Engineering the Edges of MoS₂ (WS₂) Crystals for Direct Exfoliation into Monolayers in Polar Micromolecular Solvents

Abstract

Synthesizing transition metal dichalcogenide (TMDC) monolayers through the liquid exfoliation of bulk crystals in low boiling point polar micromolecular solvents, such as water, is paramount for their practical application. However, the resulting hydrodynamic forces only appear on the crystal edges due to the mismatch in surface tension between the polar micromolecular solvents and the bulk crystals and are insufficient to overcome the strong van der Waals attraction between adjacent microscale layers. Herein, we present the novel strategy of engineering the lateral size of TMDC (MoS and WS) crystals in the nanoscale to increase the fraction of edges, leading to their direct and ready exfoliation in polar micromolecular solvents, even in pure water, to produce monolayer MoS and WS nanosheets in high yield. To examine one of their important applications, their catalytic hydrogen evolution activities were evaluated when used as cocatalysts with a photoharvester semiconductor (cadmium sulfide, CdS) in a reaction driven by solar energy. These exfoliated MoS (WS) monolayers exhibited superior cocatalytic performance in the photocatalytic hydrogen evolution reaction (HER). Notably, the cocatalytic performance of monolayer WS nanosheets is even higher than that of platinum (Pt), which is a state-of-the-art catalyst for catalytic hydrogen evolution. This work elucidates the importance of decreasing the lateral size of layered crystals to significantly enhance their exfoliability, providing a new strategy for the large-scale preparation of nanoscale TMDC monolayers by liquid exfoliation.

Synergetic Exfoliation and Lateral Size Engineering of MoS2 for Enhanced Photocatalytic Hydrogen Generation

“…Recently, we have demonstrated that lateral‐size engineered bulk MoS 2 crystal can be directly exfoliated into monolayer nanosheets in polar micromolecular solvents such as ethanol, providing a facile way to large‐scale preparation of monolayer MoS 2 through liquid exfoliation method . As illustrated in Figure , the well‐crystallized MoS 2 crystals with lateral sizes of several tens nanometer were synthesized through in situ calcining amorphous MoS x at 800 °C.…”

Heterostructured WS2‐MoS2 Ultrathin Nanosheets Integrated on CdS Nanorods to Promote Charge Separation and Migration and Improve Solar‐Driven Photocatalytic Hydrogen Evolution

“…Further increases in the amount of WS 2 -MoS 2 (> 6wt%) led to ad ecrease in the solar-driven photocatalytic activity.The excessW S 2 -MoS 2 might form very thick layersont he surface of CdS and preventt he absorption of solar light, which would lead to ad ecreased photogeneration of chargec arriers and result in ad ecrease in the photocatalytic hydrogen evolution rate. [54] Therefore, for CdS/WS 2 -MoS 2 photocatalysts, as uitable amount (6 wt %) of WS 2 -MoS 2 is favorable for efficient hydrogen evolution. In addition, the photocatalyst dose and sacrifi- Figure 3b.…”

Layered Aggregation with Steric Effect: Morphology‐Homogeneous Semiconductor MoS2 as an Alternative 2D Probe for Visual Immunoassay

“…This characteristic made 2D MoS 2 own potential to be generally visual probes for sensors . Nevertheless, up to now, inhomogeneous sizes of 2D MoS 2 in both vertical and lateral dimension remarkably impeded its practical application . To address it, a differential‐zone centrifugation (DZC) strategy was proposed for the size sorting of exfoliated MoS 2 due to the thickness‐distinguishing forces in the centrifugation process.…”