CoFe2O4纳米颗粒的结构、磁性以及离子迁移

聚乙烯醇(PVA)溶胶凝胶法制备出CoFe₂O₄纳米微粉，用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe₂O₄纳米颗粒80—873 K的变温穆斯堡尔谱，发现纳米颗粒的磁转变温度范围为793—813 K，比块体材料的磁性转变温度要低.CoFe₂O₄纳米颗粒的德拜温度θ_A=674 K，θ_B=243 K，比块体材料要小.CoFe₂O₄纳米颗粒超精细场H_f随温度的变化符合T^3/2+T^5/2定理.当温度较高时，平均同质异能移IS随温度的升高而减小，并呈线性关系. 关键词： 纳米颗粒 磁性 穆斯堡尔谱     

CoFe2O4和MnFe2O4纳米复合介质的制备及其磁性研究

采用热分解法制备了分散程度高且平均晶粒尺寸为20 nm的CoFe₂O₄和MnFe₂O₄复合介质.低温磁化曲线测量显示,制备的复合介质具有软-硬磁交换弹性耦合效应,且合成温度以及软磁和硬磁相的成分比例对磁交换弹性耦合的强度有很大的影响.变温磁测量显示,温度为20K时,复合纳米介质的表面自旋冻结效应导致饱和磁化强度显著增加.Henkel测量显示,对分散的CoFe₂O₄和MnFe₂O₄复合介质,磁偶极相互作用占主导作用.     

多孔SiO2包裹磁性纳米颗粒Fe3O4的制备与表征

采用加热分解油酸铁法制备了Fe₃O₄磁性纳米颗粒,并用有机模板和反相微乳液相结合的方法将磁性纳米颗粒包裹在多孔二氧化硅中.用红外光谱(FTIR)研究了不同的处理方式对油酸铁表面官能团的影响及油酸的反应浓度和加热分解油酸铁的过程中升温速率对Fe₃O₄纳米颗粒的影响.结果表明,用乙醇和丙酮处理后的固态蜡状油酸铁表面的油酸基团会受到损害,将不利于加热分解时形成单分散性的Fe₃O₄纳 关键词： 3O₄纳米颗粒')" href="#">Fe₃O₄纳米颗粒 2包裹')" href="#">多孔SiO₂包裹 反相微乳液法 油酸铁     

Co淀积到γ-Fe2O3表面的光电发射谱研究

在γ-Fe₂O₃表面蒸镀不同厚度Co,观察到低Co覆盖度,Co具有很大活力与O₂结合,而使Fe还原.在θ=0.2—0.8时,表面上形成类CoFe₂O₄.Co覆盖度进一步增加,Fe在表面偏析,Co开始形成第二层,破坏了形成这种氧化物的条件.因此,这种铁钴氧化物与单层或亚单层包钴磁粉磁性的改善可能有密切关系. 关键词：     

纳米Fe3 O4 颗粒的正电子湮没谱学研究

测量了磁性纳米Fe₃O₄颗粒的X射线衍射谱(XRD)、正电子湮没寿命谱(PALS)和符合多普勒展宽谱(CDBS),研究了不同压力和退火温度对磁性纳米Fe₃O₄颗粒物相、电子结构、缺陷及电子动量分布等的影响. XRD,PALS,CDBS测量结果表明:纳米Fe₃O₄颗粒的缺陷浓度随压力的增加而增大,但物相和缺陷类型并未发生变化;磁性纳米Fe₃O_{4< 关键词： 正电子 3}O₄')" href="#">Fe₃O₄ 寿命谱 多普勒展宽谱     

Al2O3薄膜/纳米Ag颗粒复合结构的光吸收谱及增强Raman散射光谱研究

Al₂O₃介质薄膜与纳米Ag颗粒构成的复合结构，被应用于表面增强Raman散射探测实验中，其中Al₂O₃介质薄膜对纳米Ag颗粒的吸收谱及增强Raman散射光谱的影响被特别关注.该复合结构的光学特性表征出纳米Ag颗粒的偶极振荡特性.从光吸收谱中可以看到，其共振吸收谱随Al₂O₃介质薄膜厚度增加而在整个谱域上发生红移，表明纳米Ag颗粒的周围介电常数随Al₂O₃介质薄膜厚度的增加而增大.采用罗丹明6G作为探针原子，6个Raman特征峰的平均增益值作为表征表面增强Raman散射衬底增益程度的量度.实验结果表明,Al₂O₃介质薄膜层的引入提高了纳米Ag颗粒的衬底介电常数，并引起了散射共振的增强，从而使表面增强Raman散射强度提高. 关键词： 纳米Ag薄膜 共振吸收 表面增强Raman散射 介电常数     

溶液燃烧法合成纳米ZnFe2O4晶体

采用溶液燃烧法合成了ZnFe₂O₄纳米晶体,系统考察了不同燃料,燃料/氧化剂的摩尔比对ZnFe₂O₄晶相组成和形貌的影响。采用XRD和SEM对产物的晶相组成、晶粒大小、晶体形貌以及表面形态进行了表征。结果表明:燃料种类和燃料/氧化剂比对合成产物晶相组成影响显著。以丙氨酸和甘氨酸为燃料合成所得的纳米晶相较好;以丙氨酸和甘氨酸为燃料时,都是在贫燃（—50%）时得到最好ZnFe₂O₄纳米晶型,尺寸分别为34.4nm和29.7nm。     

高稳定性Mn:ZnO/Mn2O3纳米复合光催化剂的制备及光催化特性

采用修饰的高分子网络凝胶法成功制备了Mn₂O₃复合Mn掺杂ZnO纳米复合光催化剂(Mn:ZnO/Mn₂O₃)，并基于模拟太阳光照射下罗丹明B(RhB)及亚甲基蓝(MB)染料的光降解研究了催化剂光催化降解有机染料的特性。X射线衍射，扫描电子显微镜及BET比表面积测试结果显示，微量(0.1 mol%)Mn掺杂再复合微量(0.2 mol%)Mn₂O₃后，Mn:ZnO/Mn₂O₃的颗粒尺寸减小且分散性提高，有效比表面积增大。紫外-可见光吸收光谱表明，相对于纯ZnO,Mn:ZnO/Mn₂O₃在可见光区域的光吸收能力明显提高。光致发光光谱表明微量Mn掺杂和微量Mn₂O₃复合促进了光生电子-空穴对的分离。结合X射线光电子能谱，发现可见光吸收能力和光生电子-空穴对分离率的提高源于催化剂表面氧空位的增加以及Mn:ZnO和Mn₂     

Ag@Fe3O4@C-CdTe@SiO2磁性荧光复合微球的制备与光学特征

先采用一步溶剂热法和水热法制备了碳包覆的Ag@Fe₃O₄核壳型磁性纳米粒子，然后通过表面氨基化改性后与巯基乙酸修饰的CdTe量子点反应，将量子点键合到磁性微球上，最后在其表面包覆上一层二氧化硅壳层，制备出具有荧光增强的Ag@Fe₃O₄@C-CdTe@SiO₂磁性荧光复合材料。实验结果表明，该纳米粒子的平均粒径大约为150 nm，磁饱和强度为224 A/g（22.4 emu/g），在室温下具有较好的磁性能。其中Ag@Fe₃O₄@C-CdTe磁性荧光纳米粒子的荧光强度大于Fe₃O₄@C-CdTe，其主要原因是内核为45 nm的Ag纳米粒子具有表面等离子体共振作用，能够使其表面或附近的量子点荧光得到增强。     

TiO2/ZnO纳米薄膜界面热导率的分子动力学模拟

采用平衡分子动力学方法及Buckingham势研究了金红石型TiO₂薄膜与闪锌矿型ZnO薄膜构筑的纳米薄膜界面沿晶面[0001](z轴方向)的热导率.通过优化分子模拟初始条件中的截断半径r_c和时间步后,计算并分析了平衡温度、薄膜厚度、薄膜截面大小对热导率的影响.研究表明,薄膜热导率受薄膜温度和厚度的影响很大,当温度由300 K升高600 K时,薄膜的热导率逐渐减小;当薄膜厚度由1.8 nm增大到5 nm时,热导率会逐渐增大;并在此基础 关键词： 热导率 分子动力学 2/ZnO纳米薄膜界面')" href="#">TiO₂/ZnO纳米薄膜界面 数值模拟     

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe₂O₄ and ferrimagnetic oxide/ferromagnetic metal CoFe₂O₄/CoFe₂ nanocomposite. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupled. Two steps were followed to synthesize the bimagnetic CoFe₂O₄/CoFe₂ nanocomposite: (i) first, preparation of CoFe₂O₄ nanoparticles using a simple hydrothermal method, and (ii) second, reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe₂O₄ nanoparticles were investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0 kOe at room temperature and 50 K. The mean diameter of CoFe₂O₄ particles is about 16 nm. Mossbauer spectra revealed two sites for Fe³⁺. One site is related to Fe in an octahedral coordination and the other one to the Fe³⁺ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe₂O₄. TEM measurements of nanocomposite showed the formation of a thin shell of CoFe₂ on the cobalt ferrite and indicate that the nanoparticles increase to about 100 nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)_max of 1.22 MGOe was achieved at room temperature for CoFe₂O₄/CoFe₂ nanocomposites, which is about 115% higher than the value obtained for CoFe₂O₄ precursor. The exchange coupling interaction and the enhancement of product (BH)_max in nanocomposite CoFe₂O₄/CoFe₂ are discussed.     

A facile synthesis of monodisperse CoFe2O4/SiO2 nanoparticles

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.     

Preparation and characterization of multi-functional CoFe2O4-ZnO nanocomposites

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%.     

Effects of applied magnetic field and pressures on the magnetic properties of nanocrystalline CoFe2O4 ferrite

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.     

Synthesis and magnetic properties of hard magnetic (CoFe2O4)-soft magnetic (Fe3O4) nano-composite ceramics by SPS technology

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.     

Synthesis and performance of core-shell structured ZnO/In2O3 composites in situ growth

Core-shell structured ZnO/In₂O₃ composites were successfully synthesized via situ growth method. Phase structure, morphology, microstructure and property of the products were investigated by X-ray diffraction (XRD), TG-DTA, field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), transmission electron microscope (TEM) and photoluminescence (PL). Results show that the core-shell structures consist of spindle-like ZnO with about 800 nm in length and 200 nm in diameter, and In₂O₃ particles with a diameter of 50 nm coated on the surface of ZnO uniformly. HMTA plays an important role in the formation of core-shell structures and the addition of In₂O₃ has a great effect on PL spectrum. Possible mechanism for the formation of core-shell structures is also proposed in this paper.     

Optical properties of (ZnO)0.5(P2O5)0.5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Binary (ZnO)_0.5(P₂O₅)_0.5 glasses doped with Eu₂O₃ and nanoparticles of Gd₂O₃:Eu were prepared by conventional melt-quench method and their luminescence properties were compared. Undoped (ZnO)_0.5(P₂O₅)_0.5 glass is characterized by a luminescent defect centre (similar to L-centre present in Na₂O-SiO₂ glasses) with emission around 324 nm and having an excited state lifetime of 18 ns. Such defect centres can transfer the energy to Eu³⁺ ions leading to improved Eu³⁺ luminescence from such glasses. Based on the decay curves corresponding to the ⁵D₀ level of Eu³⁺ ions in both Gd₂O₃:Eu nanoparticles incorporated as well as Eu₂O₃ incorporated glasses, a significant clustering of Eu³⁺ ions taking place with the latter sample is confirmed. From the lifetime studies of the excited state of L-centre emission from (ZnO)_0.5(P₂O₅)_0.5 glass doped with Gd₂O₃:Eu nanoparticles, it is established that there exists weak energy transfer from L-centres to Eu³⁺ ions. Poor energy transfer from the defect centres to Eu³⁺ ions in Gd₂O₃:Eu nanoparticles doped (ZnO)_0.5(P₂O₅)_0.5 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 luminescent centre and Eu³⁺ ions.     

Properties of Ferrofluid Nanoparticles Prepared by Coprecipitation and Acid Treatment

A new stable acid water-based CoFe₂O₄ ferrofluid is prepared by coprecipitation and acid treatment. The properties of the nanoparticles forming the ferrofluid are examined by means of X-ray diffraction, vibrating sample magnetometer, scanning tunneling microscopy, transmission electron microscopy and annihilation technique. The results show that the particles are cubic CoFe₂O₄ nanoparticles, which have an average diameter of 12.2nm and are coated with a low density porous amorphous layer. The CoFe₂O₄ particles in an acid aqueous medium exist in two kinds of forms, one is a single spherical particle and another is an aggregation of several spherical particles.     

Synthesis and characterization of TiO2/Fe2O3 core-shell nanocomposition film and their photoelectrochemical property

TiO₂/Fe₂O₃ core-shell nanocomposition film has been fabricated via two-step method. TiO₂ nanorod arrays are synthesized by a facile hydrothermal method, and followed by Fe₂O₃ nanoparticles deposited on TiO₂ nanorod arrays through an ordinary chemical bath deposition. The phase structures, morphologies, particle size, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and ultraviolet-visible (UV-vis) spectrophotometer. The results confirm that Fe₂O₃ nanoparticles of mean size ca. 10 nm coated on the surface of TiO2 NRs. After depositing Fe₂O₃, UV-vis absorption property is induces the shift to the visible-light range, the annealing temperature of 600 °C is the best condition for UV-vis absorption property of TiO₂/Fe₂O₃ nanocomposite film, and increasing Fe content, optical activity are enhanced one by one. The photoelectrochemical (PEC) performances of the as-prepared composite nanorods are determined by measuring the photo-generated currents under illumination of UV-vis light. The TiO₂ NRs modified by Fe₂O₃ show the photocurrent value of 1.36 mA/cm² at 0 V vs Ag/AgCl, which is higher than those of unmodified TiO₂ NRs.     

Hollow glass microspheres coated with CoFe2O4 and its microwave absorption property

Spinel CoFe₂O₄ coating on the surface of hollow glass microspheres of low density was synthesized by co-precipitation method. The phase structures, morphologies, particle size, shell thickness, chemical compositions of the composites have been characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and energy dispersive X-ray spectroscopy (EDS). The results show that CoFe₂O₄ coating on hollow glass microspheres can be achieved, and the coating layers are constituted by CoFe₂O₄ nanoparticles of mean size ca. 10 nm. The as-synthesized powder materials were uniformly dispersed into the phenolic cement, then the mixture was pasted on metal plate with the area of 200 mm×200 mm as the test plate. The test of microwave absorption was carried out by the radar-absorbing materials (RAM) reflectivity far field radar cross-section (RCS) method. The results indicate that the coated CoFe₂O₄/hollow glass microspheres composites can be applied in lightweight and strong absorption microwave absorbers.