Dependence of reaction time in hydrothermal synthesis of MoS2 quantum dots: An investigation using optical tools and fractal analysis

The article discusses the novel fractal nature of hydrothermally synthesized Molybdenum Disulfide (MoS2) Quantum Dots (QDs), where the key parameter controlling the process is the 'reaction time'. This parameter is adjusted from 7 to 30 h, including five intermediate values, while keeping all other synthesis conditions constant. The study employs various structural, morphological, and optical techniques, including X-ray diffraction (XRD), X-ray photoelectron Spectroscopy (XPS), High-Resolution Transmission Electron Microscopy (HRTEM) equipped with Selected Area Electron Diffraction (SAED), Scanning Transmission Electron Microscopy (STEM), UV-Vis, and photoluminescence (PL) spectroscopy to track the evolution of MoS2 samples with changing reaction times. The average size of the QDs exhibits a trend of increase followed by a decrease with longer reaction times. This trend is also compared with band gap calculations. STEM images indicate that shorter reaction times lead to the formation of MoS2 sheets, while extended reaction times cause these sheets to fragment into MoS2 QDs. The concept of compactness in the system is explored and analyzed using fractal analysis, a statistical tool. The observations from PL, absorption, and STEM align with the time-evolved fractal dimensional analysis, demonstrating the synthesis dynamics.

Automated summary

This article discusses the novel fractal nature of hydrothermally synthesized MoS2 QDs. By adjusting the reaction time, the study found that the average size of QDs increases and then decreases with longer reaction times. STEM images indicate that shorter reaction times lead to sheet formation, while extended reaction times cause sheets to fragment into QDs.