In the surge of recent successes of 2D materials following the rise of graphene, molybdenum disulfide (2D-MoS₂) has been attracting growing attention from both fundamental and applications viewpoints, owing to the combination of its unique nanoscale properties. For instance, the bandgap of 2D-MoS₂, which changes from direct (in the bulk form) to indirect for ultrathin films (few layers), offers new prospects for various applications in optoelectronics. In this review, we present the latest scientific advances in the field of synthesis and characterization of 2D-MoS₂ films while highlighting some of their applications in energy harvesting, gas sensing, and plasmonic devices. A survey of the physical and chemical processing routes of 2D-MoS₂ is presented first, followed by a detailed description and listing of the most relevant characterization techniques used to study the MoS₂ nanomaterial as well as theoretical simulations of its interesting optical properties. Finally, the challenges related to the synthesis of high quality and fairly controllable MoS₂ thin films are discussed along with their integration into novel functional devices.

A chemically vapor deposited MoS₂ nanosheets (NSs) is aged in the laboratory at ambient and at 40% average humidity for ~36 months. Nanorods of few microns in length and few nanometers in diameter are found to grow from the MoS₂ seeds. They have been growing as a result of the chemical reaction between the MoS₂ NSs and ambient O₂ and moisture, they exhibit an amorphous phase structure in the stoichiometric form of MoO₃. Density functional theory simulations further reveal the role of H₂O and O₂ in the transformation of the MoS₂ NSs. The adsorption energy of O₂ molecules on the MoS₂ sites is E_ad = −1.09 eV as compared to lowest absolute E_ad = −0.10 eV of H₂O indicating the favorable adsorption of O₂ and subsequent Mo oxidation. This study provides valuable insight into the aging phenomenon of MoS₂ exposed to O₂ and moisture which might limit their application.

We report on the investigation of graphitic carbon nitride (g-C₃N₄) for carbon dioxide (CO₂) sensor applications. g-C₃N₄ is prepared by the thermal polycondensation of thiourea and sprayed onto a substrate with interdigitated electrodes. The resulting sensor device exhibited a high sensitivity to CO₂ molecules of ~200 ppm, a high responsivity of ~730 ms at 40 °C and a full recovery time of 36 s. Furthermore, a set of various characterization measurements demonstrated the excellent stability of both the g-C₃N₄ nanosheets and the fabricated gas sensor device. Meanwhile, density functional theory (DFT) calculations for the bulk and monolayer models, based on tri-s-triazine, revealed the optoelectronic properties of g-C₃N₄ and the interaction energy with CO₂, which is evaluated at −0.59 eV. This value indicates the very good affinity of g-C₃N₄ nanosheets to CO₂ molecules. Our findings shed light on the potential for g-C₃N₄ to be used for the development of high-performing gas sensor devices.

Layered transition metals dichalcogenides such as MoS₂ and WS₂ have shown a tunable bandgap, making them highly desirable for optoelectronic applications. Here, we report on one-step chemical vapor deposited MoS₂, WS₂ and Mo_xW_1-xS₂ heterostructures incorporated into photoconductive devices to be examined and compared in view of their use as potential photodetectors. Vertically aligned MoS₂ nanosheets and horizontally stacked WS₂ layers, and their heterostructure form Mo_xW_1-xS₂, exhibit direct and indirect bandgap, respectively. To analyze these structures, various characterization methods were used to elucidate their properties including Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectrometry and high-resolution transmission electron microscopy. While all the investigated samples show a photoresponse in a broad wavelength range between 400 nm and 700 nm, the vertical MoS₂ nanosheets sample exhibits the highest performances at a low bias voltage of 5 V. Our findings demonstrate a responsivity and a specific detectivity of 47.4 mA W⁻¹ and 1.4 × 10¹¹ Jones, respectively, achieved by Mo_xW_1-xS₂. This study offers insights into the use of a facile elaboration technique for tuning the performance of Mo_xW_1-xS₂ heterostructure-based photodetectors.

Tungsten disulfide nanosheets were successfully prepared by one-step chemical vapor deposition using tungsten oxide and thiourea in an inert gas environment. The size of the obtained nanosheets was subsequently reduced down to below 20 nm in width and 150 nm in length using high-energy ball milling, followed by 0.5 and 1 wt% graphene loading. The corresponding vibrational and structural characterizations are consistent with the fabrication of a pure WS₂ structure for neat sampling and the presence of the graphene characteristic vibration modes in graphene@WS₂ compounds. Additional morphological and crystal structures were examined and confirmed by high-resolution electron microscopy. Subsequently, the investigations of the optical properties evidenced the high optical absorption (98%) and lower band gap (1.75 eV) for the graphene@WS₂ compared to the other samples, with good band-edge alignment to water-splitting reaction. In addition, the photoelectrochemical measurements revealed that the graphene@WS₂ (1 wt%) exhibits an excellent photocurrent density (95 μA/cm² at 1.23 V bias) compared with RHE and higher applied bias potential efficiency under standard simulated solar illumination AM1.5G. Precisely, graphene@WS₂ (1 wt%) exhibits 3.3 times higher performance compared to pristine WS₂ and higher charge transfer ability, as measured by electrical impedance spectroscopy, suggesting its potential use as an efficient photoanode for hydrogen evolution reaction.