Crystallization controlled by layered silicates in nylon 6–clay nano-composite

To understand the effect of the montmorillonite (MMT) particles on the crystallization kinetics and crystalline morphology of nylon 6 upon nano-composite formation, we have characterized the crystallization behaviors by using light scattering, wide-angle X-ray diffraction (WAXD), transmission electron microscope (TEM) and rheological measurement. The correlation between the nucleating effect and the growth mechanism of the different polymorphism (γ-phase) of nylon 6 in the nano-composite (N6C3.7) was probed. N6C3.7 exhibited γ-phase crystal due to the nucleating effect of the dispersed MMT particles into the nylon 6 matrix throughout the whole T_c range (=150–215 °C). The lamellar growth of the γ-phase crystal took place on both sides of the dispersed MMT particles. In comparison between the temperature dependence of the characteristic relaxation time and the crystallization time, the lamellar growth of the γ-phase crystal has been discussed. The stable growth of the γ-phase was strongly disturbed at low T_c range (=160–190 °C) due to the lack of time for crystallization.     

Magnetic and semi-conducting nano-composite films of spinel ferrite and cubic zinc oxide

Magnetic and semi-conducting nano-composite films have been prepared under bias polarization, by radio-frequency sputtering of a pure zinc ferrite target. These composite thin films are made of cubic Zn_1 − yFe_yO monoxide islands inside a spinel ferrite matrix. The relative proportion of each phase depends on the substrate polarization (i.e. bias power). When no bias is applied the films solely display the diffraction pattern of a spinel phase even if some islands inside the film can be observed by electron microscopy. When the bias power is increased, the spinel phase disappears progressively as enhanced formation of islands takes place in such a manner that the cubic Zn_1 − yFe_yO monoxide is solely revealed by X-ray diffraction for a bias power higher than 5 W. From bibliographical data and calculated phase diagrams, it can be inferred that these phases would require very low oxygen partial pressure, high temperature and mechanical pressure, to be obtained simultaneously by a conventional ceramic process. This underlines the strong potential of radio-frequency sputtering of oxide targets to prepare original oxides or composite materials.     

The transformation of Eu→Eu in SiO2-Al2O3-NaF-YF3: Eu glasses and glass ceramics

Transparent glasses and glass ceramics of SiO₂-Al₂O₃-NaF-YF₃: Eu³⁺ containing the YF₃ nano-crystals were prepared in air atmosphere and their spectroscopic properties are presented. The blue emission peaked at 433 nm shown in the spectra indicate the existence of Eu²⁺.The transformation of Eu³⁺→Eu²⁺ is related with the existence of F⁻, which is the key trigger for the transformation in air atmosphere. In addition, the emission intensities of Eu³⁺ and Eu²⁺ were also related with the concentrations of Eu³⁺. The emission intensities increased heavily with the increasing dopant of EuF₃ in both glasses and glass ceramics_. When the doped concentration of EuF₃ was higher than 0.5 mol.%, the concentration quenching effect occurred.     

纳米BN复合SiC材料的抗热震性研究

将分析纯H3BO3、CO(NH2)2按物质的量比为1∶2.5溶于无水乙醇中,搅拌过程中按质量分数为80%加入平均粒径0.2μm的β-SiC,在850℃氮气中(纯度99.99%,压力为0.92~0.93 MPa)反应15 h制得纳米BN复合SiC粉体,然后在0.92~0.93 MPa N2气氛中以30 MPa轴向压力于1 750~1 800℃保压0.5~1 h热压烧结上述粉体,制成纳米BN复合SiC试样,采用三点弯曲及透射电镜、扫描电镜等方法研究了纳米BN复合SiC材料的抗热震性。结果表明:在SiC材料中引入纳米BN,一方面可以降低材料的弹性模量,有利于抗热震性的提高。另一方面由于基体SiC与第二相六方氮化硼(h-BN)的热膨胀系数相差较大,热失配作用导致h-BN晶粒发生晶间脱层,在复相陶瓷材料内产生许多微孔,这些微孔的存在可以有效缓解由于高温引起的热膨胀作用,从而极大地改善材料的抗热震性。     

Facile synthesis of SnO2/NiO nano-composites: Structural,magnetic and catalytic properties

Environmental pollution, one of the major challenges being faced by life forms on our planet, can be controlled to some extent by degrading organic pollutants using heterostructured nanoparticles. This paper reports the fabrication of SnO₂/NiO nano-composites by a simple, environmentally benign and cost effective two – step process via precipitation using tannic acid, a green reagent. Thermal analysis shows the optimum annealing temperature as 500 °C.Fcc structured NiO and tetragonal SnO₂ in the nanocomposite is confirmed from XRD analysis. The interplanar spacing of 0.33 nm in SnO₂ for (111) and 0.20 nm in NiO for (200) planes observed in the HRTEM images confirms the composite formation. The synthesized composites characterized using UV–Vis spectra give band gap energies of the samples. The elemental composition and oxidation states have been supported by EDX and XPS analyses. VSM study carried out at room temperature show enhanced ferromagnetic properties with increase in NiO content. The probe reactions degrading Methylene Blue and Eosin Yellow show the effective catalytic potential of the synthesized SnO₂/NiO nano-composite. Efficient degradation of 98% and 97% could be achieved in 14 and 20 min, respectively, showing suitability as a promising candidate in waste water treatment.     

PPR/OMMT纳米复合材料的EWF参数与力学性能

以马来酸酐接枝无规共聚聚丙烯(PPR-g-MAH)为相容剂,采用熔融插层法制备了无规共聚聚丙烯(PPR)/有机蒙脱土(OMMT)纳米复合材料,通过对PPR/OMMT纳米复合材料的基本断裂功(EWF)的表征,并结合它们的拉伸性能和冲击强度的测试分析,探讨了PPR/OMMT纳米复合材料的断裂机理和塑性变形机理,以及OMMT用量对PPR断裂强度和拉伸强度的影响;SEM观察揭示了OMMT在PPR基体中的分散性程度随含量的增加变差。结果表明:在PPR-g-MAH的作用下OMMT能有效提高PPR/OMMT的拉伸强度,OMMT质量分数低于4%时,PPR/OMMT纳米复合材料的冲击强度(Gc)、比基本断裂功(we)和塑性变形能力均得到提高。PPR/OMMT纳米复合材料的we和Gc具有相似的变化趋势,且Gc总是大于we。     

Use of graphene-supported manganite nano-composites for methanol electrooxidation

Binary nano-composites of palladium and a metal (Fe or Cu) manganite on graphene nanosheets (GNS) have been prepared by a microwave-assisted polyol reduction method and investigated as electrocatalysts for the methanol oxidation reaction (MOR) in 1 M KOH at 25 °C. Structural and electrocatalytic surface characterizations of composites are carried out by X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy, cyclic voltammetry and chronoamperometry. Results show that new composite catalysts, particularly 40 wt%Pd–x wt%FeMn₂O₄/GNS (where x = 5, 8, 10 & 15) are MOR active and that the activity is the greatest with the catalyst containing 8 wt% of the oxide. The composite, Pd–8 wt%FeMn₂O₄/GNS, exhibits much superior catalytic activity as well as stability compared to the base (Pd/GNS) electrode. The enhanced catalytic activity and stability of the Pd/GNS catalyst in presence of the oxide can be ascribed to increased population of adsorbed OH⁻ ions/OH radicals at the electrode surface.     

原位水解法聚丙烯酸酯/纳米二氧化硅复合乳液的性能研究

将甲基丙烯酸羟乙酯(HEMA)与硅酸四乙酯经酯交换制得的二甲綦丙烯酰氧基硅酸二乙酯与丙烯酸酯进行乳液聚合,制得了不同硅酸酯用量的稳定聚丙烯酸酯/纳米二氧化硅复合乳液。利用红外光谱、透射电镜、差热扫描及热失重对乳胶膜进行了分析表征。结果表明,利用乳液聚合可以获得原位水解并稳定分散的聚丙烯酸酯/纳米二氧化硅复合乳液,二氧化硅的存在可提高材料的热性能。     

Dual-emission carbon dots-copper nanoclusters ratiometric photoluminescent nano-composites for highly sensitive and selective detection of Hg2+

A novel dual-emission photoluminescent (PL) nano-materials of carbon dots-copper nanoclusters (CDs-CuNCs) nano-composites is prepared for excellent sensitivity and selectivity toward Hg²⁺. The nano-composites are composed of blue photoluminescent CDs and red photoluminescent CuNCs with similar excitation wavelengths through the electrostatic assembly. The red photoluminescence of CuNCs was inhibited by the nano-composites exposed to Hg²⁺, while the blue photoluminescence of CDs remained stable. The color of the nano-composites slowly changed from pink to blue with the added of Hg²⁺ concentration. The limit of detection (LOD) of the nano-composites is 0.31 nmol/L (nM) toward Hg²⁺ in aqueous solution, when the signal to noise ratio is 3. In addition, a visual PL test paper is prepared. When the Hg²⁺ solution is added, the color of test paper transforms from pink to blue immediately. Therefore, the nano-composites are very important for efficient and sensitive detection of Hg²⁺, which show broad application prospects in environmental analysis, food safety detection, biological detection and medical diagnosis in daily life.     

Mechanochemical synthesis of the α-AlH3/LiCl nano-composites by reaction of LiH and AlCl3: Kinetics modeling and reaction mechanism

Mechanochemical activation-assisted synthesis, compared to conventional wet methods, exhibits advantages such as higher chemical homogeneity and better quality of the resulting nano-crystals, in preparing nano-sized aluminum hydride (AlH₃). Solid/liquid state milling is effective and convenient for production of α-AlH₃/LiCl nano-composites through a mechanochemical reaction of LiH and AlCl₃ in [2-Eim] OAc. However, the kinetics of this process has not been thoroughly studied. In this work, we studied the kinetics of mechanochemical synthesis of α-AlH₃/LiCl nano-composite to understand the reaction process and find the optimum milling parameters (including shortest time to achieve high-quality product). We performed isothermal desorption tests for as-milled samples at 80 °C. Structures of the products were analyzed using X-ray powder diffraction. Johnson-Mehl-Avrami (JMA) model was adopted to describe the process, which contains transformation fraction and chemical reaction controlled regime. Kinetics of mechanochemical reaction at the beginning was limited by diffusion rate of the reagent, and later controlled by nucleation of AlH₃. By fitting the experimental data, apparent activation energy for the mechanochemical reaction was calculated as 39.6 kJ/mol.