Abstract
Zero-dimensional MoS2 quantum dots (QDs) possess distinct physical and chemical properties, which have garnered them considerable attention and facilitates their use in a broad range of applications. In this study, we prepared monolayer MoS2 QDs using temporally shaped femtosecond laser ablation of bulk MoS2 targets in water. The morphology, crystal structures, chemical, and optical properties of the MoS2 QDs were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption spectra, and photoluminescence spectra. The analysis results show that highly pure, uniform, and monolayer MoS2 QDs can be successfully prepared. Moreover, by temporally shaping a conventional single pulse into a two-subpulse train, the production rate of MoS2 nanomaterials (including nanosheets, nanoparticles, and QDs) and the ratio of small size MoS2 QDs can be substantially improved. The underlying mechanism is a combination of multilevel photoexfoliation of monolayer MoS2 and water photoionization–enhanced light absorption. The as-prepared MoS2 QDs exhibit excellent electrocatalytic activity for hydrogen evolution reactions because of the abundant active edge sites, high specific surface area, and excellent electrical conductivity. Thus, this study provides a simple and green alternative strategy for the preparation of monolayer QDs of transition metal dichalcogenides or other layered materials.
Highlights
Is, the more stable the quantum size confinement effects and the stronger the PL properties of the QDs are
The experimental setup for the temporally shaped femtosecond laser ablation is shown in Supplementary Figure S1, wherein a conventional femtosecond pulse is temporally shaped into two subpulses with time delays ranging from 0 to 10 ps
While in the case of femtosecond laser single pulse ablation of bulk MoS2 targets in water, the laser pulse has a total fluence of 0.77 J cm−2, which is much greater than the ablation threshold of bulk MoS2
Summary
Is, the more stable the quantum size confinement effects and the stronger the PL properties of the QDs are. Several strategies for preparing MoS2 QDs have been proposed, including sonication combined with solvothermal treatment synthesis[18], lithium intercalation[19], liquid exfoliation in organic solvents[20], hydrothermal synthesis[21], electrochemical etching[22], electro-Fenton reaction processing[23], and grinding exfoliation[9] These methods all have their own advantages; for example, liquid exfoliation can provide a high yield of MoS2 QDs, chemical intercalation can yield 1T-phase MoS2 QDs with excellent HERs catalytic reactivity, and one-pot hydrothermal synthesis can yield heterostructures in a single step. The temporally shaped femtosecond laser has the potential to be a fast, uniform, green, and alternative strategy to facilely and efficiently prepare QDs of TMDs or other layered materials for abroad applications in biomedical, optical imaging, energy storage, and catalysis areas
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