Papers by Keyword: Core-Shell Structure

Abstract: The surface of the magnetite nanoparticles has been engineered by the proteins available in the leaf extract of Datura inoxia. Fourier Transform Infrared (FTIR) study and by thermo gravimetric analysis (TGA) confirms the bonding between metal ions and the amide carbonyl group preset in the plant protein confirming the formation of core-shell structure. The plant protein coated magnetic Fe₃O₄ nanoparticles under investigation have an average size of about 14 nm (˂20nm). The isothermal magnetization curve of the ferrofluid appears in S-like sigmoid shape showing soft nonhysteretic magnetic behaviour at room temperature. The saturation magnetization (M_S), remanent magnetization (M_R), squareness (M_R/M_S) and coercivity value (H_C) increased with decreasing temperature from 300 K to 10 K. The increment of magnetization (45 to 53 emu/gm) might be due to the decrease in thermal energy while the enhancement of coercivity (0-208 O_e) is attributed to the exchange interaction at the interface between the ferromagnetic (Fe₃O₄) and diamagnetic surface layer of protein on the nanocrystalline magnetite. The magnetization value is much smaller in comparison with the bulk magnetite (92emu/g) due to surface spin disorder also approves core-shell structure of diamagnetic protein layer on the surface. The results show the ease of the synthesis to reinforce the colloidal stability where the super paramagnetic behaviour has been found to be restored. The core-shell moiety could play an important role in biological systems as a means of storing Fe⁺³ for an organism.

Abstract: CIP/ZnO electromagnetic functional composites with core-shell structure were prepared by chemical precipitation method, and then the morphology, structure and electromagnetic properties in 2-18GHz were characterized by X-ray diffraction, scanning electron microscopy and vector network analyzer, respectively. In process by controlling the component ratio between core and shell, it has been found that the more ZnO particles were coated on the CIP surface, the smaller electromagnetic parameters become. Based with the Electromagnetic Wave Absorption (EMWA) Theory, the composites could prepare EMWA building coating by monolayer design, the theoretical simulation results show that the minimum RL of CIP/ZnO composites is-10.25dB, better than pure CIP particles, exhibiting excellent EMWA properties in 2-18GHz. The magnetic loss of CIP and the dielectric loss of ZnO were the main mechanisms of EMWA for the CIP/ZnO composites, which could be used for electromagnetic radiation protection.

Abstract: The core-shell structure NiFe₂O₄@TiO₂ nanoparticles was successfully prepared using a sol-gel method, the influence of shell thickness and calcination temperatures on the composition, microstructure, magnetic properties and visible-light catalytic activity of the nanoparticles was studied by XRD, TEM, Uv–vis, vibrating sample magnetometer, etc. Results showed the main composition of core in NiFe₂O₄@TiO₂ was spinel ferrite, and the shell was anatase TiO₂, and the shell thickness increased significantly with the increase of TiO₂ content, ranging from 10nm to 50nm. The M_s and M_r of nanoparticles decreased with the increase of TiO₂ content, and no obvious reaction between the magnetic core and shell occurred; visible-light degradation percent of NiFe₂O₄@TiO₂ nanoparticles increased along with the increase of TiO₂ content, whereas the recovery rate of it decreased. Degradation percent and the recovery percent of NiFe₂O₄@TiO₂-50 still reached 93.7% and 90.5%, even after 10 cycle times, respectively, possessing the excellent long-term stability.

Abstract: This work deals with the strain at the core-shell interface of Fe nanoparticles. Series of Fe nanoparticles with various mean diameters were prepared by precipitation in solid state in binary Cu-Fe alloy. Further, nanoparticles were isolated by dissolution of Cu matrix. High-energy X-ray diffraction (XRD) was used to probe structure of nanoparticles. XRD measurements suggest presence of the core-shell structure, where core and shell of the nanoparticles are formed of α-Fe and CuFe₂O₄ phase, respectively. Strains in core and shell were estimated as a function of nanoparticles size by Williamson-Hall method.

Abstract: We demonstrated the construction and performance of dye-sensitized solar cells (DSCs) based on nanoparticles of TiO₂ coated with thin shells of MgO by simple solution growth technique. The XRD patterns confirm the presence of both TiO₂ and MgO in the core-shell structure. The effect of varied shell thickness on the photovoltaic performance of the core-shell structured electrode is also investigated. We found that MgO shells of all thicknesses perform as barriers that improve open-circuit voltage (Voc) of the DSCs only at the expense of a larger decrease in short-circuit current density (Jsc). The energy conversion efficiency was greatly dependent on the thickness of MgO on TiO₂ film, and the highest efficiency of 4.1% was achieved at the optimum MgO shell layer.

Abstract: Hexagonal (β)-phase NaYF₄:Yb³⁺, Er³⁺ upconversion nanoparticles (UCNPs) with and without an inert (undoped NaYF₄) shell have been successfully synthesized and the effects of shell thickness on the upconversion luminescence (UCL) and temperature sensing properties were systematically investigated. It was found that the NaYF₄ shell and its thickness do not affect the R_HS values and thermal sensitivity, but can obviously improve the UCL intensity of NaYF₄:Yb³⁺, Er³⁺ UCNPs. It implies that the core-shell structured NaYF₄:Yb³⁺, Er³⁺@NaYF₄ UCNPs with excellent UCL properties have great potential to be used as temperature sensing probes in biomedical fields, without considering the influences of the shell thickness on their temperature sensing properties.

Abstract: Core-Shell structure Poly(vinyl acetate-butyl acrylate) emulsion is prepared by the semi-continuous emulsion polymerization. And the emulsion particles are modified by ethyleneglycol dimethacrylate crosslinker (EGDMA) to improve the properties of films in the different reaction stages. Then the emulsion particles structure is characterized by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR). The particle size and distribution are characterized by Zata Potential- Particle analyzer, as well as analysis of the film mechanical properties and thermal performance. The results show that the emulsion particles possess a clear core-shell structure. The performance of the emulsion film show better when 1% and 0.5% EGDMA are added in the second reaction and the third reaction stage respectively under the emulsion preparation process.

Abstract: Zeolite 13X@SiO₂ composites have been prepared using TEOS and CTAB as the silica source and template respectively, via hydrothermal reaction. The approach of synthesizing zeolite 13X@SiO₂ core-shell structures has been adopted followed by external surface modification by silane to achieve hydrophobicity. The materials were characterized by XRD, SEM, FTIR, etc. The results show that the zeolite 13X@SiO₂ core-shells structures have been prepared and their properties are maintained even after the modification. The CO₂ adsorption capacity was well maintained after silylation, however, the adsorption of water on samples was effectively inhibited by the surface modification.

Abstract: Coaxial nanocomposites were prepared by in–situ chemical polymerization of 4– dibromomethyl–2,5–2–octyloxy phenylene in the presence of multiwall carbon nanotubes. The morphology, microstructure and thermal and electrochemical properties of the resulting nanocomposites were investigated by scanning electron microscopy, Fournier infrared spectroscopy, thermal gravimetric analysis and cyclic voltammetry. The results indicated that the nanocomposites with uniform core-shell structure exhibited higher thermal stability than neat poly (phenylene vinylene). Furthermore, energy storage ability of these coaxial nanocomposites as electrode materials for supercapacitor was evaluated.

Abstract: A core-shell structure RuRh@Pt/C nanoparticles was prepared by using a two-step reduction method under ultrasonic promotion. The catalytic performance was tested in methanol electrooxidation. X-ray diffraction (XRD), scanning electron microscope (SEM) combined with cyclic voltammetry (CV) were used to characterize the obtained catalyst. The results showed that there was no alloy formed between the core RuRh and the shell Pt. The electrocatalytic activity of RuRh@Pt/C varied with the Ru/Rh ratio in the bimetallic core, among which the catalyst with the Ru/Rh ratio 1:2 and the Pt-shell thickness of 1.5 (Ru1Rh2@Pt1.5/C) showed the highest catalytic activity for methanol. With this catalyst, the current density of the oxidation peak for methanol electro-oxidation reached 2.3 times as that of Pt1.5/C while the corresponding peak potential shifted 60 mV negatively in comparing to that of Pt1.5/C. In addition, the catalyst with the core-shell structure of RuRh@Pt/C possessed much higher CO-tolerance for methanol electro-oxidation, indicating its promising application in low temperature fuel cell.