Cost-Effective and Highly Efficient Manganese-Doped MoS2 Nanosheets as Visible-Light-Driven Photocatalysts for Wastewater Treatment.

One of the main objectives in wastewater treatment and sustainable energy production is to find photocatalysts that are favorably efficient and cost-effective. Transition-metal dichalcogenides (TMDs) are promising photocatalytic materials; out of all, MoS2 is extensively studied as a cocatalyst in the TMD library due to its exceptional photocatalytic activity for the degradation of organic dyes due to its distinctive morphology, adequate optical absorption, and rich active sites. However, sulfur ions on the active edges facilitate the catalytic activity of MoS2. On the basal planes, sulfur ions are catalytically inactive. Injecting metal atoms into the MoS2 lattice is a handy approach for triggering the surface of the basal planes and enriching catalytically active sites. Effective band gap engineering, sulfur edges, and improved optical absorption of Mn-doped MoS2 nanostructures are promising for improving their charge separation and photostimulated dye degradation activity. The percentage of dye degradation of MB under visible-light irradiations was found to be 89.87 and 100% for pristine and 20% Mn-doped MoS2 in 150 and 90 min, respectively. However, the degradation of MB dye was increased when the doping concentration in MoS2 increased from 5 to 20%. The kinetic study showed that the first-order kinetic model described the photodegradation mechanism well. After four cycles, the 20% Mn-doped MoS2 catalysts maintained comparable catalytic efficacy, indicating its excellent stability. The results demonstrated that the Mn-doped MoS2 nanostructures exhibit exceptional visible-light-driven photocatalytic activity and could perform well as a catalyst for industrial wastewater treatment.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor.

To improve the production rate of MoS2 nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS2-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS2 nanosheets on a large scale. Then, the MnO2 nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS2 nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS2 nanosheets and MnO2 nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS2 nanosheets and MnO2 nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS2 nanosheets and MnO2 nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m2/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.

Cost-effective synthesis of 2D molybdenum disulfide (MoS2) nanocrystals: An exploration of the influence on cellular uptake, cytotoxicity, and bio-imaging.

Ultrasmall MoS2 nanocrystals have unique optoelectronic and catalytic properties that have acquired significant attraction in many areas. We propose here a simple and economical method for synthesizing the luminescent nanocrystals MoS2 using the hydrothermal technique. In addition, the synthesized MoS2 nanocrystals display photoluminescence that is tunable according to size. MoS2 nanocrystals have many advantages, such as stable dispersion, low toxicity and luminescent characteristics, offering their encouraging applicability in biomedical disciplines. In this study, human lung cancer epithelial cells (A549) are used to assess fluorescence imaging of MoS2 nanocrystals. MTT assay, trypan blue assay, flow cytometry and fluorescence imaging results have shown that MoS2 nanocrystals can selectively target and destroy lung cancer cells, especially drug-resistant cells (A549).

Edge Rich Ultrathin Layered MoS2 Nanostructures for Superior Visible Light Photocatalytic Activity.

Nanostructures of layered 2D materials have been proven one of the significant recent trends for visible-light-driven photocatalysis because of their unique morphology, effective optical adsorption, and rich active sites. Herein, we synthesized ultrathin-layered MoS2 nanoflowers and nanosheets with rich active sites by using a facile hydrothermal technique. The photocatalytic performance of the as-synthesized MoS2 nanoflowers (NF) and nanosheets (NS) were investigated for the photodegradation of MB (methylene blue), MG (malachite Green), and RhB (rhodamine B) dye under visible light irradiations. Ultrathin-layered nanoflowers showed faster degradation (96% in 150 min) in RhB under visible light irradiation, probably due to a large number of active sites and high available surface area. The kinetic study demonstrated that the first-order kinetic model best explained the process of photodegradation. The MoS2 nanoflowers catalysts has similar catalytic performance after four consecutive cyclic performances, demonstrating their good stability. The results showed that the MoS2 nanoflowers have outstanding visible-light-driven photocatalytic activity and could be an effective catalyst for industrial wastewater treatment.

Cost effective liquid phase exfoliation of MoS2 nanosheets and photocatalytic activity for wastewater treatment enforced by visible light.

Scalable production of high-quality MoS2 nanosheets remains challenging for industrial applications and research in basic sciences. N-methyl-2pyrrolidine (NMP) is a commonly used solvent for exfoliation of MoS2 nanosheets having further disadvantage of slow volatility rate. The present study demonstrates a cost-effective facile chemical route to synthesize few-layer MoS2 nanosheets using acetone as a solvent and by varying bulk initial concentration of samples to scale up the production in large scale to fulfill the demand for potential applications. In our study, we aim to obtain stable growth of high quality few layer MoS2 nanosheets by long sonication times. Optical absorption spectra, Raman spectra, size of nanosheets and layer thickness of as-grown MoS2 nanosheets were found to be matching with those obtained from other synthesis methods. Effective photocatalytic performance of MoS2 nanosheets without being consumed as a reactant was experimented by decomposing Methylene Blue dye in aqueous solution under irradiation of visible light. This study provides an idea to synthesize low-cost, sustainable and efficient photocatalytic material in large scale for the next generation to control water pollution quite efficiently by protecting the environment from the contamination coming from these dyes.

Retracted Article: Physics of excitons and their transport in two dimensional transition metal dichalcogenide semiconductors.

Two-dimensional (2D) group-VI transition metal dichalcogenide (TMD) semiconductors, such as MoS2, MoSe2, WS2 and others manifest strong light matter coupling and exhibit direct band gaps which lie in the visible and infrared spectral regimes. These properties make them potentially interesting candidates for applications in optics and optoelectronics. The excitons found in these materials are tightly bound and dominate the optical response, even at room temperatures. Large binding energies and unique exciton fine structure make these materials an ideal platform to study exciton behaviors in two-dimensional systems. This review article mainly focuses on studies of mechanisms that control dynamics of excitons in 2D systems - an area where there remains a lack of consensus in spite of extensive research. Firstly, we focus on the kinetics of dark and bright excitons based on a rate equation model and discuss on the role of previous 'unsuspected' dark excitons in controlling valley polarization. Intrinsically, dark and bright exciton energy splitting plays a key role in modulating the dynamics. In the second part, we review the excitation energy-dependent possible characteristic relaxation pathways of photoexcited carriers in monolayer and bilayer systems. In the third part, we review the extrinsic factors, in particular the defects that are so prevalent in single layer TMDs, affecting exciton dynamics, transport and non-radiative recombination such as exciton-exciton annihilation. Lastly, the optical response due to pump-induced changes in TMD monolayers have been reviewed using femtosecond pump-probe spectroscopy which facilitates the analysis of underlying physical process just after the excitation.