MoS2 Nanoflakes Research Articles

Strong Photocurrent from Solution‐Processed Ruddlesden–Popper 2D Perovskite–MoS2 Hybrid Heterojunctions

AbstractThis study reports overall improvement in structural, morphological, and optoelectronic properties of Ruddlesden–Popper (RP) perovskites of type (BA)2(MA)n−1PbnI3n+1 by forming their bulk heterojunction hybrids with few‐layer MoS2 nanoflakes. RP perovskite–MoS2 hybrid thin films have shown significantly improved packing and crystallinity compared to pristine perovskites. The presence of MoS2 at RP perovskite interface has improved the quantum confinement effects and transport of photogenerated charge carriers from perovskite to MoS2, due to suitable conduction band of MoS2 and more number of decay channels. The optoelectronic properties of RP perovskite–MoS2 hybrids are studied for various MoS2 concentrations (4.2–25.6 × 10−3 m) and at optimum concentration (12.8 × 10−3 m) the photodetectors (n = 2, 4) have shown strong, sharp, and highly stable photocurrent response. At 0.0 V bias, the RP perovskite (n = 4) and MoS2 (12.8 × 10−3 m) hybrid‐based photodetectors, prepared without any encapsulation, have shown strong photocurrent density of ≈9.8 µA cm−2 under 1 sun illumination, which is ≈17 times higher compared to the pristine RP perovskites‐based photodetector (0.6 µA cm−2). Further transient photocurrent, performed over 200 cycles for hybrid (n = 4+MoS2) thin film photodetector under laser (λex ≈ 405 nm, ≈630 mW cm−2) illumination and ambient air conditions has shown highly stable photocurrent with only ≈9.6% reduction in the peak photocurrent density.

Enhancing photocatalytic properties of continuous few-layer MoS2 thin films for hydrogen production by water splitting through defect engineering with Ar plasma treatment

Continuous few-layer MoS2 thin films composed of the stacked MoS2 nanoflakes were fabricated with a facile thermal decomposition method. These nanoflakes possess exposed active sites which are beneficial to the photocatalytic properties. Defect engineering with the aim to generate more exposed edges accompanied with abundant excited carriers by variation of Ar plasma power has been carried out. Positive results were indeed obtained. On the other hand, increasing exposed active edges/defects induced by Ar plasma was found to lead to the occurrence of oxidation in air with time. The variations of crystallinity, S/Mo ratio, and oxygen adsorption after Ar plasma treatment were investigated by high resolution transmission electron microscopy, high resolution x-ray analysis of photoemission spectroscopy as well as Raman spectroscopy. The few-layer MoS2 bombarded by Ar plasma with 30 W power provides the optimal photocatalytic enhancement in hydrogen production about 1.4 times reaching 246 mmolg−1h−1and the photocurrent density was increased by about 15 times to the pristine one. In addition, MoS2/Au system from our previous survey is also utilized this method can generate 338 mmol/g−1h−1, as high as 188% enhancement compared to pristine one. The increase in conductivity for Ar plasma treated MoS2 thin films is attributed to the formation of 2D phase of MoOx with higher electron mobility. The investigation has clarified the influence of defects on the photocatalytic performance. Nevertheless, the defects were found to be unstable when the samples were stored in the air. It is highly desired to pursue a scheme to stabilized the defects for practical applications.

SERS-based recyclable immunoassay mediated by 1T-2H mixed-phase magnetic molybdenum disulfide probe and 2D graphitic carbon nitride substrate

Recently, non-metallic SERS-based immunoassay has attracted much attention due to its attractive chemical enhancement (CM), chemical stability, and biocompatibility. Herein, metallic (1T)-semiconductor (2H) mixed-phase magnetic molybdenum disulfide (MoS2) was rationally developed and combined with two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets to realize a SERS-based recyclable immunoassay of CA125. The Fe3O4 core promoted the reliable stacking of MoS2 nanoflakes into a flower-like shape with fully-exposed active surface. Particularly, the existence of 1T phase facilitated a noble-metal-comparable SERS activity due to the high electron density-induced charge transfer process with elevated efficiency. Moreover, a conversion from bulk to 2D nanosheet was swimmingly achieved for g-C3N4 via acid etching, whose large surface area full of active electrons and functional groups triggered an enhancement factor (EF) of 7.8 × 106. Based on a typical sandwich immunostructure, a limit of detection (LOD) as 4.96 × 10−4 IU/mL was demonstrated for CA125 in a recyclable process. Finally, such an immunosensor was employed to analyze clinical samples, indicating its prodigious potentiality in the early recognition and monitoring of cancer.

Gold Nanorod-Activated Graphene/MoS2 Nanosheet-Based Photodetectors for Bidirectional Photoconductance

Graphene and its nanohybrid photodetectors (PDs) offer unique interfacial and synergistic properties in contrast to conventional semiconductor-based PDs. In this work, we compare the performance of identically fabricated PDs based on pure chemical vapor deposition-grown monolayer graphene, demonstrating a positive photoresponse, that exhibits a gain in photoresponsivity (R) with the addition of two-dimensional MoS2 (chemically exfoliated). However, further addition of plasmonic gold nanorods (AuNRs), on the MoS2/graphene PD, results in the flipping of the photoconductivity to negative. The negative photoresponse is explained by an increased dark current via the complex conductive network model and a lower photocurrent due to the photogenerated electron capture by the AuNRs in the AuNRs/MoS2/graphene PD. The contrasting shape and nature of the dynamic photoresponses are modeled using theoretical fitting and explained based on carrier transport in individual components. The highest R in the moderately fast graphene PD device is ∼2 × 104 A W–1 under 808 nm which could be slightly improved to ∼3 × 104 A W–1 by introducing MoS2 nanoflakes, albeit at the cost of the response time which slows down from ∼90 ms (in the former) to 558 ms in the latter. The introduction of AuNRs did speed up the response time in the AuNRs/MoS2/graphene PD to 20.5 ms but produced a strikingly different negative photoresponse attributed to a higher dark current in the material. We proposed a single mechanism to explain the positive and negative photoresponses reported so far for the hybrid PDs.

2H-MoS 2 Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

2H-MoS ₂ Modified Nitrogen-Doped Hollow Mesoporous Carbon Spheres as the Efficient Catalytic Cathode Catalyst for Aprotic Lithium-Oxygen Batteries

MoS2 Passivated Multilayer Graphene Membranes for Li-Ion Extraction From Seawater.

Abundant Li resources in the ocean are promising alternatives to refining ore, whose supplies are limited by the total amount and geopolitical imbalance of reserves in Earth's crust. Despite advances in Li+ extraction using porous membranes, they require screening other cations on a large scale due to the lack in precise control of pore size and inborn defects. Herein, MoS2 nanoflakes on a multilayer graphene membrane (MFs-on-MGM) that possess ion channels comprising i) van der Waals interlayer gaps for optimal Li+ extraction and ii) negatively charged vertical inlets for cation attraction, are reported. Ion transport measurements across the membrane reveal ≈6- and 13-fold higher selectivity for Li+ compared to Na+ and Mg2+ , respectively. Furthermore, continuous, stable Li+ extraction from seawater is demonstrated by integrating the membrane into a H2 and Cl2 evolution system, enabling more than 104 -fold decrease in the Na+ concentration and near-complete elimination of other cations.

Multifunctional MoSe2 @MXene Heterostructure-Decorated Cellulose Fabric for Wearable Thermal Therapy.

A booming demand for wearable electronic devices urges the development of multifunctional smart fabrics. However, it is still facing a challenge to fabricate multifunctional smart fabrics with satisfactory mechanical property, excellent Joule heating performance, highly efficient photothermal conversion, outstanding electromagnetic shielding effectiveness, and superior anti-bacterial capability. Here, a MoSe2 @MXene heterostructure-based multifunctional cellulose fabric is fabricated by depositing MXene nanosheets onto cellulose fabric followed by a facile hydrothermal method to grow MoSe2 nanoflakes on MXene layers. A low-voltage Joule heating therapy platform with rapid Joule heating response (up to 230°C in 25 s at a supplied voltage of 4V) and stable performance under repeated bending cycles (up to 1000cycles) is realized. Besides, the multifunctional fabric also exhibits excellent photothermal performance (up to 130°C upon irradiation for 25 s with a light intensity of 400mW cm-2 ), outstanding electromagnetic interference shielding effectiveness (37dB), and excellent antibacterial performances (>90% anti-bacterial rate toward Escherichia coli, Bacillus subtilis, and Staphylococcus aureus). This work offers an efficient avenue to fabricate multifunctional wearable thermal therapy devices for mobile healthcare and personal thermal management.

Geometric shapes and vacancy rates for the modulation of the electronic and transport properties in MoS2 nanoflakes

The electronic and transport properties of MoS2 nanoflakes are investigated using a six-band tight-binding model. The energy band structures are modified by changing the shape, size, vacancy rate, and vacancy distribution of the flakes, resulting in additional energy states in the energy bandgap region. For large flakes, the effects of their geometric shape are found to be negligible, because shape effects on the density of states (DOS) decrease with increasing flake size. The positions and DOS of these additional in-gap states are strongly related to the vacancy rate as well as to the distribution of vacancies. The number of in-gap states and the magnitude of the density of these states are both proportional to the vacancy rate. However, if the rate is high enough for vacancy clusters to form, the transmission is somewhat degraded at certain incident energies, owing to backscattering and capture of carriers by the clusters. Since the current transmission is determined primarily by the detailed energy band structure, the in-gap states due to vacancies enable the realization of low-energy currents in devices based on low-dimensional materials.

Sensitive dopamine sensor based on electrodeposited gold nanoparticles and electro-modulated MoS2 nanoflakes

Sensitive dopamine sensor based on electrodeposited gold nanoparticles and electro-modulated MoS2 nanoflakes

MoSe2/PVA-based wearable multi-functional platform for pulse rate monitoring, skin hydration sensor, and human gesture recognition utilizing electrophysiological signals

Multifunctional wearable sensors have gained significant popularity in recent years for point of care diagnosis, tackling the myriad of obstacles faced in coping with health-related issues. However, complex fabrication, lack of biocompatibility, non-reusability, and accuracy limit their widespread use. In this work, we report a clean-room-free fabrication of molybdenum diselenide (MoSe2) interspersed with polyvinyl alcohol (PVA) based multifunctional device for in situ and non-invasive high-fidelity human gesture recognition, pulse rate monitoring, and skin hydration sensing. Detailed morphological characterization studies reveal the formation of a rhombohedral structure for MoSe2 nanoflakes stacked vertically to form a micro flower structure. Group synaptic activity of neurons results in a subtle electrical impulse, which, in turn, generates an electric field that is detected by the as-fabricated MoSe2/PVA device when attached to the forehead and interfaced to Open Brain-Computer Interface platform-based Cyton biosensing board. The device is also used as an ultrasensitive pressure sensor for arterial pulse pressure monitoring. This detection mechanism of the multifunctional sensor can be attributed to the piezoresistive effect of MoSe2 nanoparticles, wherein the dipoles reorient to form an internal polarization upon detection of physiological information. The strategy employed here paves the way toward replacing wet electrodes in conventional electroencephalogram (EEG)/electrocardiogram (ECG) measurements that result in skin abrasion and signal quality degradation with low-cost, reliable, skin-friendly, wearable MoSe2/PVA dry electrodes for rapid assessment.

Investigation on the AgPt and AgPd hybrid alloy nanoparticles (HANPs) for the hybrid MoS2/ZnO/HANP UV photodetector application

Hybrid photodetectors made of two or more nanomaterial components can offer the high potential for advanced photodetection applications with enhanced light absorption, improved efficiency and structural tunability. A hybrid UV photodetector (PD) configuration incorporating the plasmonic hybrid alloy nanoparticles (HANP), ZnO quantum dots (QDs) and MoS2 nanoflakes, namely MoS2/ZnO/HANP PD, is demonstrated. The optimized MoS2/ZnO/HANP PD exhibits a high photocurrent of 5.66 mA at 0.34 mW/mm2 under 385 nm illumination with two orders of improvement from the bare ZnO, which is one of the highest photocurrents by the ZnO-based PDs. It also demonstrates high figure-of-merits with the responsivity of 14,523 mA/W, detectivity of 8.13 × 1011 jones, and external quantum efficiency (EQE) of 4,680 %, outperforming most of the ZnO-based hybrid architectures. The enhanced photoresponse is primarily attributed to the significantly enhanced hot electron generation by the AgPd HANPs and photocarrier collection through the ZnO QD layer. MoS2 nanoflakes also provide additional photon absorption sites and boost the photo-carrier transfer process. HANPs are grown by adapting a dual-step solid-state dewetting process (SSD) approach and the superiority of AgPd HANPs is confirmed by systematic investigation, FDTD simulation and comparison of AgPt and AgPd HANPs.

Impact of temperature on the properties of MoS2 nanoflakes synthesized by facile hydrothermal method for electrochemical supercapacitor applications

• The hexagonal crystal structure was observed by XRD. • The nanoflakes and flower-like structure were obtained using FESEM analysis. • The electrode material prepared with 160 °C temperature exhibits excellent super capacitive performances. • A maximum specific capacitance of 691 Fg −1 at current density 1 Ag −1 and good cyclic stability of 89 % over 5000 cycles. This work describes the formation of two-dimensional Molybdenum di-sulfide (MoS 2 ) nanoflakes developed by temperature varying hydrothermal method from 140 °C to 200 °C and further applied as effective electrode material for high performance supercapacitor. The structural analysis confirms the formation of hexagonal crystal structure of MoS 2 by XRD. The surface morphological study revealed uniform growth of MoS 2 nanoflakes and flower-like structure. The chemical bonding and the location of Mo-S band was confirmed at 600 cm −1 through FTIR–spectrum. The electrochemical performances of the MoS 2 electrode were analyzed by Cyclic Voltammetry, Galvanostatic Charge/discharge and electrochemical impedance techniques. The electrode material prepared at 160 °C temperature exhibits excellent super capacitive performances when compared to other temperatures. This electrode recorded a maximum specific capacitance of 691 Fg −1 at current density 1 Ag −1 and good cyclic stability of 89 % over 5000 cycles. It exhibits very less charge transfer resistance 1 Ω which is lesser than other electrodes.

Hierarchically Synthesis of Nanoflakes of Molybdenum Disulfide on Electrochemically Anodized Pencil Lead for Determination Trace Amounts of Phenolic Compounds in Water Samples

Preparation coating materials is the main point in solid-phase microextraction (SPME) fiber fabrications. So, fabricating MoS2 nanoflakes on graphenized HB (hard black) pencil lead was developed. The MoS2 nanoflakes were directionally arranged on graphenized HB pencil lead and used as a fiber coating for selectively headspace microextraction of phenolic compounds. The MoS2/graphenized pencil fibers were characterized by X-ray diffraction (XRD), field emission scanning microscopy (FESEM), thermal gravimetric analysis (TGA) and energy-dispersive X-ray spectroscopy (EDX).MoS2/graphenized pencil lead fibers indicated considerable potential due to extracting simultaneously trace amounts of some phenolic compounds in different water samples. The repeatabilities and detection limits for one fiber were between 5.5 and 7.2% and between 0.002 and 0.32 µgL−1, respectability. The purpose method was a simple, quick, stable and cheap approach.

In situ synthesis of MoS2 nanoflakes within a 3D mesoporous carbon framework for hydrodesulfurization of DBT

Two new mesoporous carbon-supported Co-Mo hydrodesulfurization catalysts with different Co contents have been successfully prepared by one-step vacuum freeze-drying, followed by calcination under a nitrogen atmosphere and washing. Evans-Showell polyoxometalate (NH4)6[Co2Mo10O38H4]·7H2O was used as the Co-Mo precursor instead of the conventional precursors, and the obtained catalysts were structurally characterized by various technologies, including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, H2 temperature programmed reduction, CO temperature programmed desorption and low temperature N2 adsorption-desorption isotherm. The results show that MoS2 particles (4.6 nm and 4.5 slabs) are homogeneously dispersed in the mesoporous carbon framework with a narrow pore size distribution centered at 3.7 nm. The catalysts were evaluated by the hydrodesulfurization of dibenzothiophene, and the results show that the dibenzothiophene conversion, overall pseudo-first order rate constant and turnover frequency can reach 95 %, 5.4 × 10−6 mol g−1 s−1 and 6.1 × 10−3 s−1 at 300 °C, respectively, indicating higher catalytic activity than previously reported catalysts. The higher proportion of the CoMoS active phase can account for the higher catalytic activity. By using in situ-produced sodium chloride crystals and thiourea as hard templates and sulfidizing agents respectively, this study opens a new avenue for the simple and environmentally friendly preparation of hydrodesulfurization catalysts with the synchronization and riveting of MoS2 nanoflakes and 3D mesoporous carbon frameworks.

Dual tumor- and subcellular-targeted photodynamic therapy using glucose-functionalized MoS2 nanoflakes for multidrug-resistant tumor ablation

Photodynamic therapy (PDT) is emerging as an efficient strategy to combat multidrug-resistant (MDR) cancer. However, the short half-life and limited diffusion of reactive oxygen species (ROS) undermine the therapeutic outcomes of this therapy. To address this issue, a tumor-targeting nanoplatform was developed to precisely deliver mitochondria- and endoplasmic reticulum (ER)-targeting PDT agents to desired sites for dual organelle-targeted PDT. The nanoplatform is constructed by functionalizing molybdenum disulfide (MoS2) nanoflakes with glucose-modified hyperbranched polyglycerol (hPG), and then loading the organelle-targeting PDT agents. The resultant nanoplatform Cy7.5-TG@GPM is demonstrated to mediate both greatly enhanced internalization within MDR cells and precise subcellular localization of PDT agents, facilitating in situ near-infrared (NIR)-triggered ROS generation for augmented PDT and reversal of MDR, causing impressive tumor shrinkage in a HeLa multidrug-resistant tumor mouse model. As revealed by mechanistic studies of the synergistic mitochondria- and ER-targeted PDT, ROS-induced ER stress not only activates the cytosine-cytosine-adenosine-adenosine thymidine/enhancer-binding protein homologous protein (CHOP) pro-apoptotic signaling pathway, but also cooperates with ROS-induced mitochondrial dysfunction to trigger cytochrome C release from the mitochondria and induce subsequent cell death. Furthermore, the mitochondrial dysfunction reduces ATP production and thereby contributes to the reversal of MDR. This nanoplatform, with its NIR-responsive properties and ability to target tumors and subcellular organelles, offers a promising strategy for effective MDR cancer therapy.

Improved charge extraction and atmospheric stability of all-inorganic Cs2AgBiBr6 perovskite solar cells by MoS2 nanoflakes

Among lead-free halide double perovskites, Cs 2 AgBiBr 6 is a potential alternative to substitute toxic and unstable organic-inorganic lead-based halide perovskites. However, the film forming ability and wide indirect bandgap have impeded its applications. Herein, we investigate to use MoS 2 nanoflakes as a hole transport interlayer to improve the crystallinity of Cs 2 AgBiBr 6 , tailor energy level alignments and enhance the stability of solar cells. With the addition of the MoS 2 nanoflakes, the Cs 2 AgBiBr 6 -based solar cell has a power conversion efficiency of 4.17% with an open circuit voltage of 1.10 V and short-circuit current of 6.12 mA cm −2 . This work would provide a new approach for developing all inorganic lead-free Cs 2 AgBiBr 6 -based solar cells with high power conversion efficiency and good stability. • MoS 2 can tailor the energy level of Cs 2 AgBiBr 6 to enhance hole extraction. • The power conversion efficiency of the device with MoS 2 nanoflakes is up to 4.17%. • The devices with MoS 2 remain 90% efficiency up to 23 days under ambient conditions.

Fabrication of ssDNA functionalized MoS[formula omitted] nanoflakes based label-free electrochemical biosensor for explicit silver ion detection at sub-pico molar level

A novel, robust, reliable, low-cost, and convenient electrochemical silver ion sensing technique is proposed based on poly(cytosine) functionalized carboxylated 2D MoS2 nanoflakes. Relying upon cytosine–cytosine mismatch, all electroanalytic measurements carried out on this sensor proved its superiority in detecting Ag(I) ions through cytosine-Ag(I)-cytosine interaction down to pico molar (pM) concentration with an approximated limit of detection of 0.8 pM in the potable water medium. In the environmental sample tests and competitive experiments with other metal ions, this proposed biosensor showed enough potential for trace amount determination of silver ions in the potable water medium for environmental monitoring applications.

Efficient and Facile Synthetic Route of MoO3:MoS2 Hybrid Thin Layer via Oxidative Reaction of MoS2 Nanoflakes.

In the present study, MoO3:MoS2 hybrid thin layers have been synthesized through partial oxidation of MoS2. We have demonstrated that the reaction requires darkness conditions to decrease the oxidation rate, thus obtaining the hybrid, MoO3:MoS2. A simple liquid-phase exfoliation (LPE) is carried out to achieve homogenous MoS2 nanoflakes and high reproducibility of the results after MoS2 oxidation. XPS analyses reveal the presence of MoO3, MoS2, and MoOxSy in the hybrid layer. These results are also confirmed by X-ray diffraction and high-resolution TEM. Optical absorbance reveals that the absorption peaks of the MoO3:MoS2 hybrid are slightly redshifted with the appearance of absorption peaks in the near-infrared region due to the defects created after the oxidation reaction. The composition and atomic percentages of each component in the hybrid layer as a function of reaction time have also been reported to give perspective guides for improving electronic and optoelectronic devices based on 2D-MoS2.

MoS2/SiNWs heterostructure based repeatable and highly responsive photodetector

This paper presents an efficient, highly responsive and highly repeatable MoS2/SiNWs heterostructure based photodetector. SiNWs samples were synthesized using metal assisted chemical etching and MoS2 nanoflakes were grown on SiNWs using wafer scalable processes. SiNWs, MoS2 and MoS2/SiNWs based devices were tested for photodetection performance in the visible region. The heterostructure interface between MoS2 and SiNWs helps to suppress dark current and enhance performance characteristics. The MoS2/SiNWs exhibits higher responsivity of 2.98 AW-1 at 450 nm illumination, which is 3 and 11 times higher than the SiNWs and MoS2 respectively. In addition, this heterojunction based device exhibits a higher detectivity of 2.7 × 1011 Jones and rise/fall time of 0.45/0.75 s. Moreover, the device fabrication method is simple and cost-effective. These results pave the way for the fabrication of scalable, highly repeatable and responsive miniaturized photodetectors based on MoS2/SiNWs for mass production.

Functionalized multiwall carbon nanotube-molybdenum disulphide nanocomposite based electrochemical ultrasensitive detection of neurotransmitter epinephrine

Epinephrine hormone as neurotransmitter is a crucial component for the efficient working of the human cardio-respiratory and central nervous or peripheral nervous systems. Efficient quantification of the epinephrine level in biological fluids is critical in diagnosing several significant diseases. The present research problem focused on the synthesized the multiwall carbon nanotubes (MW-CNTs) functionalized with MoS2 heterostructure using the hydrothermal route and further explored its applicability to detect neurotransmitter i.e. epinephrine. The morphological and structural characterization of the MoS2-MW/CNTs heterostructure was examined by employing morphological as well as spectroscopic techniques. Results showed that heterostructures were well decorated with 2-dimensional MoS2 nano-flakes, which enhance material electro-catalytic activity for better electrochemical communication. The results exhibit that the developed epinephrine biosensor exhibited a Limit of detection (LOD) of 3.0 μM, with good linearity from 9.9 to 137.9 μM, excellent selectivity and enhanced sensitivity with reproducibility. The proposed MoS2/MW-CNTs modified GCE electrode was stable in terms of performance and could be used for epinephrine sensing in the real water sample.