Pristine Basal‐ and Edge‐Plane‐Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties

The layered structure of molybdenum disulfide (MoS₂) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS₂: basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS₂ by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS₂ pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X‐ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E_2g and A_1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k⁰ of 4.96×10^?5 and 1.1×10^?3 cm s^?1 for [Fe(CN)₆]^3?/4? and [Ru(NH₃)₆]^3+/2+ redox probes, respectively, compared to the basal plane, which yielded k⁰ tending towards zero for [Fe(CN)₆]^3?/4? and about 9.3×10^?4 cm s^?1 for [Ru(NH₃)₆]^3+/2+. The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)₆]^3?/4? in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS₂ crystals is supported by DFT calculations.     

NiFe水滑石纳米片阵列负载Ru用于提升碱性电催化析氢和析氧性能

通过离子交换的方式将Ru负载到NiFe水滑石（LDH）纳米阵列表面得到（Ru/NiFe LDH），Ru的引入显著提升了NiFe LDH的活性比表面积，暴露了更多的活性位点，同时调控了其电子结构，大大提升了其本征催化活性。在碱性条件下，催化析氢反应时仅需50 mV的过电位即可达到10 mA·cm^-2的电流密度，Tafel斜率为52.3 mV·dec^-1。而相同条件下原始NiFe LDH达到10mA·cm^-2的电流密度则需要226 mV的过电位，Tafel斜率为157.5 mV·dec^-1。同时制备的Ru/NiFe LDH也展现出了良好的析氧催化活性，在50 mA·cm^-2的电流密度下，过电位仅为231 mV，而NiFe LDH则需237 mV。Ru/NiFe LDH在长时间的电催化条件下依然能保持良好的工作稳定性。     

Processable and Robust MoS2 Paper Chemically Cross‐Linked with Polymeric Ligands by the Coordination of Divalent Metal Ions

Inorganic graphene analogues (IGAs) are a huge and fascinating family of compounds that have extraordinary electronic, mechanical, and thermal properties. However, one of the largest problems that face the industrial application of IGAs is their poor processability, which has led to a “bottlenecking” in the development of freestanding, large‐area, IGA‐based thin‐film devices. Herein, we report a facile and cost‐efficient method to chemically modify IGAs by using their abundant coordination atoms (S, O, and N). Taking MoS₂ as an example, we have prepared homogeneous “solution” systems, in which MoS₂ nanosheets are chemically cross‐linked through a carboxylate‐containing polymeric ligand, poly(methyl methacrylate) (PMMA), by copper‐ion coordination. Bonding interactions between C?O bonds and sulfur atoms through copper ions were confirmed by various characterization techniques, such as UV/Vis, FTIR, and Raman spectroscopy and XPS. By using our method, freestanding MoS₂ paper with significantly improved mechanical properties was obtained, thus laying the basis for the mass production of large‐area MoS₂‐based thin‐film devices. Furthermore, copper‐ion coordination was also applied to MoS₂/PMMA nanocomposites. Direct and strong nanofiller/matrix bonding interactions facilitate efficient load transfer and endow the polymeric nanocomposites with an excellent reinforcement effect. This method may pave a new way to high‐strength polymeric nanocomposites with superior frictional properties, flame retardance, and oxidation resistance.     

La~(3+)掺杂NiCo层状双金属氢氧化物纳米片的合成及其电化学性能

稀土离子La~(3+)掺杂的NiCo层状双金属氢氧化物纳米片具有高的超级电容器性能,比容量达到1115 F/g(1A/g)、倍率性能为517 F/g(30 A/g)。研究表明,La~(3+)离子掺杂不改变NiCo层状双金属氢氧化物晶体结构,但会显著影响其电子和离子传导特性,从而改变其电化学性能。根据离子电负性标度,La~(3+)(1.327)和Co~(2+)(1.377)离子的电负性值最接近,掺杂La~(3+)会优先取代Co~(2+)离子位置。由于La~(3+)离子的尺寸作用(106 pm),使得最优掺杂比例较小仅为0.26%,电化学结果表明较少的La~(3+)掺杂比例依然会显著调节NiCo层状双金属氢氧化物的电子/离子输运性质。     

Improving Thermal and Flame Retardant Properties of Epoxy Resin with Organic NiFe‐Layered Double Hydroxide‐Carbon Nanotubes Hybrids

To improve the dispersion of carbon nanotubes (CNTs) and flame retardancy of layered double hydroxide (LDH) in epoxy resin (EP), organic nickel‐iron layered double hydroxide (ONiFe‐LDH‐CNTs) hybrids were assembled through co‐precipitation. These hybrids were further used as reinforcing filler in EP. EP/ONiFe‐LDH‐CNTs nanocomposites containing 4 wt% of ONiFe‐LDH‐CNTs with different ratios of ONiFe‐LDH and CNTs were prepared by ultrasonic dispersion and program temperature curing. The structure and morphology of the obtained hybrids were characterized by different techniques. The dispersion of nanofillers in the EP matrix was observed by transmission electron microscopy (TEM). The results revealed a coexistence of exfoliated and intercalated ONiFe‐LDH‐ CNTs in polymer matrix. Strong combination of the above nanofillers with the EP matrix provided an efficient thermal and flame retardant improvement for the nanocomposites. It showed that EP/ONiFe‐LDH‐CNTs nanocomposites exhibited superior flame retardant and thermal properties compared with EP. Such improved thermal properties could be attributed to the better homogeneous dispersion, stronger interfacial interaction, excellent charring performance of ONiFe‐LDH and synergistic effect between ONiFe‐LDH and CNTs.     

双层固相萃取-液相色谱/串联质谱法测定水稻中独脚金内酯

本文结合双层固相萃取和液相色谱-串联质谱法(LC-MS/MS),建立了水稻中内源性独角金内酯(Strigolactone,SLs)的快速分析方法。水稻根提取液经过石墨化炭黑/混合模式阴离子交换吸附剂+混合模式阳离子交换吸附剂(GCB/MAX+MCX)双层固相萃取柱除杂后,通过LC-MS/MS法分析检测。实验优化了固相萃取条件,并进行了方法学验证。结果表明,SLs在对应范围内线性关系良好(相关系数大于0.9972),方法检出限(S/N=3)为0.007~0.028ng/g,回收率为82.1%~115.8%,相对标准偏差(n=6)在1.9%~14.1%之间。建立的方法灵敏度高、重现性好,可用于水稻中内源性SLs的准确定量。     

Dynamics of Branched Polymers in Random Layered Flows with Intramolecular Hydrodynamic Coupling: Star and Dendrimer

The authors develop a theoretical formalism to incorporate the effect of intramolecular hydrodynamic interactions (HIs) on the dynamics of flexible branched polymer in the presence of random layered flows. The influence of HIs on the anomalous diffusive behavior of branched polymers is illustrated through the preaveraged Oseen tensor approach. Although the formalism is valid for polymer structures with arbitrary topology, particular attention is paid here to the study of stars and dendrimers. The macromolecular property that is evaluated is the average square displacement (ASD) of drift center of the polymer. Qualitatively, our analysis highlights two anomalous power‐law regimes, viz. subdiffusive (intermediate‐time polymer stretching and flow induced diffusion) and superdiffusive (long‐time flow induced diffusion). The time dependence of the ASD in the presence of HIs within the preaveraging approximation reveals the anomalous long‐time dynamics which is governed by scaling behavior, t ^{2 − α/2}. The introduction of HIs in random flows speeds up the dynamics resulting in the shorter crossover time (from subdiffusive to superdiffusive regime) with enhanced magnitude of ASD compared to the free‐draining limit.

     

Vibrational energy-harvesting performance of bio-sourced flexible polyamide 11/layered silicate nanocomposite films

The energy-harvesting efficiency of melt processed polyamide 11 (PA11) films and its nanocomposites have been investigated as a function of filler type and content. In the present work, nanoclays have been used as structural modifiers in a PA11 matrix. The nanocomposites were prepared using layered clays, Cloisite 20A, 10A, and Na⁺, by extrusion process through varying the filler content, 1, 2, 4, and 5?wt.%. The crystalline structure of these nanocomposites has been studied by X-ray diffractometer. It has been demonstrated that layered silicates are not significant for the structural quality of the obtained nanocomposites. Regarding the interlayer peak of different clays, it has also been revealed that Cloisite 20A is partially exfoliated, whereas 10A and Na⁺ are totally exfoliated in the PA11 matrix. From mechanical and dynamic mechanical analyses, it was found that the addition of layered silicates results in an increase in mechanical properties. The piezoelectric strain coefficient d₃₃ and dielectric constant ε_R have been measured on polarized films at ambient temperature. Among all the prepared nanocomposites only Cloisite Na⁺-loaded PA11 nanocomposites showed the best piezoelectric constant. This observation showed that piezoelectric constant not only depends on the crystalline phases but also on the nature of the filler. Cloisite Na⁺ is more polar than other modified clays and high polarity leads to a better polarization response. A specific method for the quantification of energy vibration recovery has been developed for these nanocomposites. The capabilities of vibrational energy recovery were studied on PA11 loaded with Cloisite Na⁺.