Production of monolayer-rich gold-decorated 2H–WS2 nanosheets by defect engineering

Abstract

Chemical functionalization of low-dimensional nanostructures has evolved as powerful tool to tailor the materials’ properties on demand. For two-dimensional transition metal dichalcogenides, functionalization strategies are mostly limited to the metallic 1T-polytype with only few examples showing a successful derivatization of the semiconducting 2H-polytype. Here, we describe that liquid-exfoliated WS₂ undergoes a spontaneous redox reaction with AuCl₃. We propose that thiol groups at edges and defects sites reduce the AuCl₃ to Au⁰ and are in turn oxidized to disulfides. As a result of the reaction, Au nanoparticles nucleate predominantly at edges with tuneable nanoparticle size and density. The drastic changes in nanosheet mass obtained after high loading with Au nanoparticles can be exploited to enrich the dispersions in laterally large, monolayered nanosheets by simple centrifugation. The optical properties (for example photoluminescence) of the monolayers remain pristine, while the electrocatalytic activity towards the hydrogen evolution reaction is significantly improved.

Chemical functionalization: Au-decorated WS₂ sheets show enhanced catalytic activity

Defect engineering of WS₂ nanosheets via redox chemistry in liquid phase yields enhanced catalytic activity and monolayer enrichment. A team led by Claudia Backes at Ruprecht-Karls University demonstrated that liquid-phase exfoliated WS₂ undergoes a spontaneous redox reaction with AuCl₃, whereby thiol groups occurring at edges and defect sites reduce the AuCl₃ to Au0. The reaction causes Au nanoparticles to nucleate at WS₂ edges, and in turn such Au nanoparticle loading determines a substantial change in the nanosheet mass. As the Au decoration preferentially occurs at the edges of incompletely exfoliated WS₂ flakes, the dispersions can be further enriched with monolayers by means of centrifugation. While the optical properties of Au-decorated WS₂ sheets remain unaltered, their electrocatalytic activity is highly enhanced, showing promise for applications in hydrogen evolution reactions.