Tuning CO sensing properties and magnetism of MoS2 monolayer through anchoring transition metal dopants

Achieving controllable multifunctionality through layer sliding

Dynamical variation of physical properties in a controllable fashion provides exciting possibilities to obtain multifunctional materials. In this work, layer-sliding is employed to modify the structural, interfacial electronic and optical properties of unintercalated and Mg-intercalated two-dimensional (2D) van der Waals heterostructure (vdW-HS) consisting of buckled silicene and hexagonal boron nitride (hBN). The most stable stacking configuration of silicene over hBN is screened out and then intercalated with Mg at the interface. Dynamical-dependent changes in the properties of vdW-HS are performed by sliding silicene over hBN monolayer in the absence and presence of the intercalant. Layer-sliding is carried out in equal length intervals, and various parametric quantities related to the physical characteristics of the vdW-HS are repeatedly calculated and compared. Apart from various parametric quantities, stability of unintercalated and Mg-intercalated vdW-HS is also checked by means of relative total energies, binding energies and vdW gaps along the sliding pathway. Comparison of binding energies shows that the un-slided, half-slided, and fully-slided Mg-intercalated vdW-HS are 1.52, 1.44 and 1.42 eV more stable than the unintercalated vdW-HS. Opening of a small band gap of 12, 31 and 28 meV for un-slided, half-slided and fully-slided unintercalated vdW-HS, respectively, is worth mentioning. To study the interfacial electronic behavior, planar average charge density difference (Δρ) and charge transfer (ΔQ) are also calculated and varied via layer-sliding. Further, we calculated diverse optical spectra such as the complex dielectric function (DF), electron energy loss function [L(ω)], diagonal components of dielectric tensor [ε(iω)], refractive index [n(ω)], extinction coefficient [k(ω)], absorption coefficient [α(ω)], and reflectivity [R(ω)] for un-slided, half-slided and fully-slided unintercalated and Mg-intercalated vdW-HS. Interestingly, the polarization and energy losses have been reduced in the case of Mg-intercalated vdW-HS. The suggested layer-sliding method can be established as a general scheme for bringing multifunctionality into a layered material.

Magnetically Doped Molybdenum Disulfide Layers for Enhanced Carbon Dioxide Capture

Carbon capture and storage (CCS) technologies have the potential for reducing greenhouse gas emissions and creating clean energy solutions. One of the major aspects of the CCS technology is designing energy-efficient adsorbent materials for carbon dioxide capture. In this research, using a combination of first-principles theory, synthesis, and property measurements, we explore the CO₂ gas adsorption capacity of MoS₂ sheets via doping with iron, cobalt, and nickel. We show that substitutional dopants act as active sites for CO₂ adsorption. The adsorption performance is determined to be dependent on the type of dopant species as well as its concentration. Nickel-doped MoS₂ is found to be the best adsorbent for carbon capture with a relatively high gas adsorption capacity compared to pure MoS₂ and iron- and cobalt-doped MoS₂. Specifically, Brunauer-Emmett-Teller (BET) measurements show that 8 atom % Ni-MoS₂ has the highest surface area (51 m²/g), indicating the highest CO₂ uptake relative to the other concentrations and other dopants. Furthermore, we report that doping could lead to different magnetic solutions with changing electronic structures where narrow band gaps and the semimetallic tendency of the substrate are observed and can have an influence on the CO₂ adsorption ability of MoS₂. Our results provide a key strategy to the characteristic tendencies for designing highly active and optimized MoS₂-based adsorbent materials utilizing the least volume of catalysts for CO₂ capture and conversion.

Prediction of Co and Ru nanocluster morphology on 2D MoS2 from interaction energies

Layered materials, such as MoS₂, have a wide range of potential applications due to the properties of a single layer, which often differ from the bulk material. They are of particular interest as ultrathin diffusion barriers in semiconductor device interconnects and as supports for low-dimensional metal catalysts. Understanding the interaction between metals and the MoS₂ monolayer is of great importance when selecting systems for specific applications. In previous studies the focus has been largely on the strength of the interaction between a single atom or a nanoparticle of a range of metals, which has created a significant knowledge gap in understanding thin film nucleation on 2D materials. In this paper, we present a density functional theory (DFT) study of the adsorption of small Co and Ru structures, with up to four atoms, on a monolayer of MoS₂. We explore how the metal-substrate and metal-metal interactions contribute to the stability of metal clusters on MoS₂, and how these interactions change in the presence of a sulfur vacancy, to develop insight to allow for a prediction of thin film morphology. The strength of interaction between the metals and MoS₂ is in the order Co > Ru. The competition between metal-substrate and metal-metal interaction allows us to conclude that 2D structures should be preferred for Co on MoS₂, while Ru prefers 3D structures on MoS₂. However, the presence of a sulfur vacancy decreases the metal-metal interaction, indicating that with controlled surface modification 2D Ru structures could be achieved. Based on this understanding, we propose Co on MoS₂ as a suitable candidate for advanced interconnects, while Ru on MoS₂ is more suited to catalysis applications.

Co-embedded sulfur vacant MoS2 monolayer as a promising catalyst for formaldehyde oxidation: a theoretical evaluation

In this work, we theoretically evaluated the complete catalytic oxidation of formaldehyde (HCHO) catalyzed by a cobalt embedded sulfur vacant MoS2 (COSv–MoS2) monolayer.

DFT calculations of the structure and stability of copper clusters on MoS2

Layered materials, such as MoS₂, are being intensely studied due to their interesting properties and wide variety of potential applications. These materials are also interesting as supports for low-dimensional metals for catalysis, while recent work has shown increased interest in using 2D materials in the electronics industry as a Cu diffusion barrier in semiconductor device interconnects. The interaction between different metal structures and MoS₂ monolayers is therefore of significant importance and first-principles simulations can probe aspects of this interaction not easily accessible to experiment. Previous theoretical studies have focused particularly on the adsorption of a range of metallic elements, including first-row transition metals, as well as Ag and Au. However, most studies have examined single-atom adsorption or adsorbed nanoparticles of noble metals. This means there is a knowledge gap in terms of thin film nucleation on 2D materials. To begin addressing this issue, we present in this paper a first-principles density functional theory (DFT) study of the adsorption of small Cu _n (n = 1-4) structures on 2D MoS₂ as a model system. We find on a perfect MoS₂ monolayer that a single Cu atom prefers an adsorption site above the Mo atom. With increasing nanocluster size the nanocluster binds more strongly when Cu atoms adsorb atop the S atoms. Stability is driven by the number of Cu-Cu interactions and the distance between adsorption sites, with no obvious preference towards 2D or 3D structures. The introduction of a single S vacancy in the monolayer enhances the copper binding energy, although some Cu _n nanoclusters are actually unstable. The effect of the vacancy is localised around the vacancy site. Finally, on both the pristine and the defective MoS₂ monolayer, the density-of-states analysis shows that the adsorption of Cu introduces new electronic states as a result of partial Cu oxidation, but the metallic character of Cu nanoclusters is preserved.

Hierarchical Nanoheterostructure of Tungsten Disulfide Nanoflowers Doped with Zinc Oxide Hollow Spheres: Benzene Gas Sensing Properties and First-Principles Study

This paper reports an original fabrication of a benzene gas sensor based on tungsten disulfide nanoflowers (WS₂ NFs)/zinc oxide hollow spheres (ZnO HMDs) hierarchical nanoheterostructure. The ZnO/WS₂ hierarchical composite was characterized for the inspection of its nanostructure, elementary composition, and surface morphology. The benzene-sensing properties of the ZnO/WS₂ nanofilm sensor were exactly investigated. The results illustrate that the ZnO/WS₂ sensor exhibits a remarkable sensing performance toward benzene gas, including good sensitivity, rapid detection, outstanding repeatability, and stability. This is attributed to the fact that the ZnO/WS₂ nanoheterostructure can dramatically enhance the benzene sensing performance. Furthermore, density functional theory was employed to construct the benzene gas adsorption model for the ZnO/WS₂ heterostructure, from which the determined parameters in geometry, energy, and charge provided a powerful support for the mechanism explanation. This work suggests that the ZnO/WS₂ nanoheterostructure is competent to detect trace benzene gas at room temperature.

Recent Insights in Transition Metal Sulfide Hydrodesulfurization Catalysts for the Production of Ultra Low Sulfur Diesel: A Short Review

The literature from the past few years dealing with hydrodesulfurization catalysts to deeply remove the sulfur-containing compounds in fuels is reviewed in this communication. We focus on the typical transition metal sulfides (TMS) Ni/Co-promoted Mo, W-based bi- and tri-metallic catalysts for selective removal of sulfur from typical refractory compounds. This review is separated into three very specific topics of the catalysts to produce ultra-low sulfur diesel. The first issue is the supported catalysts; the second, the self-supported or unsupported catalysts and finally, a brief discussion about the theoretical studies. We also inspect some details about the effect of support, the use of organic and inorganic additives and aspects related to the preparation of unsupported catalysts. We discuss some hot topics and details of the unsupported catalyst preparation that could influence the sulfur removal capacity of specific systems. Parameters such as surface acidity, dispersion, morphological changes of the active phases, and the promotion effect are the common factors discussed in the vast majority of present-day research. We conclude from this review that hydrodesulfurization performance of TMS catalysts supported or unsupported may be improved by using new methodologies, both experimental and theoretical, to fulfill the societal needs of ultra-low sulfur fuels, which more stringent future regulations will require.

Chemisorption of metallic radionuclides on a monolayer MoS2 nanosheet

In the process of developing nuclear energy, removing radioactive waste in the environment is a challenging problem that human beings have to face. The main work of this paper is to investigate the mechanism of the interaction between metallic radionuclides (Cs, Sr, and Ba) and a monolayer MoS₂ nanosheet, and the work is completed by using the first principles calculation method. The results show that all of the three kinds of metallic radionuclides can be chemisorbed on the monolayer MoS₂ nanosheet. The optimum adsorption site for the metallic radionuclides adsorbed on the monolayer MoS₂ is T_Mo (top of the Mo atom), because the metallic radionuclides can interact with the three nearest S atoms when the metallic radionuclides are at the T_Mo site. The chemisorption strength of the metallic radionuclides on the monolayer MoS₂ is Ba > Sr > Cs. The mechanism of the chemisorption is explored by using the total charge transfer, density of states, and electron density difference. The final analysis shows that the s orbital of S atoms plays an important role in the chemisorption.