Ab initio Calculations of the Formation Energies of Lithium Intercalations in SnSb

SnSb has attracted a great attention in recent investigations as an anode material for Li ion batteries. The formation energies and electronic properties of the Li intercalations in SnSb have been calculated within the framework of local density functional theory and the first-principles pseudopotential technique. The changes of volumes, band structures, charge density analysis and the electronic density of states for the Li intercalations are presented. The results show that the average Li intercalation formation energy per Li atom is around 2.7 eV.     

LiNbO3晶体点缺陷形成能的经验途径计算

基于通过经验参数化方法确定的铌酸锂晶体内离子间互作用势参数，计算了该晶体中点缺陷的形成能，由此判断锂Frenkel对是化学计量比铌酸锂晶体中的本征缺陷，锂空位模型为描述一致熔化组分铌酸锂晶体中点缺陷的主导类型。     

MoS2 Passivated Multilayer Graphene Membranes for Li-Ion Extraction From Seawater

Abundant Li resources in the ocean are promising alternatives to refining ore, whose supplies are limited by the total amount and geopolitical imbalance of reserves in Earth's crust. Despite advances in Li⁺ extraction using porous membranes, they require screening other cations on a large scale due to the lack in precise control of pore size and inborn defects. Herein, MoS₂ nanoflakes on a multilayer graphene membrane (MFs-on-MGM) that possess ion channels comprising i) van der Waals interlayer gaps for optimal Li⁺ extraction and ii) negatively charged vertical inlets for cation attraction, are reported. Ion transport measurements across the membrane reveal ≈6- and 13-fold higher selectivity for Li⁺ compared to Na⁺ and Mg²⁺, respectively. Furthermore, continuous, stable Li⁺ extraction from seawater is demonstrated by integrating the membrane into a H₂ and Cl₂ evolution system, enabling more than 10⁴-fold decrease in the Na⁺ concentration and near-complete elimination of other cations.     

Folded MoS2 layers with reduced interlayer coupling

We study molybdenum disulfide （MoS2） structures generated by folding single-layer and bilayer MoS2 flakes. We find that this modified layer stacking leads to a decrease in the interlayer coupling and an enhancement of the photoluminescence emission yield. We additionally find that folded single-layer MoS2 structures show a contribution to photoluminescence spectra of both neutral and charged excitons, which is a characteristic feature of single-layer MoS2 that has not been observed in multilayer MoS2. The results presented here open the door to fabrication of multilayered MoS2 samples with high optical absorption while maintaining the advantageous enhanced photoluminescence emission of single-layer MoS2 by controllably twisting the MoS2 layers.     

MoS_2与TiO_2一维纳米复合材料的制备与表征

本文采用气相还原法制备了MoS2包覆TiO2的一维纳米复合材料,首先用水热法制备TiO2纳米管,并制备前驱体(NH42)MoS4;用浸渍法将(NH4)2MoS4附着于TiO2纳米管表面;然后利用氢气还原前驱体得到MoS2包覆层。用X射线衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)表征所得产物的结构及微观形貌。结果表明当还原反应温度较高(≥600℃)时,产物呈烧结状态,而当反应温度为500℃时,可以得到表面均匀包覆MoS2的TiO2纳米管复合材料,其中包覆层MoS2的结晶程度较低。在此基础上,本文提出了该产物的生长模型,并对包覆前后的样品做荧光性能分析。     

CTAB辅助水热合成球状纳米花MoS2/C复合材料及其电化学性能研究

以钼酸钠(Na₂MoO₄·2H₂O)、硫脲(NH₂CSNH₂)、CTAB为原料, 利用水热法合成了MoS₂/C球状纳米花复合材料。通过XRD、SEM、TEM、TG等分析测试方法, 研究了不同CTAB添加量对MoS₂/C复合材料的微观结构、表面形貌的影响规律, 结果显示, 有部分无定形碳嵌入了MoS₂层间, 并抑制了MoS₂(002)面的堆积。电化学测试表明: 与纯MoS₂相比, MoS₂/C复合材料具有更好的电化学性能, 当加入0.025 g CTAB时首次放电比容量达到730 mAh/g, 在100 mA/g的电流密度下经过100次循环比容量稳定在415 mAh/g。在此基础上讨论了MoS₂/C球状纳米花复合材料的可能生长机理以及对材料电化学性能的影响规律。     

Controlling the luminescence of monolayer MoS2 based on the piezoelectric effect

We report on manipulating the stimulated emission of monolayer molybdenum disulfide (MoS2) with the piezoelectric effect.The analysis is based on quantum mechanics.The stimulated emission of this two-dimensional material has been simulated to establish the relation between the total emission rate and the energy of the photon excitation.We demonstrate that the piezoelectric-induced charges enhance the emission rate by changing the carrier concentration.It is found that the emission intensity is proportional to the carrier density in the low-density range,and eventually reaches a steady value in the high-density region.An externally applied mechanical force also leads to a change in the second harmonic generation of the monolayer MoS2.     

Effect of Adventitious Carbon on Pit Formation of Monolayer MoS2

Forming pits on molybdenum disulfide (MoS₂) monolayers is desirable for (opto)electrical, catalytic, and biological applications. Thermal oxidation is a potentially scalable method to generate pits on monolayer MoS₂, and pits are assumed to preferentially form around undercoordinated sites, such as sulfur vacancies. However, studies on thermal oxidation of MoS₂ monolayers have not considered the effect of adventitious carbon (C) that is ubiquitous and interacts with oxygen at elevated temperatures. Herein, the effect of adventitious C on the pit formation on MoS₂ monolayers during thermal oxidation is studied. The in situ environmental transmission electron microscopy measurements herein show that pit formation is preferentially initiated at the interface between adventitious C nanoparticles and MoS₂, rather than only sulfur vacancies. Density functional theory (DFT) calculations reveal that the C/MoS₂ interface favors the sequential adsorption of oxygen atoms with facile kinetics. These results illustrate the important role of adventitious C on pit formation on monolayer MoS₂.     

喷雾干燥法制备石榴状嵌套结构MoS2

将硫代钼酸盐溶液用喷雾干燥法获得前驱体,通过分解前驱体制备了嵌套结构MoS2.前驱体在650℃下分解5小时获得的MoS2颗粒,具有石榴状球形结构,且内部嵌套有较小的多面体.本文结合已有报道讨论了它的形成和生长机制.     

Controllable Design of MoS2 Nanosheets Anchored on Nitrogen‐Doped Graphene: Toward Fast Sodium Storage by Tunable Pseudocapacitance

Transition‐metal disulfide with its layered structure is regarded as a kind of promising host material for sodium insertion, and intensely investigated for sodium‐ion batteries. In this work, a simple solvothermal method to synthesize a series of MoS₂ nanosheets@nitrogen‐doped graphene composites is developed. This newly designed recipe of raw materials and solvents leads the success of tuning size, number of layers, and interplanar spacing of the as‐prepared MoS₂ nanosheets. Under cut‐off voltage and based on an intercalation mechanism, the ultrasmall MoS₂ nanosheets@nitrogen‐doped graphene composite exhibits more preferable cycling and rate performance compared to few‐/dozens‐layered MoS₂ nanosheets@nitrogen‐doped graphene, as well as many other reported insertion‐type anode materials. Last, detailed kinetics analysis and density functional theory calculation are also employed to explain the Na⁺‐ storage behavior, thus proving the significance in surface‐controlled pseudocapacitance contribution at the high rate. Furthermore, this work offers some meaningful preparation and investigation experiences for designing electrode materials for commercial sodium‐ion batteries with favorable performance.     

Direct Bandgap Transition in Many‐Layer MoS2 by Plasma‐Induced Layer Decoupling

We report a robust method for engineering the optoelectronic properties of many‐layer MoS₂ using low‐energy oxygen plasma treatment. Gas phase treatment of MoS₂ with oxygen radicals generated in an upstream N₂–O₂ plasma is shown to enhance the photoluminescence (PL) of many‐layer, mechanically exfoliated MoS₂ flakes by up to 20 times, without reducing the layer thickness of the material. A blueshift in the PL spectra and narrowing of linewidth are consistent with a transition of MoS₂ from indirect to direct bandgap material. Atomic force microscopy and Raman spectra reveal that the flake thickness actually increases as a result of the plasma treatment, indicating an increase in the interlayer separation in MoS₂. Ab initio calculations reveal that the increased interlayer separation is sufficient to decouple the electronic states in individual layers, leading to a transition from an indirect to direct gap semiconductor. With optimized plasma treatment parameters, we observed enhanced PL signals for 32 out of 35 many‐layer MoS₂ flakes (2–15 layers) tested, indicating that this method is robust and scalable. Monolayer MoS₂, while direct bandgap, has a small optical density, which limits its potential use in practical devices. The results presented here provide a material with the direct bandgap of monolayer MoS₂, without reducing sample thickness, and hence optical density.     

MoS2含量对聚酰亚胺复合膜摩擦性能的影响

为降低PI膜的摩擦系数,在PI中加入不同质量比例的MoS2作为减摩相制备复合润滑膜.考察不同MoS2含量复合膜的机械性能和摩擦性能,研究复合膜表面Mo元素分布.结果显示加入量为30%的MoS2在复合膜表面富集,且分布较为均匀,在此配比下的复合膜能够在保证机械性能的基础上有效降低摩擦系数,随载荷的增加,摩擦系数稳定.     

MoS2对铜基金属陶瓷摩擦材料性能的影响

研究了MoS2在铜基摩擦材料中的作用,结果表明,作为润滑组元加入的MoS并非以MoS2的形式影响摩擦材料的性能.在烧结过程中MoS2发生了分解反应,分解后的S大部分生成了FeS等硫化物,对材料起润滑作用.随着MoS2含量的增加,材料的耐磨性、稳定系数逐渐提高,而硬度、摩擦系数逐渐降低.     

Superlubricity between MoS2 Monolayers

The ultralow friction between atomic layers of hexagonal MoS₂, an important solid lubricant and additive of lubricating oil, is thought to be responsible for its excellent lubricating performances. However, the quantitative frictional properties between MoS₂ atomic layers have not been directly tested in experiments due to the lack of conventional tools to characterize the frictional properties between 2D atomic layers. Herein, a versatile method for studying the frictional properties between atomic‐layered materials is developed by combining the in situ scanning electron microscope technique with a Si nanowire force sensor, and the friction tests on the sliding between atomic‐layered materials down to monolayers are reported. The friction tests on the sliding between incommensurate MoS₂ monolayers give a friction coefficient of ≈10^?4 in the regime of superlubricity. The results provide the first direct experimental evidence for superlubricity between MoS₂ atomic layers and open a new route to investigate frictional properties of broad 2D materials.     

Synthesis of MoS2@C Nanotubes Via the Kirkendall Effect with Enhanced Electrochemical Performance for Lithium Ion and Sodium Ion Batteries

A MoS₂@C nanotube composite is prepared through a facile hydrothermal method, in which the MoS₂ nanotube and amorphous carbon are generated synchronically. When evaluated as an anode material for lithium ion batteries (LIB), the MoS₂@C nanotube manifests an enhanced capacity of 1327 mA h g^?1 at 0.1 C with high initial Coulombic efficiency (ICE) of 92% and with capacity retention of 1058.4 mA h g^?1 (90% initial capacity retention) after 300 cycles at a rate of 0.5 C. A superior rate capacity of 850 mA h g^?1 at 5 C is also obtained. As for sodium ion batteries, a specific capacity of 480 mA h g^?1 at 0.5 C is achieved after 200 cycles. The synchronically formed carbon and stable hollow structure lead to the long cycle stability, high ICE, and superior rate capability. The good electrochemical behavior of MoS₂@C nanotube composite suggests its potential application in high‐energy LIB.