2H MoS2 Research Articles

Optimization and scalability assessment of supercapacitor electrodes based on hydrothermally grown MoS2 on carbon cloth.

MoS2 is a well-known 2D transition metal dichalcogenide (TMD) with feasibility for energy storage applications due to its eco-friendliness and high electroactive surface area. Electrodes based on MoS2 are typically made by either immobilizing its multiphase nanocomposites, having binders and conductive fillers, or by directly growing the materials on current collectors. In this work, we follow and optimize this latter approach by applying a hydrothermal route to directly synthesize MoS2 nanostructures on carbon cloth (MoS2@CC) hence enabling binder-free current collector electrodes. Raman spectroscopy and electron microscopy analyses confirmed the formation of 2H MoS2 nanosheets with hexagonal structure. The as-prepared electrodes were used to assemble symmetric supercapacitor cells, whose performance were tested in various types of electrolytes. Electrochemical measurements indicate that both precursor concentration and growth time significantly affect the device performance. Under optimized conditions, specific capacitance up to 226 F g-1 (at 1 A g-1 in 6 M KOH) was achieved, with corresponding energy and power densities of 5.1 W h kg-1 and 2.1 W kg-1. The device showed good stability, retaining 85% capacitance after 1000 cycles. Furthermore, the electrodes assessed in PYR14-TFSI showed energy and power densities of up to 26.3 W h kg-1 and 2.0 kW kg-1, respectively, indicating their feasibility not only in aqueous but also in ionic liquid electrolytes. In addition, galvanostatic charge/discharge measurements conducted on devices having footprint sizes from 1 cm2 to 25 cm2 show very similar specific capacitances, which proves scalability and thus the practical relevance of the binder-free electrodes demonstrated in this study.

First principle calculation of Se-vacancy monolayer 2H–MoSe2

The photocurrent of intrinsic and Se-vacancy monolayer 2H–MoSe2 in zigzag direction is calculated by using first-principles method based on the Keldysh nonequilibrium Green's functional theory. Furthermore, the photo response for the circular photogalvanic effect (CPGE) and linear photogalvanic effect (LPGE) at different photon energies are investigated. The results show that the photon energy of 2.5 eV is a turning point. Lower than the photon energy of 2.5 eV, the CPGE of intrinsic monolayer 2H–MoSe2 is steadily larger than its LPGE counterpart by the amount of the absorbed photon energy. However, the curve becomes steeper as the photon energy approaches 2.5 eV and reaches the maximum at 2.7 eV. The CPGE and LPGE curves of the Se-vacancy 2H–MoSe2 also change around 2.5 eV, i.e., the CPGE is slightly smaller than LPGE with the photon energy lower than 2.5 eV and absorbs enough photon energy to become larger than LPGE with the photon energy larger than 2.5 eV. These results can be explained by the electron transition between the valence and conduction bands, which is proportional to the density of states according to the Fermi's Golden rule. In addition, we also study the relationship between the photocurrent of LPGE and CPGE and the polarization angles θ and φ. Our results have the potential to be utilized in the optimization of monolayer transition metal dihalide-based photodetectors.

An electrochemiluminescence aptasensor based on Ti3C2 QDs-1T/2H MoS2 nano-hybrid material for the highly sensitive detection of lincomycin

Developing a highly selective and sensitive analysis strategy for lincomycin (LIN) is of great significance for environmental protection and food safety. Herein, we reported a novel electrochemiluminescence (ECL) aptasensor based on Ti3C2 QDs-1T/2H MoS2 nano-hybrid luminophore for detection of LIN. The hybridization of Ti3C2 QDs and 1T/2H MoS2 endowed nanocomposite with structural and compositional advantages for boosting the ECL performance of QDs by about three times. This enhancement could be attributed to the remarkable electrocatalytic activity and high conductivity exhibited by 1T/2H MoS2. Secondly, the great surface area of 1T/2H MoS2 is conducive to the high dispersion of Ti3C2 QDs, and its good conductivity could promote charge transfer. On the other hand, the excellent catalytic performance of 1T/2H MoS2 could facilitate the reduction of S2O82− to produce more radical, which significantly enhance the ECL signal of Ti3C2 QDs. Given these features, a sensor for detection of LIN was established based on specific recognition between target and aptamer. The sensor showed a good linear relationship (0.05 ng mL−1 ∼100 μg mL−1) with a detection limit as low as 0.02 ng mL−1. It is worth noting that this work has been validated in testing milk samples, exhibiting great potential application prospects in food analysis.

Single Ru atoms dispersed on MoSe2/MXene nanosheets with multiple interfaces for enhanced acidic hydrogen evolution

Exposing more catalytic active sites is an effective strategy to enhance the catalyst activity for hydrogen evolution reaction (HER). Herein, Ti3C2Tx MXene served as a substrate to load thin and curved 2H–MoSe2 nanosheets by a typical hydrothermal method, forming MoSe2/MXene heterointerface with the fully exposed Mo edge sites. And then, atomically dispersed Ru single atoms (RuSAs) were successfully anchored on the MoSe2/MXene (RuSAs@MoSe2-MXene). The X-ray absorption near edge structure (XANES) demonstrates that Ru is loaded as single atoms on MoSe2 and MXene. The prepared sample exhibits improved catalytic activity with a small overpotential of 49 mV at 10 mA cm−2 and a low Tafel slope of 52 mV dec−1 for HER in 0.5 M H2SO4. It also exhibits excellent stability with a small attenuation voltage of 10 mV for 120 h at 10 mA cm−2 in 0.5 M H2SO4. When assembled into a two-electrode system of RuSAs@MoSe2-MXene||RuO2, it only requires a relatively low potential of 1.626 V at 10 mA cm−2 to drive overall water splitting (OWS). Control experiments disclose the highly improved performance can be primarily attributed to the introduced RuSAs and MoSe2/MXene heterointerfaces exposing more active sites of Ru and Mo. Moreover, the high conductivity of MXene can increase charge transfer in HER process. The interface engineering with multiple interfaces can provide fresh impetus for the development of efficient HER catalysts.

High-Efficiency Cycling Piezo-Degradation of Organic Pollutants and the Piezocatalysis–Adsorption Duality of MoS2 Nanoflowers

This study realized the large-scale piezo-catalytic RhB dye degradation by forming a catalytic filter of 2H phase MoS2 and carbon cloth. Over 2.5 liters of the organic pollutant can be fully decomposed through the application of a water pumping system. The results obtained indicate that 2H MoS2 NFs were highly reusable and have excellent potential for the application in industrial wastewater treatment. Furthermore, this study theoretically and experimentally investigates the piezocatalytic and adsorption effects of different phases of polymorphic MoS2 NFs. By adjusting the electrostatic surface charge of these NFs and the RhB solution, different crystalline phases of MoS2 NFs would result in either adsorption or piezo-catalytic effects toward the organic dye. The results evident that the cationic dye is adsorbed on the surfaces of the 1T MoS2 NFs; however, the few-layer 2H MoS2 NFs generate a considerable quantity of hydroxyl species for degrading RhB molecules through the mechanical-force-induced piezo-potential. Figure 1

Phase-incorporation-induced electromagnetic coupling of NFS@1T/2H–MoS2 for enhanced microwave absorption

Herein, we propose a combination strategy to induce robust room-temperature electromagnetic coupling in non-magnetic MoS2 semiconductor (2H–MoS2). The introduction of ascorbic acid (AA) is intended to introduce sulfur vacancies (sv) in the process of 2H–MoS2 nano-sheet shells coating on the surface of three-dimensional (3D) matrix. It promotes the transformation of local lattice (2H–MoS2) into metal phase (1T-MoS2). The transformed 1T-MoS2 phase improves the conductivity (σ) of the composite by 1.48 times. Due to the Mo4+4d energy state within the bandgap, the exchange interaction between the sv and the Mo4+4d bandgap state produces a robust intrinsic electromagnetic response of more than 1.2 emu/g. Density functional theory (DFT) calculations are used to analyze the above results, and a novel electromagnetic-coupling-enhanced microwave absorption mechanism is proposed. The results indicates that microwave absorption performance can be effectively improved by the phase-incorporation effect. The minimum reflection loss (RLmin) reaches −53.1 dB (1.7 mm) and the adjustable effective absorption bandwidth (EAB) covers 14.5 GHz (3.5–18 GHz) at the various matching thicknesses. This work might shed light on a new possibility of manipulating electromagnetic interaction to promote microwave absorption.

Enhanced photo-Fenton degradation of contaminants in a wide pH range via synergistic interaction between 1T and 2H MoS2 and copolymer tea polyphenols/polypyrrole

In this study, we present the successful development of a unique photo-Fenton catalyst, 1T-2H MoS2@TP/PPy (MTP), achieved through the coating of a copolymer of tea polyphenol (TP) and polypyrrole (PPy) onto the surface of heterophase molybdenum disulfide (1T-2H MoS2). This innovative approach involves the integration of hydrothermal synthesis with copolymerization techniques. Our strategy utilizes nanoflower-like 1T-2H MoS2 as the foundational framework, which is then enveloped in TP and PPy copolymer. This innovative approach involves the integration of hydrothermal synthesis with copolymerization techniques. Our strategy utilizes nanoflower-like 1T-2H MoS2 as the foundational framework, which is then enveloped in TP and PPy copolymer. This distinctive architecture demonstrates exceptional catalytic performance owing to the hetero-phase entanglement of 1T-2H MoS2, which provides a diverse array of active sites. The coupled structure of TP and iron (TP-Fe2+/Fe3+) effectively overcome the limitation associated with the iron source. The incorporation of PPy not only reduces the recombination of photogenerated electron-hole pairs but also enhances the stability of 1T-2H MoS2. Remarkably, our experiments on the degradation of methylene blue (MB) and tetracycline (TC) degradation demonstrate that TP-Fe2+/Fe3+ significantly expands the pH applicability range of the MTP composite catalyst. Additionally, we examine several factors, including different catalysts, H2O2 addition, variations in light intensity, solution pH, temperature fluctuations, and the role of active species, to comprehensively understand their impact on the photo-Fenton degradation process. In conclusion, MTP composite exhibits robust catalytic stability and demonstrates a broad pH utilization range in the photo-Fenton oxidation process, highlighting its promising potential for a wide range of applications.

Hydrothermally obtained MoSe2/Reduced graphene oxide based composite with superior electrocatalytic performance

Recent experiments have demonstrated that 1T phase of transition-metal dichalcogenides exhibits superior electro-catalytic activity for hydrogen evolution reaction (HER). Herein, we compare the HER performance of as obtained 2H-phase MoSe2 (bare) with hydrothermally synthesized 1T-2H mixed phase MoSe2 and its composites with reduced graphene oxide. Obtained MoSe2/rGO composite has displayed a Tafel slope of 55 mV dec−1 compared with mixed-phase (113 mV dec−1) and 2H–MoSe2 (125 mV dec−1, bare). Composite of MoSe2 with very small amount of rGO has shown increased HER activity with low overpotential (88 mV at 10 mA cm−2), smaller Tafel slope, longer durability and high value of turn over frequency. The weight ratio between MoSe2 and rGO is crucial in determining the HER performance of the composite. The Present work offers a facile and attractive methodology for enhancing the HER performance of 2D materials-based electrocatalysts.

Synergetic Effect and Phase Engineering by Formation of Ti3C2Tx Modified 2H/1T-MoSe2 Composites for Enhanced HER

The typical semi conductivity and few active sites of hydrogen evolution of 2H MoSe2 severely restrict its electrocatalytic hydrogen evolution performance. At the same time, the 1T MoSe2 has metal conductivity and plentiful hydrogen evolution sites, making it feasible to optimize the electrocatalytic hydrogen evolution behavior of MoSe2 using phase engineering. In this study, we, through a simple one-step hydrothermal method, composed 1T/2H MoSe2, and then used newly emerging transition metal carbides with several atomic-layer thicknesses Ti3C2Tx to improve the conductivity of a MoSe2-based electrocatalyst. Finally, MoSe2@Ti3C2Tx was successfully synthesized, according to the control of the additional amount of Ti3C2Tx, to form a proper MoSe2/ Ti3C2Tx heterostructure with a better electrochemical HER performance. As obtained MoSe2@4 mg-Ti3C2Tx achieved a low overpotential, a small Tafel slope and this work offers additional insight into broadened MoSe2 and MXenes-based catalyst’s electrochemical application.

Defect-rich 1T-MoS2 nanosheets towards efficient electrochemical hydrogen evolution by simultaneous phase and defect engineering

Molybdenum sulfide (MoS2) has been considered as a promising candidate to replace Pt for the electrochemical hydrogen evolution reaction (HER). However, the disadvantages of inert basal planes and low conductivity limit its application in HER. Herein, we report a facile strategy to achieve simultaneous phase transition and defect engineering in MoS2 by adjusting the ratio of sulfur precursor to molybdenum precursor in the synthesis process. The excess thiourea are adsorbed on the surface of as-formed MoS2 nanocrystallites, which hinders the further crystallization process and creates a large amount of defects on the basal planes. Besides, ammonia ions could in situ insert into the interlayers of MoS2 and induce a phase transition from 2H–MoS2 to 1T-MoS2. The optimized defect-rich 1T-MoS2 catalyst shows a small overpotential of 232 mV at 10 mA cm−2 and Tafel slope of 61 mV dec−1 in acidic media. The superior HER activity is attributed to the defect-rich and 1T-phase structure, which contributes significantly enhanced electronic conductivity and greatly exposed active sites.

An Investigation of PPy@1T/2H MoS2 Composites with Durable Photothermal-Promoted Effect in Photo-Fenton Degradation of Methylene Blue and in Water Evaporation.

MoS2 has garnered considerable attention as an exceptional co-catalyst that is capable of significantly enhancing the efficiency of H2O2 decomposition in advanced oxidation processes (AOPs). This improvement allows for a reduction in the required amounts of H2O2 and Fe2+. In this study, we investigated the cyclic durability of photo-Fenton catalysts, focusing on the degradation of pollutants through the introduction of PPy into heterogeneous 1T-2H MoS2 units. The resulting photothermal-Fenton catalysts, comprising non-ferrous Fenton catalysts, demonstrated excellent degradation performance for simulated pollutants. In comparison with 1T-2H MoS2, the PPy@1T-2H MoS2 composite exhibited remarkable stability and photothermal enhancement in the photo-Fenton degradation of methylene blue (MB) under visible light irradiation. The photo-Fenton reaction efficiently degraded contaminants, achieving 99% removal within 5 min and 99.8% removal within 30 min. Moreover, the co-catalyst complex displayed enhanced cyclic stability during the photo-Fenton reaction, with a contaminant removal efficiency of 92%, even after the 13th cyclic test. The combined effects of PPy and 1T-2H MoS2 demonstrated improved efficiency in both photocatalytic and photo-Fenton catalytic reactions. Furthermore, PPy@1T-2H MoS2 exhibited outstanding performance in the photothermal evaporation of water, achieving an efficiency of 86.3% under one solar irradiation.

Large area synthesis of mono/few-layer MoS2 thin films on thermal oxide silicon substrate by pulsed laser deposition technique

Two-dimensional molybdenum disulphide (2D MoS2) has emerged as an auspicious material in the development of optoelectronic devices owing to its remarkable similarities with graphene while possessing a definite bandgap. However, the production of these devices is restricted due to the difficulties in producing high-quality 2D MoS2 films on a large scale. Here we report the growth of mono/few layers of MoS2 - on thermal oxide silicon (Si/SiO2) substrate using pulsed laser deposition (PLD). The presence of Raman peaks corresponding to A1g and E12g modes of vibration confirmed the formation of 2D MoS2. The difference in Raman shift of A1g and E12g modes was used to find out the number of layers of the PLD-grown MoS2 thin films, which was found to be increasing with deposition time. Photoluminescence spectra also revealed the formation of mono/few-layered MoS2 thin films, and the thickness of the films was determined using atomic force microscopy. The MoS2 thin films were then deposited on a quartz substrate to record the absorption spectra of MoS2, and the existence of four excitonic peaks A, B and C, D further confirmed the formation of 2H MoS2. The calculation of the bandgap was done using Tauc plot studies, and a bandgap value of 1.77 eV was obtained for monolayer MoS2. The stoichiometry of Mo and S in the PLD-grown samples was determined using X-ray photoelectron spectroscopy analysis. The morphology and crystallinity of the monolayer MoS2 were studied by performing transmission electron microscopy analysis.

Hybrid Heterostructures of a Spin Crossover Coordination Polymer on MoS2 : Elucidating the Role of the 2D Substrate.

Controlling the deposition of spin-crossover (SCO) materials constitutes a crucial step for the integration of these bistable molecular systems in electronic devices. Moreover, the influence of functional surfaces, such as 2D materials, can be determinant on the properties of the deposited SCO film. In this work, ultrathin films of the SCO Hofmann-type coordination polymer [Fe(py)2 {Pt(CN)4 }] (py = pyridine) onto monolayers of 1T and 2H MoS2 polytypes are grown. The resulting hybrid heterostructures are characterized by GIXRD, XAS, XPS, and EXAFS to get information on the structure and the specific interactions generated at the interface, as well as on the spin transition. The use of a layer-by-layer results in SCO/2D heterostructures, with crystalline and well-oriented [Fe(py)2 {Pt(CN)4 }]. Unlike with conventional Au or SiO2 substrates, no intermediate self-assembled monolayer is required, thanks to the surface S atoms. Furthermore, it is observed that the higher presence of Fe3+ in the 2H heterostructures hinders an effective spin transition for [Fe(py)2 {Pt(CN)4 }] films thinner than 8nm. Remarkably, when using 1T MoS2 , this transition is preserved in films as thin as 4nm, due to the reducing character of this metallic substrate. These results highlight the active role that 2D materials play as substrates in hybrid molecular/2D heterostructures.

Boosting the gas sensing performances of 2H–MoSe2 bilayer upon alkali metal intercalation: Insights from DFT calculations

Realizing the multilayer or bulk MoSe2 cross from indirect bandgap to direct bandgap has drawn increasing attention due to the more practically useable and novel optoelectronic properties. In this work, the feasibility to realize indirect-to-direct band gap transition by intercalating alkali metals into 2H–MoSe2 bilayer was explored and its effect on the gas adsorption performance was evaluated utilizing first-principles calculation. The calculated results show that only Li and Na can be stably intercalated into the interlayer of 2H–MoSe2 bilayer. And the intercalated alkali metals as n-type dopant can realize the band gap transition from indirect to direct of 2H–MoSe2 bilayer, which is mainly ascribed to the decoupled interlayer interaction and built-in electric field in 2H–MoSe2 bilayer. Additionally, the adsorption performance of reducing gases is basically unchanged, while that of oxidizing gases (NO, NO2 and O2) is gradually enhanced with the intercalation concentrations of alkali metals increasing. The enhancement in adsorption performance for oxidizing gases is mainly ascribed to an indirect-to-direct bandgap transition along with the built-in electric field along the z-axis of 2H–MoSe2 bilayer. Through alkali metal intercalation, this research can provide a new method for the design and synthesis of transition metal dichalcogenides with enhanced gas-sensing performances.

Controllable Synthesis of 2H-1T' Mox Re(1- x ) S2 Lateral Heterostructures and Their Tunable Optoelectronic Properties.

Constructing heterostructures and doping are valid ways to improve the optoelectronic properties of transition metal dichalcogenides (TMDs) and optimize the performance of TMDs-based photodetectors. Compared with transfer techniques, chemical vapor deposition (CVD) has higher efficiency in preparing heterostructures. As for the one-step CVD growth of heterostructures, cross-contamination between the two materials may occur during the growth process, which may provide the possibility of one-step simultaneous realization of controllable doping and formation of alloy-based heterostructures by finely tuning the growth dynamics. Here, 2H-1T' Mox Re(1- x ) S2 alloy-to-alloy lateral heterostructures are synthesized through this one-step CVD growth method, utilizing the cross-contamination and different growth temperatures of the two alloys. Due to the doping of a small amount of Re atoms in 2H MoS2 , 2H Mox Re(1- x ) S2 has a high response rejection ratio in the solar-blind ultraviolet (SBUV) region and exhibits a positive photoconductive (PPC) effect. While the 1T' Mox Re(1- x ) S2 formed by heavily doping Mo atoms into 1T' ReS2 will produce a negative photoconductivity (NPC) effect under ultraviolet (UV) laser irradiation. The optoelectronic property of 2H-1T' Mox Re(1- x ) S2 -based heterostructures can be modulated by gate voltage. These findings are expected to expand the functionality of traditional optoelectronic devices and have potential applications in optoelectronic logic devices. This article is protected by copyright. All rights reserved.

Intercalated hydrates stabilize bulky MoS2 anode for Lithium-Ion battery

Bulky molybdenum disulfide (MoS2) has rarely been considered as a promising anode for lithium-ion battery due to the high volume strain and structural collapse caused by conversion reaction. In this work, a bulky K(H2O)MoS2 is rationally designed by intercalating hydrated potassium into commercial 2H MoS2, which exhibits a high volumetric capacity of 1566.7 mAh cm−3 along with an extremely enhanced capacity retention from 16% to 102% after 400 cycles at 1 A/g. Moreover, the assembled LiCoO2//K(H2O)MoS2 full cell delivers an energy density of 223.2 Wh/kg and a capacity retention of 89.6% after 100 cycles at 0.5 A/g. Based on the results of in situ X-ray diffraction (XRD) and Raman spectrum, differential electrochemical mass spectrometry (DEMS), time-of-flight secondary mass spectrometry (TOF-SIMS), and theoretical calculations, the stable lithium storage of K(H2O)MoS2 benefits from the buffer interlayers composed of “confined Li-O species and S-H bonds”, which limit the complete conversion reaction and preserve the layered structure. The proposed strategy of introducing intercalated hydrates for improving the cycling stability of bulky MoS2 raises the prospect of practical applications in layered metal chalcogenides anodes.

Laser induced crystallization of sputtered MoS2 thin films

The integration of transition metal dichalcogenides (TMDs) thin films into Si CMOS-based devices requires the development of new bottom-up material growth approaches producing high crystallinity films without affecting the SiO2/Si substrate. For this purpose, sputtering is a suitable deposition method due to its simplicity, jointly with high reliability and large area deposition capabilities. However, sputtered layers are amorphous and require a post-deposition thermal treatment to obtain a highly crystalline film. Nanosecond pulsed laser annealing (PLA) has recently emerged as promising route to achieve large-scale crystalline TMDs films without significantly heating or affecting the underlying substrate. The aim of this work is to explore the possibility to produce crystalline 2H–MoS2 on large areas directly on a SiO2-on-Si substrate. The film structure, composition and morphology were monitored as a function of the laser pulse energy density by Raman spectroscopy, X-rays diffraction, Rutherford backscattered spectroscopy (RBS), scanning transmission electron microscopy (STEM) and atomic force microscopy (AFM). The electrical properties of the film with optimized crystallinity were finally investigated through deposition of Cr/Au contacts using shadow masks. This approach can be scaled to other TMDs materials and substrates, also paving the way for the fabrication of heterostructures and electrical devices on the top of a single substrate.

Europium Molybdate/Molybdenum Disulfide Nanostructures with Efficient Electrocatalytic Activity for the Hydrogen Evolution Reaction

The design of hybrid nanostructures of molybdenum disulfide (MoS2) has been extensively explored as potent electrocatalysts for hydrogen generation reactions. Here, we report the in situ synthesis of a nanocomposite containing europium molybdate [Eu2(MoO4)3] and molybdenum disulfide (MoS2) for an enhanced electrochemical hydrogen evolution reaction (HER). The characteristic X-ray diffraction (XRD) peaks of both 2H–MoS2 and α-Eu2(MoO4)3 confirm the formation of the nanocomposite. The nanoflower (NF) architecture of MoS2 coupled with flakes of europium molybdate is observed in the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images, which lead to an enhanced surface area of the nanocomposite. Raman and X-ray photoelectron spectroscopy (XPS) studies reveal a variation in the layer thickness of MoS2 and a significant interfacial electronic interaction between Eu2(MoO4)3 and MoS2. As evident from the small onset potential of −0.05 V vs reversible hydrogen electrode (RHE) and a lower overpotential value of 186 mV (at a current density of 10 mA/cm2), the nanocomposite outperforms pristine MoS2 nanoflowers in terms of electrocatalytic HER. The charge-transfer resistance of the nanocomposite (80.02 Ω) is significantly low compared to pristine MoS2 (158.37 Ω), thus confirming the enhanced interfacial charge transfer. The Tafel slope value of the nanocomposite (189 mV/dec) is notably less than that of pristine MoS2 (313 mV/dec), indicating the enhanced HER activity of the nanocomposite. The fabrication of lanthanide-containing MoS2 nanocomposites appears to be promising for an efficient electrocatalytic activity for the hydrogen evolution reaction.

Radio-frequency controlled crystalline phase transformation of MoS2 thin film fabricated by unique vapour-plasma mixing technique

Successful fabrication of molybdenum disulfide thin films on silicon substrates by a unique vapour-plasma mixing technique at a relatively low temperature of 300 °C is reported. This mixing technique involves simultaneous sputtering of a molybdenum target and thermal evaporation of sulphur flakes to form MoS2 molecules. Raman studies confirm the formation of MoS2 with characteristic E12g and A1g modes observed at ∼384 and ∼408 cm−1. The effects of radio frequency (RF) power on the physical properties of MoS2 film at a constant sulphur evaporation rate are investigated. The Raman and X-Ray photon spectroscopy reveal that a controlled crystalline phase transition between metallic tetragonal (1 T-MoS2) and semiconducting hexagonal (2H–MoS2) has been successfully achieved upon variation of the RF power. Furthermore in X-Ray diffraction analysis, Scherrer's, Williamson-Hall and Size-Strain Plot methods are used to extract relevant correlations between structural properties (viz. Crystallite sizes, strains) and the thin film growth controlling parameters.

2H–MoSe2 nanosheet as noble-metal-free co-catalyst over Cd0·7Zn0·3S: optimizing interfacial charge transfer for enhanced photocatalytic hydrogen evolution

Developing highly efficient and low-cost noble-metal-free cocatalysts is significant for visible-light photocatalytic water splitting. Herein, 2H phase MoSe2 nanosheets were successfully synthesized via a solvent-assisted hydrothermal method and used as cocatalysts to construct heterostructure with hexagonal Cd0·7Zn0·3S nanoparticles. This well-designed heterostructure will significantly shorten the distance of charge migration to achieve efficient electron transfer between Cd0·7Zn0·3S and MoSe2. As expected, the optimized composites exhibited excellent photocatalytic hydrogen evolution (PHE) activity (3363.4 μmol g−1 in 5 h), which was 3.3 times than that of pristine Cd0·7Zn0·3S, and higher than that of 1%Pt–Cd0.7Zn0.3S. Based on electrochemical and photoluminescence results, the enhanced activity could be attributed to the lower overpotential (−0.27 V) and superior carrier separation of Cd0·7Zn0·3S/MoSe2 heterojunction. Meanwhile, 2H–MoSe2 nanosheets with large specific surface area can afford highly active Se-edge sites to absorb the protons for boosting hydrogen evolution. Moreover, Cd0·7Zn0·3S/MoSe2 photocatalysts also displayed a long-term stability without apparent debasement. This work provides new inspiration that transition metal dichalcogenides (TMDCs) as cocatalysts are promising to effectively enhance the PHE performance of sulfide solid solutions.