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1.
Aminated-CoFe2O4/SiO2 magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe2O4/SiO2 NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe2O4/SiO2 NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe2O4/SiO2 NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe2O4/SiO2 NPs can be used as an effective carrier for the enzyme immobilization. 相似文献
2.
B. Bittova J. Poltierova VejpravovaM.P. Morales A.G. Roca A. Mantlikova 《Journal of magnetism and magnetic materials》2012,324(6):1182-1188
Collective magnetic behavior of CoFe2O4 nanoparticles with diameters of 76, 16, 15 and 8 nm, respectively, prepared by different chemical methods has been investigated. Particle composition, size and structure have been characterized by inductive coupled plasma (ICP), transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). Basic magnetic properties have been determined from the temperature dependence of magnetization and magnetization isotherms measurements. The three samples exhibit characteristic of a superparamagnetic system with the presence of strong interparticle interactions. Magnetic relaxation phenomena have been examined via frequency-dependent ac susceptibility measurements and aging and memory effect experiments. For the particles coated with oleic acid, it has been demonstrated that the sample reveals all attributes of a super-spin glass (SSG) system with strong interparticle interactions. 相似文献
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4.
The spinel CoFe2O4 has been synthesized by combustion reaction technique. X-ray photoelectron spectroscopy shows that samples are near-stoichiometric, and that the specimen surface both in the powder and bulk sample is most typically represented by the formula (Co0.4Fe0.6)[Co0.6Fe1.4]O4, where cations in parentheses occupy tetrahedral sites and those within square brackets in octahedral sites. The results demonstrate that most of the iron ions are trivalent, but some Fe2+ may be present in the powder sample. The Co 2p3/2 peak in powder sample composed three peaks with relative intensity of 45%, 40% and 15%, attributes to Co2+ in octahedral sites, tetrahedral sites and Co3+ in octahedral sites. The O 1s spectrum of the bulk sample is composed of two peaks: the main lattice peak at 529.90 eV, and a component at 531.53 eV, which is believed to be intrinsic to the sample surface. However, the vanishing of the O 1s shoulder peak of the powder specimen shows significant signs of decomposition. 相似文献
5.
Guoxin Zhang 《Journal of magnetism and magnetic materials》2009,321(10):1424-1427
Multi-functional magnetic, photoluminescent and photocatalytic CoFe2O4-ZnO nanocomposites were successfully synthesized by a collosol method. The average diameter of the prepared CoFe2O4-ZnO nanocomposites was 30±5 nm, and a diffusion layer was formed to link CoFe2O4 and ZnO. The saturation magnetization of the CoFe2O4-ZnO nanocomposites was 8.99 emu/g. Generation of ZnO from Zn(OH)2 collosol was nearly complete after thermal decomposition at about 380 °C. A photoluminescence emission peak was observed at 443 nm when excitated at 350 nm. Degradation of methyl orange is performed by CoFe2O4-ZnO nanocomposites under ultraviolet radiation, with a degradation rate of up to 93.9%. 相似文献
6.
Ruixin Wang 《Applied Surface Science》2010,256(20):6029-6034
Poly(4vinylpyridine-co-styrene) (P(4VP-co-St)) was grafted on silica gel particles in the manner of “grafting from”, and the grafting particle P(4VP-co-St)/SiO2 was gained. The chloromethylation reaction for the tetraphenylporphyrin (TPP) was performed using a chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which was uncarcinogenic, and the tetra-chloromethylphenyl-porphyrin (TMCPP) was prepared. Then, the quaternization reaction between the benzyl chloride groups on TMCPP and pyridine groups of the grafted P(4VP-co-St) macromolecules occurred and the bonding of TMCPP on the particles P(4VP-co-St)/SiO2 was realized, resulting in the functional composite-type particles TMCPP-P(4VP-co-St)/SiO2. Subsequently, the metallation of the bonded particles TMCPP-P(4VP-co-St)/SiO2 was carried out via the coordination reaction between TMCPP-P(4VP-co-St)/SiO2 and metal salt, resulting in the supported metalloporphyrin (MP) catalysts MP-P(4VP-co-St)/SiO2. The supported catalysts were characterized by UV-Vis spectra. The effects of various factors on the bonding process of TMCPP on P(4VP-co-St)/SiO2 were studied in detail. In addition, the catalytic activity of the supported catalysts MP-P(4VP-co-St)/SiO2 have been studied in oxidation process of ethyl benzene with molecular oxygen to acetophenone without the use of sacrificial co-reductant. The experimental results showed that the tetra-chloromethylphenyl-porphyrin (TMCPP) could be successfully bonded onto the P(4VP-co-St)/SiO2 surfaces by means of the quaternization reaction between TMCPP and the pyridine groups on grafted P(4VP-co-St) macromolecules. The supported catalysts MP-P(4VP-co-St)/SiO2 exhibited the fine catalytic activity. Moreover, the supported cobalt porphyrin was more active than the supported iron and manganese porphyrins. 相似文献
7.
Ryan Comes Man GuMikhail Khokhlov Jiwei LuStuart A. Wolf 《Journal of magnetism and magnetic materials》2012,324(4):524-527
CoFe2O4 (CFO) epitaxial thin films of various thicknesses were grown on MgO substrates using the pulsed electron-beam deposition technique. The films have excellent in-plane coherence with the substrate, exhibit layer-by-layer growth and have well-defined thickness fringes in x-ray diffraction measurements. Atomic force microscopy (AFM) measurements indicate that misfit dislocations form in thicker films and the critical thickness for the dislocation formation is estimated. Perpendicular magnetic anisotropy in CFO due to epitaxial in-plane tensile strain from the substrate was found. A stripe-like domain structure in the demagnetized state is demonstrated using magnetic force microscopy (MFM), in agreement with previous predictions. Coercivity increased in thicker films, which is explained by domain wall pinning due to misfit dislocations at the CFO/MgO interface. 相似文献
8.
L.J. Zhao 《Journal of magnetism and magnetic materials》2010,322(17):2485-2487
Nanocrystalline CoFe2O4 ferrite with crystallite sizes of 30 nm have been successfully prepared by an emulsion method. X-ray diffractometer (XRD) shows that nanocrystalline CoFe2O4 ferrite possesses face center cubic structure. Crystal structure of the CoFe2O4 nanocrystals will not be changed by the applied magnetic field and pressures. The obtained CoFe2O4 nanocrystalline powders were pressed into thin columns with different pressures. Meanwhile, the dependences of the applied pressures and the direction of applied magnetic field on the magnetic properties of the CoFe2O4 nanocrystals were investigated in detail using vibrating sample magnetometer (VSM). The pressed CoFe2O4 nanocrystal gains the most excellent magnetisms in a parallel applied magnetic field. 相似文献
9.
Chunlong FeiYue Zhang Zhi YangYong Liu Rui Xiong Jing Shi Xuefeng Ruan 《Journal of magnetism and magnetic materials》2011,323(13):1811-1816
CoFe2O4/Fe3O4 nano-composite ceramics were synthesized by Spark Plasma Sintering. The X-ray diffraction patterns show that all samples are composed of CoFe2O4 and Fe3O4 phases when the sintering temperature is below 900 °C. It is found that the magnetic properties strongly depend on the sintering temperature. The two-step hysteresis loops for samples sintered below 500 °C are observed, but when sintering temperature reaches 500 °C, the step disappears, which indicates that the CoFe2O4 and Fe3O4 are well exchange coupled. As the sintering temperature increases from 500 to 800 °C, the results of X-ray diffractometer indicate the constriction of crystalline regions due to the ion diffusion at the interfaces of CoFe2O4/Fe3O4 phases, which have great impact on the magnetic properties. 相似文献
10.
Two-layer ZrO2/SiO2 and SiO2/ZrO2 films were deposited on K9 glass substrates by sol–gel dip coating method. X-ray photoelectron spectroscopy (XPS) technique was used to investigate the diffusion of ZrO2/SiO2 and SiO2/ZrO2 films. To explain the difference of diffusion between ZrO2/SiO2 and SiO2/ZrO2 films, porous ratio and surface morphology of monolayer SiO2 and ZrO2 films were analyzed by using ellipsometry and atomic force microscopy (AFM). We found that for the ZrO2/SiO2 films there was a diffusion layer with a certain thickness and the atomic concentrations of Si and Zr changed rapidly; for the SiO2/ZrO2 films, the atomic concentrations of Si and Zr changed relatively slowly, and the ZrO2 layer had diffused through the entire SiO2 layer. The difference of diffusion between ZrO2/SiO2 and SiO2/ZrO2 films was influenced by the microstructure of SiO2 and ZrO2. 相似文献
11.
Al2O3/SiO2 films have been prepared by electron-beam evaporation as ultraviolet (UV) antireflection coatings on 4H-SiC substrates and annealed at different temperatures. The films were characterized by reflection spectra, ellipsometer system, atomic force microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. As the annealing temperature increased, the minimum reflectance of the films moved to the shorter wavelength for the variation of refractive indices and the reduction of film thicknesses. The surface grains appeared to get larger in size and the root mean square (RMS) roughness of the annealed films increased with the annealing temperature but was less than that of the as-deposited. The Al2O3/SiO2 films maintained amorphous in microstructure with the increase of the temperature. Meanwhile, the transition and diffusion in film component were found in XPS measurement. These results provided the important references for Al2O3/SiO2 films annealed at reasonable temperatures and prepared as fine antireflection coatings on 4H-SiC-based UV optoelectronic devices. 相似文献
12.
Micron-sized LiMn2O4 particles were easily coated on LiCoO2 cathodes using an amphoteric gelatin surfactant at pH4–5. The coated LiCoO2 material showed a significantly higher thermal stability during charging and capacity retention on cycling at 4.6 V, compared to the bare LiCoO2. 相似文献
13.
Byeol HanSeung-Won Lee Kwangchol ParkChong-Ook Park Sa-Kyun RhaWon-Jun Lee 《Current Applied Physics》2012,12(2):434-436
We produced dielectric stacks composed of ALD SiO2 and ALD Al2O3, such as SiO2/Al2O3, Al2O3/SiO2, and SiO2/Al2O3/SiO2, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO2/Al2O3 shows lowest leakage current for negative bias region below 6.4 V, and Al2O3/SiO2 showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al2O3 and SiO2/Al2O3. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO2 (6.5 nm)/Al2O3 (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO2 layer. 相似文献
14.
The magnetic properties of (Cox Fe1-x)A (Zn1-x Fe1+x)B O4 are studied using mean-field theory and the probability distribution law to obtain the saturation magnetization, the coercive field, the critical temperature, and the exchange interactions with different values of D (nm) and x. High-temperature series expansions (HTSEs) combined with the Pade approximant are used to calculate the critical temperature of (CoxFe1-x)A(Znl-xFe1+x)BO4, and the critical exponent associated with magnetic susceptibility is obtained. 相似文献
15.
D. MohantyH. Gabrisch 《Solid State Ionics》2011,194(1):41-45
Thermal stability of cathode material in the charged state is an important aspect for the safety of rechargeable batteries. It is well known that layered LixCoO2 decomposes to a mixture of LiCoO2 and Co3O4 at elevated temperatures. However, not many experimental evidences exist on intermediate phases those may form during the decomposition. Using magnetic measurements we show that it is possible to distinguish between the spinels LiCo2O4 and Co3O4 and thereby follow the decomposition of LixCoO2. We characterize the magnetic behavior of thermally aged LixCoO2 (x = 0.98, 0.76, 0.55) with increasing annealing time. Our results reveal the appearance of magnetic ordering in the thermally degraded products. The detailed analysis illustrates that the formation of Co3O4 is preceded by the formation of a meta stable LiCo2O4 phase. 相似文献
16.
Dheeraj Jain 《Journal of luminescence》2009,129(5):439-3684
Zinc phosphate glasses doped with Gd2O3:Eu nanoparticles and Eu2O3 were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P2O5 glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu3+ ions has been observed when Eu2O3 is incorporated in ZnO-P2O5 glasses. Lack of energy transfer from these defect centres to Eu3+ in Gd2O3:Eu nanoparticles doped ZnO-P2O5 glass has been attributed to effective shielding of Eu3+ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu3+ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd2O3:Eu nanoparticles or Eu2O3 incorporation. 相似文献
17.
We describe the structural properties and electrical characteristics of thin thulium oxide (Tm2O3) and thulium titanium oxide (Tm2Ti2O7) as gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were explored by X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy, measurements. It is found that the Tm2Ti2O7 film annealed at 800 °C exhibited a thinner capacitance equivalent thickness of 19.8 Å, a lower interface trap density of 8.37 × 1011 eV−1 cm−2, and a smaller hysteresis voltage of ∼4 mV than the other conditions. We attribute this behavior to the Ti incorporated into the Tm2O3 film improving the interfacial layer and the surface roughness. This film also shows negligible degrees of charge trapping at high electric field stress. 相似文献
18.
用超声水解方法制备MgO纳米颗粒,用化学沉淀法制备α-Fe2O3纳米颗粒,将MgO/α-Fe2O3混合体常温下超声活化2h,400℃固相合成制备出MgFe2O4纳米颗粒.通过X射线衍射和透射电子显微镜测试产品的化学成分、晶体结构和形貌尺寸,分析声化学反应机理及其影响因素.研究结果表明:所制备的MgFe2O4为尖晶石铁氧体,颗粒尺寸分布在20-30nm之间,粒度分布均匀;超声空化效应提高了化学反应活性、增加反应物的比表面积和反应物之间的接触面积,促进固相合成反应速度,降低反应温度,实现了一般条件下难以完成的化学反应. 相似文献
19.
Yunsheng Zhang Aili Wang Min Ren Zhuomin Gu Yumin Liu Yutang Shen Longbao Yu Tingshun Jiang 《Applied Surface Science》2010,257(4):1351-1360
Binary Al2O3/SiO2-coated rutile TiO2 composites were prepared by a liquid-phase deposition method starting from Na2SiO3·9H2O and NaAlO2. The chemical structure and morphology of binary Al2O3/SiO2 coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al2O3/SiO2 coating layers both in amorphous phase were formed at TiO2 surfaces. The silica coating layers were anchored at TiO2 surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO2-coated TiO2 surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al2O3/SiO2 coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al2O3/SiO2-coated TiO2 composites had a high dispersibility in water. The whiteness and brightness of the binary Al2O3/SiO2-coated TiO2 composites were higher than those of the naked rutile TiO2 and the SiO2-coated TiO2 samples. The relative light scattering index was found to depend on the composition of coating layers. 相似文献
20.
Novel egg-shell structured monometallic Pd/SiO2 and bimetallic Ca-Pd/SiO2 catalysts were prepared by an impregnation method using porous hollow silica (PHS) as the support and PdCl2 and Ca(NO3)2·4H2O as the precursors. It was found from transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) that Pd was loaded on PHS with a particle size of 5-12 nm in Pd/SiO2 samples and the Pd particle size in Ca-Pd/SiO2 was smaller than that in Pd/SiO2 since Ca could prevent Pd particles from aggregating. X-ray photoelectron spectroscopy (XPS) analyses exhibited that Pd 3d5/2 binding energies of Pd/SiO2 and Ca-Pd/SiO2 were 0.2 and 0.9 eV lower than that of bulk Pd, respectively, as a result of the shift of the electron cloud from Pd to oxygen in Pd/SiO2 and to both oxygen and Ca in Ca-Pd/SiO2. The activity of Ca-Pd/SiO2 egg-shell catalyst for CO hydrogenation and the selectivity to methanol, with a value of 36.50 mmolCO mol−1Pd s−1 and 100%, respectively, were much higher than those of the catalysts prepared with traditional silica gel as the support, owing to the porous core-shell structure of the PHS support. 相似文献