In situ preparation of few-layered WS2 nanosheets and exfoliation into bilayers on CdS nanorods for ultrafast charge carrier migrations toward enhanced photocatalytic hydrogen production

Abstract

Transition-metal dichalcogenides (TMD) have emerged as a fascinating new class of noble-metal-free materials for photocatalytic hydrogen evolution from the water. Recently, numerous approaches have been established to develop single- or few-layered TMDs to improve their physical properties. Although WS2 has a higher intrinsic electric conductivity than the MoS2 analogue, most photocatalytic studies using TMD have focused on the nanocomposite using MoS2 as a co-catalyst. In the present study, we synthesized in situ and highly efficient few-layered WS2 nanosheets and exfoliated them to bilayers (i.e., ultrathin) on CdS nanorods (UWC) by a simple ultrasonication process. The optimized UWC-6 photocatalyst exhibits a tremendous rate of H2 production of ∼185.79mmolh−1g−1 using simulated solar light irradiation, with a quantum efficiency of 40.5%. The performance of this photocatalyst is 33 times greater than that of pristine CdS and 3.5-fold greater than that of few-layered WS2–CdS nanocomposite (BWC) photocatalysts. The ultrathin WS2 nanosheets are long and discontinuously stacked along the CdS nanorods, with high coverage of mixed-phase layers. This combination leads to the efficient photogeneration of charge carriers and enhances the surface shuttling properties of the photocatalyst for greater effective H2 production via active edge sites and superior intrinsic electrical conductivity. The H2 evolution rate reported here is much higher than for bulk or few-layered WS2-assisted CdS photocatalysts. To the best of our knowledge, this is the highest H2 production rate achieved by a WS2-based CdS photocatalyst by splitting water using simulated solar light irradiation.