Covalent Cross-Linking of 2H-MoS2 Nanosheets

The combination of 2D materials opens a wide range of possibilities to create new-generation structures with multiple applications. Covalently cross-linked approaches are a ground-breaking strategy for the formation of homo or heterostructures made by design. However, the covalent assembly of transition metal dichalcogenides flakes is relatively underexplored. Here, a simple covalent cross-linking method to build 2H-MoS₂–MoS₂ homostructures is described, using commercially available bismaleimides. These assemblies are mainly connected vertically, basal plane to basal plane, creating specific molecular sized spaces between MoS₂ sheets. Therefore, this straightforward approach gives access to the controlled connection of sulfide-based 2D materials.     

Tuning the Photo-electrochemical Performance of RuII-Sensitized Two-Dimensional MoS2

Covalently tethering photosensitizers to catalytically active 1T-MoS₂ surfaces holds great promise for the solar-driven hydrogen evolution reaction (HER). Herein, we report the preparation of two new Ru^II-complex-functionalized MoS₂ hybrids [Ru^II(bpy)₂(phen)]-MoS₂ and [Ru^II(bpy)₂(py)Cl]-MoS₂. The influence of covalent functionalization of chemically exfoliated 1T-MoS₂ with coordinating ligands and Ru^II complexes on the HER activity and photo-electrochemical performance of this dye-sensitized system was studied systematically. We find that the photo-electrochemical performance of this Ru^II-complex-sensitized MoS₂ system is highly dependent on the surface extent of photosensitizers and the catalytic activity of functionalized MoS₂. The latter was strongly affected by the number and the kind of functional groups. Our results underline the tunability of the photovoltage generation in this dye-sensitized MoS₂ system by manipulation of the surface functionalities, which provides a practical guidance for smart design of future dye-sensitized MoS₂ hydrogen production devices towards improved the photofuel conversion efficiency.     

Enhanced Thermal Decomposition Properties and Catalytic Mechanism of Ammonium Perchlorate over CuO/MoS2 Composite

In this report, CuO/MoS₂ composites were successfully prepared by the hydrothermal method where nano‐sized CuO was uniformly distributed on the surface of hierarchical MoS₂ substrates (CuO/MoS₂ composites). Their physicochemical properties and catalytic performance in ammonium perchlorate (AP) decomposition were investigated and characterized by XRD, SEM, TEM, BET, XPS, TG/DSC and combustion measurement. The results showed that it could decrease AP decomposition temperature at high decomposition stage from 416.5 °C to 323.5 °C and increase the heat release from 378 J/g (pure AP) to 1340 J/g (AP with catalysts), which was better than pure CuO nanoparticles (345.5 °C and 1046 J/g). Meanwhile, it showed excellent performance in combustion reaction either in N₂ or air atmosphere. The results obtained by photocurrent spectra, photoluminescence spectra and time‐resolved fluorescence emission spectra indicated that loading CuO mediated the generation rate and combination rate of electrons and holes, thus tuning the catalytic performance on AP decomposition. This study proved that employing the supports that can synergistically interact with CuO is an efficient strategy to enhance the catalytic performance of CuO.     

Molybdenum Disulfide Based Nanomaterials for Rechargeable Batteries

The rapid development of electrochemical energy storage systems requires new electrode materials with high performance. As a two-dimensional material, molybdenum disulfide (MoS₂) has attracted increasing interest in energy storage applications due to its layered structure, tunable physical and chemical properties, and high capacity. In this review, the atomic structures and properties of different phases of MoS₂ are first introduced. Then, typical synthetic methods for MoS₂ and MoS₂-based composites are presented. Furthermore, the recent progress in the design of diverse MoS₂-based micro/nanostructures for rechargeable batteries, including lithium-ion, lithium-sulfur, sodium-ion, potassium-ion, and multivalent-ion batteries, is overviewed. Additionally, the roles of advanced in situ/operando techniques and theoretical calculations in elucidating fundamental insights into the structural and electrochemical processes taking place in these materials during battery operation are illustrated. Finally, a perspective is given on how the properties of MoS₂-based electrode materials are further improved and how they can find widespread application in the next-generation electrochemical energy-storage systems.     

Controlled Synthesis of Ni-Doped MoS2 Hybrid Electrode for Synergistically Enhanced Water-Splitting Process

The development of high-efficiency, low-cost, and earth-abundant electrocatalysts for overall water splitting remains a challenge. In this work, Ni-modified MoS₂ hybrid catalysts are grown on carbon cloth (Ni-Mo-S@CC) through a one-step hydrothermal treatment. The optimized Ni-Mo-S@CC catalyst shows excellent hydrogen evolution reaction (HER) activity with a low overpotential of 168 mV at a current density of 10 mA cm⁻² in 1.0 m KOH, which is lower than those of Ni-Mo-S@CC (1:1), Ni-Mo-S@CC (3:1), and pure MoS₂. Significantly, the Ni-Mo-S@CC hybrid catalyst also displays outstanding oxygen evolution reaction (OER) activity with a low overpotential of 320 mV at a current density of 10 mA cm⁻², and remarkable long-term stability for 30 h at a constant current density of 10 mA cm⁻². Experimental results and theoretical analysis based on density functional theory demonstrate that the excellent electrocatalytic performance can be attributed mainly to the remarkable conductivity, abundant active sites, and synergistic effect of the Ni-doped MoS₂. This work sheds light on a unique strategy for the design of high-performance and stable electrocatalysts for water-splitting electrolyzers.     

Topological nature of in‐gap bound states in disordered large‐gap monolayer transition metal dichalcogenides

We propose a physical model based on disordered (a hole punched inside a material) monolayer transition metal dichalcogenides (TMDs) to demonstrate a large‐gap quantum valley Hall insulator. We find an emergence of bound states lying inside the bulk gap of the TMDs. They are strongly affected by spin–valley coupling, rest‐ and kinetic‐mass terms and the hole size. In addition, in the whole range of the hole size, at least two in‐gap bound states with opposite angular momentum, circulating around the edge of the hole, exist.Their topological insulator (TI) feature is analyzed by the Chern number, characterized by spacial distribution of their probabilities and confirmed by energy dispersion curves (energy vs. angular momentum). It not only sheds light on overcoming low‐temperature operating limitation of existing narrow‐gap TIs, but also opens an opportunity to realize valley‐ and spin‐qubits. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

纳米二硫化钼的掺杂及催化电解水产氢的研究进展

电催化水分解制氢是可以形成闭环的生产过程, 起始原料与副产物均为水、 过程清洁无污染, 是极具希望的产氢策略. 目前制约其发展的瓶颈之一是价格昂贵的Pt基贵金属催化剂. 为推动电催化分解水制氢的普及, 亟待开发低成本非贵金属催化剂. 在众多备选非贵金属催化材料中, 纳米层状结构二硫化钼(MoS₂)因催化效果可期、 价格低而获得了广泛关注. 然而, 通常条件下易于获得的层状结构2H相MoS₂大面积的基面部分显示惰性, 仅在片层边缘处存在少量活性位点, 且导电性较差, 因而尚不能替代Pt基催化剂, 而如何增加其活性位点数量和提高其导电性成为亟待解决的问题; 另一方面, 1T相MoS₂虽然活性高、 导电性好, 但却存在制备困难及稳定性差的问题. 鉴于此, 研究者通过对纳米MoS₂进行掺杂改性实现了其活性与稳定性的有效提升. 本文对非贵金属纳米MoS₂催化剂掺杂改性的方法、 机理及其电催化水解制氢性能的相关研究进行了总结与讨论. 作为典型的非贵金属电解水析氢催化剂, MoS₂具有巨大发展潜力, 本文能够对相关非贵金属催化剂的研发提供有益的参考.     

金属相1T´ MoS2增强类石墨相C3N4的可见光催化性能

通过煅烧和静电自组装的方法制备了1T′ MoS₂超薄纳米片和类石墨烯相氮化碳(g-C₃N₄)纳米片的复合材料. 该材料在光催化实验中展现出6.24 μmol?g^?1?h^?1的产氢速率, 优于贵金属铂修饰的g-C₃N₄纳米片的性能(4.64 μmol?g^?1?h^?1). 此外, 该复合材料在光催化降解有机染料甲基橙的实验中表现出0.19 min^?1的催化速率, 而纯g-C₃N₄纳米片只有0.053 min^?1的催化速率. 材料光催化性能的提升可归结于1T′MoS₂ 和g-C₃N₄之间的协同效应, 包括光吸收的增强以及因1T′MoS₂优异电子导电性而得到的高效电荷分离.     

Water‐Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence

Uniform water‐soluble monolayer MoS₂ quantum dots (MQDs) with lateral sizes of ≈2.1 nm, a clearly zigzag‐terminated edge, and a hexagonal lattice structure are achieved using ammonium molybdate, thiourea, and N‐acetyl‐l ‐cysteine (NAC) as precursors and the capping reagent in a facile one‐pot hydrothermal approach. MQDs have good dispersity and high stability in aqueous suspension and exhibit a significantly larger direct bandgap (3.96 eV) compared to monolayer MoS₂ nanosheets (1.89 eV). Pronounced blue‐shifts in the wavelengths of both the excitonic absorption and intrinsic state emission with activated strong luminescence at room temperature beyond monolayer MoS₂ nanosheets is demonstrated. Unusual upconversion photoluminescence is also observed and is caused by two successive transfers of energy from the near‐infrared (NIR) absorption generated by the NAC capping reagent to the hexagonal structure of MQDs. Additional optical properties of MQDs may provide numerous exciting technological applications. Here, MQDs are demonstrated as a highly selective fluorescent reagent for detecting tetracycline hydrochloride under UV and NIR irradiation.