利用聚合物乳液合成聚甲基丙烯酸甲酯/二氧化硅纳米杂化材料

通过正硅酸乙酯分别在聚甲基丙烯酸甲酯乳液和四氢呋喃溶液中的溶胶－凝胶反应制备出不同的聚甲基丙烯酸甲酯／二氧化硅复合材料。利用扫描电镜、透镜电镜、差热分析和热失重对试样进行了分析。结果表明，利用聚合物乳液可以获得纳米分散的聚甲基丙烯酸甲酯／二氧化硅复合材料，并且在某种程度上其分散尺度小于利用聚合物溶液获得的复合材料。同时，利用聚合物乳液来制备聚甲基丙烯酸甲酯／二氧化硅杂化材料更有利于凝胶过程中二氧化硅网络的形成。     

Magnetic, electronic, and structural characterization of nonstoichiometric iron oxides at the nanoscale

We have investigated the structural, magnetic, and electronic properties of nonstoichiometric iron oxide nanocrystals prepared by decomposition of iron(II) and iron(0) precursors in the presence of organic solvents and capping groups. The highly uniform, crystalline, and monodisperse nanocrystals that were produced enabled a full structural and compositional survey by electron microscopy and X-ray diffraction. The complex and metastable behavior of nonstoichiometric iron oxide (wüstite) at the nanoscale was studied by a combination of Mossbauer spectroscopy and magnetic characterization. Deposition from hydrocarbon solvents with subsequent self-assembly of iron oxide nanocrystals into superlattices allowed the preparation of continuous thin films suitable for electronic transport measurements.     

An assessment of the relative contributions of redox and steric issues to laccase specificity towards putative substrates

Laccases catalyze the one-electron oxidation of a broad range of substrates coupled to the 4 electron reduction of O2 to H2O. Phenols are typical substrates, because their redox potentials (ranging from 0.5 to 1.0 V vs. NHE) are low enough to allow electron abstraction by the T1 Cu(II) that, although a relatively modest oxidant (in the 0.4-0.8 V range), is the electron-acceptor in laccases. The present study comparatively investigated the oxidation performances of Trametes villosa and Myceliophthora thermophila laccases, two enzymes markedly differing in redox potential (0.79 and 0.46 V). The oxidation efficiency and kinetic constants of laccase-catalyzed conversion of putative substrates were determined. Hammett plots related to the oxidation of substituted phenols by the two laccases, in combination with the kinetic isotope effect determination, confirmed a rate-determining electron transfer from the substrate to the enzyme. The efficiency of oxidation was found to increase with the decrease in redox potential of the substrates, and the Marcus reorganisation energy for electron transfer to the T1 copper site was determined. Steric hindrance to substrate docking was inferred because some of the phenols and anilines investigated, despite possessing a redox potential compatible with one-electron abstraction, were scarcely oxidised. A threshold value of steric hindrance of the substrate, allowed for fitting into the active site of T. villosa laccase, was extrapolated from structural information provided by X-ray analysis of T. versicolor lac3B, sharing an identity of 99% at the protein level, thus enabling us to assess the relative contribution of steric and redox properties of a substrate in determining its susceptibility to laccase oxidation. The inferred structural threshold is compatible with the distance between two phenylalanine residues that mark the entrance to the active site. Interaction of the substrate with other residues of the active site is commented on.     

Controlled Synthesis of Nanoscale CdTe Urchins

We presented a simple route to prepare nanoscale CdTe urchins in a tri-n-octylphosphine oxide(TOPO)system.CdTe urchins consisted of a core and several attached arms.The arms were ca.3 nm wide,and their lengths could be controlled with the reaction time.The authors investigated the optical absorption and structural properties of the prepared CdTe.The lengths of the arms could be tuned into CdTe nanourchins,which led to a change in the photophysical properties of the nanoscale CdTe urchins.The results,including transmission electron microscopy(TEM) and absorption spectra,indicated that mesoporous silica and aminopropyltriethoxysilane(APTES) contributed to the formation of nanoscale CdTe urchins.     

Radiation Stability of Copper Films under Irradiation with He<Superscript>2+</Superscript> Ions

The effect of irradiation of copper films with low-energy He²⁺ ions on their structural properties has been studied. The surface morphology and structural properties of the samples before and after irradiation have been examined by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction. Bombardment of the initial samples with He²⁺ ions at a fluence of 1 × 10¹⁶ion/cm² alters the surface morphology of copper films and leads to the formation of nanoscale inclusions of hexagonal shape. An increase in the fluence to 1 × 10¹⁷ ion/cm² and higher results in the formation of cracks and amorphous oxide inclusions on the sample surface.     

纳米氧化锰表面功能化木材的制备及性质

采用水热反应法制备了纳米氧化锰负载木材.通过扫描电子显微镜和能谱分析对样本进行了微观形貌和元素含量检测,并探讨了在不同处理条件下得到的纳米氧化锰负载木材在耐腐性和抗菌性方面的表现.数据分析显示,氧化锰负载木材的耐腐性和抗菌性均优于未处理的木材,水热反应中采用十二烷基硫酸钠作为表面活性剂时木材表面的氧化锰物相最纯净,且木材样本的性能优于其它条件下制备的样本.     

The effect of diameter on the thermal properties of the modeled shape-stabilized phase change nanofibers (PCNs)

The main objective of the present study is to investigate the effect of diameter on thermal properties of phase change fibers at nanoscale in order to develop a shape-stabilized phase change material (PCM). In this regard, polyethylene glycol/cellulose acetate (PEG/CA) electrospun nanofibers as a model of PCM/polymer structure were electrospun. The electrospinning process was optimized using response surface methodology (RSM) to produce phase change nanofibers (PCNs) with achievable minimum and maximum diameter at nanoscale range. Therefore, PCNs with minimum and maximum diameter (223 nm and 545 nm, respectively) were successfully prepared. According to differential scanning calorimetry (DSC) results, the PCNs sample with maximum diameter exhibited higher efficiency of enthalpy (49.41 %) than the PCNs sample with minimum diameter (46.24 %). On the other hand, a test based on the T-history method revealed that PCNs with maximum diameter enjoy higher thermal insulation effect. Scanning electron microscopy (SEM) as well as DSC results showed that the PCNs samples exposed to thermal cycling test not only preserved their structural durability, but also exhibited about twofold increasing in the efficiency of enthalpy than the non-exposed samples. According to thermogravimetric analysis (TG) results, due to successful entrapping, a fraction of PCMs within the structure of polymer matrix, PCNs sample display greater thermal stability comparing to the pure PCM. The present work emphasises that at nanoscale range, higher diameter of PCNs can present more favorable thermal behavior; suggesting a great potential for advanced applications of thermal energy storage and thermal regulating materials fields.     

Determination of the textural characteristics of carbon samples using scanning electronic microscopy images: comparison with mercury porosimetry data

In this paper, scanning electron microscopy (SEM) images of carbon samples were analysed, and some textural characteristics were obtained and compared with those determined using mercury porosimetry data. Fractal dimensions were calculated from both mercury porosimetry and SEM images as methods for characterising the porous distribution (heterogeneity) of the samples. Lacunarity is easily determined from SEM images as a measure of the degree of heterogeneity of a porous surface. A relationship between the lacunarity and the fractal dimensions calculated using both methods is shown. Pore-size distributions were also determined from the analysis of SEM images. We show that the analysis of SEM images is a valuable complement to mercury porosimetry measurements and a useful tool for the characterisation of porous surfaces. This method offers the possibility of evaluating the features of porous materials and comparing the results to those obtained using mercury intrusion analysis.     

Polydopamine-based nanoreactors: synthesis and applications in bioscience and energy materials

Polydopamine (PDA)-based nanoreactors have shown exceptional promise as multifunctional materials due to their nanoscale dimensions and sub-microliter volumes for reactions of different systems. Biocompatibility, abundance of active sites, and excellent photothermal conversion have facilitated their extensive use in bioscience and energy storage/conversion. This minireview summarizes recent advances in PDA-based nanoreactors, as applied to the abovementioned fields. We first highlight the design and synthesis of functional PDA-based nanoreactors with structural and compositional diversity. Special emphasis in bioscience has been given to drug/protein delivery, photothermal therapy, and antibacterial properties, while for energy-related applications, the focus is on electrochemical energy storage, catalysis, and solar energy harvesting. In addition, perspectives on pressing challenges and future research opportunities regarding PDA-based nanoreactors are discussed.

The structural and compositional diversity of PDA-based nanoreactors has triggered fast development of their applications in bioscience and energy fields.     

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Redox and acid-base properties of dispersed oxide nanostructures change markedly as their local structure and electronic properties vary with domain size. These changes give rise to catalytic behavior, site structures, and reaction chemistries often unavailable on bulk crystalline oxides. Turnover rates for redox and acid catalysis vary as oxide domains evolve from isolated monomers to two-dimensional oligomers, and ultimately into clusters with bulk-like properties. These reactivity changes reflect the ability of oxide domains to accept or redistribute electron density in kinetically-relevant reduction steps, in the formation of temporary acid sites via reductive processes, and in the stabilization of cationic transition states. Reduction steps are favored by low-lying empty orbitals prevalent in larger clusters, which also favor electron delocalization, stable anions, and strong Br?nsted acidity. Isomerization of xylenes and alkanes, elimination reactions of alkanols, and oxidation of alkanes to alkenes on V, Mo, Nb, and W oxide domains are used here to demonstrate the remarkable catalytic diversity made available by changes in domain size. The reactive and disordered nature of small catalytic domains introduces significant challenges in their synthesis and their structural and mechanistic characterization, which require in situ probes and detailed kinetic analysis. The local structure and electronic properties of these materials must be probed during catalysis and their catalytic function be related to specific kinetically-relevant steps. Structural uniformity can be imposed on oxide clusters by the use of polyoxometalate clusters with thermodynamically stable and well-defined size and connectivity. These clusters provide the compositional diversity and the structural fidelity required to develop composition-function relations from synergistic use of experiments and theory. In these clusters, the valence and electronegativity of the central atom affects the acid strength of the polyoxometalate clusters and the rate constants for acid catalyzed elementary steps via the specific stabilization of cationic transition states in isomerization and elimination reactions.     

Local Surface Structure and Composition Control the Hydrogen Evolution Reaction on Iron Nickel Sulfides

In order to design more powerful electrocatalysts, developing our understanding of the role of the surface structure and composition of widely abundant bulk materials is crucial. This is particularly true in the search for alternative hydrogen evolution reaction (HER) catalysts to replace platinum. We report scanning electrochemical cell microscopy (SECCM) measurements of the (111)‐crystal planes of Fe_4.5Ni_4.5S₈, a highly active HER catalyst. In combination with structural characterization methods, we show that this technique can reveal differences in activity arising from even the slightest compositional changes. By probing electrochemical properties at the nanoscale, in conjunction with complementary structural information, novel design principles are revealed for application to rational material synthesis.     

Engine lubricating oil classification by SAE grade and source based on dielectric spectroscopy data

Dielectric spectroscopy (DS) is one of the most powerful and prevailing structural analysis techniques for dielectric materials. Engine lubricating oil is a typical dielectric material. But DS for qualitative or quantitative analysis of engine lubricating oil has received little attention. In this paper, DS in association with support vector machines (SVM) classification technique was employed to classify 20 samples of engine lubricating oils from Mobil, Shell and Esso by Society of Automotive Engineers (SAE) viscosity grade and source (manufacturer). Both distinguishing the multi-grade from the single-grade according to SAE grade and classification according to manufacturer were done perfectly, which proved that DS can provide useful compositional and structural information on engine lubricating oil. The work in this article has laid the foundation for further quantitative determination of properties of engine lubricating oil and will be a good start to application of DS to petroleum analysis and testing.     

A Stable Hexakis(guanidino)benzene: Realization of the Strongest Neutral Organic Four‐Electron Donor

The growing demand for efficient batteries has stimulated the search for redox‐active organic compounds with multistage redox behavior, as materials with large charge capacity. Herein we report the synthesis and properties of the first hexakis(guanidino)benzene derivative: a strong neutral organic electron donor with reversible multistage redox behavior and a record low redox potential for donation of four electrons. Detailed structural and spectroscopic characterization of three redox states (0, +2, and +4) reveal its unique electronic features. Despite its nitrogen richness, the compound is thermally robust and can be readily purified by sublimation.     

Potentialities of silane-modified silicas to regulate palladium nanoparticles sizes

A promising approach to control palladium nanoparticle sizes by application of silane modified silicas was suggested. The combination of reductive properties of silicon hydride groups and hydrophobic properties of alkylsilyl groups which act as agglomeration limiters for metal nanoparticles gives an opportunity to synthesize uniformly distributed particles with a specified size. Silicas modified with triethoxysilane (TES) and diisopropylchlorosilane (DIPCS), as well as, the combination of hexamethyldisilazane (HMDS) and triethoxysilane were applied for formation of such bifunctional matrices. Properties of the silane-modified silica samples and changes occurred during the formation of palladium nanoparticles were studied by IR spectroscopy. Thermal stability of surface chemical compounds was investigated by thermogravimetric analysis (TGA); low-temperature nitrogen adsorption was used to study structural properties of the applied materials. With the use of transmission electron microscopy (TEM) the dependence of palladium nanoparticle size on the nature of support surface layer was found.     

Fire behavior of flame retarded unsaturated polyester resin with high nitrogen content additives

The novel flame retarded unsaturated polyester resins have been developed and prepared by introduction of high nitrogen content additives into the polymer matrix in order to verify their effectiveness in the formation of swollen carbonaceous char inhibiting the burning process of the polymer. The intumescent flame retardants (IFRs) based on mixture or metal complex were developed and characterized by particle size distribution, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), powder X-ray diffraction (XRD), elemental analysis (CHN) and thermogravimetric analysis (TGA). The evaluation of the efficiency of IFRs addition on the flammability and smoke emission of the unsaturated polyester resins (UP) was carried out using the fire hazard (UL-94), limiting oxygen index (LOI) and cone calorimeter (CC) tests, as well as smoke density chamber tests. The volatile compounds evolved during the burning of materials were determined using a steady state tube furnace and a gas chromatograph with mass spectrometer. Furthermore, the prepared materials were subjected to differential scanning calorimetry (DSC), thermogravimetric analysis and water resistance tests. The mechanical properties of the materials were investigated using Shore D hardness and dynamic mechanical thermal analysis (DMA). The structural evaluation of the manufactured materials and samples after the cone calorimetry tests was carried out using scanning electron microscopy (SEM). It was found that the incorporation of new intumescent flame retardants led to the formation of carbonaceous char layers’ inhibiting the decomposition process and limiting the smoke emission. The most promising results were obtained for the resin containing complex designated as ZN3AT, for which the highest reduction in maximum values of heat release rate (419 kW/m²) compared to unmodified polymer (792 kW/m²) were recorded. Apart from that, the prepared intumescent flame retardants affect the cross-linking process as well as the thermal and mechanical properties of the UP.     

Transmission electron microscopy studies of the nanoscale structure and chemistry of Pt50Ru50 electrocatalysts.

The structural and chemical heterogeneity of 2.5-nm Pt50Ru50 electrocatalysts was studied by transmission electron microscopy using selected area diffraction, lattice imaging, electron-energy loss spectroscopy, and energy-dispersive X-ray spectroscopy. The catalysts with the highest methanol oxidation activities exhibit oxidation-induced phase separation on the nanoscale to from Pt-rich metal embedded in Ru-rich hydrous and anhydrous oxide. Reduction of the oxide-on metal samples produces a true bimetallic face-centered cubic Pt50Ru50 alloy, with 275 times lower oxidation activity.     

以C60为媒介的网状金纳米粒子聚集体的构筑

通过全甲基化环糊精和卟啉之间的"Click"反应,合成了一种不对称环糊精修饰的卟啉衍生物,并对其结构进行了表征.该化合物与氯金酸作用可以形成平均粒径为5 nm的水溶性金纳米粒子,该金纳米粒子进一步与C60作用形成网状纳米聚集体,并通过紫外光谱和透射电子显微镜验证了聚集体的结构.     

Mesoporous carbon/zirconia composites: a potential route to chemically functionalized electrically-conductive mesoporous materials

Mesoporous nanocomposite materials in which nanoscale zirconia (ZrO(2)) particles are embedded in the carbon skeleton of a templated mesoporous carbon matrix were prepared, and the embedded zirconia sites were used to accomplish chemical functionalization of the interior surfaces of mesopores. These nanocomposite materials offer a unique combination of high porosity (e.g., ～84% void space), electrical conductivity, and surface tailorability. The ZrO(2)/carbon nanocomposites were characterized by thermogravimetric analysis, nitrogen-adsorption porosimetry, helium pychnometry, powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Comparison was made with templated mesoporous carbon samples prepared without addition of ZrO(2). Treatment of the nanocomposites with phenylphosphonic acid was undertaken and shown to result in robust binding of the phosphonic acid to the surface of ZrO(2) particles. Incorporation of nanoscale ZrO(2) surfaces in the mesoporous composite skeleton offers unique promise as a means for anchoring organophosphonates inside of pores through formation of robust covalent Zr-O-P bonds.     

Pd2+/Pd0 redox cycling in hexagonal YMn(0.5)Fe(0.5)O3: implications for catalysis by PGM-substituted complex oxides

Complex oxides--containing at least two different cations on crystallographically distinct sites--have recently been shown to display redox cycling of platinum group metals (PGMs), such as Pd; for example, Pd-substituted complex oxides can reversibly extrude metallic Pd under reducing conditions and then reincorporate Pd(2+) ions into the lattice under oxidizing conditions. The title compounds, YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) (0 ≤ x ≤ 0.07) crystallizing in the noncentrosymmetric YMnO(3) structure, were prepared using a sol-gel process at 800 °C, and the structures were refined from high-resolution synchrotron X-ray powder diffraction data. Their redox cycling behavior was monitored using synchrotron X-ray diffraction and EXAFS studies. In contrast to the previously studied complex oxide host compounds, YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) is only modestly tolerant to cycling: repeated redox cycling leads to the formation of PdO, which, on the time-scale of the oxidation cycles, does not reincorporate in the complex oxide lattice. Both oxidized and reduced samples were tested for the oxidation of CO to CO(2) under CO-lean conditions. YMn(0.5)Fe(0.5-x)Pd(x)O(3-δ) performs essentially as well as previously studied YFe(1-x)Pd(x)O(3-δ). The CO oxidation light-off characteristics of the hexagonal hosts are very similar to finely dispersed PdO. Despite evidence that Pd is almost fully dispersed as divalent ions in the host lattice, which is presumably accompanied by the concurrent creation of oxygen vacancies (2 Pd(2+):1 V(O(2-))), the as-prepared hexagonal materials do not display any significant improvement in catalytic activity as a function of Pd substitution level. This suggests that the corner-connected trigonal bipyramids that characterize this structural family do not enable the transport of oxygen through the bulk of the lattice. The study casts light on factors in the solid-state chemistry of precious metal-substituted complex oxides that influence the efficacy of redox cycling of the precious metal, and catalytic performance.     

Application of particle-induced X-ray emission, backscattering spectrometry and scanning electron microscopy in the evaluation of orthodontic materials

The focus of this investigation was on orthodontic materials used in the manufacture of dental brackets. The properties of these dental materials are subjected to various physical parameters such as elongation, yield strength and elasticity that justify their application. In turn, these parameters depend on the quantitative elemental concentration distribution (QECD) in the materials used in the manufacture. For compositional analysis, proton-induced X-ray emission (PIXE), backscatter spectrometry (BS) and scanning electron microscopy (SEM) were applied. QECD analysis was performed to correlate the physical parameters with the composition and to quantify imperfections in the materials. PIXE and BS analyses were performed simultaneously with a 3 MeV proton beam while electrons accelerated at 25 keV were used for the SEM analysis. From the QECDs it was observed that: (1) the major elements Cr, Fe and Ni were homogeneously distributed in the orthodontic plate; (2) the distribution of Mo and O correlated with one another; (3) there was a spread of Cr around regions of high C concentration; and, (4) areas of high concentrations of Mo and O corresponded to a decrease in C concentrations. Elemental concentration correlations are shown to indicate the similarities and differences in the ease of formation of phases, based on the tangent of linearity.