ZnO/CdS nanocomposites: Synthesis,structure and morphology

Uncoated ZnO, CdS and ZnO/CdS nanocomposites were successfully synthesized chemically in atmospheric air using a water–ethanol matrix. The as-obtained samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), UV–vis and photoluminescence (PL) spectrophotometry. The luminescence measurements of ZnO/CdS nanocomposites showed narrow and enhanced PL emission in the blue region. PL quenching was observed in ZnO/CdS nanocomposites by increasing Cd and S concentrations.     

Solvent-less synthesis of zinc oxide nanostructures from Zn(salen) as precursor and their optical properties

ZnO nanoparticles, 10–20 nm in size, were synthesized by heat treatment in air at 500 °C for 5 h., using [N,N′-bis(salicylaldehydo) ethylene diamine]zinc(II), i.e., Zn(salen), as precursor, which was obtained by a solvent-free solid–solid reaction. Heat-treated products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Room temperature photoluminescence spectra of ZnO nanostructures are dominated by green emission attributed to oxygen vacancy related donor–acceptor transition.     

Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO2 core/shell composite hollow spheres

Anatase TiO2 shells assembled on hollow glass microspheres(HGM)with tunable morphologies were successfully prepared through a controllable chemical precipitation method with urea as the precipitator. Thus,glass/TiO2 core/shell composite hollow spheres with low particle density(0.40 g/cm3)were fabricated.The phase structures,morphologies,particle sizes,shell thicknesses,and chemical compositions of the composite microspheres were characterized by X-ray diffraction(XRD),scanning electron microscopy (SEM),and energy dispersive X-ray spectroscopy(EDS).The morphology of the TiO2 shell can be tailored by properly monitoring the reaction system component and parameters.The probable growth mechanism and fabrication process of the core/shell products involving the nucleation and oriented growth of TiO2 nanocrystals on hollow glass microspheres was proposed.A low infrared radiation study revealed that the radiation properties of the products are greatly influenced by the unique product shell structures. A thermal conductivity study showed that the TiO2/HGM possess low thermal conductivity that is similar to that of the pristine HGMs.This work provides an additional strategy to prepare low-density thermal insulating particles with tailored morphologies and properties.     

Statistical morphological identification of low-dimensional nanomaterials by using TEM

Nanomaterials with low-dimensional morphology display unique properties in catalysis and related fields, which are highly dependent on the structure and aspect ratio. Thus, accurate identification of the structure and morphology is the basis to correlate to the performance. However, the widely adopted techniques such as XRD is incapable to precise identify the aspect ratio of low-dimensional nanomaterials, not even to quantify the morphological uniformity with statistical deviation value. Herein, ZnO nanorod and nanosheet featured with one- and two-dimensional morphology were selected as model materials, which were prepared by the hydrothermal method and statistically characterized by transmission electron microscopy (TEM). The results indicate that ZnO nanorods and nanosheets display rod-like and orthohexagnal morphology, which mainly encapsulated with {100} and {001} planes, respectively. The 7.36 ± 0.20 and 0.39 ± 0.02 aspect ratio (c/a) of ZnO nanorods and nanosheets could be obtained through the integration of the (100) and (002) diffraction rings in selected area electron diffraction (SAED). TEM combining with the SAED is favorable compare with XRD, which not only provides more accurate aspect ratio results with standard deviation values but also requires very small amounts of sample. This work is supposed to provide a convenient and accurate method for the characterization of nanomaterials with low-dimensional morphology through TEM.     

Synthesis of Fe3O4 nanoparticles by wet milling iron powder in a planetary ball mill

Fe3O4 nanoparticles with sizes ranging from 30 to 80 nm were synthesized by wet milling iron powders in a planetary ball mill. The phase composition and the morphologies of the as-synthesized products were measured by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Nanosized Fe3O4 particles were prepared by wet milling metallic iron powder （-200 mesh, 99%） in a planetary ball mill equipped with stainless steel vials using iron balls under distilled water with a ball-to-powder mass ratio of 50：1 and at a rotation speed of 300 rpm. The use of the iron balls in this method played a key role in Fe3O4 formation. The present technique is simple and the process is easy to carry out.     

A microemulsion method for preparation of thiol-functionalized gold nanoparticles

A new microemulsion method using tetraoctylammonium bromide as a cationic surfactant has been formulated to fabricate thiol-functionalized gold nanoparticles. The nanoparticles were compared with those synthesized by the multistep Brust two-phase method. The nanoparticle sizes and size distributions fabricated by the two methods were characterized by UV–vis absorbance spectroscopy and transmittance electron microscopy. The simple microemulsion method produced the same results as those obtained by the Brust method.     

类石墨烯二硫化钼的制备及其真空摩擦学性能研究

采用电化学剥离法制备了类石墨烯二硫化钼(MoS_2)片层,采用场发射扫描电子显微镜、透射电子显微镜表征了类石墨烯二硫化钼的结构.利用真空摩擦试验机测试了含类石墨烯MoS_2添加剂离子液体(IL-MoS_2)的摩擦学性能并与纯离子液体(IL)进行了对比.利用光学显微镜和扫描电子显微镜观察磨斑处的形貌并用X射线光电子能谱仪表征了IL-MoS_2摩擦前后的化学状态,并对润滑机理进行了分析.结果表明:电化学剥离法成功制备了类石墨烯MoS_2,这种制备方法简单易行,制得的类石墨烯MoS_2面积大,质量好,能保持二硫化钼固有的结构.IL-MoS_2对钢/钢摩擦副具有优异的减摩抗磨作用;摩擦过程中,纳米尺寸的二硫化钼吸附在钢/钢摩擦副界面形成了保护层,避免摩擦副的直接接触,降低摩擦磨损.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene (PSt) microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate (KPS) as initiator in ethanol-water mixed solvents.Emulsifier-free seeded emulsion copolymerization of styrene (St) with acrylonitrile (AN) was carried out in the presence of poly(ethylene glycol) monomethoxymonomethacrylate (PEGm)macromonomer as reactive stabilizer and 2,2'-azobisisobutyronitrile (AIBN) as initiator to obtain submicron-sized PEGm graft poly(styrene-co-acrylonitrile) (PEGm-g-PSAN) composite particles with unique morphology.Scanning electron microscopy (SEM) indicated that St and AN together contributed to forming the unusual morphology.The concentration of St and AN,total monomer concentration,initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO2 core/shell composite hollow spheres

Anatase TiO₂ shells assembled on hollow glass microspheres (HGM) with tunable morphologies were successfully prepared through a controllable chemical precipitation method with urea as the precipitator. Thus, glass/TiO₂ core/shell composite hollow spheres with low particle density (0.40 g/cm³) were fabricated. The phase structures, morphologies, particle sizes, shell thicknesses, and chemical compositions of the composite microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The morphology of the TiO₂ shell can be tailored by properly monitoring the reaction system component and parameters. The probable growth mechanism and fabrication process of the core/shell products involving the nucleation and oriented growth of TiO₂ nanocrystals on hollow glass microspheres was proposed. A low infrared radiation study revealed that the radiation properties of the products are greatly influenced by the unique product shell structures. A thermal conductivity study showed that the TiO₂/HGM possess low thermal conductivity that is similar to that of the pristine HGMs. This work provides an additional strategy to prepare low-density thermal insulating particles with tailored morphologies and properties.     

Synthesis of submicron-sized composite particles with unique morphology by emulsifier-free seeded emulsion copolymerization

Polystyrene （PSt） microspheres with diameter of 375 nm to be used as the seeds for seeded emulsion polymerization were prepared via emulsion polymerization using potassium persulfate （KPS） as initiator in ethanol-water mixed solvents. Emulsifier-free seeded emulsion copolymerization of styrene （St） with acrylonitrile （AN） was carried out in the presence of poly（ethylene glycol） monomethoxymonomethacrylate （PEGm） macromonomer as reactive stabilizer and 2,2＇-azobisisobutyronitrile （AIBN） as initiator to obtain submicron-sized PEGm graft poly（styrene-coacrylonitrile） （PEGm-g-PSAN） composite particles with unique morphology. Scanning electron microscopy （SEM） indicated that St and AN together contributed to forming the unusual morphology. The concentration of St and AN, total monomer concentration, initiator type and the monomer adding method remarkably affected the morphology of the composite polymer particles.     

Preparation of HNS microspheres by rapid membrane emulsification

In order to improve the dispersibility and loading efficiency of 2,2′,4,4′,6,6′-hexanitrostilbene (HNS), HNS microspheres were prepared by rapid membrane emulsification method with nitrocellulose (NC) as binder. The effects of NC solution concentration, stirring speed and polyvinyl alcohol (PVA) solution concentration on microspheres were investigated. It was characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), differential thermal analysis (DTA) and angle of repose analyzer. The results show that the HNS microspheres prepared with 5 wt% NC solution concentration, stirring speed of 100 rpm and 2 wt% PVA solution concentration have better regular morphology, higher sphericity, unchanged crystalline shape, increased activation energy and significantly improved dispersibility compared with the refined HNS. Rapid membrane emulsification has a series of advantages such as green, low cost and easy scale up, which provides a better way to prepare microspheres of energy materials.     

Residual stresses and mechanical properties of a ZnO pyroelectric sensor

The multilayer composite film stack is a common feature of the microsensors based on thin film technology. In this paper, we propose an analytical model to investigate the Young’s moduli, hardness, and residual stresses of the constitutive film layers of a multilayer film stack. A multilayer film stresses model is derived to evaluate the residual stress distributions in the constitutive film layers of a ZnO pyroelectric sensor. A good agreement among the multilayer film stresses model, the grain morphologies characterized by scanning electron microscopy, the mechanical properties testing by nanoindentation, and the voltage responsivity measurement of the ZnO pyroelectric sensor is found in this paper. The proposed multilayer film stresses model can therefore be used to quantitatively analyze the film stresses and proceed to the optimization of thin film deposition process.     

Effect of system parameters on the size distributions of hollow nickel microspheres produced by an ultrasound-aided electrical discharge machining process

Ultrasound-aided electric discharge machining（EDM） is an emerging technology for producing hollow nickel microspheres.This technology combines traditional EDM with the cavitation and vibration effects of ultrasound to produce hollow microspheres.In this paper,ultrasound-aided EDM was carried out in a kerosene medium（the working solution）.The effects of various parameters on the sizes of microspheres were investigated using scanning electronic microscopy（SEM）.Smileview software was used to measure the sizes of the microspheres.Originpro software was used for statistical analysis to determine the size distributions of the microspheres.To study the effects of the system parameters on the sizes of the microspheres,we first investigated the necessity of using an ultrasonic wave with EDM.After comparing the experimental results with and without the ultrasonic field,we found that ultrasound-induced cavitation and vibration effects reduced the diameters of the microspheres.We then studied the effects of several electrical parameters,including the arc current,pulse width,and gap voltage,on the sizes of the microspheres at an ultrasound frequency of 40 kHz.Smaller microspheres could be obtained by lowering the arc current,pulse width,and gap voltage.     

Composition and morphology of the thermal decomposition products of 3Mg(OH)2·MgCl2·8H2O nanowires

The thermal decomposition of 3Mg(OH)₂·MgCl₂·8H₂O (318MHCH) nanowires synthesized from agglomerated Mg(OH)₂ microspheres was investigated. The influence of heating rate and temperature on the composition and morphology of the products was investigated. Thermogravimetric-differential scanning calorimetry, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction showed that increasing the heating rate from 1 to 20 °C/min promoted the escape of crystalline water from the 318MHCH nanowires. 318MHCH nanowires were dehydrated stepwise to 310MHCH porous nanowires from room temperature to 320 °C, and then to MgO cubic nanoparticles from 420 to 700 °C. The nanowires retained their one-dimensional morphology, until the phase changed to MgO. The immediate collapse of the one-dimensional structure was attributed to the presence of Mg–O/Cl chains.     

核壳结构PS/CeO2复合微球弹性模量的AFM测定

利用原子力显微镜测定了聚苯乙烯(Polystyrene, PS)微球和核壳结构PS/CeO₂复合微球的力-位移曲线,并根据Hertz接触理论计算了微球样品的弹性模量.结果表明:粒径在120 nm左右的PS微球的平均弹性模量约为2.80 GPa,其数值略低于聚苯乙烯块体材料的弹性模量.复合微球的弹性模量随CeO₂壳层厚度的增加而增大,当CeO₂壳厚分别约为8、12和16 nm时,其平均弹性模量依次约为7.93、8.25和10.67 GPa.与纯氧化铈相比,PS/CeO₂复合微球的弹性模量更接近于聚苯乙烯微球.     

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core–shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO₃·2Ni(OH)₂·2H₂O- and Fe₂O₃·nH₂O-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core–shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600 °C for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders (10 g/L), sulfate solution (0.2 mol/L), rate of adding reactants (3 mL/min) and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer (VSM). The results show that the core–shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-performance functional materials and devices.     

基于原位和RNT技术的铜锌合金摩擦磨损性能

采用基于原位全息显微技术和放射性核素技术的摩擦磨损试验装置,在润滑条件下对Cu Zn36/100Cr6配对摩擦体系中Cu Zn36的磨损行为进行了研究.利用装置中的全息显微镜对Cu Zn36磨痕表面微观形貌和粗糙度进行原位分析,利用放射性核素磨损量测量系统精确测量Cu Zn36的实时磨损量;利用扫描电镜对Cu Zn36及100Cr6钢球磨面进行观察和分析,利用X射线光电子能谱分析仪对Cu Zn36磨痕表层的元素化合态进行定量分析.结果表明:在试验法向载荷为1.9~3.0 MPa范围内时,Cu Zn36表现出良好耐磨性,原因是Cu Zn36在试验过程中形成了具有高硬度和自润滑性的Zn O强化层,主要磨损方式为疲劳磨损.在较差磨合试验过程中,磨痕表面耐磨层一直处于"形成-破坏-再形成-再破坏"的动态过程,主要磨损方式为磨粒磨损和黏着磨损.     

Microwave-hydrothermal preparation of a graphene/hierarchy structure MnO2 composite for a supercapacitor

Graphene/hierarchy structure manganese dioxide （GN/MnO2） composites were synthesized using a simple microwave-hydrothermal method. The properties of the prepared composites were analyzed using field emission scanning electron microscopy （FE-SEM）, X-ray diffraction （XRD）, transmission electron microscopy （TEM）, and X-ray photoelectron spectroscopy （XPS） measurements. The electrochemical performances of the composites were analyzed using cyclic voltammetry, electrochemical impedance spectrometry （EIS）, and chronopotentiometry. The results showed that GN/MnO2 （10 wt% graphene） displayed a specific capacitance of 244 F/g at a current density of 100 mA/g. An excellent cyclic stability was obtained with a capacity retention of approximately 94.3% after 500 cycles in a 1 mol/L Li2SO4 solution. The improved electrochemical performance is attributed to the hierarchy structure of the manganese dioxide, which can enlarge the interface between the active materials and the electrolyte. The prepa- ration route provides a new approach for hierarchy structure graphene composites; this work could be readily extended to the preparation of other graphene-based composites with different structures for use in energy storage devices.     

In situ synthesis of Ag-SiO_2 Janus particles with epoxy functionality for textile applications

A facile method for the synthesis of silver-silica(Ag-SiO_2) Janus particles with functionalities suitable for textile applications is reported.Silica nanoparticles prepared by the Stober method were functionalized with epoxy,amine,and thiol groups,which were confirmed by Fourier transform infrared analysis.The functionalized silica nanoparticles were used to produce Pickering emulsions,and the exposed surface was used for the attachment of silver nanoparticles(AgNPs) via the low-temperature chemical reduction method.The morphology and structure of the Ag-SiO_2 Janus particles were characterized by scanning electron microscopy,scanning transmission electron microscopy,high-resolution transmission electron microscopy,energy-dispersive X-ray analysis,and UV-vis spectroscopy.Because of their specific functionalities,these Ag-SiO_2 Janus particles are proposed for applications on textile substrates,as they can overcome several drawbacks of direct application of AgNPs on textiles,such as leaching,agglomeration,and instability during storage.     

纳米氧化锌填充超高分子量聚乙烯复合材料的摩擦磨损性能研究

采用热压成型工艺制备了纳米ZnO填充超高分子量聚乙烯(UHMWPE)复合材料,采用销-盘式摩擦磨损试验机考察了纳米粒子对复合材料摩擦磨损性能的影响;采用扫描电子显微镜观察复合材料磨损表面形貌.结果表明:填充15%～20%的纳米ZnO可以显著改善UHMWPE的摩擦磨损性能;复合材料的磨损机理随纳米粒子含量的增加而变化,纯UHMWPE的磨损机理主要为粘着磨损和疲劳磨损,随着复合材料中纳米粒子含量增加,疲劳磨损特征逐渐消失,当其纳米粒子含量大于15%时,其磨损机理主要为粘着磨损;复合材料磨损表面出现了贫ZnO区和富ZnO区,且富ZnO区以"岛"的形式分布在贫ZnO区中.