When the size of the molybdenum disulfide (MoS₂) is reduced to a few nanometers, a distinctive photoluminescence is observed due to the strong effect of quantum confinement. In this study, we fabricated MoS₂ quantum dots (QDs) using a simple and green process. We dissolved the powder of MoS₂ in various solvents, including N-Methyl-2-pyrrolidone (NMP), ethanol (EtOH), and deionized water (DIW), and dispersed it by sonication or solvent-thermal exfoliation. The synthesized MoS₂ QDs were characterized for their optical properties. Transmission electron microscopy (TEM) was used to analyze the particle size and morphology; UV-visible spectrometer and photoluminescence tests were employed to measure optical absorption, bandgaps, and optical emission. The photothermal test was designed for the evaluation of the optothermal conversion. In vitro cultures of 3T3 fibroblast cells were evaluated for the biocompatibility of the MoS₂ QDs. Results from different experiments were cross-examined and analyzed to understand the relation among different syntheses, microstructures, and optical properties of MoS₂ QDs. A yield of 15% MoS₂ QDs was obtained when synthesized in ethanol by thermal exfoliation. They also showed satisfactory optothermal effects.

The transition metal dichalcogenides (MX₂, TMD) are a family of two-dimensional compounds, and MoS₂ is perhaps the most representative material among them. MoS₂, in its bulk form, is semiconductive, with an indirect band gap of around 1.2–1.3 eV. Monolayer MoS₂, nevertheless, exhibits a direct band gap of 1.8–1.9 eV. For zero-dimensional MoS₂ (quantum dots), the band gap would be even wider. These changes are mainly due to quantized energy levels arising from geometric confinement. Quantum effects directly yield distinct optoelectronic properties, such as photoluminescence, which are absent in the material’s bulk form. In this study, we developed an economical, scalable one-pot synthesis of MoS₂ nanoparticles at atmospheric pressure, eliminating the need for high-pressure autoclaves commonly employed in hydrothermal synthesis at around 150–270 °C. This one-pot synthesis was tested by two exfoliation methods—ultrasonication and thermal heating at 80 °C in three solvents: ethanol, deionized water, and N-methyl-2-pyrrolidone. Our focus is on the empirical study of nanoparticles’ photoluminescence and photothermal effects. The material characterization includes transmission electron microscopy for morphology and crystal structure, X-ray photoelectron spectroscopy for chemical bonding energies, and a UV–visible–NIR spectrometer for optical absorption. Photoluminescent spectroscopy of the nanoparticles was assessed using laser excitation between 300 and 400 nm, and photothermal effects were measured as temperature variations in DI water under continuous irradiation by an 808 nm laser. Results show that MoS₂ nanoparticles synthesized in ethanol exhibit an additional broad optical absorption in the red–infrared range, in addition to the usual high absorption in the UV–blue range. This photothermal absorption would raise the temperature of DI water to 50 °C in 300 s. A simplified numerical analysis by finite elements was also carried out as a numerical confirmation of the photothermal test. On the cell biological side, both in vitro cultures with NIH/3T3 fibroblasts and antibacterial against E. coli show that critical tolerance of MoS₂ is no more than 0.25 mg/mL in the media.