Facile shape-controlled synthesis of palladium nanostructures on copper for promising Surface-enhanced Raman scattering

In this letter, size-controlled Pd nanocubes, hexagonal prism and Pd dendrites nanostructures were synthesized by a simple galvanic displacement process between Pd ion and Cu. The sizes and morphology of Pd nanostructures could be controlled by simply regulating the reaction parameters, such as concentration of palladium dichloride, reaction time and types of surfactant. A possible formation mechanism of Pd nanocubes was also briefly discussed. Furtherly, Surface-enhanced Raman scattering (SERS) investigation demonstrated the nanostructures on copper foils were SERS-active by using 4-aminothiophenol (PATP) as probe molecule. We believe the unique Pd nanostructures on copper foils would be a flexible and promising SERS substrate.     

Synthesis of flower-like CuO nanostructures via a simple hydrolysis route

We describe a facile route for the synthesis of flower-like CuO nanostructures by hydrolyzing of Cu(OAc)₂ solution without any surfactants. SEM and TEM observations indicate that the CuO products are composed of microspheres with diameters of 0.4-0.8 μm. The microspheres are in fact built from small needle-like nanocrystals with diameters of 10-15 nm. The method provides a convenient, low-cost, nontoxic route for the synthesis of nanostructures of oxide materials, and it is important for exploring oxide-based nanostructures for applications in nanodevices.     

Synthesis of polyacrylonitrile/Ag core–shell nanowire by an improved electroless plating method

A simple synthetic route for fabricating continuous Ag shell on electrospun polyacrylonitrile (PAN) nanofibers has been presented via an improved electroless plating method. To avoid the complex steps (wet surface activation, pre-treatment) of the electroless plating methods reported before, UV photoreduction is used to fabricate dense Ag nanoparticles on the outer surfaces of PAN nanofibers. These Ag nanoparticles act as seeds in the following metal electroless plating step for the growth of continuous Ag shell. Additionally, our method can be easily applied to synthesize other metallic shell on the outer surfaces of PAN nanofibers with Ag nanoparticles as seeds.     

Facile one-pot synthesis of superfine palladium nanoparticles on polydopamine-functionalized carbon nanotubes as a nanocatalyst for the Heck reaction

Heterogeneous Pd nanocatalysts are efficient catalysts for the Heck reaction but require multi-step,sophisticated procedures and harsh reaction conditions.In this work,a green and facile strategy has been developed to decorate Pd nanoparticles on polydopamine(PDA)-coated multi-walled carbon nano-tubes(Pd/CNTs-PDA)via a one-pot method.The obtained nanoparticles were characterized by various techniques including transmission electron microscopy,X-ray diffraction,and X-ray photoelectron spec-troscopy,which proved that Pd NPs are well-dispersed on the PDA and between the surfaces of the PDA and CNTs.The resultant Pd/CNTs-PDA catalysts exhibit excellent catalytic reactivity toward the Heck reaction at low temperatures.Moreover,by DFT simulation,we found that during the PDA polymeriza-tion process,a large number of unsaturated-N=and C=O species are more active than the groups on the PDA end product to anchor Pd NPs.The results provide evidence that the catalyst synthesized by the one-pot method exhibited good activity because sufficient active sites could be created to effectively promote Pd NPs dispersion during the dopamine polymerization process.Additionally,the Pd/CNTs-PDA catalyst was successfully employed in Heck cross-coupling reactions with various functionalized substrates.This method opens a window for the fabrication of high-performance nanocomposite catalysts under mild conditions using simple methods and has several potential applications.     

Synthesis and characterization of PbTe micro/nanostructures through hydrothermal method by using a novel capping agent

For the first time, a Schiff base compound derived from 1,8-diamino-3,6-dioxaoctane and 2-hydroxybenzophenone marked as (2-HBP)-(DaDo) was synthesized, characterized and then used as capping agent for the preparation of PbTe micro/nanostructures. Besides the as-synthesized Schiff base compound, Pb(NO₃)₂ and Te powders were applied as lead and telluride precursors. In addition, effect of preparation parameters like reaction time and temperature in hydrothermal synthesis on the morphology of the final products was tested. The products were analysed with the aid of SEM, XRD, FT-IR and EDS. Based on the obtained results, it was found that pure cubic phased PbTe has been obtained by this method. According to SEM images, it was found that uniform PbTe micro/nanocubes have been obtained at 180 °C for 12 h. On the other hand, by increasing the reaction temperature from 3 to 24 h, the production of cubic-like shapes increased.     

Synthesis of platinum nanostructures in zeolite mordenite using a solid-state reduction method

Platinum nanoparticles and nanowires have been synthesized inside zeolite mordenite using a solid-state reduction method. Tetrammine platinum nitrate was introduced into the pores via incipient wetness impregnation and it was reduced using powder sodium borohydride. With this method it was possible to obtain single crystal nanowires along the edges of the zeolite particle. The molar ratio of the reducing agent to platinum atoms was a critical parameter for the formation of either uniform nanoparticles or nanowires. Using a regular aqueous sodium borohydride solution reduction it was not possible to obtain nanowires in this zeolite. To the best of the author's knowledge this is the first time sodium borohydride in its solid form is used as a reducing agent to form nanostructures and this is also the first time a solid-state method is used to form nanostructures in a zeolite.     

改进化学气相沉积法在炭纤维表面生长碳纳米管(英文)

采用一种改进的化学气相沉积法在炭纤维表面制备碳纳米管。为了提高炭纤维表面的润湿性能,炭纤维在浸渍之前先在CVD设备中在真空下973 K的高温处理,然后在硝酸和浓硫酸体积比为3∶1的混合酸中酸处理30 min。而改进的化学气相沉积法关键在于让催化剂的还原步骤和碳纳米管的生长步骤同时进行。这样通过减小过渡金属元素与炭纤维之间的接触时间从而降低了它们之间的相互扩散,在确保了炭纤维本身的力学性能下降程度明显小于用普通化学气相法制备的情况下生长出长且茂密的碳纳米管阵列。另外,经过对工艺参数的优化发现当用乙醇作溶剂,Fe(NO3)3.9H2O溶度为100 mmol/L,氢气和碳源气体比值为4/1,而生长时间为30 min时得到最好的碳纳米管阵列。     

Synthesis of molybdenum (IV) disulfide using a single-source method

Molybdenum(IV) disulfide was prepared by the thermalysis of the single molecule precursor [Mo₂O₄(S₂CNEt₂)₂] (Et: ethyl group). The thermalysis was monitored by thermogravimetric analysis and FT-infrared spectroscopy. The MoS₂ materials obtained during the thermalysis experiments were characterized in terms of their morphological and optical characteristics.     

Synthesis of KNbO3 nanostructures by a microwave assisted hydrothermal method

One-dimensional nanostructures of KNbO₃ have attracted a great interest in the scientific community, mainly because of their promising application as nanoelectromechanical systems (NEMS). However, the synthesis of KNbO₃ structures becomes complex due to the natural tendency to form non-stoichiometric potassium niobates. In this context, we report on the crystallization of one-dimensional KNbO₃ nanostructures through the reaction between Nb₂O₅ and KOH under microwave-assisted hydrothermal synthesis (M-H). The use of this synthesis method made possible a very fast synthesis of singlecrystalline powders. Based on SEM, TEM and XRD characterizations, the influence of the synthesis time and the reactants concentration in the structure and morphology of the resultant KNbO₃ was established. The conditions that favor the crystallization of nanofingers were determined to be small amounts of Nb₂O₅ and short reaction times.     

分散法合成树枝状超支化聚酯及其表征

以三羟甲基丙烷、邻苯二甲酸酐和环氧丙醇为原料,探索了发散法合成末端含大量羧基和羟基的第一代、第二代树枝状超支化聚酯,并且通过测定分析研究了合成条件及性能.这种树枝状超支化聚酯具有可控的精确结构,大量分子末端基团易于改性,粘度低,热稳定性好,是一种性能优良的高分子材料,在光固化涂层和粘合剂等领域具有广阔的应用前景.     

Synthesis and characterization of novel flower-like CeF3 nanostructures via a rapid microwave method

Novel flower-like CeF₃ nanostructures with a mean diameter of 190 nm were successfully synthesized via a rapid and facile microwave irradiation route using ethylenediaminetetraacetic acid disodium as the complexing reagent. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and photoluminescence (PL). XRD patterns showed that the CeF₃ nanoflowers were hexagonal phase and had good crystallinity and purity. TEM and SEM images showed that the as-prepared CeF₃ samples displayed 3D flower-like nanostructures and had uniform sizes and morphologies. The experimental results revealed that the as-prepared CeF₃ nanoflowers might be assembled by nanodisks. The formation process of the CeF₃ nanoflowers was preliminarily investigated.     

Synthesis of single-crystalline BaCO3 nanostructures with different morphologies via a simple PVP-assisted method

Single-crystalline BaCO₃ with different morphologies, such as peanut-like, ellipsoids-like, rod-like and dumbbell-like has been successfully synthesized by a simple PVP-assisted method. Reaction conditions, such as pH value, the ratio of EDTA/Ba²⁺ and the concentration of the Ba²⁺ ions are found to play important roles in determining the morphologies and growth process of the final products. X-ray diffraction (XRD), transmission electron microscope (TEM), selected area electron diffraction (SAED) and the infrared (IR) spectrum of the sample are used to characterize the obtained products.     

Effects of control mode and R-ratio on the fatigue behaviour of a metal matrix composite

Thick specimens of [0]₃₂ SiC/Ti-15-3 were cycled under a variety of loading conditions. Specimens were fatigued in strain- and load-controlled modes at both R = 0 (zero-tension) and R = −1 (fully reversed) loading ratios. In addition, a hybrid strain-controlled mode at R = 0 was used to simulate the true strain-controlled behaviour. The strain-controlled specimens had longer lives compared with the load-controlled specimens when cycled at an R-ratio of zero. Under fully reversed loading, there was no difference between the strain- and load-controlled modes. The hybrid strain-controlled data were found to approximate the load-controlled data better, rather than the true strain-controlled situation. Damage occurred through transverse fibre cracks for R = 0 loading for both the load- and strain-controlled modes. However, fully reversed loading caused matrix cracking to be the operative damage mechanism.     

Synthesis of thorny BaCO3 dendritic structures via a simple PEG-assisted method

Thorny BaCO₃ dendritic structures were successfully synthesized by a simple PEG-assisted method. The results revealed that reaction conditions, such as aging time, and the concentration of the PEG, are important factors which determines the morphologies and growth process of the final products. The obtained barium carbonate was characterized by scanning electronic microscopy (SEM) and X-ray powder diffraction (XRD). As a result, it was found that the morphologies are different in different reaction system.     

Ligand grafting method for immobilization of metal complexes on a carbon electrode

Immobilization of metal complexes on a carbon electrode was successfully carried out via their ligand, of which the functional group on the opposite side of the central metal ion is covalently bonded to the carbon electrode. This method is viewed as a ligand grafting method. The functional group is primary or secondary amine, but not tertiary amine. As metal complexes, Os(bpy)₂Cl₂ (bpy4,4′-bipyridyl), Ru(bpy)₂Cl₂, and Os(phen)₂Cl₂ were used, and as ligands, which act as a bridge between the complex and the carbon electrode, 4-aminopyridine and 4-aminoethylpyridine, were used. Two ligand grafting methods were developed: in one, a ligand by itself was first grafted on carbon through electrochemical cation radical formation in ethanol solution, and then metal complex was refluxed with ligand-grafted carbon to generate metal complex grafted carbon. A second method is for the metal complex to be directly bonded to carbon by the electrochemical cation radical formation.     

新型工艺制备Fe/Cr/Si复合薄膜的结构研究

采用改进的水热法和新型工艺在SUS304不锈钢表面制备了Fe/Cr掺杂SiO2薄膜,并通过扫描电镜(SEM)、X射线衍射(XRD)、电子探针(EPMA)和X射线光电子能谱深度分析(XPS)等检测手段对薄膜结构进行了分析.结果表明膜层主要分为两层:表层为共溶氧化物层;底层为Cr、Fe的氧化物,主要为尖晶石结构和Si网状结构.通过XPS检测结果得知,Si元素的加入不是简单的物理混合,而是与金属元素生成了Si-Fe键,进一步提高了膜层的结合力和耐酸性.     

The effects of thermal cycle and nanostructure reinforcement on the shear load in adhesively bonded joints

Abstract

In this study, the shear strength of a nanocomposite adhesive was experimentally and numerically investigated under ambient temperature and thermal cycling conditions. This study used the Thick Adherend Shear Test method, which is commonly used to determine the shear stress–displacement of adhesives. Shear–displacement was determined by an extensometer to accurately compare results obtained from the Thick Adherend Shear Test results for joints with numerical analyses. As a result, when the shear failure load obtained from experiments was examined, the nanocomposite adhesives, obtained by adding a nanostructure into the adhesive, improved both the ambient temperature and thermal cycling performances of the joints.     

Synthesis, characterization and dielectric properties of nanocrystalline strontium zirconate prepared through a modified reverse micellar route

Nanocrystalline strontium zirconate has been synthesized using a modified reverse micellar route (avoiding Sr-alkoxide). Powder X-ray diffraction studies show the monophasic nature of the powder of SrZrO₃ after heating at 800 °C. The particle size has been obtained from X-ray line broadening studies (62 nm) and transmission electron microscopic studies (72 nm). The average grain size of 85 nm was found to be reasonably stable to sintering till 1000 °C. A dielectric constant of 19.8 is observed for nanocrystalline SrZrO₃ sintered at 1000 °C. Detailed dielectric studies have been carried out with respect to frequency and temperature.     

Investigation of shape effect of silver nanostructures and governing physical mechanisms on photo-activity: Zinc oxide/silver plasmonic photocatalyst

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e^?/h⁺ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.     

二氧化硅对碳黑/环氧树脂复合材料渗透特性的影响

通过溶剂化过程制备碳黑-二氧化硅-环氧树脂聚合物基复合材料,并研究复合材料的导电渗透特性。当碳黑的体积分数低于15.5%时,复合材料的导电性可以用经典的渗透理论来描述,并发现渗透阈值约为14.7%,这与理论预测值相接近。当碳黑的体积分数高于15.5%时,材料的电导率与理论预测值偏离较大。这可能是因为:此时材料中的二氧化硅的用量较少,其对碳黑颗粒的空间体积排除效应较差;由于氢键和范德华力作用,纳米级的碳黑颗粒容易形成聚集态,这与渗透理论中导电颗粒必须是单个分布的这一前提假设相违背。扫描电镜分析及模拟计算结果支持该结论。