MoS2/Graphene Nanosheets from Commercial Bulky MoS2 and Graphite as Anode Materials for High Rate Sodium‐Ion Batteries

Tuning heterointerfaces between hybrid phases is a very promising strategy for designing advanced energy storage materials. Herein, a low‐cost, high‐yield, and scalable two‐step approach is reported to prepare a new type of hybrid material containing MoS₂/graphene nanosheets prepared from ball‐milling and exfoliation of commercial bulky MoS₂ and graphite. When tested as an anode material for a sodium‐ion battery, the as‐prepared MoS₂/graphene nanosheets exhibit remarkably high rate capability (284 mA h g^?1 at 20 A g^?1 (≈30C) and 201 mA h g^?1 at 50 A g^?1 (≈75C)) and excellent cycling stability (capacity retention of 95% after 250 cycles at 0.3 A g^?1). Detailed experimental measurements and density functional theory calculation reveal that the functional groups in 2D MoS₂/graphene heterostructures can be well tuned. The impressive rate capacity of the as‐prepared MoS₂/graphene hybrids should be attributed to the heterostructures with a low degree of defects and residual oxygen containing groups in graphene, which subsequently improve the electronic conductivity of graphene and decrease the Na⁺ diffusion barrier at the MoS₂/graphene interfaces in comparison with the acid treated one.     

Ultrastable In‐Plane 1T–2H MoS2 Heterostructures for Enhanced Hydrogen Evolution Reaction

Metallic 1T MoS₂ is highly desirable for catalyzing electrochemical hydrogen production from water owing to its high electrical conductivity. However, stable 1T MoS₂ is difficult to be produced in large‐scale by either common chemical or physical approaches. Here, ultrastable in‐plane 1T–2H MoS₂ heterostructures are achieved via a simple one‐pot annealing treatment of 2H MoS₂ bulk under a mixture gas of Ar and phosphorous vapor, where phosphorus cannot only occupy the interspace of MoS₂ bulk, resulting in the expansion of MoS_2, but also embed into the lattice of MoS_2, inducing the partial phase transition from 2H to 1T phases of MoS₂. Benefiting from its significantly improved electrical conductivity, highly exposed active sites, and hydrophily property, in‐plane 1T–2H MoS₂ heterostructures exhibit largely improved electrocatalytic properties for hydrogen evolution reaction (HER) in alkaline electrolytes.     

Strong Visible‐Light Absorption and Hot‐Carrier Injection in TiO2/SrRuO3 Heterostructures

Correlated electron oxides prove a diverse landscape of exotic materials' phenomena and properties. One example of such a correlated oxide material is strontium ruthenate (SrRuO₃) which is known to be a metallic itinerant ferromagnet and for its widespread utility as a conducting electrode in oxide heterostructures. We observe that the complex electronic structure of SrRuO₃ is also responsible for unexpected optical properties including high absorption across the visible spectrum (commensurate with a low band gap semiconductor) and remarkably low reflection compared to traditional metals. By coupling this material to a wide band gap semiconductor (TiO₂) we demonstrate dramatically enhanced visible light absorption and large photocatalytic activities. The devices function by photo‐excited hot‐carrier injection from the SrRuO₃ to the TiO₂ and the effect is enhanced in thin films due to electronic structure changes. This observation provides an exciting new approach to the challenge of designing visible‐light photosensitive materials.     

二硫化钼纳米材料在生物传感器中的应用

近年来纳米材料的不断引入，为生物传感技术提供了新的研究途径，大大提高了生物传感器的性能。其中，二硫化钼(MoS₂)纳米材料由于比表面积大、带隙可调、电子迁移率高等独特性质，在生物传感器中被广泛应用。本文首先介绍了基于MoS₂纳米材料的电化学、场效应晶体管、表面增强拉曼散射、比色、双模式生物传感器的基本原理、研究进展及性能对比，重点分析了MoS₂纳米复合材料的结构、组分等对传感器灵敏度、检测范围、检测限、特异性等性能的影响，总结了MoS₂生物传感器的优势并对其未来发展趋势进行了展望，为MoS₂生物传感器在生物检测领域的进一步应用以及未来研究方向提供了思路。     

Improving Efficiency of TiO<Subscript>2</Subscript>:Ag /Si Solar Cell Prepared by Pulsed Laser Deposition

Titanium dioxide (TiO₂) has been extensively studied and demonstrated to be suitable to enhance the efficiency of solar cell. In this work, TiO₂ is doped with silver nanoparticles (AgNP’s) on glass and the Si substrate by using Pulsed Laser Deposition (PLD) technique. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM), electrical conductivity (σ _dc), Hall coefficient (R_H), current–voltage (I–V), and capacity–voltage (C–V) characterizations have been used to examine the optical, the morphological, and the electrical properties of the films. It has been found that 5 wt.% (Ag) doped TiO₂ thin film has the most effect on efficiency of TiO₂:Ag /Si solar cell. The (I–V) characteristics showed that the (TiO₂) thin film enhances the efficiency of the (p–n) junction solar cell from 1.26 % pure TiO₂ to 7.19 % with doping of noble metal (Ag) representing improvement in the efficiency of solar cell leading to estimate empirical equations between efficiency, extinction coefficient, and energy band gap which have a total fit with the experimental data.     

Supercapacitor Electrodes Obtained by Directly Bonding 2D MoS2 on Reduced Graphene Oxide

Layered molybdenum disulfide (MoS₂) is deposited by microwave heating on a reduced graphene oxide (RGO). Three concentrations of MoS₂ are loaded on RGO, and the structure and morphology are characterized. The first layers of MoS₂ are detected as being directly bonded with the oxygen of the RGO by covalent chemical bonds (Mo‐O‐C). Electrochemical characterizations indicate that this electroactive material can be cycled reversibly between 0.25 and 0.8 V in 1 m HClO₄ solution for hybrids with low concentrations of MoS₂ layers (LCMoS₂/RGO) and between 0.25 and 0.65 V for medium (MCMoS₂/RGO) and high concentrations (HCMoS₂/RGO) of MoS₂ layers on graphene. The specific capacitance measured values at 10 mV s^?1 are 128, 265, and 148 Fg^?1 for the MoS₂/RGO with low, medium, and high concentrations of MoS₂, respectively, and the calculated energy density is 63 W h kg^?1 for the LCMoS₂/RGO hybrid. This supercapacitor electrode also exhibits superior cyclic stability with 92% of the specific capacitance retained after 1000 cycles.     

Plasmonic Au-MoO<Subscript>3</Subscript> Colloidal Nanoparticles by Reduction of HAuCl<Subscript>4</Subscript> by Blue MoO<Subscript>x</Subscript> Nanosheets and Observation of the Gasochromic Property

Defective colloids of blue MoO_x nanosheets were prepared by anodizing exfoliation method in water. This colloidal solution exhibits an optical plasmonic absorption band in the infrared region at about 760 nm. Merely mixing HAuCl₄ solution with the MoO_x leads to loss of the blue color, decaying of 760 nm plasmonic peak and simultaneous formation of the gold plasmon absorption peak at 550–570 nm. Some spectral variations in gold plasmonic peak and MoO_x optical band gap were observed for Mo:Au ratio of 10:1, 20:1, 30:1, and 40:1. The size of the gold nanoparticles was in the 5–6 nm range with fcc crystalline structure. X-ray photoelectron spectroscopy (XPS) revealed that the initial solution contains Mo⁵⁺ states and hydroxyl groups, which after reduction, hydroxyl groups are eliminated and the Mo⁵⁺ states converted to Mo⁶⁺. The obtained Au-MoO₃ colloids have a gasochromic property in which they are colored back to blue in the presence of hydrogen gas and the molybdenum oxide absorption peak recovered again. Furthermore, it was observed that both gold and Mo oxide plasmonic peaks redshift by insertion of hydrogen gas which is attributed to change in solution refractive index and formation of defect concentration.     

Retracted: Single layer molybdenum disulfide as an optical nanoprobe for 2 photon luminescence and second harmonic generation cell imaging

More recently, tremendous progress has been achieved in the development of two‐dimensional semiconductor materials applied in catalyst, energy application, sensor device and bioengineering since the birth of graphene isolated from graphite. Layered molybdenum disulfide (MoS₂) as an indirect gap semiconductor can efficiently emit photoluminescence (PL) excited by visible light, which shows a great potential in adaptive biological imaging. However, 1 photon PL of MoS₂ for cell imaging purposes suffers from strong autofluorescence and ion‐induced PL quenching. Herein, we report single layer small chitosan decorated MoS₂ nanosheets as a nonbleaching, nonblinking optical nanoprobe under near infrared femtosecond laser excitation and their applications for strong 2 photon luminescence (TPL) and strong second harmonic generation (SHG) bioimaging. Furthermore, the TPL can resist the ion‐induced quenching on the cellular membrane. The proposed TPL and SHG of single‐layer MoS₂ show great potential for real‐time, deep, multiphoton and three‐dimensional bioimaging under low‐power laser excitation.      

Room Temperature NO<Subscript>2</Subscript> Gas Sensor Based on SnO<Subscript>2</Subscript>-WO<Subscript>3</Subscript> Thin Films

Metal oxide semiconductors (MOS) are important and promising materials in optoelectronics, and it has been widely used in various catalytic applications such as gas sensing due to its high reactivity with many gases. In current work, mixtures of SnO₂-WO₃ (1:1) were prepared to synthesize nanostructured thin films by pulsed laser deposition as gas sensors. The sensitivity of sensors was measured for a relatively low concentration (200 ppm) of NO₂ gas at room temperature; sensors prepared with target exposed to (200) laser shots have higher sensitivity with a maximum value of 96.49 % at time 65 s as compared with the sensors prepared with (150) laser shots where the sensitivity has a maximum value 71.82 % at time 110 s; XRD pattern shows a better crystalline and high intensity with increasing laser shots up to 200; scanning electron microscopy (SEM) micrographs show approximate homogeneity of grains that cover the substrate without cracks and pinholes with nanoparticles fall in micro and nanometer range 50–200 nm. The values of the direct band gap were found to be 2.07143 eV for films prepared with 150 laser shots and 2.02899 eV for films prepared with 200 laser shots which have higher absorbance than the former films due to the increment in thickness and particle size. Empirical equations between sensitivity and gas exposure time have been formulated with great coincidence with the experimental data.     

Few‐Layer MoS2 Flakes as Active Buffer Layer for Stable Perovskite Solar Cells

Solution‐processed few‐layer MoS₂ flakes are exploited as an active buffer layer in hybrid lead–halide perovskite solar cells (PSCs). Glass/FTO/compact‐TiO₂/mesoporous‐TiO₂/CH₃NH₃PbI₃/MoS₂/Spiro‐OMeTAD/Au solar cells are realized with the MoS₂ flakes having a twofold function, acting both as a protective layer, by preventing the formation of shunt contacts between the perovskite and the Au electrode, and as a hole transport layer from the perovskite to the Spiro‐OMeTAD. As prepared PSC demonstrates a power conversion efficiency (η) of 13.3%, along with a higher lifetime stability over 550 h with respect to reference PSC without MoS₂ (Δη/η = ?7% vs. Δη/η = ?34%). Large‐area PSCs (1.05 cm² active area) are also fabricated to demonstrate the scalability of this approach, achieving η of 11.5%. Our results pave the way toward the implementation of MoS₂ as a material able to boost the shelf life of large‐area perovskite solar cells in view of their commercialization.     

Boosting the Performance of WO3/n‐Si Heterostructures for Photoelectrochemical Water Splitting: from the Role of Si to Interface Engineering

Metal oxide/Si heterostructures make up an exciting design route to high‐performance electrodes for photoelectrochemical (PEC) water splitting. By monochromatic light sources, contributions of the individual layers in WO₃/n‐Si heterostructures are untangled. It shows that band bending near the WO₃/n‐Si interface is instrumental in charge separation and transport, and in generating a photovoltage that drives the PEC process. A thin metal layer inserted at the WO₃/n‐Si interface helps in establishing the relation among the band bending depth, the photovoltage, and the PEC activity. This discovery breaks with the dominant Z‐scheme design idea, which focuses on increasing the conductivity of an interface layer to facilitate charge transport, but ignores the potential profile around the interface. Based on the analysis, a high‐work‐function metal is predicted to provide the best interface layer in WO₃/n‐Si heterojunctions. Indeed, the fabricated WO₃/Pt/n‐Si photoelectrodes exhibit a 2 times higher photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) and a 10 times enhancement at 1.6 V versus RHE compared to WO₃/n‐Si. Here, it is essential that the native SiO₂ layer at the interface between Si and the metal is kept in order to prevent Fermi level pinning in the Schottky contact between the Si and the metal.     

Drastic Layer‐Number‐Dependent Activity Enhancement in Photocatalytic H2 Evolution over nMoS2/CdS (n ≥ 1) Under Visible Light

Exploiting noble‐metal‐free cocatalysts is of huge interest for photocatalytic water splitting using solar energy. As an efficient cocatalyst in photocatalysis, MoS₂ is shown promise as a low‐cost alternative to Pt for hydrogen evolution. Here we report a systematical study on controlled synthesis of MoS₂ with layer number ranging from ≈1 to 112 and their activities for photocatalytic H₂ evolution over commercial CdS. A drastic increase in photocatalytic H₂ evolution is observed with decreasing MoS₂ layer number. Particularly for the single‐layer (SL) MoS₂, the SL‐MoS₂/CdS sample reaches a high H₂ generation rate of ≈2.01 × 10^?3m h^?1 in Na₂S–Na₂SO₃ solutions and ≈2.59 × 10^?3m h^?1 in lactic acid solutions, corresponding to an apparent quantum efficiency of 30.2% and 38.4% at 420 nm, respectively. In addition to the more exposed edges and unsaturated active S atoms, valence band–XPS and Mott–Schottky plots analysis indicate that the SL MoS₂ has the more negative conduction band energy level than the H⁺/H₂ potential, facilitating the hydrogen reduction.     

Metal-Dielectric-Graphene Hybrid Heterostructures with Enhanced Surface Plasmon Resonance Sensitivity Based on Amplitude and Phase Measurements

Metal-dielectric-graphene hybrid heterostructures based on oxides Al₂O₃, HfO₂, and ZrO₂ as well as on complementary metal–oxide–semiconductor compatible dielectric Si₃N₄ covering plasmonic metals Cu and Ag have been fabricated and studied. We show that the characteristics of these heterostructures are important for surface plasmon resonance biosensing (such as minimum reflectivity, sharp phase changes, resonance full width at half minimum and resonance sensitivity to refractive index unit (RIU) changes) can be significantly improved by adding dielectric/graphene layers. We demonstrate maximum plasmon resonance spectral sensitivity of more than 30,000 nm/RIU for Cu/Al₂O₃ (ZrO₂, Si₃N₄), Ag/Si₃N₄ bilayers and Cu/dielectric/graphene three-layers for near-infrared wavelengths. The sensitivities of the fabricated heterostructures were?~?5–8 times higher than those of bare Cu or Ag thin films. We also found that the width of the plasmon resonance reflectivity curves can be reduced by adding dielectric/graphene layers. An unexpected blueshift of the plasmon resonance spectral position was observed after covering noble metals with high-index dielectric/graphene heterostructures. We suggest that the observed blueshift and a large enhancement of surface plasmon resonance sensitivity in metal-dielectric-graphene hybrid heterostructures are produced by stationary surface dipoles which generate a strong electric field concentrated at the very thin top dielectric/graphene layer.

     

MoS2‐Based All‐Purpose Fibrous Electrode and Self‐Powering Energy Fiber for Efficient Energy Harvesting and Storage

Here an all‐purpose fibrous electrode based on MoS₂ is demonstrated, which can be employed for versatile energy harvesting and storage applications. In this coaxial electrode, ultrathin MoS₂ nanofilms are grown on TiO₂ nanoparticles coated carbon fiber. The high electrochemical activity of MoS₂ and good conductivity of carbon fiber synergistically lead to the remarkable performances of this novel composite electrode in fibrous dye‐sensitized solar cells (showing a record‐breaking conversion efficiency of 9.5%) and high‐capacity fibrous supercapacitors. Furthermore, a self‐powering energy fiber is fabricated by combining a fibrous dye‐sensitized solar cell and a fibrous supercapacitor into a single device, showing very fast charging capability (charging in 7 s under AM1.5G solar illumination) and an overall photochemical‐electricity energy conversion efficiency as high as 1.8%. In addition, this wire‐shaped electrode can also be used for fibrous Li‐ion batteries and electrocatalytic hydrogen evolution reactions. These applications indicate that the MoS₂‐based all‐purpose fibrous electrode has great potential for the construction of high‐performance flexible and wearable energy devices.     

Plasmonic Perovskite Solar Cells Utilizing Au@SiO<Subscript>2</Subscript> Core-Shell Nanoparticles

The role of Au@SiO₂ core-shell nanoparticles on optical properties of perovskite solar cells has been explored using both the theoretical computations and the experiments. A quasi-static model is used to study the surface plasmon resonances (SPRs) of Au@SiO₂ core-shell nanospheres. Au@SiO₂ core-shell nanoparticles, with varying shell thickness and core radius, were assumed to be embedded in methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite active layer. Enhanced absorption in the active layer is obtained due to the near-field plasmonic effect of the embedded core-shell nanoparticles. Theoretical modelling shows that a shell thickness of 1 nm and core diameter of 20 nm provide absorption enhancement in the orange-red region of the electromagnetic spectrum. Experiments performed using ～20-nm-sized Au@SiO₂ core-shell nanoparticles (with a shell thickness of ～1 nm) clearly demonstrate the enhanced absorption and the resulting enhancement in photocurrent due to the plasmonic effects. An efficiency enhancement of over 18 % is obtained for the best plasmonic perovskite solar cell containing Au@SiO₂ nanoparticles in Au@SiO₂-TiO₂ weight ratio of ～1 %. Incident photon-to-current conversion efficiency (IPCE) data also showed enhancement in photocurrent for the plasmonic device. The quasi-static modelling approach provides a good correlation between theory and experiment.     

Large‐Area,Ultrathin Inorganic Network Coverages–Graphene Hierarchical Electrodes for Flexible,Heat‐Resistant Energy Storage Application

Graphene and quasi‐2D graphene‐like materials with an ultrathin thickness have been investigated as a new class of nanoscale materials due to their distinctive properties. A novel “molecular tools‐assistances” strategy is developed to fabricate two kinds of graphene‐based electrodes, ultrathin Fe‐doped MnO₂ network coverage–graphene composites (G‐MFO) and ultrathin MoS₂ network coverage–graphene composites (G‐MoS₂) with special hierarchical structures. Such structures enable a large contact interface between the active materials and graphene and thus fully exploit the synergistic effect from both the high specific capacitance of MFO or MoS₂ and the superb conductivity of graphene. Benefiting from their unique structural features, G‐MFO and G‐MoS₂ films directly use as free‐standing electrodes for flexible asymmetric supercapacitors with a nonaqueous gel electrolyte. The device achieves a high energy/power density, superior flexibility, good rate capability as well as outstanding performance stability even at a high temperature. This work represents a promising prototype to design new generation of hybrid supercapacitors for future energy storage devices.     

Structural and Optical Properties of Novel In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticle-Assembled Nanorods

In₂O₃ nanoparticle-assembled nanorods with distinct surface morphologies have been newly synthesized by a dehydration process of self-assembled In(OH)₃ nanorods obtained from a liquid-based route. The reaction mechanism and the structural transformation between these two one-dimensional nanorods, In₂O₃ and In(OH)₃, were precisely characterized by means of various qualitative and quantitative analyses with X-ray scattering simulations. The broad absorption band in the UV–visible spectrum evidently originates from the nanoparticle-assembling effect within the In₂O₃ nanorods. An intensive photoluminescence emission at 440 nm observed under an excitation wavelength of 325 nm is attributed to the existence of oxygen vacancies within the In₂O₃ nanorods.     

Crystal and electronic structures and high-pressure behavior of AgSO<Subscript>4</Subscript>, a unique narrow band gap antiferromagnetic semiconductor: LDA(+U) picture

We demonstrate that DFT calculations performed with the local density approximation (LDA) allow for significantly better reproduction of lattice constants, the unit cell volume and the density of Ag(II)SO₄ than those done with generalized gradient approximation (GGA). The LDA+U scheme, which accounts for electronic correlation effects, enables the accurate prediction of the magnetic superexchange constant of this strongly correlated material and its band gap at the Fermi level. The character of the band gap places the compound on the borderline between a Mott insulator and a charge transfer insulator. The size of the band gap (0.82 eV) indicates that AgSO₄ is a ferrimagnetic semiconductor, and possibly an attractive material for spintronics. A bulk modulus of 27.0 GPa and a compressibility of 0.037 GPa^–1 were determined for AgSO₄ from the third-order Birch–Murnaghan isothermal equation of state up to 20 GPa. Several polymorphic types compete with the ambient pressure P-1 phase as the external pressure is increased. The P-1 phase is predicted to resist pressure-induced metallization up to at least 20 GPa.     

Graphene-MoS2 with TiO2SiO2 layers based surface plasmon resonance biosensor: Numerical development for formalin detection

In this article, numerically a surface plasmon resonance (SPR) biosensor is developed based on Graphene-M_OS₂ with TiO₂SiO₂ hybrid structure for the detection of formalin. Based on attenuated total reflection (ATR) method, we used angular interrogation technique to sense the presence the formalin by observing the change of “minimum reflectance with respect to SPR angle” and “maximum transmittance with respect to surface plasmon resonance frequency (SPRF)”. Here, we used Chitosan as probe analyte to perform chemical reaction with formalin (formaldehyde) which is consider as target analyte. Simulation results show a negligible variation of SPRF and SPR angle for improper sensing of formalin that confirms absence of formalin whereas for proper sensing is considerably countable that confirms the presence of formalin. Thereafter, a comparison of sensitivity for different sensor structure is made. It is observed that the sensitivity without TiO₂, SiO₂, MoS₂ and Graphene (conventional structure) is very poor and 73.67% whereas the sensitivity with graphene but without TiO₂, SiO₂ and MoS₂ layers is 74.67% consistently better than the conventional structure. This is due to the electron loss of graphene, which is accompanying with the imaginary dielectric constant. Furthermore, the sensitivity without TiO₂, SiO₂ and graphene but with MoS₂ layer is 79.167%. After more if both graphene and MoS2 are used and TiO₂ and SiO₂ layers are not used then sensitivity improves to 80.5%. This greater than before performance is due to the absorption ability and optical characteristics of graphene biomolecules and high fluorescence quenching ability of MoS₂. Further again, if TiO₂SiO₂ composite layer is used with the Graphene-MoS2 then the sensitivity enhances from 80.5% to 82.5%. Finally, the sensitivity for the proposed structure has been carried out, and result is 82.83%, the highest value among all the previous structures to integrate the advantages of graphene, MoS₂, TiO₂ and SiO₂.     

Enhanced Potassium Ion Battery by Inducing Interlayer Anionic Ligands in MoS1.5Se0.5 Nanosheets with Exploration of the Mechanism

The strategy of inducing interlayer anionic ligands in 2D MoS_1.5Se_0.5 nanosheets is employed to consolidate the interlayer band gap and optimize the electronic structure for the potassium ion battery. It combines complementary advantages from two kinds of anionic ligands with high conductivity and good affinity with potassium ions. The potassium ion diffusion rate is accelerated as well by an optimized lower energy barrier for ion diffusion pathways, with the formation of highly reversible KMo₃Se₃ crystal other than K_0.4MoS₂/K₂MoS_4, which encounters a much slower electro/ion diffusion rate upon discharging. These advances deliver enhanced potassium storage properties with excellent cycling stability, with retained specific capacity of 531.6 mAh g^?1 at a current density of 200 mA g^?1 even after 1000 cycles, and high rate capability with specific capacity of 270.1 mAh g^?1 at 5 A g^?1. The insertion and conversion mechanism are also elucidated by a combination of density functional theory computations and in situ synchrotron measurements.