As-prepared MoS2 Research Articles

Enhanced Triethylamine Detection at Room Temperature Using a Layered MoS2 Nanosheet-Coated PPy Nanorod: A Comprehensive Study.

The rapid and reliable detection of triethylamine (TEA), a toxic, explosive, volatile organic compound at room temperature, is highly significant for food safety, environmental, and human health monitoring. This manuscript reports a layered molybdenum disulfide (MoS2) nanosheet-coated polypyrrole (PPy) nanorod-based heterostructure sensor (MsPy) which offers superior sensing properties toward TEA at room temperature (25 °C). Herein, different MsPy nanocomposites were synthesized, followed by a controlled sulfidation reaction through dissolution, diffusion, and regrowth mechanisms. Optimizing the ratio of the precursor of molybdenum trioxide (MoO3/PPy) is crucial for achieving effective deposition of a layered MoS2 nanosheet on the PPy surface. The as-prepared MoS2 nanosheet-coated PPy sensor (MsPy_40) enables one to selectively detect trace TEA vapor at 25 °C with a detection lower limit of 0.5 ppm. The MsPy_40 sensor exhibits 17 times higher response than the pristine MoS2 nanosheet to 50 ppm TEA, with rapid response (∼3.9 s) and recovery (∼19.6 s), along with better stability, good selectivity, and remarkable repeatability. The significantly enhanced sensing performance is attributed to the unique surface morphology of the layered MoS2 nanosheet-coated PPy nanorod and the formation of a p-n heterojunction between PPy and MoS2.

Fluorescent Molybdenum Disulfide Quantum Dots for Sensitive Detecting Curcumin in Food Samples through FRET Mechanism.

A selective and sensitive fluorometric assay was developed for specific determination of curcumin (Cur) based on fluorescence resonance energy transfer (FRET) between molybdenum disulfide quantum dots (MoS2 QDs) and Cur. The MoS2 QDs were prepared via a one-step hydrothermal protocol using sodium molybdate dihydrate, L-cysteine (Cys) as precursors, and sodium cholate (SC) as a modification agent. The as-prepared MoS2 QDs possessed maximum fluorescence emission at 460nm with a 20% of fluorescence quantum yield (FQY). It was found that the fluorescence of MoS2 QDs could be quantitatively quenched by Cur through FRET mechanism. Therefore, Cur could be detected in the range of 0.1-20µg mL- 1 with a detection limit of 5 ng mL- 1. Additionally, the developed MoS2 QDs based fluorescent assay has been successfully applied for real food sample analysis with satisfactory results.

Facile and efficient preparation of hemicellulose-assisted MoS2 nanosheets via green liquid-phase exfoliation method

A facile, environmental-friendly and efficient exfoliation process has been reported to produce MoS2 nanosheets at room temperature via liquid-phase exfoliation method using hemicellulose as an assistant in aqueous solution. It is found that bulk MoS2 has been successfully exfoliated into few-layered MoS2 nanosheets. The non-polar sites of hemicellulose can firmly adhere to MoS2 surface, whereas the hydrophilic branches can facilitate the dispersion, resulting in the effective exfoliation in aqueous solution. The exfoliated dispersions of MoS2 nanosheets are homogeneous and highly stable over 7 months, even stored at ambient conditions. The optical properties of exfoliated MoS2 nanosheets were investigated by UV–Vis, and the morphological characterizations were examined by SEM, TEM, AFM, XRD and Raman. The results show that the hemicellulose-assisted MoS2 nanosheets produced by 10 mg/ml initial concentration have approximately 8–9 layers. Also, the surface-enhanced Raman scattering (SERS) capability of as-prepared MoS2 nanosheets is observable with the enhancement factor (EF) of about 4 × 104, indicating that the hot-spots can be generated on nanosheets. It demonstrates a plausible application of exfoliated MoS2 nanosheets as a SERS substrate as well as a great potential for other solution-based device fabrication. This present liquid-phase exfoliation method is a green, simple and effective process for mass production of MoS2 nanosheets.

Quantifying photoluminescence variability in monolayer molybdenum disulfide films grown by chemical vapour deposition

Monolayer molybdenum disulfide (MoS2) is a promising candidate for inclusion in optoelectronic technologies, owing to its two-dimensional (2D) nature and resultant novel photoluminescence (PL). Chemical vapour deposition (CVD) is an important method for the preparation of large-area films of monolayer MoS2. The PL character of as-prepared monolayer MoS2 must be well understood to facilitate detailed evaluation of any process-induced effects during device fabrication. We comparatively explore the PL emission from four different commercially available CVD-grown MoS2 monolayer films. We characterize the samples via Raman and PL spectroscopy, using both single-spot and mapping techniques, while atomic force microscopy (AFM) is applied to map the surface structure. Via multipeak fitting, we decompose the PL spectra into constituent exciton and trion contributions, enabling an assessment of the quality of the MoS2 monolayers. We find that the PL character varies significantly from sample to sample. We also reveal substantial inhomogeneity of the PL signal across each individual MoS2 film. We attribute the PL variation to non-uniform MoS2 film morphologies that result from the nucleation and coalescence processes during the CVD film development. Understanding the large variability in starting PL behaviour is vital to optimize the optoelectronic properties for MoS2-based devices.

Spectrofluorometric detection of mercury ions in aqueous medium and cellular milieu using MoS2 nanoflakes

This communication reports the facile hydrothermal synthesis of fluorescent two-dimensional layered MoS2 nanoflakes using a biomolecule (l-cysteine) for efficient and sensitive detection of mercury ions (Hg2+) in aqueous solution by monitoring the fluorescence quenching of MoS2 in a ratiometric approach. This fluorescence quenching of MoS2 was successfully utilized to detect Hg2+ ions in both normal (H9c2 cell line) and cancer (A549 cell line) cells as well via fluorescence imaging microscopy. The as-synthesized MoS2 nanostructured sample was characterized using UV–vis absorption, steady-state fluorescence emission, X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The strong fluorescence emission of nanostructured MoS2 was heavily quenched by Hg2+ ions in aqueous medium as confirmed by fluorescence spectroscopic results. The binding of Hg2+ with MoS2 nanoflakes and the resulting fluorescence quenching were also supported by Stern–Volmer analysis. The selectivity and sensitivity of the interaction of Hg2+ ions with the as-prepared MoS2 nanoflakes among all other interfering metal ions were analyzed. The selective interaction of Hg2+ with MoS2 was also accompanied by a distinct color change from bluish-green to flaxen or pale yellowish-gray in aqueous medium. The limit of detection of Hg2+ ions in aqueous medium was 0.63 nM. The possible interactions between Hg2+ and MoS2 were confirmed by Fourier transform infrared spectroscopy, time-resolved fluorescence, and cyclic voltammetry studies. Density functional theoretical calculations provided useful information to correlate the electronic structure and energy band distributions with the spectroscopic results for the interaction of Hg2+ with MoS2 nanoflakes. The MoS2 nanoflakes showed no significant cytotoxicity during their interaction with Hg2+ ions in the intracellular medium, as confirmed by MTT assay, thereby ensuring possible future biomedical applications.

Construction of UiO-66-NH2 decorated by MoS2 QDs as photocatalyst for rapid and effective visible-light driven Cr(VI) reduction

The photoactive metal-organic frameworks (MOFs) are good candidates for photocatalysts, but the quick electron-hole pairs recombination has greatly restricted the photocatalytic ability of MOFs. To improve the photoactivity of MOFs, MOFs-based composite materials have been extensively studied. Here, we successfully integrated MoS2 quantum dots (QDs) with UiO-66-NH2 for the first time under hydrothermal conditions. The as-prepared MoS2 QDs/UiO-66-NH2 (MS-U) had good visible light response ability (absorption edge at 445 nm), and charge separation and transfer ability, which lays the foundation for the photocatalytic Cr(VI) reduction. Photocatalytic studies revealed that MoS2 QDs-5/UiO-66-NH2 (MS-U-5) had superior Cr(VI) reduction activity than pure MoS2 QDs and UiO-66-NH2. MS-U-5 could remove 98% Cr(VI) at pH= 2 with visible light irradiation for 20 min, which is the fastest visible light driven Cr(VI) reduction rate among the reported MOFs-based composite photocatalysts without the presence of any cocatalysts or scavengers as far as we know. Importantly, MS-U-5 could be reused at least three times. In the end, the possible electron transfer path and mechanism of Cr(VI) reduction was also investigated.

Improvement of MoS2 electrocatalytic activity for hydrogen evolution reaction by ion irradiation

Molybdenum disulfide (MoS2) is considered promising noble metal-free catalysts for the hydrogen evolution reaction (HER). Whereas the bulk MoS2 does not exhibit significant activity, the catalytic properties of various nanostructures are noticeable. Therefore we synthesized flower-like molybdenum disulfide with the simple, one-step hydrothermal method. To enhance the catalytic activity of the material, low-energy ion irradiation is employed. As-prepared MoS2 is irradiated with hydrogen and carbon ions of various energies (20–40 keV) and fluences (1014-1017 ion/cm2). Our results show that irradiation has beneficial influence on MoS2 catalytic activity toward hydrogen evolution reaction. By producing morphological changes and defects in the structure, ion irradiation also impacts the conductivity of the material, which shows predominant effect on hydrogen evolution. The increase of current density at an overpotential of 300 mV with hydrogen ion irradiation is even 6 times higher than for as-synthesized catalyst.

Vertically molybdenum disulfide nanosheets on carbon cloth using CVD by controlling growth atmosphere for electrocatalysis

Molybdenum disulfide (MoS2) has been deemed as one of the promising noble-metal-free electrocatalysts for hydrogen evolution reaction (HER), but it suffers from the inert basal plane and low electronic conductivity. Regulating the morphology of MoS2 during the synthesis on conductive substrates is a synergistic strategy for enhancing the HER performance. In this work, vertical MoS2 nanosheets were fabricated on carbon cloth (CC) using an atmospheric pressure chemical vapor deposition method. The growth process could be effectively tuned through introducing hydrogen gas during vapor deposition process, resulting in nanosheets with increased edge density. The mechanism for edge-enriching through controlling the growth atmosphere is systematically studied. The as-prepared MoS2 exhibits excellent HER activity due to the combination of optimized microstructures and coupling with CC. Our findings provide new insights to design advanced MoS2-based electrocatalysts for HER.

Thin-walled hollow MoS2 microspheres as sulfur hosts for high-performance lithium sulfur batteries

The thin-walled hollow MoS2 microsphere was synthesized by a facile released online NH3-blowing during the reduction of ammonium tetrathiomolybdate ((NH4)2MoS4) in N-methylpyrrolidone (NMP) solvent by hydrazine hydrate at 80℃and investigated electrochemically as sulfur host for lithium sulfur battery. The results show that the as-prepared MoS2 @S electrode delivers an initial specific capacity of as high as 1801 mAh g−1, albeit partly due to the formation of SEI membrane, indicating the modulation of MoS2 on the electrochemical reaction of sulfur when compared with bare sulfur electrode. Moreover, the as-prepared MoS2 @S electrode exhibits excellent cycling stability and good rate capability, corroborating the interaction of MoS2 with lithium polysulfides (LiPSs) due to the severe shuttling effect in lithium sulfur battery, which is further authenticated by cyclic voltammetry, Tafel plot and electrochemical impedance spectroscopy techniques. This is anticipated to be a straightforward strategy for the practical implementation of lithium sulfur battery as an alternative to the state-of -the-art lithium ion battery.

Exfoliation of MoS2 by zero-valent transition metal intercalation.

Exfoliation of bulk molybdenum disulfide (MoS2) into few-layered nanosheets is achieved with the assistance of zero-valent transition metal (Co0, Ni0, Cu0) intercalation. The as-prepared MoS2 nanosheets are characterized to consist of 1T- and 2H-phases with an enhanced electrocatalytic hydrogen evolution reaction (HER) activity. This work provides a novel strategy to prepare 2D MoS2 nanosheets using mild reductive reagents, which is expected to avoid the undesired structural damage from conventional chemical exfoliation.

One-Step Hydrothermal Synthesis of Highly Fluorescent MoS2 Quantum Dots for Lead Ion Detection in Aqueous Solutions.

Lead ions in water are harmful to human health and ecosystems because of their high toxicity and nondegradability. It is important to explore effective fluorescence probes for Pb2+ detection. In this work, surface-functionalized molybdenum disulfide quantum dots (MoS2 QDs) were prepared using a hydrothermal method, and ammonium tetrathiomolybdate and glutathione were used as precursors. The photoluminescence quantum yield of MoS2 QDs can be improved to 20.4%, which is higher than that for MoS2 QDs reported in current research. The as-prepared MoS2 QDs demonstrate high selectivity and sensitivity for Pb2+ ions, and the limit of detection is 0.056 μM. The photoluminescence decay dynamics for MoS2 QDs in the presence of Pb2+ ions in different concentrations indicate that the fluorescence quenching originated from nonradiative electron transfer from excited MoS2 QDs to the Pb2+ ion. The prepared MoS2 QDs have great prospect and are expected to become a good method for lead ion detection.

Enhanced Catalytic Activity of a New Nanobiocatalytic System Formed by the Adsorption of Cytochrome c on Pluronic Triblock Copolymer Stabilized MoS2 Nanosheets.

The formation of nanobiohybrids through the immobilization of enzymes on functional nanomaterials has opened up exciting research opportunities at the nanobiointerfaces. These systems hold great promise for a wide range of applications in biosensing, biocatalytic, and biomedical fields. Here, we report the formation of a hybrid nanobiocatalytic system through the adsorption of cytochrome c (Cyt c) on pluronic triblock copolymer, P123 (PEO-b-PPO-b-PEO), stabilized MoS2 nanosheets. The use of pluronic polymer has helped not only to greatly stabilize the exfoliated MoS2 nanosheets but also to allow easy adsorption of Cyt c on the nanosheets without major structural changes due to its excellent biocompatibility and soft protein-binding property. By comparing the catalytic activity of the Cyt c–MoS2 nanobiohybrid with that of the free Cyt c and as-prepared MoS2 nanosheets, we have demonstrated the active role of the nanobiointeractions in enhancing the catalytic activity of the hybrid. Slight structural perturbation at the active site of the Cyt c upon adsorption on MoS2 has primarily facilitated the peroxidase activity of the Cyt c. As the MoS2 nanosheets and the native Cyt c individually exhibit weaker intrinsic peroxidase activities, their mutual modulation at the nanobiointerface has made the Cyt c–MoS2 a novel nanobiocatalyst with superior activity.

Rapid and green synthesis of highly luminescent MoS2 quantum dots via microwave exfoliation of MoS2 powder and its application as a fluorescence probe for cortisol detection in human saliva

We have introduced a simple, straightforward, green, and fast microwave exfoliation of MoS2 powder to prepare highly luminescent MoS2 quantum dots (QDs). The microwave irradiation of MoS2 powder was evaluated in the different solvents, including EtOH 30%, MeOH 30%, NaOH 1 M, and NH4OH 1 M in both open and closed microwave system setups. The results indicated that the highest luminescent MoS2 QDs is obtained when MoS2 powder was dispersed in 1 M ammonium solution and exposed to 850 W microwave radiation in a closed microwave system at 30 bars for 30 min. Different microscopic and spectroscopic techniques were used to characterize as-prepared MoS2 QDs. The MoS2 QDs have shown the maximum emission at 413 nm with excitation at 310 nm. The Quantum yield of as-prepared QDs was 1.98%. Cu2+, Pb2+, Cd2+, Ag+, Fe3+, and Al3+ quenched the luminescence intensity of MoS2 QDs. The luminescence of MoS2 QDs-Ag+ and Cu2+ mixtures were recovered on addition of cortisol with the higher emission recovery for Cu2+ ion. Therefore, proof-of-concept for cortisol sensing in human saliva was evaluated and discussed using off-on protocol. A linear cortisol calibration curve was obtained in the range of 100 ng mL−1 to 500 ng mL−1, with a detection limit of 16 ng mL−1 (S / N = 3). The method was successful in determining the cortisol content of saliva.

Solvent-Free Preparation of Closely Packed MoS2 Nanoscrolls for Improved Photosensitivity.

Due to their enhanced light absorption efficiency, one-dimensional (1D) transition metal dichalcogenide (TMDC) nanoscrolls derived from two-dimensional (2D) TMDC nanosheets have shown excellent optoelectronic properties. Currently, organic solvent and alkaline droplet-assisted scrolling methods are popular for preparing TMDC nanoscrolls. Unfortunately, the adsorption of organic solvent or alkaline impurities on TMDC is inevitable during the preparation, which affects the optoelectronic properties of TMDC. In this work, we report a solvent-free method to prepare closely packed MoS2 nanoscrolls by dragging a deionized water droplet onto the chemical vapor deposition grown monolayer MoS2 nanosheets at 100 °C (referred to as MoS2 NS-W). The as-prepared MoS2 NS-W was well characterized by optical microscopy, atomic force microscopy, and ultralow frequency (ULF) Raman spectroscopy. After high temperature annealing, the height of MoS2 nanoscrolls prepared using an ethanol droplet (referred to as MoS2 NS-E) greatly decreased, indicating the loss of encapsulated ethanol in MoS2 NS-E. While the height of MoS2 NS-W was almost unchanged under the same conditions, implying that no water was embedded in the scroll. Compared to the MoS2 NS-E, the MoS2 NS-W shows more ULF breathing mode peaks, confirming the stronger interlayer interaction. In addition, the MoS2 NS-W shows a higher Young's modulus than MoS2 NS-E, which could arise from the closely packed scroll structure. Importantly, the MoS2 NS-W device showed a photosensitivity 1 order of magnitude higher than that of the MoS2 NS-E device under blue, green, and red lasers, respectively. The decreased photosensitivity of MoS2 NS-E was attributed to the larger dark current, which might be assigned to the adsorbed ethanol between the adjacent layers in MoS2 NS-E. Our work provides a solvent-free method to prepare closely packed MoS2 nanoscrolls at large scale and demonstrates their great potential for high-performance optoelectronic devices.

Toward layered MoS2 anode for harvesting superior lithium storage.

As a typical transition metal dichalcogenide (TMD), molybdenum disulphide (MoS2) has become one of the most promising anode materials for lithium-ion batteries (LIBs) due to its desirable electrochemical properties. But the development of commercial MoS2 is limited by the problem of agglomeration. Thus, the production of MoS2 nanosheets with few (<10) layers is highly desired but remains a great challenge. In this work, a facile and scalable approach is developed to prepare large-flake, few-layer (4–8) MoS2 nanosheets with the assistance of ultrasonics. Simultaneously, the as-prepared MoS2 nanosheets and commercial bulk MoS2 were analysed under multiple spectroscopic techniques and a series of electrochemical tests to understand the dependence of electrochemical performance on structural properties. When used as anode materials for LIBs, the obtained MoS2 nanosheets provide a reversible capacity of 716 mA h g−1 at 100 mA g−1 after 285 cycles, and demonstrated an excellent capacity retention rate of up to 80%. Compared with that of commercial MoS2 (14.8%), the capacity retention rate of our MoS2 nanosheets has a significant improvement. This work explored the ability of few-layered MoS2 nanosheets in the field of LIBs while suggesting the commercialization of the MoS2 by an ultrasonicated ball milling exfoliation technique.

Facile exfoliation of MoS2 powders into nanosheets with excellent fluorescence quenching performance of perovskite

MoS2 nanosheets of pure semi-conducting hexagonal phase (2H-phase) have lots of potential applications due to their unique and novel property, and the fluorescence resonance energy transfer is very easy to happen between zero-dimensional (0D) perovskite quantum dots and two-dimensional (2D) MoS2 nanosheets. Herein, we demonstrate that a facile and green method to fabricate MoS2 nanosheets by sonication-assisted exfoliation of MoS2 powders in pure water after a hydrothermal reaction. The experimental results confirm that MoS2 ultrathin sheets obtained from powders are monolayer and few-layer 2H-phase nanosheets with size of 100–300 nm. Interestingly, the as-prepared MoS2 nanosheets have excellent performance to quench the fluorescence of CsPbBr3 quantum dots. It can provide a new way for us to explore energy resonance transfer between 0D quantum dots and 2D layered materials.

MoS2 QDs/8-Armed Poly(Ethylene Glycol) Fluorescence Sensor for Three Nitrotoluenes (TNT) Detection.

In this work, ammonia cross-linked 8-armed polyethylene glycol hydrogel material was successfully synthesized and used as a template for synthesizing nanoparticles with fluorescent properties. The 8-armed polyethylene glycol hydrogel template was used to prepare molybdenum disulfide quantum dots (MoS2 QDs). The ammonium tetrathiomolybdate functioned as a molybdenum source and hydrazine hydrate functioned as a reducing agent. The fluorescence properties of the as-prepared MoS2 QDs were investigated. The bursting of fluorescence caused by adding different concentrations of explosive TNT was studied. The study indicated that the synthesized MoS2 QDs can be used for trace TNT detection with a detection limit of 6 nmol/L and a detection range of 16–700 nmol/L. Furthermore, it indicated that the fluorescence-bursting mechanism is static bursting.

Luminous MoS2 nanosheet-based electrochemiluminescence biosensor with biomimetic vesicle for miRNA-210 detection

In this work, a novel electrochemiluminescence (ECL) sensor has been developed to detect miRNA-210 in the serum of triple negative breast cancer (TNBC) patients. The luminous MoS2 nanosheets were synthesized via the solvothermal method and served as ECL emitters for the first time. As a result, the ECL properties of as-prepared MoS2 nanosheets were significantly improved. Furthermore, the biomimetic magnetic vesicles were used as capture platform in the ECL sensing strategy. Due to the highly efficient fluidity and magnetic property, the biomimetic vesicles with hairpin aptamers can capture target gene in the serum. After magnetic separation, the captured miRNA-210 can trigger the target-catalyzed hairpin assembly (CHA) sensing process on the magnetic electrode and hybridize MoS2 nanosheets labeled probe DNA. The concentration of miRNA-210 can be quantified by the ECL enhancement of the MoS2 nanosheets. This approach has achieved the sensitive detection for miRNA-210 in a range from 1 fM to 100 pM with the detection limit of 0.3 fM. The luminous MoS2 nanosheets-based ECL sensing system with the biomimetic vesicles would provide a new pathway to explore 2D nanomaterials for developing a wide range of bioanalytical applications.

MoS2||CoP heterostructure loaded on N, P-doped carbon as an efficient trifunctional catalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reaction

Exploring multifunctional electrocatalysts is crucial for the development of energy conversion and storage equipments, such as fuel cells, water splitting devices and zinc-air batteries. Herein, we provide a rational design whereby the cobalt phosphide particles are introduced into molybdenum sulfide nanosheets to form a heterostructure (MoS2||CoP) through the ultrasonic method and calcination. Subsequently, N, P-doped carbon (NPC) is obtained synchronously. The as-prepared MoS2||CoP/NPC demonstrates highly effective multifunctional catalytic performance for oxygen evolution and hydrogen evolution reaction at lower overpotential, as well as oxygen reduction reaction at high half-wave potential. What this reveals is higher power density and superior stability in zinc-air battery. The excellent electrocatalytic activity of MoS2||CoP/NPC may be attributed to the presence of the MoS2||CoP heterostructure, as well as N, P-doped carbon coupled with a high percentage of pyridinic-N. This work proposes a novel and facile strategy to prepare the heterostructure compound and serves as a good reference for constructing efficient and low-cost electrocatalysts.

Boosting Photovoltaic Performance in Organic Solar Cells by Manipulating the Size of MoS2 Quantum Dots as a Hole-Transport Material.

The design of photoactive materials and interface engineering between organic/inorganic layers play a critical role in achieving enhanced performance in energy-harvesting devices. Two-dimensional transitional dichalcogenides (TMDs) with excellent optical and electronic properties are promising candidates in this regard. In this study, we demonstrate the fabrication of size-controlled MoS2 quantum dots (QDs) and present fundamental studies of their optical properties and their application as a hole-transport layer (HTL) in organic solar cells (OSCs). Optical and structural analyses reveal that the as-prepared MoS2 QDs show a fluorescence mechanism with respect to the quantum confinement effect and intrinsic/extrinsic states. Moreover, when incorporated into a photovoltaic device, the MoS2 QDs exhibit a significantly enhanced performance (5/10-nanometer QDs: 8.30%/7.80% for PTB7 and 10.40%/10.17% for PTB7-Th, respectively) compared to those of the reference device (7.24% for PTB7 and 9.49% for PTB7-Th). We confirm that the MoS2 QDs clearly offer enhanced transport characteristics ascribed to higher hole-mobility and smoother root mean square (Rq) as a hole-extraction material. This approach can enable significant advances and facilitate a new avenue for realizing high-performance optoelectronic devices.