强磁响应的超顺磁尖晶石型纳米簇形成机理的原位量热研究

Nanosized spinel-style ferrites (MFe2O4 M = Zn, Mn, Co et al.) are often applied in various fields due to their chemical/magnetic stability and low cytotoxicity. However, a challenge is still found for the preparation of the ferrite showing superparamagnetic property and enhanced magnetic response. In order to solve this problem, three kinds of ferrites will be synthesized as the aiming samples through a solvothermal method, such as normal, mixed, and anormal ferrites. Clusters composed of nanosized ferrites will be first prepared, which show superparamagnetic property and enhanced magnetic response. Second, rare earth elements will be added into the clusters for improving their magnetic response. The content of the rare earth element will be obtained, which the saturation magnetization of the cluster reaches the highest. Third, different kinds of surfactants will be further used to enhance the magnetic response of the ferrite through modified occupation of cationic ions, where the content of the rare earth element keeps the same as that of the sample with the maximum saturation magnetization. A microcalorimeter will be used in situ to determine the power-time curve of the sample forming processes. Samples can be obtained at every forming process based on these curves. These samples are characterized by various technologies, such as XRD, FT-IR, ICP-AES, XPS, DSC, TG, SEM, TEM, HRTEM, VSM, SQUID, and Mössbauer. Effects of rare earth elements on magnetic property of the clusters and surfactants on occupation of cationic ions at tetrahedral and octahedral sites in the spinel structure will be studied. The formation mechanism of the nanosized clusters showing superparamagnetic property and enhanced magnetic response will be investigated by combining the characterized results and the thermokinetic parameters observed through analysis of the power-time curve. These results may be very useful to give new idea, and find novel method for the formation of the nanosized ferrite with superparamagnetic property and higher saturation magnetization.

尖晶石型纳米铁氧体是应用最广泛的磁性纳米材料之一。基于超顺磁和强磁响应这一对矛盾特性是制约该类型材料发展的关键瓶颈，本课题拟制备正、复合和反型三种具有代表性的尖晶石铁氧体，采用联合调控磁性的方法，即通过制备由小颗粒组装的纳米簇，在保持超顺磁的同时增强其磁响应；添加稀土离子，增强纳米簇的磁响应；应用表面活性剂有效调控金属离子在尖晶石结构中四面体和八面体间隙的分布，进一步提高纳米簇的磁响应。采用微量热技术原位测量纳米簇形成过程的热谱曲线，通过解析热谱曲线获知该过程经历的不同变化和相应的热动力学参数，并关联物相结构、形貌、磁性等表征技术，研究稀土离子对纳米簇磁性的影响，考察表面活性剂对金属离子分布的调控作用，探索在表面活性剂作用下尖晶石型铁氧体纳米簇磁性质的变化规律，揭示强磁响应的超顺磁纳米簇形成机理，为研制该类型纳米材料提供新思路、新方法和理论指导。

针对尖晶石型纳米铁氧体的超顺磁和强磁响应这一对矛盾特性，本课题采用微量热技术原位测量超顺磁、强磁响应的铁氧体形成过程的热谱曲线。通过解析热谱曲线获知其形成经历的不同变化过程和相应的热动力学参数，并关联物相结构、形貌、磁性等表征技术，研究其生长机理。考察表面活性剂等对尖晶石型铁氧体磁性质的影响规律。为研制超顺磁、强磁响应的铁氧体提供了新思路、新方法和理论指导。进一步探索了该类型材料在吸附、Fenton反应催化剂、模拟酶等方面的应用潜力。具体研究结果如下：.1、.应用原位量热技术，深入探索了超顺磁、强磁响应的尖晶石纳米簇的形成机理。其中-OCH2CH2O-的桥联作用是形成簇状结构的关键。.2、.应用原位量热技术，探索了乙二胺(EDA)对尖晶石纳米簇的形成机理的影响。在制备ZnFe2O4的体系中， Fe(EDA)3]3+和[Zn(EDA)3]2+配合物的生成，降低了溶液中Fe3+和 Zn2+的浓度，由纳米簇转化为纳米片。.3、.采用原位微量热技术，研究表面活性剂对Ni0.3Fe2.7O4纳米簇形成过程的影响。结果表明，表面活性剂的添加改变了Ni0.3Fe2.7O4的平均晶粒尺寸、金属阳离子分布以及样品的磁性。.4、.采用原位微量热技术并结合 XRD、TEM、FT-IR、TG、XPS等表征手段，深入探索有超顺磁性及高饱和磁化强度的Zn0.2Fe2.8O4纳米颗粒的形成机理。结果表明，首先生成α-(Fe, Zn)OOH和α-Fe2O3，体系中的部分Fe3+被乙二醇还原成Fe2+并生成Fe3O4，最后Fe3O4转化成Zn0.2Fe2.8O4。.5、.采用微量热技术研究了八面体状蛋黄壳结构的ZnFe2O4/SiO2形成机理。首先，Fe3+和Zn2+通过中空的介孔壳进入SiO2球的空腔，在空心球的内外表面形成八面体形态的α-(Fe，Zn)OOH和α-Fe2O3。最后，α-Fe2O3转化为八面体状蛋黄壳状的ZnFe2O4，同时SiO2空心球转变为纳米片。.6、.在研究了尖晶石型铁氧体生长机理的基础上，探索了其形成复合材料的吸附及催化性能，如Zn0.2Fe2.8O4@SBA-15的吸附、八面体状蛋黄壳结构的ZnFe2O4/SiO2和NiFe2O4/NiS的Fenton催化、Cu-CuFe2O4的Fenton催化和模拟酶等。