SiO_2@Ag@Au复合颗粒的制备与表征

SiO2-金属核壳结构的粒子作为一种复合材料具有广泛的应用前景,其所含金属为贵金属时,其复合颗粒更加受到各界青睐。通过化学镀法在纳米级SiO2表面镀上了均匀厚度的Ag、Au双金属层,成功制备出了SiO2@Ag@Au核壳结构的复合颗粒。并着重研究了活化工艺、还原剂滴加速度、镀液浓度对SiO2表层化学镀的影响,同时对复合颗粒进行了SEM、XRD、EDS表征。     

Effective in situ material properties of micron-sized SiO2 particles in SiO2 particulate polymer composites

Several analytical models exist for determination of the Young’s modulus and coefficient of thermal expansion (CTE) of particulate composites. However, it is necessary to provide accurate material properties of the particles as input data to such analytical models in order to precisely predict the composite’s properties, particularly at high particle loading fractions. In fact, the constituent’s size scale often presents a technical challenge to accurately measure the particles’ properties such as Young’s modulus or CTE. Moreover, the in situ material properties of particles may not be the same as the corresponding bulk properties when the particles are embedded in a polymer matrix. To have a better understanding of the material properties and provide useful insight and design guidelines for particulate composites, the concept of “effective in situ constituent properties” and an indirect method were employed in this study. This approach allows for the indirect determination of the particle’s in situ material properties by combining the experimentally determined composite and matrix properties and finite element (FE) models for predicting the corresponding composite properties, then backing out the effective in situ particle properties. The proposed approach was demonstrated with micron-size SiO₂ particle reinforced epoxy composites over a range of particle loading fractions up to 35 vol.% by indirectly determining both the effective Young’s modulus and the effective CTE of the particles. To the best of our knowledge, this study is the first published report on the indirect determination of both the Young’s modulus and the CTE of micron size particles in particulate composites. Similar results on Young’s modulus of micron-size SiO₂ particles measured from nano-indentation testing are encouraging.     

不同包裹型态SiO2-PS复合微粒子的制备研究

在种子生长法制备不同粒径的单分散二氧化硅颗粒的基础上,采用KH-570(3-甲基丙烯酰氧丙基三甲氧基硅烷)在乙醇溶液中作为氧化硅颗粒的表面处理剂进行表面接枝改性.再将改性SiO2与苯乙烯单体进行分散聚合反应,在聚合时间不改变的前提下通过改变参与反应的SiO2颗粒粒径、浓度以及SiO2的加入时间可以得到SiO2与PS复合的3种不同构型.     

Synthesis and characterization of Fe doped CeO2 nanoparticles for pigmented ultraviolet filter applications

Iron doped CeO2 nanoparticles with doping concentrations between 0 and 30 mol% were synthesized by the co-precipitation method for potential application as a pigmented ultraviolet filtration material. Each sample was calcined in air and in argon. The iron solubility limit in the CeO2 lattice was found to be between 10 and 20 mol%. Raman spectroscopy results revealed that both iron doping and argon calcination increase the concentration of oxygen vacancies in the CeO2 lattice. Iron doping causes a blue-shift of the absorbance spectrum, which can be linked to the decreased crystallite size, as obtained by XRD peak broadening using the Scherrer formula. The undoped samples showed weak ferromagnetic behaviour whereas the doped samples were all paramagnetic.     

The effect of SiO2 addition on porous silica composite strength

A porous silica composite was prepared by the resin-impregnated method with natural clay and silica as the starting materials. Its compressive strength is up to 1.59 MPa when the mass-blending ratio of silica and clay is 3/7. The effect of silica addition on product strength was significantly investigated.     

Enhanced optical properties of heterostructured ZnO/CeO2 nanocomposite fabricated by one-pot hydrothermal method: Fluorescence and ultraviolet absorption and visible light transparency

Many researchers investigated the properties of either discrete metal oxide CeO₂ or ZnO materials. However, less attention has been paid to the various nanostructure and performances of CeO₂ and ZnO nanocomposite up to now. In this paper, a facile and low cost one-pot hydrothermal synthesis method has been adopted to obtained directly precursors of CeCO₃OH and Zn₅(CO₃)₂(OH)₆ with different Ce atom molar ratios to Zn, which are transformed into their corresponding metal oxide to form the ZnO/CeO₂ heterostructure nanocomposites (HSNCs) by pyrolysis. The heterostructure is composed of ZnO and CeO₂ monocrystals, simultaneously, CeO₂ monocrystals are well dispersed on the surface of ZnO monocrystal for cosmetics. Bing dependent on the analysis results of XRD and TEM for the obtained precursors before and after pyrolysis, the formation mechanism of HSNCs was proposed. To the best of our knowledge, the paper first reported heterostructured ZnO/CeO₂ nanocomposite grown in one-pot mixed aqueous solution of cerium nitrate, zinc acetate and urea without other extra surfactant. Additionally, the influence of various Ce/Zn molar ratios on the heterostructure, fluorescence emission and UV–visible absorption properties of HSNCs was investigated in detail. ZnO/CeO₂ HSNCs display higher fluorescence emission with the increasing Ce/Zn molar ratio. Meanwhile, the larger Ce/Zn molar ratio of ZnO/CeO₂ HSNCs, the stronger transparency in the visible light region and the weaker UV absorption. The results are due to the fact that the band gap of ZnO/CeO₂ HSNCs will decrease from 3.25 to 3.08 eV when Ce/Zn atom molar ratio is increased from 0 to 0.08. By the comprehensive analysis on the optical performances of HSNCs with the different Ce/Zn atom molar ratios, ZnO/CeO₂-0.04 HSNCs could become UV absorber materials and transparent material in the visible region. ZnO/CeO₂-0.04 HSNCs with the UV-filtering and Vis-transparent properties is appropriate for personal-care cosmetics.     

Synthesis of Cu/SiO2 composite films via gamma-irradiation route and their optical absorption properties

The Cu particles or clusters dispersed mesoporous SiO₂ composite films were prepared by a new method: first the matrix SiO₂ films were prepared by sol–gel process combined with the dip-coating technique, and then they were soaked in Cu(NO₃)₂ solutions followed by γ-ray irradiation at room temperature and in ambient pressure. Thus, the prepared Cu/SiO₂ composite films were examined by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and optical absorption spectroscopy. It has been shown that the Cu particles grown within the porous SiO₂ films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With the Cu particles size changing, an interesting peak shift was observed in the optical absorption measurement. Possible mechanisms of this behavior are discussed in this paper.     

Preparation and visible-light photocatalytic activity of Au-supported porous CeO2 spherical particles using templating

Porous spherical CeO₂ particles were prepared by impregnation of a cerium precursor solution into organic monolith sphere particles, with subsequent firing at 500 °C in air. The single-phase CeO₂ powder had specific surface area of greater than 140 m²/g. Photodeposition with UV illumination loaded Au onto the CeO₂ particle surface, which changed from yellowish to purple because of localized surface plasmon resonance (LSPR). The Au-loading increased photocatalytic decomposition activity of the CeO₂ powder for gaseous 2-propanol (IPA) under visible light. Thermal desorption of IPA, which was adsorbed to all porous spheres, provided flux to the photocatalytic reaction field of the sphere outer surface.     

Pechini溶胶-凝胶法制备SiO2/TiO2复合微粒

采用超声St(o)ber法制备了单分散性的纳米载体SiO2,再采用Pechini溶胶-凝胶制备法制备出SiO2/TiO2复合微球.通过X射线衍射仪、场发射扫描电子显微镜(FESEM)对粉体的晶型和显微形貌进行测试分析.结果表明:纳米载体SiO2球形颗粒为无定形态,Ti02粉体为形貌多样的块状颗粒,大颗粒粒径大于10μm...     

Fe／SiO2复合微颗粒的微结构及电磁特性研究

采用机械球磨法制备了Fe／SiO2复合微米量级颗粒粉体。用X射线衍射、扫描电镜和透射电镜研究样品结构形貌；测量了不同成分配比下的磁滞回线；测试了在2～18GHz频段下的电磁性能参数。结果表明，微米量级铁颗粒的饱和磁化强度比纳米量级的铁颗粒显著增大．在2～18GHz频段内，复合微米颗粒的相对介电常数的实部稳定，虚部很小；磁导率虚部在0．7～1．2之间。该微米复合颗粒作为微波吸收材料，具有良好的应用潜力。     

Reverse saturable absorption of fullerodendrimers in porous SiO2 sol–gel matrices

The non-linear absorption properties and the dynamics of porous sol–gel SiO₂ glasses, doped with fullerodendrimers, i.e., fullerene derivatives functionalized with dendritic branches have been investigated using a double-pump–probe technique. A frequency doubled mode locked Nd:YAG laser (25 ps (FHWM), 532 nm) was applied as irradiation source. A reverse saturable absorption (induced absorption) in the samples containing the fullerodendrimers has been observed. A similar induced absorption was also obtained in the pure C₆₀ samples. In addition, the dendritic branches, which prevent aggregation of the molecules, lead also to an increase of the triplet quantum yield due to a faster singlet–triplet relaxation.     

Controlled synthesis of porous particles via aerosol processing and their applications

Aerosol processes such as spray drying and/or spray pyrolysis for the controlled synthesis of porous particles were introduced in this review. Typical experimental setup, general experimental procedure for the preparation of porous particles, as well as key factors affecting the properties of final porous particles, was described. We then discussed the various routes for the controlled synthesis of porous particles: (1) the preparation of self-assembled porous particles with ordered pores by using organic template particles; (2) the preparation of pore size- and porosity-controlled particles from aggregated nanoparticles; (3) the preparation of nanoparticle-laden encapsulated porous particles from graphene nano-sheets and nanoparticles. Finally, we introduced interesting applications of the porous particles such as photocatalysts, drug delivery carriers, and biosensors.     

CeO2 induced dispersive distribution of TiB2 particles in in situ TiB2/Al composite

Abstract

The roles of CeO₂ additive during preparation of in situ TiB₂/Al composite, alleviating particle settlement in composite melt and significantly improving particle dispersion in final microstructure, are studied in this paper. It is evidenced that the CeO₂ additive reacts with Al melts to release Ce solute into the melts, and the released surface active Ce is absorbed in the Al/TiB₂ interfaces without any other reaction products. First principles calculations show that the interfacial energy of Al/TiB₂ interfaces is reduced owing to the presence of Ce in Al/TiB₂ interfacial area. Therefore, the wettability of molten Al on TiB₂ surface is increased and the dispersion of TiB₂ particles in Al matrix is eventually improved.     

PTFE-SWNT composite for microwave absorption application

The Polytetrafluoroethylene-single walled carbon nanotube (PTFE-SWNT) composites are prepared and its dielectric properties are investigated as a function of SWNT loading both at 1 MHz and microwave frequencies. The relative permittivity and the conductivity increases with carbon nanotube loading. The addition of 0.02-volume fraction of SWNT increases the relative permittivity of the polymer from 2.1 to 7.5 × 10⁶ and the conductivity from 4.887 × 10^− 9 to 8.52 × 10^− 3 S/cm at 1 MHz. As the volume fraction of SWNT increases from 0.01 to 0.05 the relative permittivity of the PTFE-SWNT composite increases from 4 to 6.6 at X-band (8-12 GHz) and the power attenuation coefficient varies from 9.5 to 17 dB/mm.     

Synthesis of TiO2-doped SiO2 composite films and its applications

The TiO₂-doped SiO₂ composite films were prepared by two-step sol-gel method and then it was applied in the degradation of methylene red (MR) as photocatalysts. In XRD, FT-IR, and TEM investigations of these TiO₂-doped SiO₂ composite films, the titanium oxide species are highly dispersed in the SiO₂ matrixes and exist in a tetrahedral form. And special attention has been focused on the relationship between the local structure of the titanium oxide species in the TiO₂-doped SiO₂ composite films and the photocatalytic reactivity in order to provide vital information for the design and application of such highly efficient photocatalytic systems in the degradation of toxic compounds diluted in a liquid phase.     

Preparation and microwave absorption of porous hollow ZnO by CO2 soft-template

The porous hollow ZnO samples were prepared by calcination of ZnCO₃ precursor at 450 °C. The structural properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis and differential thermal analysis (TG-DTA). A possible mechanism for the formation of porous hollow microstructure was proposed. The microwave absorption properties of the porous hollow structural ZnO have been investigated. The reflection loss (RL) of the ZnO was calculated based on the relative complex permeability and permittivity. A minimum reflection loss of the wax-composite with 25 wt% porous hollow ZnO is −36.3 dB at 12.8 GHz with a thickness of 4.0 mm. The results indicate that porous hollow structural ZnO can be used as a desirable material for the microwave absorption.     

Equations of anomalous absorption onto swelling porous media

Absorption is a very common process which takes place on various types of materials ranging from porous media to new nano-materials and biological tissues. The majority of studies reported on absorption to date are concentrated on “rigid” porous media, which contradict the properties of real porous media which undergo swelling and shrinking changes. Here we present new absorption equations derived from a fractional diffusion-wave equation (fDWE) for absorption onto swelling porous media in a material coordinate. We show that the cumulative anomalous absorption is I(t) = St^β/2 and the absorption rate , where S is the anomalous sorptivity and β the order of fractional derivative in fDWE. Using published data on cumulative absorption against time, the two adsorption parameters are determined: β = 1.2448 and S = 2.7775 cm²/h. The value of β = 1.2448 implies that absorption onto this swelling porous media belong to the category of super-diffusion, which is a phenomenon unknown to us before. In comparison, the traditional absorption equations do not have such features. When S is determined, the anomalous diffusivity, D_m, is calculated using its relation with S. We expect that the proposed new absorption equations will be valuable for explaining new phenomena and processes encountered in broader disciplines of science and engineering applications.     

Highly porous acrylonitrile-based submicron particles for UO2(2+) absorption in an immunosensor assay

Our laboratory has previously reported an antibody-based assay for hexavalent uranium (UO(2)(2+)) that could be used on-site to rapidly assess uranium contamination in environmental water samples (Melton, S. J.; et al. Environ. Sci. Technol. 2009, 43, 6703-6709). To extend the utility of this assay to less-characterized sites of uranium contamination, we required a uranium-specific adsorbent that would rapidly remove the uranium from groundwater samples, while leaving the concentrations of other ions in the groundwater relatively unaltered. This study describes the development of hydrogel particles containing amidoxime groups that can rapidly and selectively facilitate the uptake of uranyl ions. A miniemulsion polymerization technique using SDS micelles was employed for the preparation of the hydrogel as linked submicrometer particles. In polymerization, acrylonitrile was used as the initial monomer, ethylene glycol dimethacrylate as the crosslinker and 2-hydroxymethacrylate, 1-vinyl-2-pyrrolidone, acrylic acid, or methacrylic acid were added as co-monomers after the initial seed polymerization of acrylonitrle. The particles were characterized by transmission electron spectroscopy, scanning electron microscopy (SEM) and cryo-SEM. The amidoximated particles were superior to a commercially available resin in their ability to rapidly remove dissolved UO(2)(2+) from spiked groundwater samples.     

Synthesis and luminescence of Sr2CeO4 superfine particles by citrate-gel method

A strong blue-white emission phosphor Sr₂CeO₄ superfine particles, containing SrCe₄O₇, have been synthesized using a citrate-gel method. The crystalline phase and luminescence properties of superfine particles are reported. The results show that the strong blue-white emission is assigned to Ce⁴⁺–O²⁻ charge-transfer transition (CTT) of Sr₂CeO₄ and is not related to a lattice defect. The emission spectrum of post-heat-treated particles exhibits a broad band maximum at 470 nm, and the emission intensity is not affected by the existence of SeCe₄O₇.     

纳米TiO2与水泥复合材料的吸波机理探讨

纳米TiO2作为微波吸收剂,掺入到水泥材料中,使水泥基复合材料具有一定的吸波功能.通过对掺有锐钛型TiO2、纳米锐钛型TiO2和纳米金红石型TiO2的水泥基复合材料的导电性能、电磁参数和反射率的分析比较,探讨了纳米TiO2与水泥复合材料的吸波机理.由于纳米TiO2的小尺寸效应、表面效应和量子尺寸效应,使纳米TiO2与水泥复合材料在高频段体现更好的吸波性能,当纳米TiO2掺量为5%时,在12.5～18GHz频率范围内复合材料的反射率基本上都＜-0dB,最小反射率达-16.34dB.