In this study, MoS ₂ nanoflakes were directly grown on different substrates—Si/SiO ₂ and quartz—by one-step thermal chemical vapor deposition using MoO ₃ and sulfide powders as precursors. Scanning electron microscopy and x-ray diffraction patterns demonstrated the formation of MoS ₂ structures on both substrates. Moreover, UV-visible and photoluminescence analysis confirmed the formation of MoS ₂ few-layer structures. According to Raman spectroscopy, by assessment of the line width and frequency shift differences between the and A _1g , it was inferred that the MoS ₂ grown on the silicon substrate was monolayer and that grown on the quartz substrate was multilayer. In addition, open-aperture and close-aperture Z -scan techniques were employed to study the nonlinear optical properties including nonlinear absorption and nonlinear refraction of the grown MoS ₂ . All experiments were performed using a diode laser with a wavelength of 532 nm as the light source. It is noticeable that both samples demonstrate obvious self-defocusing behavior. The monolayer MoS ₂ grown on the silicon substrate displayed considerable two-photon absorption while, the multilayer MoS ₂ synthesized on the quartz exhibited saturable absorption. In general, few-layered MoS ₂ would be useful for the development of nanophotonic devices like optical limiters, optical switchers, etc.

Here, nitrogen doped molybdenum disulfide quantum dots (N-MoS₂ QDs) are fabricated by making use of the pulsed laser ablation (PLA) process in liquid nitrogen (LN₂) as a dopant agent. In fact, LN₂ contributes the rapid condensation of the plasma plume to form MoS₂ QDs, optimizing the conditions for the synthesis of N-doped MoS₂ with p-type property. The structural/optical features of the synthesized products are studied using transmission electron microscopy (TEM), absorption spectroscopy, photoluminescence (PL) spectroscopy techniques, and X-ray photoelectron spectroscopy (XPS). The TEM image shows the creation of MoS₂ QDs with 5.5 nm average size. UV-vis and PL spectroscopy confirm the formation of N-MoS₂ QDs according to the dominant peaks. The Tuck plot gives a direct band-gap of 4.34 eV for MoS₂ QDs. Furthermore, XPS spectroscopy reveals Mo-N bonding, indicating nitrogen doping as evidence of p-type MoS₂ QDs. Thus, PLA provides a single-stage way to the clean and green synthesis of the MoS₂ QDs suspension without a need for high vacuum devices and additional chemical components. Regarding the pristine MoS₂, the N-MoS₂ QDs benefit from a low overpotential of −0.35 V at −10 mA/cm² per µg alongside a low Tafel slope of 300 mV/dec. Subsequently, the lower R_ct value of N-MoS₂ QDs verifies the enhancement of the charge transfer kinetics mainly due to the elevated electronic conductivity. Furthermore, the quasi-rectangular cyclic voltammetry (CV) as well as the larger current window demonstrate a notable electrocatalytic activity. The former is based on the enhanced active sites in favor of N-MoS₂ QDs against other samples of interest. Thereby, it is discovered that the N-doped MoS₂ QD acts as an effective catalyst to notably improve the performance of the hydrogen evolution reaction (HER).

Multi-walled carbon nanotubes were synthesized using a Fe-Ni bimetallic catalyst supported by MgO using thermal chemical vapor deposition. Purification processes to remove unwanted carbon structures and other metallic impurities were carried out by boiling in sulfuric acid solution. Various analytical techniques such as TGA/DSC, Raman spectroscopy, SEM, HRTEM and EDAX were employed to investigate the morphology, graphitization and quality of the carbon nanotubes. The obtained results reveal the molarity of sulfuric acid and immersed time of the carbon nanotubes in the acid solution is very effective at purifying multi-walled carbon nanotubes. It was also found that 5 M concentration of boiling sulfuric acid for a 3 h treatment duration led to the highest removal of the impurities with the least destructive effect. Moreover, it was observed that acid treatment results in decreasing of CNTs’ diameter.