Structure and Properties of Single-Layer MoS₂ for Nano-Photoelectric Devices

Molybdenum disulfide (MoS2)-based nanostructures for tissue engineering applications: prospects and challenges

Molybdenum disulfide (MoS₂) nanostructures have recently earned substantial thoughts from the scientific communities owing to their unique physicochemical, optical and electrical properties. Although MoS₂ has been mostly highlighted for its industrial applications, its biological applicability has not been extensively explored. The introduction of nanotechnology in the field of tissue engineering has significantly contributed to human welfare by displaying advancement in tissue regeneration. Assimilation of MoS₂ nanostructures into the polymer matrix has been considered a persuasive material of choice for futuristic tissue engineering applications. The current review provides a general discussion on the structural properties of different MoS₂ nanostructures. Further, this article focuses on the interactions of MoS₂ with biological systems in terms of its cellular toxicity, and biocompatibility along with its capability for cell proliferation, adhesion, and immunomodulation. The article continues to confer the utility of MoS₂ nanostructure-based scaffolds for various tissue engineering applications. The article also highlights some emerging prospects and possibilities of the applicability of MoS₂-based nanostructures in large organ tissue engineering. Finally, the article concludes with a brief annotation on the challenges and limitations that need to be overcome in order to make plentiful use of this wonderful material for tissue engineering applications.

Simultaneous Enhancement of Charge Separation and Hole Transportation in a W:α-Fe2O3/MoS2 Photoanode: A Collaborative Approach of MoS2 as a Heterojunction and W as a Metal Dopant

In this study, a facile approach has been successfully applied to synthesize a W-doped Fe₂O₃/MoS₂ core-shell electrode with unique nanostructure modifications for photoelectrochemical performance. A two-dimensional (2D) structure of molybdenum disulfide (MoS₂) and tungsten (W)-doped hematite (W:α-Fe₂O₃) overcomes the drawbacks of the α-Fe₂O₃ and MoS₂ semiconductor through simple and facile processes to improve the photoelectrochemical (PEC) performance. The highest photocurrent density of the 0.5W:α-Fe₂O₃/MoS₂ photoanode is 1.83 mA·cm^-2 at 1.23 V vs reversible hydrogen electrode (RHE) under 100 mW·cm² illumination, which is higher than those of 0.5W:α-Fe₂O₃ and pure α-Fe₂O₃ electrodes. The overall water splitting was evaluated by measuring the H₂ and O₂ evolution, which after 2 h of irradiation for 0.5W:α-Fe₂O₃/MoS₂ was determined to be 49 and 23.8 μmol.cm^-2, respectively. The optimized combination of the heterojunction and metal doping on pure α-Fe₂O₃ (0.5W:α-Fe₂O₃/MoS₂ photoanode) showed an incident photon-to-electron conversion efficiency (IPCE) of 37% and an applied bias photon-to-current efficiency (ABPE) of 26%, which are around 5.2 and 13 times higher than those of 0.5W:α-Fe₂O₃, respectively. Moreover, the facile fabrication strategy can be easily extended to design other oxide/carbon-sulfide/oxide core-shell materials for extensive applications.

2D Semiconductor Nanomaterials and Heterostructures: Controlled Synthesis and Functional Applications

Two-dimensional (2D) semiconductors beyond graphene represent the thinnest stable known nanomaterials. Rapid growth of their family and applications during the last decade of the twenty-first century have brought unprecedented opportunities to the advanced nano- and opto-electronic technologies. In this article, we review the latest progress in findings on the developed 2D nanomaterials. Advanced synthesis techniques of these 2D nanomaterials and heterostructures were summarized and their novel applications were discussed. The fabrication techniques include the state-of-the-art developments of the vapor-phase-based deposition methods and novel van der Waals (vdW) exfoliation approaches for fabrication both amorphous and crystalline 2D nanomaterials with a particular focus on the chemical vapor deposition (CVD), atomic layer deposition (ALD) of 2D semiconductors and their heterostructures as well as on vdW exfoliation of 2D surface oxide films of liquid metals.

A mechanism for the variation in the photoelectric performance of a photodetector based on CVD-grown 2D MoS2

Two-dimensional transition-metal dichalcogenides are considered as promising candidates for next-generation flexible nanoelectronics owing to their compelling properties. The photoelectric performance of a photodetector based on CVD-grown 2D MoS₂ was studied. It is found that annealing treatment can make the photoresponsivity and specific detectivity of the CVD-grown 2D MoS₂ based photodetector increase from 0.1722 A W^-1 and 10^14.65 Jones to 0.2907 A W^-1 and 10^14.84 Jones, respectively, while vulcanization can make the rise response time and fall response time decrease from 0.9013 s and 2.173 s to 0.07779 s and 0.08616 s, respectively. A method to determine the O-doping concentration in the CVD-grown 2D MoS₂ has been obtained. The criterion for the CVD-grown 2D MoS₂ to transition from an oxygen-doped state to a pure state has been developed. A mechanism explaining the variation in the photoelectric performance of the CVD-grown 2D MoS₂ has been proposed. The CVD-grown 2D MoS₂ and the annealed CVD-grown 2D MoS₂ are oxygen-doped MoS₂ while the vulcanized CVD-grown 2D MoS₂ is pure MoS₂. The variation in the photoelectric performance of CVD-grown 2D MoS₂ results from differences in the O-doping concentration and the bandgap.

Fate assessment of commercial 2D MoS2 aqueous dispersions at physicochemical and toxicological level

The physicochemical properties and the toxicological potential of commercially available MoS₂ nanoparticles with different lateral size and degradation stage were studied in the present research work. To achieve this, the structure and stoichiometry of fresh and old aqueous suspensions of micro-MoS₂ and nano-MoS₂ was analyzed by Raman, while x-ray photoelectron spectroscopy allowed to identify more quantitatively the nature of the formed oxidized species. A, the toxicological impact of the nanomaterials under analysis was studied using adenocarcinomic human alveolar basal epithelial cells (A549 cells) and the unicellular fungus S. cerevisiae as biological models. Cell viability assays and reactive oxygen species (ROS) determinations demonstrated different toxicity levels depending on the cellular model used and in function of the degradation state of the selected commercial nanoproducts. Both MoS₂ nanoparticle types induced sublethal damage on the A549 cells though the increase of intracellular ROS levels, while comparable concentrations reduced the viability of yeast cells. In addition, the old MoS₂ nanoparticles suspensions exhibited a higher toxicity for both human and yeast cells than the fresh ones. Our findings demonstrate that the fate assessment of nanomaterials is a critical aspect to increase the understanding on their characteristics and on their potential impact on biological systems along their life cycle.

Formation of Highly Ordered Self-Assembled Monolayers on Two-Dimensional Materials via Noncovalent Functionalization

Functionalized two-dimensional materials (2DMs) are attracting much attention due to their promising applications in nanoscale devices. Producing continuous and homogeneous surface assemblies with a high degree of order has been challenging. In this work, we demonstrate that by noncovalently self-assembling molecular platforms on 2DMs, high-quality and highly ordered monolayers can be generated. The high degree of order and uniformity of the self-assembled monolayer layers were confirmed by a variety of analytic techniques including time-of-flight secondary ion mass spectrometry, scanning tunnelling microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. Furthermore, by selectively enhancing the molecular vibrations of the molecular platform, via a combination of graphene-enhanced Raman spectroscopy (GERS) and surface-enhanced Raman spectroscopy (SERS), we were able to determine the orientation of self-assembled molecular platforms with respect to the surface normal. The selective enhancement of the vibrational modes occurs by taking advantage of the distance dependence of the Raman enhancement either by the graphene surface (GERS) or the silver nanoparticules (SERS) that are located on top of the self-assembled monolayer.