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1.
A luminescent superparamagnetic nanocomposite with an Fe 3 O 4-SiO 2-CdS structure is synthesized.Coated with a silica shell,Fe 3 O 4 nanoparticles and CdS quantum dots (QDs) are successfully assembled together.Analysed from the test results of X-ray diffraction (XRD),transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),hysteresis loop,and photoluminescence (PL) spectrum,these nanocomposites exhibit superparamagnetic and photoluminescent properties. 相似文献
2.
Magnetite polycrystalline films are grown by variously oxidizing a Fe film on the Si(111) surface covered by a thin (1.5 nm)
SiO 2 layer. It is found that defects in the SiO 2 layer influence silicidation under heating of the Fe film. The high-temperature oxidation of the Fe film results in the formation
of both Fe 3O 4 and iron monosilicide. However, the high-temperature deposition of Fe in an oxygen atmosphere leads to the growth of a compositionally
uniform Fe 3O 4 film on the SiO 2 surface. It is found that such a synthesis method causes [311] texture to arise in the magnetite film, with the texture axis
normal to the surface. The influence of the synthesis method on the magnetic properties of grown Fe 3O 4 films is studied. A high coercive force of Fe 3O 3 films grown by Fe film oxidation is related to their specific morphology and compositional nonuniformity. 相似文献
3.
Non-stoichiometric Co xFe 3???xO 4/SiO 2 (x = 0.8, 0.9, 1.0, 1.1) nanocomposites have been prepared by sol-gel method. The structure, morphology and magnetic properties of the obtained samples were characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and Mössbauer spectroscopy at room temperature. As the Co 2?+? content increases, the average particle size of the spherical Co xFe 3???xO 4 in the samples decreases and the lattice constants increases. The hyperfine fields for both A- and B-site decrease, while the fraction of Co 2?+? occupying the A-site increases. Magnetization measurements show the saturation magnetization and coercivity of Co xFe 3???xO 4/SiO 2 decrease with increasing Co 2?+? content. The decrease in magnetization results from the weakened A-B interactions between Fe 3?+?, and the change in coercivity can be related to the variation of Co 2?+? at B-site and the decreasing particle size. 相似文献
4.
The method of obtaining nanoclusters α-Fe2O3 in the pores of monodisperse spherical particles of mesoporous silica (mSiO2) by a single impregnation of the pores with a melt of crystalline hydrate of ferric nitrate and its subsequent thermal destruction has been proposed. Fe3O4 nanoclusters are synthesized from α-Fe2O3 in the pores by reducing in thermodynamically equilibrium conditions. Then particles containing Fe3O4 were annealed in oxygen for the conversion of Fe3O4 back to α-Fe2O3. In the result, the particles with the structure of the core-shell mSiO2/Fe3O4@mSiO2/α-Fe2O3 are obtained. The composition and structure of synthesized materials as well as the field dependence of the magnetic moment on the magnetic field strength have been investigated. 相似文献
5.
Magnetic Fe 3O 4/SiO 2 particles with rod-like structure and hollow interior have been constructed by a template method. During this procedure, β-FeOOH was firstly synthesized as the rod-like template to fabricate β-FeOOH/SiO 2 core/shell-like particles. These β-FeOOH/SiO 2 nanorods could be further transformed to Fe 3O 4/SiO 2 via the decomposition-reducing method. These particles showed ferromagnetic behavior at room temperature with high coercivity and may provide potential applications in biological area. 相似文献
6.
To attain the complete filling of the channels of MCM-41 with magnetite and maghemite, we have tried out an alternative method to the incipient wetness impregnation. The mesoporous material was instilled with a Fe-carrying organic salt after subjecting the matrix to a silylation treatment. Thus, a solid of 7.7 wt.% iron-loaded MCM-41 was obtained. Different subsequent thermal treatments were used to produce γ-Fe 2O 3 or Fe 3O 4. The Mössbauer and magnetic results show that after this method, the as-prepared composite displays a size-distribution of magnetic particles. It is mainly made up of fine particles that display a superparamagnetic relaxation at room temperature and get blocked at ≈42 K for the AC susceptibility time-scale measurements both for γ-Fe 2O 3 and Fe 3O 4 particles. For both samples, about 24% of larger iron-containing phases are magnetically blocked at room temperature. For the Fe 3O 4 particles, this fraction undergoes the Verwey transition at about 110 K; in addition, there is a minor Fe (III) fraction that remains paramagnetic down to 4.2 K. 相似文献
7.
Nanosized ZSM-5 type ferrisilicates were successfully prepared using hydrothermal process. Several parameters including gel initiative compositions (Na + or K + alkali system), SiO 2/Fe 2O 3 molar ratios and hydrothermal temperature were systematically investigated. The samples were characterized by XRD, TEM, SEM-EDS, BET surface area and ICP techniques. It was found that surface areas and the total pore volume increase with increasing in the SiO 2/Fe 2O 3 molar ratio at Na-FZ ferrisilicates. The catalytic performance of the synthesized catalysts was evaluated in ethylbenzene dehydrogenation to styrene in the presence of N 2O or steam at temperatures ranging from 400 °C to 660 °C under atmospheric pressure. The effects of gel initiative compositions, SiO 2/Fe 2O 3 molar ratio as well as the hydrothermal synthesis temperature on the catalytic performance of these catalysts have been addressed. It was shown that styrene yield significantly influenced by altering in the SiO 2/Fe 2O 3 ratio but was not greatly influenced by changes in hydrothermal synthesis temperatures. The comparison between performance of potassium and sodium containing catalysts was shown that the one with potassium has higher yield and selectivity toward styrene production at an optimum temperature of 610 °C. 相似文献
8.
Recently, we have demonstrated the successful synthesis of Fe
x
Co 1−x
/Co
y
Fe 3−y
O 4 nanocomposites with various alkaline solutions by using surfactants-assisted-hydrothermal (SAH) process. In this article,
the synthesis of Fe
x
Co 1−x
/Co yFe 3−y
O 4 nanocomposites with their sizes varying between 20 nm and 2 μm was reported. X-ray powder diffraction (XRD) analyses showed
that the surfactants, pH, precipitator, and temperature of the system play important roles in the nucleation and growth processes.
The magnetic properties tested by vibrating sample magnetometer (VSM) at room temperature exhibit ferromagnetic behavior of
the nanocomposites. These Fe
x
Co 1−x
/Co
y
Fe 3−y
O 4 nanocomposites may have a potential application as magnetic carriers for drug targeting because of their excellent soft-magnetic
properties. 相似文献
9.
Nanocomposites composed of multi-wall carbon nanotubes (MWNTs) and Fe 3O 4 nanoparticles were fabricated using solvothermal method. Transmission and scanning electron microscopy, energy dispersive
spectroscopy, and X-ray powder diffraction measurements confirmed that these mulberry-like Fe 3O 4 microparticles which were combined with the MWNTs in a random pattern are constructed with tiny nanocrystallites (12 nm in
average diameter). The magnetic properties of the Fe 3O 4/MWNTs nanocomposites were measured using a vibrating sample magnetometer. Results showed that the Fe 3O 4/MWNTs nanocomposites exhibited superparamagnetism at room temperature and possessed a lower saturation magnetization (around
27.6 emu/g) than that of the pure Fe 3O 4 nanoparticles (around 33.7 emu/g). The Fe 3O 4/MWNTs nanocomposites have potential applications in engineering and medicine. 相似文献
10.
A series of highly ordered mesoporous materials (CF-SBA-15) with heat-resistant magnetism have been successfully prepared from impregnation of cobalt salt, iron salt, and citric acid with as-synthesized SBA-15. XRD and N 2 isotherms indicate that these materials have highly ordered hexagonal mesoporous symmetry and open pore systems. The measurement of magnetic property shows that these materials are ferromagnetic even if calcined at 550 °C for 10 h in air, indicating their good heat-resistant magnetism. These results would be very important for recycle and regeneration of adsorbents and catalysts in practical applications. Moreover, this method may be useful for other mesoporous materials with thermally stable magnetism from a combination of other mesoporous materials such as MCM-41 with magnetic nanoparticles of MnFe 2O 4 and NiFe 2O 4. 相似文献
11.
Magnetic Fe 3O 4 materials with mesoporous structure are synthesized by co-precipitation method using yeast cells as a template. The X-ray diffraction (XRD) pattern indicates that the as-synthesized mesoporous hybrid Fe 3O 4 is well crystallized. The Barrett-Joyner-Halenda (BJH) models reveal the existence of mesostructure in the dried sample which has a specific surface area of 96.31 m 2/g and a pore size distribution of 8-14 nm. Transmission electron microscopy (TEM) measurements confirm the wormhole-like structure of the resulting samples. The composition and chemical bonds of the Fe 3O 4/cells composites are studied by Fourier transform infrared (FT-IR) spectroscopy. Preliminary magnetic properties of the mesoporous hybrid Fe 3O 4 are characterized by a vibrating sample magnetometer (VSM). The magnetic Fe 3O 4/cells composites with mesoporous structure have potential applications in biomedical areas, such as drug delivery. 相似文献
12.
In this paper, fluorescent-magnetic Fe 3O 4@LaF 3:Ce,Tb nanocomposites were synthesized by combining fluorescent LaF 3:Ce,Tb and magnetic Fe 3O 4 nanoparticles into new ‘two-in-one’ entities. The obtained Fe 3O 4@LaF 3:Ce,Tb nanocomposites were small (about 30 nm in diameter) and well dispersed in water. Under ultraviolet light irradiation, the Fe 3O 4@LaF 3:Ce,Tb nanocomposites emitted bright green fluorescence, and they could be easily manipulated by an external magnetic field. Such bifunctional nanocomposites may find many biomedical applications, such as cancer detection and drug delivery. And the method we used can be extended to the synthesis of other nanocomposites based on lanthanide-doped materials and metal oxides. 相似文献
13.
Nanosized iron oxide, a moderately large band-gap semiconductor and an essential component of optoelectrical and magnetic
devices, has been prepared successfully inside the restricted internal pores of mesoporous silica material through in-situ reduction during impregnation. The samples were characterized by powder XRD, TEM, SEM/EDS, N 2 adsorption, FT-IR and UV-visible spectroscopies. Characterization data indicated well-dispersed isolated nanoclusters of
(Fe 2O 3)
n
, within the internal surface of 2D-hexagonal mesoporous silica structure. No occluded Fe/Fe 2O 3 crystallites were observed at the external surface of the mesoporous silica nanocomposites. Inorganic mesoporous host, such
as hydrophilic silica in the pore walls, directs a physical constraint necessary to prevent the creation of large Fe 2O 3 agglomerates and enables the formation of nanosized Fe 2O 3 particles inside the mesopore 相似文献
14.
The surface of spinel LiMn 2O 4 was modified with Fe 2O 3 (1.0, 2.0, 3.0, 4.0, and 5.0 wt%) by a simple sol-gel method to improve its electrochemical performance at room temperature. Compared with bare LiMn 2O 4, surface modification improved cycling stability of the material. Among the surface-modified cathode materials, the 3.0- and 4.0-wt% surface-modified cathodes have lesser capacity loss than the others. While the bare LiMn 2O 4 showed 25.4 % capacity loss in 70 cycles at room temperature, 3.0 and 4.0 wt% of Fe 2O 3-modified LiMn 2O 4 only exhibited the capacity loss of 2.6 and 2.3 % in 70 cycles at room temperature, respectively. The structure and phase were identified with X-ray diffractometer along with the lattice constant calculated by a Win-Metric program. 相似文献
15.
Ni 0.53Cu 0.12Zn 0.35Fe 2O 4/SiO 2 nanocomposites with different weight percentages of NiCuZn ferrite dispersed in silica matrix were prepared by microwave-hydrothermal method using tetraethylorthosilicate as a precursor of silica, and metal nitrates as precursors of NiCuZn ferrite. The structure and morphology of the composites were studied using X-ray diffraction and scanning electron microscopy. The structural changes in these samples were characterized using Fourier Transform Infrared Spectrometer in the range of 400-1500 cm −1. The bands in the range of 580-880 cm −1 show a slight increase in intensity, which could be ascribed to the enhanced interactions between the NiCuZnFe 2O 4 clusters and silica matrix. The effects of silica content and sintering temperature on the magnetic properties of Ni 0.53Cu 0.12Zn 0.35Fe 2O 4/SiO 2 nanocomposites have been studied using electron spin resonance and vibrating sample magnetometer. 相似文献
16.
采用溶胶-凝胶工艺和高温高压实验技术,制备了纳米CoFe 2O 4/SiO 2复合材料。利用X射线衍射仪、扫描电子显微镜和振动样品磁强计,对样品的结构、微观形貌和磁性进行了研究,并对CoFe 2O 4中阳离子的占位情况进行了讨论。结果表明,随着处理压力的升高,样品的晶粒尺寸增大,晶格常数减小,比饱和磁化强度增大。通过计算结果可以推断,压力的升高导致CoFe 2O 4中的部分Fe 3+从A位移向了B位,而部分Co 2+则从B位移向了A位。 相似文献
17.
Nanocrystalline NiFe 2O 4 was in‐situ prepared in amorphous silica using tetramethylor‐thosilicate and nickel (iron) nitrate hydrate as the starting materials in a sol‐gel reaction. The magnetic nanocrystals in the amorphous silica glasses grew slowly with increasing temperature. Above 600 ○C, nickel ferrite nanoparticles began to precipitate from the amorphous silica matrix. Mössbauer spectroscopy of the nanocomposites suggested that in the silica glasses, Fe ions were present exclusively as Fe 3+ in octahedral coordination, and the chemical environment of the Fe 3+ ions appeared to remain unchanged until the crystallization of nickel ferrite nanocrystals. The formation of NiFe 2O 4 nanocrystals was the result of partial transformation of the FeO 6 octahedra to FeO 4 tetrahedra. The nanocrystalline NiFe 2O 4 are characterized by super‐paramagnetic behaviour at room temperature. 相似文献
18.
采用溶胶-凝胶法结合静电纺丝技术制备了Ni 0.5Zn 0.5Fe 2O 4/SiO 2复合纳米纤维.利用热重-差热分析、X射线衍射、场发射扫描电镜、高分辨透射电镜和振动样品磁强计研究了前驱体纤维的热分解及相转化过程以及焙烧温度和SiO 2含量对目标纳米纤维的相组成、微观结构、形貌及磁性能的影响.结果表明,在450 ℃焙烧时,立方尖晶石结构已基本形成.随着焙烧温度由450 ℃升高到100 相似文献
19.
本文针对α-Al2O3有序介孔材料的导热特性开展分子动力学模拟分析.提出了一种保证电中性的孔道结构构造方法;采用逆非平衡分子动力学方法(muller-plathe法),选取Matsui势为作用势,模拟计算了Al2O3介孔晶体材料在不同环境温度下沿孔道轴向方向的热导率;并借助全面实验分析法,设计了模拟条件,以考察孔径和孔隙率对热导率的影响.模拟结果显示:介孔Al2O3热导率先随温度的升高呈上升趋势,并在200—400 K之间取得极值;而后在400—1400 K范围内,热导率随温度的升高几乎呈线性下降.孔隙率一定时,随孔径增大,介孔Al2O3材料比表面积降低,界面散射的抑制作用减弱,使材料热导率略有上升;孔径一定时,随孔隙率上升,孔道壁面声子数减少,材料热导率下降明显;相对于孔径因素,材料孔隙率对声子导热影响更大. 相似文献
20.
Fe 3O 4/C nanocomposites have been prepared by one-pot PEG-assisted co-precipitation method. The structure and morphology of the as-prepared materials were analyzed by X-ray diffraction and transmission electron microscopy. The results showed that Fe 3O 4/C nanocomposites were well crystallized. Carbon nanoparticles dispersed among Fe 3O 4 particles forming a carbon layer, which prevent Fe 3O 4 particles from contacting each other. Electrochemical performance tests showed that Fe 3O 4/C nanocomposites keep at a high discharge capacity of 902.4 mAh g ?1 at 1 C after 110 cycles. Furthermore, the samples showed much improved rate capability and better cycle stability compared with pure Fe 3O 4. The excellent electrochemical performance of Fe 3O 4/C nanocomposites can be attributed to unique nanostructure and existence of amorphous carbon in the composites. The existence of the amorphous carbon not only enhanced electric conductivity, but also buffered volume variation of Fe 3O 4/C nanocomposites during charge/discharge process. 相似文献
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