Mo 4d Orbitals Research Articles

Electronic and Atomic Structural Properties Associated with Enhanced Photodegradation Activity in Mo-Doped TiO2 Nanoparticles.

The efficacy and structural evolution of Mo-doped titania nanoparticles (MTNPs) as advanced photocatalysts for degrading methyl blue (MB) are investigated by X-ray absorption spectroscopy (XAS). The 3 wt % MTNP, characterized by uniform size and anatase structure, exhibits higher efficiency. The spectral analyses unveiled structural variations in the TiO6 octahedral structure and revealed an active site of the distorted square pyramidal structure symmetry (C4v). The in situ XAS spectra illustrate that MTNPs, particularly at 3 wt % doping, effectively enhanced the hole carriers in Ti 3d orbitals with a charge transfer to Mo 4d orbitals and impeded electron-hole pair merging, significantly enhancing the photodegradation under light illumination. This study deepens our understanding of the crucial role of Mo doping in optimizing TiO2 nanoparticle performance for efficient environmental remediation, showcasing the potential of MTNPs as sustainable photocatalytic materials.

Hydration mechanism of molybdenite affected by surface oxidation: New insights from DFT and MD simulations

The oxidation and hydration of molybdenite surfaces cannot be avoided during the crushing and flotation processes in industry, which adversely affects its clean separation and extraction. In this study, the hydration mechanism under the influence of molybdenite surface oxidation was investigated using density functional theory (DFT) and molecular dynamics (MD) simulations. The results showed that the adsorption energy of a single water molecule on the molybdenite (0 0 1) surface changed from −0.33 kcal/mol to −2.07 kcal/mol after oxidation. Dissociated O acted as a bridging link on the molybdenite (0 0 1) surface, inducing hybridization of the Hw 1 s orbitals with the Os 2p orbitals, thereby enhancing the adsorption of water molecules. The adsorption energy of a single water molecule on the molybdenite (1 1 0) surface changed from −33.97 kcal/mol to −3.37 kcal/mol after oxidation. The dissociated O hindered the hybridization of the Mo 4d and Ow 2p orbitals, thus preventing the adsorption of water molecules on the (1 1 0) surface. After oxidation, the interfacial interaction between the molybdenite (0 0 1) surface and water molecules was enhanced, while the interfacial interaction between the molybdenite (1 1 0) surface and water molecules was weakened. The water molecules near the surface of molybdenite are adsorbed through hydrogen bonding and gradually form a hydrated film consisting of three layers of water molecules with a thickness of 8–9 Å as the water coverage increases.

Tuning d–p Orbital Hybridization of NiMoO4@Mo15Se19/NiSe2 Core‐Shell Nanomaterials via Asymmetric Coordination Interaction Enables the Water Oxidation Process

AbstractThe electrocatalytic performance of MoNi‐based nanomaterials undergo selenization has garnered significant interest due to their modified electronic structure, while still posses certain challenges for obtained bimetallic selenides. Here, a novel MoNi‐based electrocatalyst of NiMoO4@Mo15Se19/NiSe2 core‐shell nanomaterials is constructed to promote the desorption of OOH* which can facilitate the water oxidation process. NiMoO4@Mo15Se19/NiSe2 core‐shell nanoarrays show that the “cores” are mainly NiMoO4 nanorods while the “shells” are the bimetallic selenides nanoflakes, which are super architectures that can expand more active sites and accelerate the electron transfer. Moreover, the hybridization interaction between Ni 3d, Mo 4d, and Se 4p orbitals leads to an asymmetric distribution of electric clouds, which decreases the adsorption energy and transformation of oxygen‐containing species. Electrochemical data displays that the overpotentials of NiMoO4@Mo15Se19/NiSe2 core‐shell nanomaterials are only 195 mV, 220 mV, and 224 mV for oxygen evolution reaction (OER) in alkaline freshwater, alkaline simulated seawater, and alkaline natural seawater. The current density decay is negligible after 100 h stability at about 1.46 V with a three‐electrode system in alkaline natural seawater. The low cost and the unique MoNi‐based bimetallic selenides in this work provide a more constructive solution for designing efficient and stable OER catalysts in the future.

Bifunctional activity and theoretical study of transition metal molybdates for hydrogen and oxygen evolution reaction

Effective, sturdy and cheap electrocatalysts are extremely desirable for water electrolysis. In this work, transition metal molybdates (MMoO4, M = Fe, Co, Ni) with extraordinary oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in basic electrolyte solution was reported. β-Fe2(MoO4)3 catalyst exhibits better electrocatalytic performance and robustness for both HER and OER compared to NiMoO4 and CoMoO4. Theoretical study (DFT calculation) disclose that the Fe atoms increase the energy states near the Fermi level in β-Fe2(MoO4)3 which makes it more conductive leading to superior OER and HER activity. Compared to CoMoO4 and NiMoO4, β-Fe2(MoO4)3 have well defined multiple Mo 4d orbitals at the conduction band. These are empty states in conduction band, ready to receive the electrons. Further, the computed overpotential values for NiMoO4, CoMoO4, and β-Fe2(MoO4)3 surfaces follow the trend, β-Fe2(MoO4)3 < NiMoO4 < CoMoO4, corroborating with the experimental results.

Electron Configuration Modulation Induced Stabilized 1T-MoS2 for Enhanced Sodium Ion Storage.

1T-MoS2 has become an ideal anode for sodium-ion batteries (SIBs). However, the metastable feature of 1T-MoS2 makes it difficult to directly synthesize under normal conditions. In addition, it easily transforms into 2H phase via restacking, resulting in inferior electrochemical performance. Herein, the electron configuration of Mo 4d orbitals is modulated and the stable 1T-MoS2 is constructed by nickel (Ni) introduction (1T-Ni-MoS2). The original electron configuration of Mo 4d orbitals is changed via the electron injection by Ni, which triggers the phase transition from 2H to 1T phase, thus improving the electrical conductivity and accelerating the redox kinetics of the material. Consequently, 1T-Ni-MoS2 exhibits superior rate capability (266.8 mAh g-1 at 10 A g-1) and excellent cycle life (358.7 mAh g-1 at 1 A g-1 after 350 cycles). In addition, the assembled Na3V2(PO4)3/C||1T-Ni-MoS2 full cells deliver excellent electrochemical properties and show great prospects in energy storage devices.

Molecular Intercalation Enables Phase Transition of MoSe2 for Durable Na-Ion Storage.

1T-MoSe2 is recognized as a promising anode material for sodium-ion batteries, thanks to its excellent electrical conductivity and large interlayer distance. However, its inherent thermodynamic instability often presents unparalleled challenges in phase control and stabilization. Here, a molecular intercalation strategy is developed to synthesize thermally stable 1T-rich MoSe2, covalently bonded to an intercalated carbon layer (1TR/2H-MoSe2@C). Density functional theory calculations uncover that the introduced ethylene glycol molecules not only serve as electron donors, inducing a reorganization of Mo 4d orbitals, but also as sacrificial guest materials that generate a conductive carbon layer. Furthermore, the C─Se/C─O─Mo bonds encourage strong interfacial electronic coupling, and the carbon layer prevents the restacking of MoSe2, regulating the maximum 1T phase to an impressive 80.3%. Consequently, the 1TR/2H-MoSe2@C exhibits an extraordinary rate capacity of 326mAhg-1 at 5Ag-1 and maintains a long-term cycle stability up to 1500 cycles, with a capacity of 365mAhg-1 at 2Ag-1. Additionally, the full cell delivers an appealing energy output of 194Whkg-1 at 208Wkg-1, with a capacity retention of 87.3% over 200 cycles. These findings contribute valuable insights toward the development of innovative transition metal dichalcogenides for next-generation energy storage technologies.

First-principles study of the electronic and optical properties of Nb-doped MoSe2 by tensile strain

A first-principles method was used to explore the influence of tensile strain on the electrical and optical characteristics of Nb-doped MoSe2. The tensile strain has been discovered to have a higher influence on the electrical structure of the Nb-doped MoSe2 system than pure monolayer MoSe2. According to the energy band structure study, the pure monolayer MoSe2 is a direct bandgap semiconductor, but the system doped with Nb instead of Mo atoms is a p-type-doped semiconductor. The bandgap of the Nb-doped MoSe2 system decreases gradually with the increase of tensile strain, but still maintains the p-type semiconductor properties, and the bandgap of the pure monolayer MoSe2 also decreases gradually with the increase of tensile strain. From the density of states analysis, it is found that for the total density of states of the doped system at different tensile strains, it is mainly contributed by the Mo-4d and Se-4p orbitals. The optical properties analysis showed that the doped system under tensile strain had higher absorption coefficient and reflectance peak than the Nb-doped MoSe2 system without tensile strain. Additionally, the doped system showed redshift phenomenon in both the absorption and reflection peaks as the tensile strain increased.

Electron Modulated and Phosphate Radical Stabilized 1T‐Rich MoS2 for Ultra‐Fast‐Charged Sodium Ion Storage

AbstractMetallic phase molybdenum sulfide (1T‐MoS2) is considered as an attractive electrode material for sodium‐ion batteries (SIBs) owing to its abundant active sites, metallic conductivity and high theoretical capacity. Unfortunately, the thermodynamic unstable characteristic under natural conditions makes 1T‐MoS2 difficult to synthesize directly, which greatly hinders its further applications. Herein, an electron modulated and phosphate radical stabilized strategy is employed to construct stable 1T‐rich MoS2 (1T‐P‐MoS2). The PO43− groups are intercalated into MoS2 via a simple one‐step synthesis process, which enlarges the interlayer spacings and improves the insertion/extraction kinetics of Na+. Density functional theory (DFT) calculations and experiments demonstrate that the PO43− can give partial electrons to Mo upon PO43− intercalation, which triggers the reorganization of Mo 4d orbitals, resulting in a spontaneous phase transition of MoS2 from 2H to 1T phase, thereby enhancing the electrical conductivity of MoS2. The obtained 1T‐P‐MoS2 exhibits ultra‐fast charged properties (up to 277.1 mAh g−1 at 40 A g−1, discharged/charged within 25 s) and excellent cycling performance (up to 498.9 mAh g−1 after 300 cycles at 1 A g−1). This work provides a feasible technical solution and analyses the deep mechanisms on tuning of metal sulfide electrodes for advanced SIBs.

Field electron emission performance of Janus MoSSe and MoSSe-MWCNTs composite: Corroboration by Hall measurement and DFT simulation

Janus MoSSe and its composite with multiwalled carbon nanotubes (MWCNTs) have been synthesized using a facile one pot hydrothermal route. Formation of Janus MoSSe has been confirmed from the X-ray Diffraction, Raman, and X-ray Photoelectron spectroscopic analysis. Furthermore, field electron emission (FEE) behaviour of the as-synthesized Janus MoSSe and MoSSe-MWCNTs composite has been investigated at base pressure of ∼ 1 × 10−8 mbar in a planar diode configuration. Interestingly, the MoSSe-MWCNTs emitter exhibited enhanced FEE characteristics in terms of lower values of turn-on and threshold fields, competency to deliver large emission current density, in contrast to the pristine Janus MoSSe and MWCNTs emitters. An attempt has been made to reveal the underlying physics facilitating improvement in FEE behavior using computational analysis. In this regard, density functional theory (DFT) simulation was carried out to find electronic structure of the as-synthesized emitters. The DFT results indicate charge transfer from C 2p to Mo 4d orbitals, thereby enhancing electrical conductivity and reduction in work function of MoSSe-MWCNTs composite. Moreover, the experimental validation due to Hall measurements undoubtedly revealed noticeable increase in carrier concentration. The observed results clearly exemplify modulation electronic properties of Janus materials thereby highlighting their potential for various applications, including vacuum microelectronic devices.

Quantum anomalous Hall effect with high Chern numbers in functionalized square-octagon Sb monolayers

The quantum anomalous Hall (QAH) effect has attracted continuous attention due to its intriguing properties and potential applications in future electronics. Here, we present our investigation of the electronic and topological properties of a square-octagon Sb monolayer with Mo atoms adsorbed (Mo@so-Sb) using first-principles calculations. Our studies reveal how a trivial insulator can be first engineered into an unusual bipolar magnetic semiconductor (BMS) and then further tuned by strain into a spintronics-favorable half semiconductor (HS) or half metal. Remarkably, with 3.7% compressive strain applied, we achieve a QAH state in Mo@so-Sb with a high Chern number (C = 4) which is much larger than that (C = ±1 or ±2) of the previously predicted Chern insulators. This QAH state is characterized by the appearance of four gapless chiral edge states within the nontrivial band gap, enabling a robust multi-channel low-power-consumption transport. Its nontrivial topology primarily originates from the band inversion between the non-degenerate Mo 4d and Sb 5p orbitals. Additionally, we demonstrate the interesting BMS, HS, and QAH states can be controlled by the Mo adsorption concentrations. Our findings not only provide a versatile means of transforming trivial insulators into the desired spintronics-favorable and topological states, but also open new possibilities for high-performance electronic devices.

Superconductivity in Mo4Ga20As with endohedral gallium clusters

We report the discovery and detailed investigation of superconductivity in Mo4Ga20As. Mo4Ga20As crystallizes in a space group of I4/m (No. 87), with the lattice parameters a = 12.86352 Å and c = 5.30031 Å. The resistivity, magnetization, and specific heat data reveal Mo4Ga20As to be a type-II superconductor with T c = 5.6 K. The upper and lower critical fields are estimated to be 2.78 T and 22.0 mT, respectively. In addition, electron-phonon coupling in Mo4Ga20As is possibly stronger than the BCS weak-coupling limit. First-principles calculations suggest the Fermi level being dominated by the Mo-4d and Ga-4p orbitals.

Band Alignments, Electronic Structure, and Core-Level Spectra of Bulk Molybdenum Dichalcogenides (MoS2, MoSe2, and MoTe2).

A comprehensive study of bulk molybdenum dichalcogenides is presented with the use of soft and hard X-ray photoelectron (SXPS and HAXPES) spectroscopy combined with hybrid density functional theory (DFT). The main core levels of MoS2, MoSe2, and MoTe2 are explored. Laboratory-based X-ray photoelectron spectroscopy (XPS) is used to determine the ionization potential (IP) values of the MoX2 series as 5.86, 5.40, and 5.00 eV for MoSe2, MoSe2, and MoTe2, respectively, enabling the band alignment of the series to be established. Finally, the valence band measurements are compared with the calculated density of states which shows the role of p-d hybridization in these materials. Down the group, an increase in the p-d hybridization from the sulfide to the telluride is observed, explained by the configuration energy of the chalcogen p orbitals becoming closer to that of the valence Mo 4d orbitals. This pushes the valence band maximum closer to the vacuum level, explaining the decreasing IP down the series. High-resolution SXPS and HAXPES core-level spectra address the shortcomings of the XPS analysis in the literature. Furthermore, the experimentally determined band alignment can be used to inform future device work.

Crucial Role of Crystal Field on Determining the Evolution Process of Janus MoSSe Monolayer: A First-Principles Study.

Two-dimensional Janus MXY materials have been successfully synthesized from their parent species by CVD, SEAR, or PLD techniques. However, their detailed evolution process and underlying atomistic mechanism are far from understood conclusively, which are prompts for further research. Here, taking Janus MoSSe as a representation, the evolution process from MoS2 is systematically investigated by first-principles calculation. The simulation shows that the lowest formation energy of MoS(2-δ)Seδ increases with selenylation ratio δ. Unexpectedly, Se atoms prefer to form a pair in next-nearest neighboring state (Se-NN-Se), eventually transferred into a growth rule of (6n + 1) during the evolution process. Particularly, it is demonstrated that the stability of the intermediate is mainly governed by the Mo 4d orbitals in different distorted triangular crystal fields, rendering a different degree of orbital splitting. Both the occupied and unoccupied Mo 4d orbitals of Se-NN-Se are farther from the Fermi level than other cases, which is clearly illustrated by d-band center theory. These findings will be helpful to understand the evolution process and the underlying atomistic mechanism of Janus MXY.

Strain-induced strengthening in superconducting β-Mo2C through high pressure and high temperature

High-strain-induced microstructural refinement and dislocations are critical for the strengthening of metallic materials; however, this is difficult to achieve in ceramic materials due to their unique bonding characteristics and electronic structure. Here, a series of β-Mo2C bulk ceramics are consolidated by the high pressure and high temperature (HPHT) strategy. Our results demonstrate that high strain-induced grain plastic deformation at high pressure produces a lamellar sub-grain structure with high-density dislocations, and that the dislocations at the lath-like grain boundaries eventually evolve into low-angle grain boundaries. The mechanical properties, superconducting behavior, and onset of oxidation of the specimens are investigated. It is found that superconductivity and hardness arise from the high density of states at the Fermi level, while the high intrinsic hardness is attributed to the strong hybridization between Mo-4d orbitals and C-2p orbitals. Furthermore, strain-induced defect structure (dislocations and low-angle grain boundaries) mainly mainly enhances the intrinsic structure of β-Mo2C.

Synthesis, Characterization, and First-Principles Analysis of the MAB-Like Ternary Transition-Metal Boride Fe(MoB)2.

Novel transition-metal borides have attracted considerable attention because they exhibit high stability under extreme conditions. Compared with binary borides, ternary transition-metal borides (TTMBs) exhibit novel boron substructures and diverse properties, which result in excellent designability. In this study, we synthesized the MAB-like (where M = iron, A = molybdenum, and B = boron) phase Fe(MoB)2 using a high-pressure and high-temperature method. Fe(MoB)2 exhibited ferromagnetic metastable characteristics with a saturation magnetization of 8.35 emu/g at room temperature. Microhardness measurement revealed an indentation hardness of 10.72 GPa, which was higher than those of conventional magnetic materials. First-principles calculations revealed excellent mechanical properties, which mainly originated from the strong covalent short B2 chains. Furthermore, magnetism was attributed to the Fe 3d electrons. Numerous d-d hybridizations existed between the Fe 3d eg and Mo 4d orbitals, and the antibonding/nonbonding state difference for up/down-spin electrons in the hybridization orbitals led to the local magnetic moment of Fe(MoB)2. The magnetic anisotropy energy analyses reveal that Fe(MoB)2 prefers the easy magnetization axis along the z direction, and Mo atom acts as a medium to realize the exchange action between two Fe atoms. The B-B and Fe-B bonds were considerably stronger than the Fe-Mo and Mo-B bonds, and Fe(MoB)2 exhibited a class of atomically laminate composed of FeB2 and Mo layers. These results may provide guidance for the design of novel multifunctional TTMBs by adjusting the interactions between binary metal components.

A theoretical descriptor for screening efficient NO reduction electrocatalysts from transition-metal atoms on N-doped BP monolayer

An electrochemical nitric oxide (NO) reduction reaction (NORR) is proposed as an attractive method for simultaneous realization of NO removal and ammonia (NH3) synthesis. Here, the potentials of 29 transition-metal atoms anchored on the nitrogen-doped BP monolayer (MN3/BP) as efficient NORR catalysts are systematically examined using first-principles calculations. Combining the adsorption Gibbs free energies of the N and OH species, a simple descriptor is constructed and a volcano plot of the NORR limiting potentials on the single atom catalysts (SACs) is established. Consequently, the MoN3/BP and IrN3/BP SACs are picked out as promising NORR electrocatalysts for NH3 synthesis with the limiting potentials of −0.10 V and −0.06 V, respectively. Their corresponding rate constants are significantly larger than or close to that of the excellent Pt(111) surface. The electronic analysis shows that the Mo-4d or Ir-5d orbitals can be well hybridized with the NO-2p orbitals, sufficiently activating the adsorbed NO species. Particularly, the MoN3/BP and IrN3/BP SACs possess high thermal stabilities and can be easily synthesized by using MoCl3 and IrCl3 as precursors, respectively. This work not only offers a simple descriptor to efficiently design NORR electrocatalysts but also provides a comprehensive atomic understanding on the mechanism of NO-to-NH3 conversion.

Electronic and Near-Infrared-II Optical Properties of I-Doped Monolayer MoTe2: A First-Principles Study.

Near-infrared-II (NIR-II, 1000–1700 nm) fluorescence imaging is widely used for in vivo biological imaging. With the unique electronic structures and capability of band-gap engineering, two-dimensional (2D) materials can be potential candidates for NIR-II imaging. Herein, a theoretical investigation of the electronic structure and optical properties of iodine (I)-doped monolayer MoTe2 systems with different doping concentrations is carried out through simulations to explore their NIR optical properties. The results suggest that the emergence of impurity levels due to I doping effectively reduces the bandwidth of I-doped monolayer MoTe2 systems, and the bandwidth decreases with the increase in the I doping concentration. Although the I and Mo atoms possess clear covalent-bonding features according to the charge density difference, impurity levels induced by the strong hybridization between the I 5p and Mo 4d orbitals cross the Fermi level, making the doped systems exhibit metallic behavior. In addition, with the increase in the I doping concentration, the energy required for electron transition from valence bands to impurity levels gradually decreases, which can be linked to the enhancement of the optical absorption in the red-shifted NIR-II region. Meanwhile, with a higher I doping concentration, the emission spectra, which are the product of the absorption spectra and quasi-Fermi distributions for electrons and holes, can be enhanced in the NIR-II window.

High zinc-ion intercalation reaction activity of MoS2 cathode based on regulation of thermodynamic metastability and interlayer water

Divalent zinc-ion with sluggish reaction kinetics limits the choice of cathode materials for aqueous zinc-ion batteries. Metastable 1T-MoS2 shows higher electrochemical activity of ion intercalation reaction in comparison with the thermodynamically stable 2H-MoS2. Herein, the monolayer water inserted 1T-MoS2 nanosheets have been prepared by solvothermal method, investigated as the cathode in zinc-ion batteries. The monolayer water between interlayers can not only expand interlayer spacing but also maintain the metastable structure of 1T-MoS2 nanosheets, conducing to reduce activation energy for Zn2+ intercalation and enhance specific capacity. The obtained 1T-MoS2 cathode with changed 4d orbitals of Mo4+ delivers specific capacity of 164.1 mAh g−1 at 100 mA g−1 and 120.1 mAh g−1 at 2000 mA g−1, which is 6–8 times that of 2H-MoS2 cathode. The open circuit voltage of the 1T-MoS2 cathode increased to 0.96 V compared with 0.64 V of 2H-MoS2. The DFT calculations are executed to explore the influence of interlayer water on interlayer spacing and the energy storage behavior of Zn2+. Combined with the experimental results and DFT calculations, the roles of the crystalline phase and interlayer water in electronic configuration varies of Mo 4d orbitals are discussed and the Zn2+ intercalation process and storage mechanism are revealed.

NaFe2PO4(MoO4)2: A Promising NASICON-Type Electrode Material for Sodium-Ion Batteries.

Searching for polyanionic electrode materials with high Na+ and electronic conductivity is pivotal to realize high-performance sodium-ion batteries. Here, we report a novel polyanionic-based NASICON-type compound, NaFe2PO4(MoO4)2 (NFPM), that does not crystallize in the common space group R-3c or C2/c but in the rare P2/c. The studies on bond valence sum maps show that NFPM has high Na+ conductivity because the large volumes of MoO4 groups make the interstitial channels wider, thus making the energy barrier of Na+ diffusion decrease along these channels. Density functional theory calculations demonstrate that NFPM has high electronic conductivity because the contribution of Mo 4d orbitals on the formation of the bottom of the conduction band makes the connected MoO4 groups take part in electron transport. Electrochemical tests exhibit that NFPM can deliver a capacity of ∼80 mAh g-1 with good reversible cyclability utilizing the Fe3+/Fe2+ redox couple. In situ X-ray diffraction measurements indicate that NFPM undergoes one-phase reaction mechanism in the process of charge and discharge.

A novel hard superconductor obtained in di-molybdenum carbide (Mo2C) with Mo–C octahedral structure

Hard superconducting materials are of particular interest for electromechanical applications under high strain and stress. In this work, Mo2C was synthesized using high temperature and high pressure (HPHT) methods. In view of characterizations, Mo2C transforms into a superconductivity state below the temperature of 7.5 K and the asymptotic Vickers hardness is about 13.4 GPa. Its hardness is compatible with that of commonly used hard alloys, which is a potential hard superconducting material. Based on the results of our first-principle calculations, superconductivity and hardness come from the high density of states at the Fermi energy level and high hardness originates from the strong hybridization between Mo-4d orbitals and C-2p orbitals. By introducing the light element C atoms into the transition metal Mo to form a ‘covalent metal’ structure, the hardness and mechanical properties of the superconducting material can be improved which gives a way to design hard superconducting materials.