Development of novel melt-processable biopolymer nanocomposites based on poly(L-lactic acid) and WS2 inorganic nanotubes.

The use of tungsten disulphide inorganic nanotubes (INT-WS2) offers the opportunity to produce novel and advanced biopolymer-based nanocomposite materials with excellent nanoparticle dispersion without the need for modifiers or surfactants via conventional melt blending. The study of the non-isothermal melt-crystallization kinetics provides a clear picture of the transformation of poly(L-lactic acid) (PLLA) molecules from the non-ordered to the ordered state. The overall crystallization rate, final crystallinity and subsequent melting behaviour of PLLA were controlled by both the incorporation of INT-WS2 and the variation of the cooling rate. In particular, it was shown that INT-WS2 exhibits much more prominent nucleation activity on the crystallization of PLLA than other specific nucleating agents or nano-sized fillers. These features may be advantageous for the enhancement of mechanical properties and process-ability of PLLA-based materials. PLLA/INT-WS2 nanocomposites can be employed as low cost biodegradable materials for many eco-friendly and medical applications, and the exceptional crystallization behaviour observed opens new perspectives for scale-up and broader applications.

Novel poly(3-hydroxybutyrate) nanocomposites containing WS2 inorganic nanotubes with improved thermal, mechanical and tribological properties

Poly(3-hydroxybutyrate) (PHB) nanocomposites containing environmentally-friendly tungsten disulphide inorganic nanotubes (INTeWS2) have been successfully prepared by a simple solution blending method. The dynamic and isothermal crystallization studies by differential scanning calorimetry (DSC) demonstrated that the INTeWS2 exhibits much more prominent nucleation activity on the crystallization of PHB than specific nucleating agents or other nanoscale fillers. Both crystallization rate and crystallinity significantly increase in the nanocomposites compared to neat PHB. These changes occur without modifying the crystalline structure of PHB in the nanocomposites, as shown by wide-angle X-ray diffraction (WAXS) and infrared/Raman spectroscopy. Other parameters such as the Avrami exponent, the equilibrium melting temperature, global rate constant and the fold surface free energy of PHB chains in the nanocomposites were obtained from the calorimetric data in order to determine the influence of the INTeWS2 filler. The addition of INTeWS2 remarkably influences the energetics and kinetics of nucleation and growth of PHB, reducing the fold surface free energy by up to 20%. Furthermore, these nanocomposites also show an improvement in both tribological and mechanical (hardness and modulus) properties with respect to pure PHB evidenced by friction and nanoindentation tests, which is of important potential interest for industrial and medical applications.

Bio-based polymer nanocomposites based on nylon 11 and WS2 inorganic nanotubes

Tungsten disulphide nanotubes (INT-WS2) have been successfully dispersed in a bio-based polyamide matrix (nylon 11) by conventional melt processing. The effect of INT-WS2 content on the morphology, thermal stability, crystallization behaviour and dynamic mechanical properties is investigated. The results indicate that these inorganic nanotubes can be efficiently incorporated into the bio-based polymer matrix without the need for modifiers or surfactants. Additionally, it is found that the non-isothermal crystallization behaviour of nylon 11/INT-WS2 depends on both the cooling rate and INT-WS2 concentration. In particular, crystallization kinetics results demonstrate that the nucleating activity of INTs plays a dominant role in accelerating the crystallization of nylon 11. This fact leads to the appearance of the more-disordered phase at higher temperature. More significantly, it was shown that these INT-WS2 nanocomposites can facilitate a good processability and cost efficiency, and will be of interest for many eco-friendly and medical applications.

Electronic properties of the MoS2-WS2 heterojunction

We study the electronic structure of a heterojunction made of two monolayers of MoS2 and WS2. Our first-principles density functional calculations show that, unlike in the homogeneous bilayers, the heterojunction has an optically active band gap, smaller than the ones of MoS2 and WS2 single layers. We find that the optically active states of the maximum valence and minimum conduction bands are localized on opposite monolayers, and thus the lowest energy electron-holes pairs are spatially separated. Our findings portray the MoS2-WS2 bilayer as a prototypical example for band-gap engineering of atomically thin two-dimensional semiconducting heterostructures.

A Comparison Between Graphene and WS2 as Solid Lubricant Additives to Aluminum for Automobile Applications

The purpose of this thesis was to compare graphene nanoplatelets (GNP) and WS2 as solid lubricant additives to aluminum in order to reduce friction and wear. The central hypothesis of this work relied on lubricating properties of 2D materials, which consist layers that slip under a shear force. Two aluminum composites were made (Al-2 vol.% GNP and Al-2 vol.% WS2) by spark plasma sintering. Tribological properties were evaluated by ball-on-disk wear tests at room temperature (RT) and 200°C. WS2 not only presented the lowest COF (0.66) but also improved the wear resistance of aluminum by 54% at RT. Al-2 vol.% GNP composite displayed poor densification (91%) and low hardness resulting in poor wear resistance. The wear rate of Al-2 vol.% GNP composite increased by 233% at RT and 48% at 200°C as compared to pure aluminum. GNP addition also resulted in lower COF (0.79) as compared to pure aluminum (0.87).

A new application for transition metal chalcogenides:WS2 catalysed esterification of carboxylic acids

The first application of WS2, a well-known graphene analogue, as a solid acid catalyst for carboxylic acid esterification is reported. WS2 exhibits excellent specific activities and high conversion to methyl esters of (65–90%) for C2–C16 carboxylic acid esterification with methanol under mild conditions, with Turnover Frequencies between 80 and 180 h−1, and outstanding water tolerance even under equimolar water spiking. WS2 also exhibits good stability towards methyl propanoate in the continuous esterification of propanoic acid, and is a promising candidate for biofuels production.

Molecular camouflage : making use of protecting groups to control the self-assembly of inorganic janus particles onto metal–chalcogenide nanotubes by Pearson Hardness

Hard and soft: Binding of inorganic Pt@Fe3O4 Janus particles to WS2 nanotubes through their Pt or Fe3O4 domains is governed by the difference in Pearson hardness: the soft Pt block has a higher sulfur affinity than the harder magnetite face; thus the binding proceeds preferentially through the Pt face. This binding preference can be reversed by masking the Pt face with an organic protecting group.

Inorganic Analogues of Graphene

The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two-dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene-like MoS2 and WS2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO2.

Nanotubes of the disulfides of groups 4 and 5 metals

The layered chalcogenides, having structures analogous to graphite, are known to be unstable toward bending and show high propensity to form curved structures, thus eliminating dangling bonds at the edges. Since the discovery of fullerene and nanotube structures of WS2 and MoS2 by Tenne et al. [1-3], there have been attempts to prepare and characterize nanotubes of other layered dichalcogenides with structures analogous to MoS2. Nanotubes of MoS2 and WS2 were prepared by Tenne et al. by reducing the corresponding oxides to the suboxides followed by heating in an atmosphere of forming gas (5 % H-2 + 95 % N-2) and H2S at 700-900 degreesC [1-3]. Alternative methods of synthesis of MoS2 and WS2 nanotubes have since been proposed by employing the decomposition of the ammonium thiometallates or the corresponding trisulfide precursors. This alternative procedure was based on the observation that the trisulfide seems to be formed as an intermediate in the synthesis of the MoS2 and WS2 nanotubes [4]. Accordingly, the decomposition of the trisulfides of MoS2 and W in a reducing atmosphere directly yielded nanotubes of the disulfides MoS2 and WS2 [5]. In this article, we describe the synthesis, structure, and characterization of a few novel nanotubes of the disulfides of groups 4 and 5 metals. These include nanotubes of NbS2, TaS2, ZrS2, and HfS2. The study enlarges the scope of the inorganic nanotubes significantly and promises other interesting possibilities, including the synthesis of the diselenide nanotubes of these metals.

Performance limits of transition metal dichalcogenide (MX2) nanotube surround gate ballistic field effect transistors

We theoretically analyze the performance of transition metal dichalcogenide (MX2) single wall nanotube (SWNT) surround gate MOSFET, in the 10 nm technology node. We consider semiconducting armchair (n, n) SWNT of MoS2, MoSe2, WS2, and WSe2 for our study. The material properties of the nanotubes are evaluated from the density functional theory, and the ballistic device characteristics are obtained by self-consistently solving the Poisson-Schrodinger equation under the non-equilibrium Green's function formalism. Simulated ON currents are in the range of 61-76 mu A for 4.5 nm diameter MX2 tubes, with peak transconductance similar to 175-218 mu S and ON/OFF ratio similar to 0.6 x 10(5)-0.8 x 10(5). The subthreshold slope is similar to 62.22 mV/decade and a nominal drain induced barrier lowering of similar to 12-15 mV/V is observed for the devices. The tungsten dichalcogenide nanotubes offer superior device output characteristics compared to the molybdenum dichalcogenide nanotubes, with WSe2 showing the best performance. Studying SWNT diameters of 2.5-5 nm, it is found that increase in diameter provides smaller carrier effective mass and 4%-6% higher ON currents. Using mean free path calculation to project the quasi-ballistic currents, 62%-75% reduction from ballistic values in drain current in long channel lengths of 100, 200 nm is observed.

Two-step Synthesis of MoS2 Nanotubes using Shock Waves with Lead as Growth Promoter

A new two-step procedure for the synthesis of MoS2 nanotubes using lead as a growth promoter is reported. In the first step, molybdenum suboxide nanowhiskers containing a small amount of lead atoms were created by exposing a pressed MoS2+Pb mixture to highly compressed shock-heated argon gas, with estimated temperatures exceeding 9900 K. In the second step, these molybdenum suboxide nanowhiskers served as templates for the sulfidization of the oxide into MoS2 nanotubes (by using H2S gas in a reducing atmosphere at 820 degrees C). Unlike the case of WS2 nanotubes, the synthesis of a pure phase of MoS2 nanotubes from molybdenum oxide has proven challenging, due mostly to the volatile nature of the latter at the high requisite reaction temperatures (>800 degrees C). In contrast, the nature and apparent reaction mechanism of the method reported herein are amenable to future scale-up. The high-temperature shockwave system should also facilitate the synthesis of new nanostructures from other layered materials.

Amorphous W-S-N thin films: The atomic structure behind ultra-low friction

Amorphous W-S-N in the form of thin films has been identified experimentally as an ultra-low friction material, enabling easy sliding by the formation of a WS2 tribofilm. However, the atomic-level structure and bonding arrangements in amorphous W-S-N, which give such optimum conditions for WS2 formation and ultra-low friction, are not known. In this study, amorphous thin films with up to 37 at.% N are deposited, and experimental as well as state-of-the-art ab initio techniques are employed to reveal the complex structure of W-S-N at the atomic level. Excellent agreement between experimental and calculated coordination numbers and bond distances is demonstrated. Furthermore, the simulated structures are found to contain N bonded in molecular form, i.e. N-2, which is experimentally confirmed by near edge X-ray absorption fine structure and X-ray photoelectron spectroscopy analysis. Such N-2 units are located in cages in the material, where they are coordinated mainly by S atoms. Thus this ultra-low friction material is shown to be a complex amorphous network of W, S and N atoms, with easy access to W and S for continuous formation of WS2 in the contact region, and with the possibility of swift removal of excess nitrogen present as N-2 molecules. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Promoting effects in hydrogenation and hydrodesulfurization reactions on the zirconia and titania supported catalysts

Tetralin hydrogenation (HYD) and thiophene hydrodesulfurization (HDS) were studied for the supported MoS2 and WS2 sulfides, either non-promoted or promoted with Co and Ni. The supports used were ZrO2, alumina-stabilized TiO2 and pure alumina. Preparation of catalysts included presulfidation of non-promoted system with subsequent addition of promoter and resulfidation. It has been found that the nature of promoter plays determining role for the catalytic performance. The most active in both HYD and HDS reactions are Ni-promoted Mo and W catalysts, supported on ZrO2. (C) 2003 Published by Elsevier B.V.

地幔副矿物和硫化物的热（PVT）状态方程研究

矿物PVT状态方程是研究矿物在一定温压条件下的晶胞体积与温度、压力之间的关系，依据这个基本关系，可以了解矿物在高温高压下的密度、弹性、热膨胀等性质。矿物PVT状态方程的研究可以了解矿物在地球深部存在的结构状态，为进一步的理论计算提供基础的数据，其结果也可以与天然和人工地震的地震波反演的结果对比，对地球深部的地质作用过程、物质结构状态和组成进行限制。然而，目前矿物PVT状态方程的研究主要集中在氧化物矿物和上地幔主要矿物（橄榄石和辉石）及其高压相（瓦兹利石、林伍德石、方镁铁矿、Majorite、Mg-Perovskite、Ca-Perovskite）的研究上，对石榴石、尖晶石等地幔常见副矿物和硫化物矿物的PVT状态方程的研究很少。 作者在参与搭建并完善金刚石压腔外加温系统的基础上，利用北京同步辐射X射线衍射实验技术结合金刚石压腔外加温技术对天然铁铝榴石、锰铝榴石、铬尖晶石进行了PVT状态方程的研究，同时对闪锌矿、辰砂、方铅矿、辉钼矿、辉锑矿等硫化物矿物进行了相变及状态方程的研究。结合前人研究成果，讨论了类质同象置换对镁铝－铁铝系列石榴石、锰铝－铁铝系列石榴石、尖晶石和硫化物矿物相变及状态方程的影响。获得了以下研究结果： 1）镁铝－铁铝系列石榴石和锰铝－铁铝系列石榴石的体弹模量都随着铁铝榴石组分的增加而增大。其主要原因是在二价阳离子位置上Fe2+取代了Mg2+、Mn2+。在镁铝－铁铝榴石系列中Mg2+的共价键半径（1.36Å）要大于Fe2+的共价键半径（1.17Å），而Mg2+－O键长（2.270Å）与铁铝榴石中的Fe2+－O（2.299Å）键长基本相当。在锰铝－铁铝榴石系列中， 尽管Mn2+的共价键半径（1.17Å）与铁铝榴石中的Fe2+共价键半径（1.17Å）相等，但是Mn2+－O键长（2.326Å）大于Fe2+－O键长（2.299Å）。较小的键长和共价键半径将会增强离子间的结合力，从而具有较强的抗压缩能力，因此随铁铝榴石组分的增加，镁铝－铁铝榴石系列和锰铝－铁铝榴石系列具有较大的体弹模量。 2）首次获得了铬尖晶石（(Mg0.6766Fe0.2808Na0.0073Ti0.0014)0.9661(Cr1.4874Al0.5367)2.0241O4）的体弹模量的温度导数。结合前人关于其他组分尖晶石的实验结果发现，尖晶石中在四面体位置上发生Fe2+－Mg2+置换对体弹模量的影响要大于在八面体位置上发生Cr3+－Al3+置换对体弹模量的影响。而造成铬尖晶石的体弹模量值比其他组分尖晶石的体弹模量值大的主要原因也是四面体位置上的Fe2+－Mg2+的类质置换。 3）依据获得的尖晶石和石榴石的状态方程计算了不同地幔岩模型（橄榄岩和榴辉岩模型）的密度值在上地幔温压条件下的变化情况。结果表明，在尖晶石二辉橄榄岩模型中尖晶石含量的改变（2％－10％）会引起较大的密度变化（2.2％）；在石榴石二辉橄榄岩（石榴石含量14％－20％）和榴辉岩（石榴石含量37％－45％）模型中石榴石含量的变化几乎未引起其密度值的变化，但石榴石是这两种地幔岩模型中的重要组成矿物。 4）首次获得了辰砂的Cinnabar相、方铅矿的B33相、辉钼矿、辉锑矿体弹模量的温度导数和热膨胀系数。讨论了闪锌矿、辰砂、方铅矿的相变情况。 5）总结了锌的、汞的、铅的硫族化合物发生结构相变的规律。认为造成锌的、汞的、铅的硫族化合物的相变压力随阴离子原子序数的增加（S→Se→Te）而逐渐减小的原因是：元素周期表中相对较大原子序数的原子具有更多的核内电子，引起价电子及导带电子的有效位能相对变弱，引起电离能降低，因此在相对较低的压力下就容易发生结构相变。 6）分析了ZnS中Fe2+替代Zn2+、Sb2S3－Bi2S3、MoS2－WS2以及同族相同结构不同组分的简单硫化物矿物的阴、阳离子对体弹模量值的影响。认为简单硫化物矿物的体弹模量值取决于阴、阳离子的离子半径、电负性以及键长。

Synthesis and characterization of metal-chalcogenide MQ 2-Nanoparticles (M = Mo, W, Zr; Q = S, O)

Here, we present the adaptation and optimization of (i) the solvothermal and (ii) the metal-organic chemical vapor deposition (MOCVD) approach as simple methods for the high-yield synthesis of MQ2 (M=Mo, W, Zr; Q = O, S) nanoparticles. Extensive characterization was carried out using X-ray diffraction (XRD), scanning and transmission electron micros¬copy (SEM/TEM) combined with energy dispersive X-ray analysis (EDXA), Raman spectroscopy, thermal analyses (DTA/TG), small angle X-ray scattering (SAXS) and BET measurements. After a general introduction to the state of the art, a simple route to nanostructured MoS2 based on the decomposition of the cluster-based precursor (NH4)2Mo3S13∙xH2O under solvothermal conditions (toluene, 653 K) is presented. Solvothermal decomposition results in nanostructured material that is distinct from the material obtained by decomposition of the same precursor in sealed quartz tubes at the same temperature. When carried out in the presence of the surfactant cetyltrimethyl¬ammonium bromide (CTAB), the decomposition product exhibits highly disordered MoS2 lamellae with high surface areas. The synthesis of WS2 onion-like nanoparticles by means of a single-step MOCVD process is discussed. Furthermore, the results of the successful transfer of the two-step MO¬CVD based synthesis of MoQ2 nanoparticles (Q = S, Se), comprising the formation of amorphous precursor particles and followed by the formation of fullerene-like particles in a subsequent annealing step to the W-S system, are presented. Based on a study of the temperature dependence of the reactions a set of conditions for the formation of onion-like structures in a one-step reaction could be derived. The MOCVD approach allows a selective synthesis of open and filled fullerene-like chalcogenide nanoparticles. An in situ heating stage transmission electron microscopy (TEM) study was employed to comparatively investigate the growth mechanism of MoS2 and WS2 nanoparticles obtained from MOCVD upon annealing. Round, mainly amorphous particles in the pristine sample trans¬form to hollow onion-like particles upon annealing. A significant difference between both compounds could be demonstrated in their crystallization conduct. Finally, the results of the in situ hea¬ting experiments are compared to those obtained from an ex situ annealing process under Ar. Eventually, a low temperature synthesis of monodisperse ZrO2 nanoparticles with diameters of ~ 8 nm is introduced. Whereas the solvent could be omitted, the synthesis in an autoclave is crucial for gaining nano-sized (n) ZrO2 by thermal decomposition of Zr(C2O4)2. The n-ZrO2 particles exhibits high specific surface areas (up to 385 m2/g) which make them promising candidates as catalysts and catalyst supports. Co-existence of m- and t-ZrO2 nano-particles of 6-9 nm in diameter, i.e. above the critical particle size of 6 nm, demonstrates that the particle size is not the only factor for stabilization of the t-ZrO2 modification at room temperature. In conclusion, synthesis within an autoclave (with and without solvent) and the MOCVD process could be successfully adapted to the synthesis of MoS2, WS2 and ZrO2 nanoparticles. A comparative in situ heating stage TEM study elucidated the growth mechanism of MoS2 and WS2 fullerene-like particles. As the general processes are similar, a transfer of this synthesis approach to other layered transition metal chalcogenide systems is to be expected. Application of the obtained nanomaterials as lubricants (MoS2, WS2) or as dental filling materials (ZrO2) is currently under investigation.