ZnO nanostructures (including nano-plates and nano-rods (NRs)) are grown in various temperatures and Ar/O ₂ flow rates using thermal chemical vapor deposition, which affect the structure, nano-plate/NR population, and the quality of ZnO nanostructures. X-ray diffraction (XRD) attests that the peak intensity of the crystallographic plane (1 0 0) is correlated to nano-plate abundance. Moreover, optical properties elucidate that the population of nano-plates in samples strongly affect the band gap, binding energy of the exciton, and UV–visible (UV–vis) absorption and spectral luminescence emissions. In fact, the exciton binding energy reduces from ~100 to 80 meV when the population of nano-plates increases in samples. Photovoltaic characteristics based on the drop-casting on Si solar cells reveals three dominant factors, namely, the equivalent series resistance, decreasing reflectance, and down-shifting, in order to scale up the absolute efficiency by 3%. As a consequence, the oxygen vacancies in ZnO nanostructures give rise to the down-shifting and increase of free-carriers, leading to a reduction in the equivalent series resistance and an enlargement of fill factor. To obtain a larger I _sc , reduction of spectral reflectance is essential; however, the down-shifting process is shown to be dominant by lessening the surface electron-hole recombination rate over the UV–blue spectral range.

Water splitting is a promising pathway for hydrogen production, providing an environmentally friendly fuel source. More recently, great attention has been given to transition metal dichalcogenides (TMDCs) because of their interesting chemical and physical properties. In particular, tungsten disulfide (WS₂) has garnered significant attention as a catalyst for this application due to its unique layered 2D structure. In this study, few-layered WS₂ and phosphorus-doped WS₂ (WS₂/P) nanoflakes are synthesized on SiO₂/Si substrates as electrocatalysts for hydrogen evolution reactions (HER) in acidic conditions. Analyses of the synthesized WS₂ and WS₂/P films reveal that the few-layered WS₂ is of high quality, exhibiting continuity and uniformity. The presence of a strong peak in the photoluminescence spectrum confirms the mono/few layer nature of the synthesized samples. In additionally, scanning force microscopy in quantitative imaging mode reveals that the thinnest layers observed on the substrate have a height of 1.35 nm, indicating the presence of double-layer WS₂. The WS₂/P electrocatalyst demonstrates superior HER performance compared to pristine WS₂, showing a low overpotential of 245 mV at 10 mA.cm⁻² and a small Tafel slope of 123 mV.dec⁻¹. Furthermore, WS₂/P exhibits a greater electrochemical surface area and excellent catalytic stability under acidic conditions. Consequently, few layer phosphorus-doped WS₂ proves to be a highly suitable electrocatalyst for hydrogen production compared to the WS₂.

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.