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 H-2 production of similar to 185.79 mmol h(-1) g(-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 H-2 production via active edge sites and superior intrinsic electrical conductivity. The H-2 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 H-2 production rate achieved by a WS2-based CdS photocatalyst by splitting water using simulated solar light irradiation. (C) 2017 Elsevier Inc. All rights reserved.