Direct Observation of the Light-Induced Exfoliation of Molybdenum Disulfide Sheets in Water Medium

Abstract

Single and a few atomic-layer molybdenum disulfide (MoS2) is a promising material in the fields of hydrogen generation, battery, supercapacitor, and environmental protection, owing to the outstanding electronic, optical, and catalytic properties. Although many approaches have been developed for exfoliation of MoS2 sheets, it is still essential to develop simple, convenient, and environmental friendly exfoliation methods. More importantly, the microscopic exfoliation process and the mechanism are still not clear, limiting a deeper understanding of the exfoliation. Herein, we develop a convenient and clean method for exfoliation of the 2H phase MoS2 (2H-MoS2) deposited on an indium tin oxide (ITO) surface. Importantly, the exfoliation process is observed directly and continuously under an optical microscope to reveal the detailed exfoliation process and mechanism. As illustrated, the light illumination triggers the exfoliation of the 2H-MoS2 sheets, and the presence of water is essential in this exfoliation process. The light intensity and wavelength, humidity, and bias all affect the exfoliation process obviously. The exfoliation is caused by the vaporization of the water molecules intercalated in 2H-MoS2 interlayers. By using this method, 2H-MoS2 nanosheets with different thicknesses are prepared on the ITO substrate, and microscopic catalysis mapping of the exfoliated sheets is demonstrated with single-molecule fluorescence microscopy, revealing that the prepared thin-layer 2H-MoS2 nanosheets show improved electrocatalysis activity (roughly 20 times). Our work will not only help deepen the understanding of exfoliation process of two-dimensional nanosheets but also provide an effective tool for the in situ study of various properties of the exfoliated sheets.

Synthesis of Thin Bi9O7.5S6 Nanosheets for Improved Photodetection in a Wide Wavelength Range

“…As known, the energy bands of semiconductors are bended on the surface of nanosized semiconductor crystals. [39][40][41] Because of the bended valence and conduction bands of the Bi 9 O 7.5 S 6 nanosheets under light irradiation (Figure 5d), the electrons and holes can easily transfer to different parts of the nanosheets under bias, prolong the lifetime of the carriers. Therefore, an increase in free carrier concentration produces an increase in photocurrent and a fast response.…”

Molecular Cocatalyst of p-Mercaptophenylboronic Acid Boosts the Plasmon-Mediated Reduction of p-Nitrothiophenol

“…Introducing cocatalysts is a widely used approach to improve the efficiency of many photochemical catalytic reactions. − Metal, oxide, and chalcogenide nanoparticles have already been used as cocatalysts for various metal and semiconductor catalysts. − Cocatalysts have also been introduced to enhance the catalytic performance in plasmonic photocatalysis. However, it is usually challenging to choose suitable cocatalysts, since their band structures need to match perfectly with that of plasmonic metals.…”

Controlling the Hierarchical Structures of Molybdenum Disulfide Nanomaterials via Self-Assembly of Supramolecular Polymers in Water

“…The fabrication of high-quality, few-layer TMDCs is of significant interest and importance to both fundamental studies and various potential applications. Therefore, the exfoliation of MoS 2 crystals into few/monolayer nanosheets represents a critical step toward achieving the high optical activity required for construction of high-performance devices. − Various physical and chemical synthesis methods have been developed to prepare few-layer MoS 2 nanosheets with valuable properties, such as chemical exfoliation through ion intercalation, thermal ablation, chemical vapor deposition on substrates, direct solvothermal synthesis, micromechanical cleavage, and liquid-phase exfoliation (LPE). − However, chemical exfoliation through ion intercalation can alter the crystal structure and thus destroy the semiconducting nature and affect the electrical and optoelectronic characteristics of MoS 2 nanosheets. Chemical vapor deposition, solvothermal synthesis, and micromechanical cleavage methods are high-energy, time-consuming processes and are thus unsuitable for fast, economical, large-scale production of few-layer MoS 2 nanosheets.…”