Preparation of Monolayer MoS2 Quantum Dots using Temporally Shaped Femtosecond Laser Ablation of Bulk MoS2 Targets in Water

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.

Controllable Synthesis of Nanosized Amorphous MoSx Using Temporally Shaped Femtosecond Laser for Highly Efficient Electrochemical Hydrogen Production

“…As shown in Figure , the as‐prepared a‐MoS x materials homogeneously dispersed with little aggregation, which is beneficial to the expression of active sites. Besides, as the pulse energy of the femtosecond laser two‐subpulse train is increased from 200 to 300 mW, there are little differences in the size and morphology of the as‐prepared a‐MoS x (Figure b,d,f), which are all variously sized from ≈5 to 20 nm and thus proving the effectiveness of the size control for femtosecond laser. By contrast, as displayed in Figure S2 (Supporting Information), a‐MoS x ‐300/0 exhibited a different size distribution and morphology compared with the materials prepared using the two‐subpulse train of the femtosecond laser.…”

“…By contrast, as displayed in Figure S2 (Supporting Information), a‐MoS x ‐300/0 exhibited a different size distribution and morphology compared with the materials prepared using the two‐subpulse train of the femtosecond laser. The a‐MoS x ‐300/0 materials exhibited a chain structure with aggregation and had a wide size distribution of 10–50 nm . These results indicate that using temporally shaped femtosecond laser two‐subpulse train may cause the processing mechanism of the laser irradiation of ATTM to change from photothermal‐induced to photoinduced reduction/oxidation, which contributes to a narrow size distribution with limited aggregation .…”

“…Whereas, the interval between the two conventional single pulses has a microsecond time scale (the repetition rate of the laser system is 1 kHz), which is considerably larger than the aforementioned characteristic time scale. However, because the second subpulse with a 10 ps time delay (smaller than the aforementioned characteristic time scale) continuously irradiates, the production of solvated electrons through ionization can be enhanced, which contributes to the domination of the photoinduced reduction/oxidation mechanism in the preparation process . Furthermore, the ratios of the Mo V defect species, bridging S 2 2− ligands, and terminal S 2 2− ligands can be optimized through laser‐induced electrons transfer of the a‐MoS x materials …”

“…Generally, many methods have been applied to improve the catalytic activity of the c‐MoS 2 . For example, various strategies have been explored to increase the exposure number of active edges by producing different MoS 2 ‐based nanostructures, such as nanoparticles, nanodots, nanoflowers, and quantum dots . Different techniques have been adopted to activate the basal planes of the c‐MoS 2 by engineering defects or generating sulfur vacancies .…”

Doping‐Assisted Phase Changing Effect on MoS2 Towards Hydrogen Evolution Reaction in Acidic and Alkaline pH

“…These four characteristic absorption peaks were absent in both the hybrid phase (NMS1 and NMS2) due to the formation of metallic phase along with the 2H phase. Only a single peak at near UV region (represented by a dotted line) was observed for both NMS1 and NMS2 at less than 300 nm region . This peak was attributed to the excitonic behavior of 1T@2H hybrid phase composition.…”