Mechanism for Redox Exfoliation of Layered Transition Metal Dichalcogenides

Abstract

Liquid processing of layered transition metal dichalcogenides (LTMDs) is enabling a variety of applications, ranging from catalysts and coatings, to electronics, flexible sensors, and optical filters. Current strategies, such as sonication or shear mixing, are challenged by small yields (<1%), low production rates (<mg/min), short-term oxidative stability, and low dispersion concentration in a limited number of solvents. These factors inhibit the transition from lab to bulk production. Here, we establish the mechanism for the liquid processing route of Redox Exfoliation and establish the roles that chemical species formed in situ play in the exfoliation process of LTMDs. The mechanism proceeds via surface adsorption of polyoxometalate macroanions (POMs) and can be optimized by controlling the formation rate and size of these POMs through reagent level stoichiometric parametrization. Based on this mechanism, few-to-monolayer yields for MoX2 (X = S, Se, Te) may exceed 10% of the starting LTMD powder, and delamination may be reinitiated after reagent depletion, minimizing the starting LTMD waste.

Few-Layered Metal–Organic Framework Nanosheets as Catalysts for the Synthesis of 2,3-Dihydroquinazolinone and Propargylamines

“…Zeta potential measurement shows that the ultrathin MON 1 exhibits a nearly zero potential (−0.601 mV), whereas the ζ-potential of bulk LMOF 1 is 7.56 mV, suggesting the favorable stability accorded to colloidal science. 10,59,60 The prepared suspension can be stable at room temperature for at least 2 days without obvious precipitation and aggregation, indicating the good monodispersity of nanosheets.…”

“…It is well known that the utilization of bulk MOF in catalysis will be hindered by the limitation of pore size, the number of the exposing active sites, and the diffusion of the substrates/products in the long channels. − Therefore, the inherent layered structure of LMOF 1 prompted us to exfoliate it into nanosheets. Liquid exfoliation assisted by sonication, featured by the simple operation and cost effectiveness, has been proven to be one of the most effective and extensive methods for the exfoliation of a bulk-layered MOF into ultrathin 2D-MONs. − Owing to the existence of the weak van der Waals force among the interlayers, we speculate that ultrathin 2D-MONs may be obtained easily by peeling LMOF 1 via ultrasonic liquid exfoliation. Figure a schematically illustrates the process of delamination of LMOF 1 into ultrathin 2D-MONs with the assistance of sonication.…”

High-Throughput Production of 1T MoS2 Monolayers Based on Controllable Conversion of Mo-Based MXenes

“…21 The resultant TMD monolayers in the products are less than 1 wt % and are very difficult to be separated from the products with mixed phases. 22 In comparison, the bottom-up approach mainly refers to chemical vapor deposition, in which the precursors are reacted or decomposed on specific substrates to create atomic layers of nanomaterials. In this regard, although TMD monolayers can be produced, the output is only on the level of micrometers.…”

“…The top-down approach usually involves the exfoliation of layered TMD bulks via mechanical, liquid-phase and electrochemical procedures. ,, In this manner, the weak van der Waals force between the neighbor TMD layers would be gradually reduced or broken under the foreign functions such as shearing forces or sonication, thus producing monolayers and multilayers of TMDs with a low production yield below 4 wt % . The resultant TMD monolayers in the products are less than 1 wt % and are very difficult to be separated from the products with mixed phases . In comparison, the bottom-up approach mainly refers to chemical vapor deposition, in which the precursors are reacted or decomposed on specific substrates to create atomic layers of nanomaterials.…”

Nonlinear Optical Interactions and Relaxation in 2D Layered Transition Metal Dichalcogenides Probed by Optical and Photoacoustic Z-Scan Methods

“…The samples were synthesized using the redox exfoliation method. 10 In a 2018 report by Tsipas et al, 11 thin film semimetallic (2D single and few layers) 1T phase ZrTe 2 prepared by molecular beam epitaxy were grown on InAs and morphologically characterized. Theoretical calculations confirmed the semimetallic character, with the bands crossing at a point near the Fermi level, which indicates massless 3D Dirac Fermions, characteristic of a topological Dirac semimetal behavior.…”