Enhancing interfacial charge transfer in mesoporous MoS2/CdS nanojunction architectures for highly efficient visible-light photocatalytic water splitting

Abstract

Modulating the heterojunction interfaces at the nanoscale is paramount to developing effective photocatalysts. Nanodimensional heterostructures, essentially, expose a large fraction of active edge sites, which, along with excellent electronic communication, can result in high solar energy to chemical fuel conversion efficiencies. In this work, mesoporous heterojunction architectures made of ultrasmall MoS₂ nanolayers (ca. 10–15 nm in lateral size) and sub 5 nm sized CdS nanocrystals have been prepared through a polymer-templated oxidative aggregation of CdS nanocrystals followed by a wet-chemical deposition of exfoliated MoS₂ nanosheets on the CdS surface. Thorough chemical, morphological and structural investigations by electron microprobe analysis, X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy and N₂ physisorption prove that the MoS₂-modified CdS nanocatalysts are composed of a porous network of connected cubic CdS nanocrystals and 2H-phase MoS₂ nanosheets and possess a high internal BET surface area (ca. 159–225 m² g⁻¹) and uniform pores (ca. 6–9 nm in diameter). Photocatalytic studies coupled with UV–vis/NIR, photoluminescence and electrochemical impedance spectroscopy measurements indicate that the nanoscale MoS₂/CdS junctions provide more efficient electronic connectivity and charge carrier dissociation across the catalyst interfaces, resulting in a remarkable enhancement in the photocatalytic H₂ production activity. The optimized MoS₂/CdS catalyst at 20 wt% MoS₂ content achieves a H₂ production rate up to ∼0.4 mmol h⁻¹ (or ∼19 mmol h⁻¹ g⁻¹ mass activity) with remarkable stability under visible light irradiation, corresponding to an overall 6.7× enhancement of H₂ generation efficiency relative to the unmodified CdS. We also obtained an apparent quantum yield (AQY) of 51.2% for the hydrogen generation reaction using monochromatic light of 420 nm.