRD), electron microscopy (EM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance absorption spectroscopy (DRS), and photoluminescence spectroscopy (PL). XRD demonstrated that highly crystalline hexagonal CdS was obtained in CdS/CdLa ₂S ₄. EM results revealed that CdLa ₂S ₄ microspheres assembled from a large number of nanoprisms, were intimately enwrapped by the surrounding CdS nanocrystals with a particle size below 20 nm. This unique architecture resulted in the appropriate dispersion of CdS nanocrystals and intimate multipoint contacts between the CdS nanocrystals and CdLa ₂S ₄, which led to significant enhancement of charge separation in CdS/CdLa ₂S ₄. Especially, the CdLa ₂S ₄ microspheres decorated with 3 wt% CdS nanocrystals containing 0.4 wt% of Pt showed a high rate of H ₂-production at 2.25 mmol h ^-1 with an apparent quantum efficiency of 54% under 420 nm monochromatic light. The rate of hydrogen evolution from water splitting was 9 times faster in comparison with the rate observed on pure CdLa ₂S ₄, which is ascribed to the presence of CdS nanocrystals that alter the energy levels of the conduction and valence bands in the coupled semiconductor system.