Papers by Keyword: Core-Shell

Abstract: Hybrid nanoparticles were prepared by direct polymerization of methyl methacrylate, vinyl acetate, and styrene monomers onto the unmodified hydrophilic surfaces of 33 nm silica nanoparticles in a semi-continuous soap-free emulsion polymerization at a monomer starved condition. The polymerization was initiated by potassium persulfate with constant monomer feed at 0.01, 0.02, or 0.04 mL/min. The growth of the core-shell nanoparticles were measured by a laser particle size analyzer. FT-IR spectra analysis confirmed the hybrid structures of the synthesized nanoparticles. SEM images and size exclusion chromatography (SEC) results indicated regular core-shell microsphere structures. The hybrid nanoparticles increased in monodispersity and size over 100 nm with the reaction. However, SiO₂/polystyrene (PS) nanoparticles grew much faster compared with SiO₂/polymethyl methacrylate (PMMA) and SiO₂/polyvinyl acetate (PVAC). There was particle coagulation, about 12 SiO₂/PS particles aggregating to one, in the early stage of the seeded process. In addition, PS secondary particles were formed before the particle coagulation, and then merged with the SiO₂/PS nanoparticles in the particle coagulation. The formation of SiO₂/polymer hybrid nanoparticles depended on the hydrophilic characteristics of the polymer, and the size of silica seeds.

Abstract: Submicron hybrid particles were prepared by direct polymerization of three monomers of styrene, methyl methacrylate (MMA), and vinyl acetate (VAC) onto the hydrophilic surface of 230 nm silica submicron particles without any coupling agent in a semi-continuous emulsifier-free emulsion polymerization at a monomer starved condition. The polymerization was initiated by potassium persulfate with constant monomer feed at 0.01, 0.02, or 0.04 mL/min, after adding 230 nm silica seed particles. The particle growth was investigated with a laser particle size analyzer and SEM, and the particle surfaces by Fourier transform infrared spectroscopy (FT-IR). It was founded that the growth of the hybrid particles depended on the hydrophobic characteristics of the polymers. When monomer was the most hydrophobic styrene, polystyrene (PS) shells split off from the hydrophilic surface of the unmodified silica particle whenever the shells reached a limit of ~20 nm. However, both polymethyl methacrylate (PMMA) and polyvinyl acetate (PVAC) shells grew constantly on the hydrophilic surface of silica particles. In the process of the whole reaction, the SiO₂/PMMA and SiO₂/PVAC hybrid particles kept almost monodisperse.

Abstract: Intermediate temperature solid oxide fuel cells (IT-SOFCs) operating at 400-700°C utilizes proton conducting electrolytes and are now being one of the focus of many research studies with regards to efficient, clean power sources and energy conversion. Potential electrolyte materials include acceptor-doped barium zirconates and barium cerates. In this study, preparation of a core-shell structured proton-conducting solid electrolytes of 20 vol% BaZr_0.8Y_0.2O_3-δ (20BZY20) for the core and 80 vol% BaCe_0.8Y_0.2O_3-δ (80BCY20) for the shell is done by wet chemistry route. The synthesized core-shell structured material (20BZY20/80BCY20) is developed to possibly address the problem of high grain boundary impedance of Y-doped BaZrO₃ and low chemical stability of Y-doped BaCeO₃. The obtained samples were characterized for its structure, thermal stability, morphology and elemental distribution of the material. At a lower sintering temperature of 1150°C, a densified pellet was obtained as observed by SEM analysis. The diffraction pattern of 20BZY20/80BCY20 powder shows two distinct phases corresponding to BZY20 and BCY20 suggesting a successful synthesis of the core-shell solid electrolyte.

Abstract: In this paper, a two-step method is developed for efficient preparation of Cu/Pt-Pd core-shell structured catalyst on Nafion-bonded carbon paper electrodes for a polymer electrolyte membrane fuel cell. Copper nanoparticles with diameter distribution of 80-160 nm are obtained by potential-modulation electrodeposition. In copper electrodeposition the charge-transfer step is fast and the rate of growth is controlled by the rate of mass transfer of copper ions to the growing centers. After the copper electrodeposition the replacement of Cu by PtPd occurs spontaneously by an irreversible redox process. The nature and composition of PtPd/Cu on pretreated carbon paper are characterized by field emission–scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) spectroscopy, respectively. The as prepared Cu/PtPd electrode is found in the form of core-shell structure with uniform dispersion on the surface with average nanoparticles of 41.5 nm diameter. Electrochemical activity of PtPd/Cu and conventional Pt/C on pretreated carbon paper electrodes towards oxygen reduction is studied by linear sweep voltammetry experiments. Low values of Tafel slope and free activation energy reveal that Cu/PtPd with core-shell structure shows greater electrochemical activity than conventional Pt/C catalyst. Electrochemical surface area (ECSA) results also show that Cu/PtPd with core-shell structure has greater stability than the Pt/C electrode.

Abstract: This essay employed the "successive ion layer adsorption and reaction (SILAR)"technology to form PbSe/CdSe core/shell.We use the Pbse/CdSe core/shell replaced PbSe nanocrystals and obtained one new quantum dot solar cells of the inorganic.This new solar cells constituted by the metal oxide films retain the photoelectric conversion efficiency of quantum dot solar cells.At the same time,the stability of the new solar cells is tremendously improved with the oxidation resistance of inorganic oxide.Finally,when J_sc=25.2mA/cm²and V_oc=0.36V ,we can conclude the conversion efficiency of the solar cell can be evaluated as 3.929%.

Abstract: Polyurethane/acrylate(PUA) core-shell hybrid emulsion as the binder has been widely used into inks recently and the different modifications for it with element reagents and resin reagents are displayed in the article as well. Moreover, the relationship between structure and properties and application of PUA core-shell hybrid emulsion in inks are also put forward in detail. Ultimately, the novel modified materials, rational molecule design and synthetic process were prospected in this review.

Abstract: Uniform Fe₃O₄@TiO₂ nanocomposites were successfully synthesized via a sol-gel method and then characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD). The obtained composites were monodispersed spherical nanoparticles with average diameter of ~ 230 nm. In vitro cytotoxicity experiment, Fe₃O₄@TiO₂ nanocomposites exhibited good biocompatibility and obvious sonodynamic therapy (SDT) effect. Over 50% cells were killed when the cells were treated with Fe₃O₄@TiO₂ and ultrasound for 1 min. The results indicated the potential of Fe₃O₄@TiO₂ for targeted sonodynamic therapy of tumor.

Abstract: A core-shell composite polymer was produced by the method of high internal phase emulsion polymerization. The continuous phase of emulsion contained styrene(St), butyl methacrylate(BMA), octamethylcylotetrasiloxane(D4), and azobisisobutyronitrile (AIBN) which worked as an initiator. The block copolymers with St, BMA, D4 units are particularly promising for surface modification and hydrophobicity. The core-shell structure is proved by the use of Transmission electron microscopy (TEM). In addition, the water contact angle increased with the increasing weight ratio of D4. The results show that the concentrated emulsion system has good stability and the water resistance of the polymer has been improved greatly.

Abstract: Zinc oxide (ZnO) is recognized as one of the most attractive metal oxides because of its direct wide band gap (3.37 eV) and large exciton binding energy (60 meV), which make it promising for various applications in solar cells, gas sensors, photocatalysis and so on. Here, we report a facile synthesis to grow well-aligned ZnO nanorod arrays on SnO₂: F (FTO) glass substrates without the ZnO seed layer using a Galvanic-cell-based method at low temperature (<100°C). CdS quantum dot thin films were then deposited on the nanorod arrays in turn by an effective successive ionic layer adsorption and reaction (SILAR) process to form a ZnO/CdS core-shell structure electrode. Structural, morphological and optical properties of the ZnO/CdS nanorod heterojunctions were investigated. The results indicate that CdS quantum dot thin films were uniformly deposited on the ZnO nanorods and the thickness of the CdS shell can be controlled by varying the number of the adsorption and reaction cycles. The number of quantum dots layers affects on photovoltaic performance of the ZnO/CdS core-shell nanorod arrays has been investigated as photoanodes in quantum dots sensitized solar cells.

Abstract: The growing necessity of biomaterials has increased the interest in calcium phosphates, particularly hydroxyapatite. In this paper, monodisperse and spherical SiO₂ particles have been coated with Ca₁₀(PO₄)₆(OH)₂:Eu³⁺ layers via a Pechini sol-gel process, resulting in core-chell ctructured SiO₂/Ca₁₀(PO₄)₆(OH)₂:Eu³⁺ samples. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL) spectra were employed to characterize the SiO₂/Ca₁₀(PO₄)₆(OH)₂:Eu³⁺ core-shell particles. The resulted core-shell particles have perfect spherical shape with narrow size distribution, smooth surface and non-agglomeration.