Site-Selective Oxidation of Monolayered Liquid-Exfoliated WS2 by Shielding the Basal Plane through Adsorption of a Facial Amphiphile

In recent years, various functionalization strategies for transition-metal dichalcogenides have been explored to tailor the properties of materials and to provide anchor points for the fabrication of hybrid structures. Herein, new insights into the role of the surfactant in functionalization reactions are described. Using the spontaneous reaction of WS₂ with chloroauric acid as a model reaction, the regioselective formation of gold nanoparticles on WS₂ is shown to be heavily dependent on the surfactant employed. A simple model is developed to explain the role of the chosen surfactant in this heterogeneous functionalization reaction. The surfactant coverage is identified as the crucial element that governs the dominant reaction pathway and therefore can severely alter the reaction outcome. This study shows the general importance of the surfactant choice and how detrimental or beneficial a certain surfactant can be to the desired functionalization.     

WS2 Nanowires as a High‐Performance Anode for Sodium‐Ion Batteries

We report the synthesis and anode application for sodium‐ion batteries (SIBs) of WS₂ nanowires (WS₂ NWs). WS₂ NWs with very thin diameter of ≈25 nm and expanded interlayer spacing of 0.83 nm were prepared by using a facile solvothermal method followed by a heat treatment. The as‐prepared WS₂ NWs were evaluated as anode materials of SIBs in two potential windows of 0.01–2.5 V and 0.5–3 V. WS₂ NWs displayed a remarkable capacity (605.3 mA h g^?1 at 100 mA g^?1) but with irreversible conversion reaction in the potential window of 0.01–2.5 V. In comparison, WS₂ NWs showed a reversible intercalation mechanism in the potential window of 0.5–3 V, in which the nanowire‐framework is well maintained. In the latter case, the interlayers of WS₂ are gradually expanded and exfoliated during repeated charge–discharge cycling. This not only provides more active sites and open channels for the intercalation of Na⁺ but also facilitates the electronic and ionic diffusion. Therefore, WS₂ NWs exhibited an ultra‐long cycle life with high capacity and rate capability in the potential window of 0.5–3 V. This study shows that WS₂ NWs are promising as the anode materials of room‐temperature SIBs.     

High‐Resolution Electrochemical Mapping of the Hydrogen Evolution Reaction on Transition‐Metal Dichalcogenide Nanosheets

High‐resolution scanning electrochemical cell microscopy (SECCM) is used to image and quantitatively analyze the hydrogen evolution reaction (HER) catalytically active sites of 1H‐MoS₂ nanosheets, MoS₂, and WS₂ heteronanosheets. Using a 20 nm radius nanopipette and hopping mode scanning, the resolution of SECCM was beyond the optical microscopy limit and visualized a small triangular MoS₂ nanosheet with a side length of ca. 130 nm. The electrochemical cell provides local cyclic voltammograms with a nanoscale spatial resolution for visualizing HER active sites as electrochemical images. The HER activity difference of edge, terrace, and heterojunction of MoS₂ and WS₂ were revealed. The SECCM imaging directly visualized the relationship of HER activity and number of MoS₂ nanosheet layers and unveiled the heterogeneous aging state of MoS₂ nanosheets. SECCM can be used for improving local HER activities by producing sulfur vacancies using electrochemical reaction at the selected region.     

Vanadium‐Doped WS2 Nanosheets Grown on Carbon Cloth as a Highly Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Two‐dimensional transition‐metal dichalcogenides have been widely studied as electrocatalysts for the hydrogen evolution reaction (HER). However, limited active sites and poor conductivity hinder their application. To solve these disadvantages, heteroatom doping has attracted wide attention because it can not only increase the active sites but also affect the intrinsic catalytic properties of the electrocatalyst. Herein, we grew vanadium‐doped WS₂ nanosheets on carbon cloth (V‐WS₂/CC) as an electrocatalyst for HER under acidic and alkaline conditions. With a proper vanadium doping concentration, the electrochemical surface areas of V_0.065‐WS₂/CC were 9.6 and 2.6 times as large as that of pure WS₂ electrocatalyst under acidic and alkaline conditions, respectively. In addition, the charge‐transfer resistance also decreased with moderate vanadium doping. Based on this, the synthesized vanadium‐doped WS₂ nanosheets exhibited good stability with high HER catalytic activity and could reach a current density of 10 mA cm⁻² at overpotentials of 148 and 134 mV in 0.5 m H₂SO₄ and 1 m KOH, respectively. The corresponding Tafel slopes were 71 and 85 mV dec⁻¹. Therefore, our synthesized vanadium‐doped WS₂ nanosheets can be a promising electrocatalyst for the production of hydrogen over a wide pH range.     

Superior Electrical Conductivity in Hydrogenated Layered Ternary Chalcogenide Nanosheets for Flexible All‐Solid‐State Supercapacitors

As the properties of ultrathin two‐dimensional (2D) crystals are strongly related to their electronic structures, more and more attempts were carried out to tune their electronic structures to meet the high standards for the construction of next‐generation smart electronics. Herein, for the first time, we show that the conductive nature of layered ternary chalcogenide with formula of Cu₂WS₄ can be switched from semiconducting to metallic by hydrogen incorporation, accompanied by a high increase in electrical conductivity. In detail, the room‐temperature electrical conductivity of hydrogenated‐Cu₂WS₄ nanosheet film was almost 10¹⁰ times higher than that of pristine bulk sample with a value of about 2.9×10⁴ S m^?1, which is among the best values for conductive 2D nanosheets. In addition, the metallicity in the hydrogenated‐Cu₂WS₄ is robust and can be retained under high‐temperature treatment. The fabricated all‐solid‐state flexible supercapacitor based on the hydrogenated‐Cu₂WS₄ nanosheet film shows promising electrochemical performances with capacitance of 583.3 F cm^?3 at a current density of 0.31 A cm^?3. This work not only offers a prototype material for the study of electronic structure regulation in 2D crystals, but also paves the way in searching for highly conductive electrodes.     

Fabrication of Two‐Dimensional Lateral Heterostructures of WS2/WO3⋅H2O Through Selective Oxidation of Monolayer WS2

Two‐dimensional (2D) lateral heterostructures have emerged as a hot topic in the fast evolving field of advanced functional materials , but their fabrication is challenging. The layer‐structured WS₂ was theoretically demonstrated to be inert to oxidation except for the monolayer, which can be selectively oxidized owing to the simultaneous interaction of oxygen with both sides. Combined with the theoretical calculations, a new method was developed for the successful construction of 2D lateral heterostructures of WS₂/WO₃?H₂O in an ambient environment, based on a simple liquid‐phase solution exfoliation. These lateral heterostructures of WS₂/WO₃?H₂O have interesting properties, as indicated by enhanced photocatalytic activity toward the degradation of methyl orange (MO).     

Two‐Dimensional Layered Heterostructures Synthesized from Core–Shell Nanowires

Controlled stacking of different two‐dimensional (2D) atomic layers will greatly expand the family of 2D materials and broaden their applications. A novel approach for synthesizing MoS₂/WS₂ heterostructures by chemical vapor deposition has been developed. The successful synthesis of pristine MoS₂/WS₂ heterostructures is attributed to using core–shell WO_3?x/MoO_3?x nanowires as a precursor, which naturally ensures the sequential growth of MoS₂ and WS₂. The obtained heterostructures exhibited high crystallinity, strong interlayer interaction, and high mobility, suggesting their promising applications in nanoelectronics. The stacking orientations of the two layers were also explored from both experimental and theoretical aspects. It is elucidated that the rational design of precursors can accurately control the growth of high‐quality 2D heterostructures. Moreover, this simple approach opens up a new way for creating various novel 2D heterostructures by using a large variety of heteronanomaterials as precursors.     

WS<Subscript>2</Subscript> grafted on silicon and nano-silicon particles etched: a high-performance electrocatalyst for hydrogen evolution reaction

Most of research has been carried out for the development of electrocatalysts for hydrogen evolution reaction (HER), which are high activity and low cost. In this study, a practical, usable, highly active, cheap, and none noble metal catalyst was developed for HER. To this end, tungsten disulfide supported on silicon (WS₂/Si) and on silicon nanoparticles (WS₂/nano-Si) were prepared. To increase the catalytic activity of WS₂/nano-Si, chemical etching was used to prepare WS₂/nano-Si etched. The synthesized electrocatalysts were characterized using Fortier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction methods. To evaluate the electrochemical attributes of WS₂/Si and WS₂/n-Si before and after chemical etching, electrochemical impedance spectroscopy, linear sweep, and cyclic voltammetry were used. The electrochemical measurements indicated an intense activity of the WS₂/nano-Si/etched, through a high density of the current and low overpotential for HER, with a small overpotential of 0.14 V, Tafel slopes as small as 45 mV dec^?1, and large cathodic currents. These results show that through etching process of silicon in HF the quantities of the active sites have been changed and increased considerably.     

Ultrathin WS2 Nanoflakes as a High‐Performance Electrocatalyst for the Hydrogen Evolution Reaction

Much has been done to search for highly efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER), which is critical to a range of electrochemical and photoelectrochemical processes. A new, high‐temperature solution‐phase method for the synthesis of ultrathin WS₂ nanoflakes is now reported. The resulting product possesses monolayer thickness with dimensions in the nanometer range and abundant edges. These favorable structural features render the WS₂ nanoflakes highly active and durable catalysts for the HER in acids. The catalyst exhibits a small HER overpotential of approximately 100 mV and a Tafel slope of 48 mV/decade. These ultrathin WS₂ nanoflakes represent an attractive alternative to the precious platinum benchmark catalyst and rival MoS₂ materials that have recently been heavily scrutinized for the electrocatalytic HER.     

Significance of epoxy network properties for the toughening effect of flaky and fullerene‐like WS2 nanoparticles

This work deals with the toughening effect of flaky WS₂ and fullerene‐like WS₂ (IF‐WS₂) nanoparticles on epoxy with varying network properties. Reducing the amount of curing agent resulted in decreased crosslink density as measured by dynamic‐mechanic analysis and double‐quantum nuclear magnetic resonance spectroscopy. Although that lead to moderate changes in the epoxy's tensile properties, its fracture toughness dropped drastically, probably due to an increased defect fraction. IF‐WS₂ could be dispersed significantly more effectively within epoxy resin than flaky WS₂, possibly due to its spherical shape, but caused less toughening. IF‐WS₂ tended to debond from the epoxy, while flaky WS₂ introduced more secondary cracks. Both increased the fracture toughness of the (brittle) substoichiometric, but not that of the (tough) stoichiometric epoxy, possibly due to their interaction with molecular defects. Irrespective of which mechanism resulted in the toughening effect, its effectiveness depended strongly on the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1738–1747     

Improved peroxidase mimetic activity of a mixture of WS<Subscript>2</Subscript> nanosheets and silver nanoclusters for chemiluminescent quantification of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and glucose

It is reported that a mixture of WS₂ nanosheets (WS₂ NS) and silver nanoclusters (AgNCs) displays strongly enhanced peroxidase-mimicking activity. The catalytic effect of the mixture was studied by colorimetry, fluorometry, chemiluminescence (CL) and electrochemistry. The effect is interpreted in terms of a difference between the Fermi energy level of the two nanomaterials. This leads to the formation of charge separation regions which act as active sites for enzyme mimetic interaction with the substrates. The mixture of WS₂ NS and AgNCs was exploited for the non-enzymatic determination of H₂O₂ and glucose. A stopped-flow method was applied as a sensitive CL detection system using the bicarbonate-H₂O₂ reaction. The mixture has a powerful peroxidase mimicking activity on the bicarbonate-H₂O₂ CL reaction, and this effect is much larger than that of any single constituent. In addition, the CL emission is improved several times by using the stopped-flow technique. Under optimum condition, H₂O₂ can be determined in the 2.5–1500 nM concentration range. Moreover, glucose levels in human serum can be quantified via glucose oxidase based oxidation which leads to the generation of H₂O₂. Using this CL assay, a linear relationship was obtained between the intensity of the CL emission and glucose concentration in the range of 0.03–20 μM, with a limit of detection (3S) of 13 nM.

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Graphical abstract An enhanced peroxidase-like catalytic activity for WS₂ nanosheets (WS₂ NS) was revealed in the presence of silver nanoclusters (AgNCs), and was exploited for the non-enzymatic determination of H₂O₂, and of glucose (via glucose oxidase; GOx) using a stopped-flow CL method.

     

Ruthenium‐Catalyzed Cascade CH Functionalization of Phenylacetophenones

Three orthogonal cascade C? H functionalization processes are described, based on ruthenium‐catalyzed C? H alkenylation. 1‐Indanones, indeno indenes, and indeno furanones were accessed through cascade pathways by using arylacetophenones as substrates under conditions of catalytic [{Ru(p‐cymene)Cl₂}₂] and stoichiometric Cu(OAc)₂. Each transformation uses C? H functionalization methods to form C? C bonds sequentially, with the indeno furanone synthesis featuring a C? O bond formation as the terminating step. This work demonstrates the power of ruthenium‐catalyzed alkenylation as a platform reaction to develop more complex transformations, with multiple C? H functionalization steps taking place in a single operation to access novel carbocyclic structures.     

Bis­(tetra­phenyl­phospho­nium) (μ‐tetra­thio­tungstenio‐κ4S,S′:S′′:S′′′)­bis­[(cyano‐κC)­cuprate](2–) aceto­nitrile solvate monohydrate

The reaction of CuCN and KCN with (NH₄)₂[WS₄] followed by cation exchange with PPh₄Br produced the title compound, (C₂₄H₂₀P)₂[Cu₂WS₄(CN)₂]·CH₃CN·H₂O or (PPh₄)₂[(NC)Cu(μ‐S)₂W(μ‐S)₂Cu(CN)]·MeCN·H₂O. In the structure of the dianion, [(NC)Cu(μ‐S)₂W(μ‐S)₂Cu(CN)]²⁻, the WS₄ moiety acts as a bidentate ligand that binds two CuCN groups, thus forming a slightly bent WCu₂ core with approximate D_2d symmetry. The W—Cu distances are in the range 2.6463 (6)–2.6545 (6) Å.     

Modification of WS2 nanosheets with beta-cyclodextrone and N-isopropylacrylamide polymers for tamoxifen adsorption and investigation of in vitro drug release

In this research, tungsten disulfide (WS₂) nanosheets were modified with beta-cyclodextrone (βCD) N-isopropylacrylamide polymers (NIPAAP) for adsorption of tamoxifen (TAM) drug. The synthesized WS₂/βCD/NIPAAP samples were characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) analyses. The adsorption experiments of TAM on WS₂/βCD/NIPAAP were performed as a function of pH, reaction contact time, temperature and drug concentration. The adsorption kinetic data were well fitted to the pseudo-second-order model. Also, the equilibrium data were well described by Langmuir isotherm model. The maximum adsorption capacity of WS₂/βCD/NIPAAP for TAM drug was found to be 62.0 mg/g. The results of regeneration tests showed that the synthesized WS₂/βCD/NIPAAP adsorbent can be easily reused after 6 cycles of adsorption–desorption. Furthermore, TAM drug release was investigated in a simulated system with pH 7.4 at different temperatures. The results showed that the release of TAM drug from WS₂/βCD/NIPAAP carrier at 50 °C and 37 °C was greater than TAM release at 25 °C. Also, the experimental data of drug release were studied by Higuchi, Ritger-Peppas, zero-order and first-order models. The release data were well fitted to the zero-order model indicating a case II transport. The results showed a high stability for TAM drug.

     

1,3‐Propane­di­ammonium tetra­thio­tungstate and N,N,N′,N′‐tetra­methyl­ethyl­enedi­ammonium tetra­thio­tungstate

The title complexes, (C₃H₁₂N₂)[WS₄] and (C₆H₁₈N₂)[WS₄], contain tetrahedral [WS₄]²⁻ dianions, which accept a complex series of hydrogen bonds from the organic dications. The strength and number of these hydrogen bonds affect the W—S distances.     

Functionalization of Hydrogenated Graphene: Transition‐Metal‐Catalyzed Cross‐Coupling Reactions of Allylic C−H Bonds

The chemical functionalization of hydrogenated graphene can modify its physical properties and lead to better processability. Herein, we describe the chemical functionalization of hydrogenated graphene through a dehydrogenative cross‐coupling reaction between an allylic C?H bond and the α‐C?H bond of tetrahydrothiophen‐3‐one using Cu(OTf)₂ as the catalyst and DDQ as the oxidant. The chemical functionalization was confirmed by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy and visualized by scanning electron microscopy. The functionalized hydrogenated graphene material demonstrated improved dispersion stability in water, bringing new quality to the elusive hydrogenated graphene (graphane) materials. Hydrogenated graphene provides broad possibilities for chemical modifications owing to its reactivity.     

One‐Pot Solvothermal Synthesis of Highly Water‐Dispersible Size‐Tunable Functionalized Magnetite Nanocrystal Clusters for Lipase Immobilization

A facile one‐pot synthesis of highly water‐dispersible size‐tunable magnetite (Fe₃O₄) nanocrystal clusters (MNCs) end‐functionalized with amino or carboxyl groups by a modified solvothermal reduction reaction has been developed. Dopamine and 3,4‐dihydroxyhydroxycinnamic acid were used for the first time as both a surfactant and interparticle linker in a polylol process for economical and environment‐friendly purposes. Morphology, chemical composition, and magnetic properties of the prepared particles were investigated by several methods, including FESEM, TEM, XRD, XPS, Raman, FTIR, TGA, zeta potential, and VSM. The sizes of the particles could be easily tuned over a wide range from 175 to 500 nm by varying the surfactant concentration. Moreover, ethylene glycol/diethylene glycol (EG/DEG) solvent mixtures with different ratios could be used as reductants to obtain the particles with smaller sizes. The XRD data demonstrated that the surfactants restrained the crystal growth of the grains. The nanoparticles showed superior magnetic properties and high colloidal stability in water. The cytotoxicity results indicated the feasibility of using the synthesized nanocrystals in biology‐related fields. To estimate the applicability of the obtained MNCs in biotechnology, Candida rugosa lipase was selected for the enzyme immobilization process. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with the free enzyme. This novel strategy would simplify the reaction protocol and improve the efficiency of materials functionalization, thus offering new potential applications in biotechnology and organocatalysis.     

Cationic Reverse Micelles Create Water with Super Hydrogen‐Bond‐Donor Capacity for Enzymatic Catalysis: Hydrolysis of 2‐Naphthyl Acetate by α‐Chymotrypsin

Reverse micelles (RMs) are very good nanoreactors because they can create a unique microenvironment for carrying out a variety of chemical and biochemical reactions. The aim of the present work is to determine the influence of different RM interfaces on the hydrolysis of 2‐naphthyl acetate (2‐NA) by α‐chymotrypsin (α‐CT). The reaction was studied in water/benzyl‐n‐hexadecyldimethylammonium chloride (BHDC)/benzene RMs and, its efficiency compared with that observed in pure water and in sodium 1,4‐bis‐2‐ethylhexylsulfosuccinate (AOT) RMs. Thus, the hydrolysis rates of 2‐NA catalyzed by α‐CT were determined by spectroscopic measurements. In addition, the method used allows the joint evaluation of the substrate partition constant K_p between the organic and the micellar pseudophase and the kinetic parameters: catalytic rate constant k_cat, and the Michaelis constant K_M of the enzymatic reaction. The effect of the surfactant concentration on the kinetics parameters was determined at constant W₀=[H₂O]/[surfactant], and the variation of W₀ with surfactant constant concentration was investigated. The results show that the classical Michaelis–Menten mechanism is valid for α‐CT in all of the RMs systems studied and that the reaction takes place at both RM interfaces. Moreover, the catalytic efficiency values k_cat/K_M obtained in the RMs systems are higher than that reported in water. Furthermore, there is a remarkable increase in α‐CT efficiency in the cationic RMs in comparison with the anionic system, presumably due to the unique water properties found in these confined media. The results show that in cationic RMs the hydrogen‐bond donor capacity of water is enhanced due to its interaction with the cationic interface. Hence, entrapped water can be converted into “super‐water” for the enzymatic reaction studied in this work.     

水热合成二硫化钨/石墨烯复合材料及其氧还原性能

以六氯化钨、硫代乙酰胺、氧化石墨烯为原料,采用一步水热法合成了二维的二硫化钨/石墨烯(WS₂/RGO)复合材料。水热合成的WS₂/RGO具有薄层的二维结构,且由于石墨烯的存在,WS₂以较少的层数形成薄片状生长在石墨烯的表面。尝试将这种非Pt类材料用于电催化氧化原反应,测试结果表明,WS₂在碱性条件下氧还原活性非常低,但是复合RGO形成WS₂/RGO复合材料后,电催化氧化原性能有了极大的提高,其起始电位为-0.17 V(vs SCE),转移电子数为3.7,极限电流密度为2.5 mA·cm^-2,同时其具有较好的抗甲醇性能和循环稳定性。这是因为WS₂/RGO复合材料的二维结构具有更高的电子传输速率,同时硫化钨和石墨烯可以发挥协同催化作用。这种新型的二硫化钨/石墨烯(WS₂/RGO)复合材料作为非贵金属催化剂表现出良好的氧还原性能,在燃料电池上具有较好的应用前景。     

Manganese‐Mediated Intermolecular Arylation of H‐Phosphinates and Related Compounds

The intermolecular radical functionalization of arenes with aryl and alkyl H‐phosphinate esters, as well as diphenylphosphine oxide and H‐phosphonate diesters, is described. The novel catalytic Mn^II/excess Mn^IV system is a convenient and inexpensive solution to directly convert C_sp2?H into C?P bonds. The reaction can be employed to functionalize P‐stereogenic H‐phosphinates since it is stereospecific. With monosubstituted aromatics, the selectivity for para‐substitution increases in the order (RO)₂P(O)H<R¹P(O)(OR)H<Ph₂P(O)H, a trend that may be explained by steric effects.