Nitrogen (N)-doped graphene with different atomic percentages (2.3–4.7 at%) of N has been synthesized by thermal annealing of reduced graphene oxide (RGO) in ammonia gas for different times. The effects of annealing time on the structure, electrical and optical properties of N-doped graphene have been systematically investigated by using various analytical techniques. XPS, FTIR, Raman, and XRD studies show that there is a gradual structural change in N-doped graphene sheets with increasing annealing time, resulting from the increase of carbon and simultaneous decrease of oxygen and N contents. High resolution N1s spectra reveal that the pyridine-N and pyrrolic-N contents decrease with increasing annealing time, whereas the amount of quaternary-N increases. Importantly, it has been found that the annealing time caused significant changes in both the electrical and the optical properties of N-doped graphene. The electrical resistance of N-doped graphene is greatly reduced compared to that of GO and RGO, and found to further decrease with increasing annealing time, possibly due to the increase of sp² carbon networks and decrease of oxygen content as well as defects associated with the incorporation of N. The room-temperature photoluminescence (PL) properties of graphene oxide (GO), RGO and N-doped graphene were systematically studied with regard to the annealing time. The results showed that the PL spectrum of GO exhibits a peak emission maximum at around 700 nm, while that of RGO is found to be strongly blue-shifted with two distinct emission peaks: green emission at 485–500 nm and blue emission at 420–428 nm. For N-doped graphene samples, the blue emission intensity could significantly be enhanced by controlling the annealing time, which leads to a promising blue and green light-emitting material with controllable optical properties.

A simple and efficient method to enhance the quaternary nitrogen doping (N-doping) of graphene has been demonstrated. Recent studies have shown that quaternary N in the graphene network provides more efficient electrocatalytic activity. Therefore, a novel strategy to enhance the quaternary N-doping is currently in high demand. The strategy employed in this work was to modify graphene oxide (GO) prior to thermal annealing so as to provide a more efficient structure for quaternary N doping. GO was first chemically reduced with hydrazine to substantially increase the formation of CC bonds and simultaneously decrease the atomic oxygen concentration. The reduced graphene oxide (RGO) was then annealed in the presence of NH₃ . Although N-doping via the replacement of oxygen is preferred, the probability of carbon being substituted with N dopants in the graphitic structure of RGO could increase due to the relatively higher content of CC when compared to the atomic oxygen concentration. In addition, due to the decreased atomic oxygen concentration, the electro-conductivity was enhanced. Cyclic voltammograms (CVs) of 5 mM K₃Fe(CN)₆ and 2 mM H₂O₂ were used to examine the electrochemical response of the quaternary N-maximized RGO. An improvement in electrocatalytic reduction and a higher electro-conductivity were confirmed based on an analysis of the obtained CVs.

In this study, molybdenum disulfide (MoS₂) nanostructures were synthesized by a facile hydrothermal process, using ammonium heptamolybdate tetrahydrate ((NH₄)₆Mo₇O₂₄.4H₂O) and thiourea (CH₄N₂S) as the reactants. The effects of experimental parameters including reaction temperatures and reaction times on the structure and morphology of MoS₂ have primarily been investigated. The morphology, microstructure, chemical composition and optical properties of as‐synthesized MoS₂ were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), Raman and Photoluminescence spectroscopy. The FESEM and TEM results indicate that depending on the reaction temperature, the three types of morphologies of MoS₂ crystals could be obtained. Morphologies of MoS₂ changed gradually from aggregated particles to flake‐like structure, then finally to nanosheet morphology with increasing reaction temperature from 160 to 220 ^oC. However, it was found that the reaction time contributed significantly to the restacking and refinement of MoS₂ crystal structure, rather than affecting the morphology of the investigated samples. Both XRD and Raman investigations reveal that the as‐synthesized MoS₂ has a hexagonal phase structure (2H‐MoS₂). Interestingly, the as‐prepared MoS₂ nanosheets exhibit photoluminescence in the visible range with the emitted photon energy of ~1.81 and ~1.95 eV, these properties make MoS₂ a promising candidate as the material of choice for next‐generation optoelectronic and photonic devices.