空心Fe_3O_4纳米微球的制备及超顺磁性

采用水热控制合成法,以六水三氯化铁、柠檬酸三钠和尿素为原料,聚丙烯酰胺为稳定剂, 200?C下反应12 h制备得到了超顺磁性空心Fe_3O_4纳米微球.通过X射线衍射仪、扫描电子显微镜、透射电子显微镜对样品的结构和形貌进行表征,并采用振动样品磁强计测试了样品的磁性能.结果表明:所得样品为具有尖晶石结构的Fe_3O_4纳米微球,尺寸为160 nm左右,呈分等级结构,即整个微球由粒径约18 nm的初级晶粒自组装堆叠而成;室温下表现为典型的超顺磁性,且饱和磁化强度为73.3 emu/g (1 emu/g=1 A·m~2/kg),这种高饱和磁化强度可以由其初级晶粒晶化程度高且粒径较大以及这种特殊的二次自组装结构进行解释.这种Fe_3O_4纳米微球为疏松多孔的空心球状结构,具有粒径分布均匀、分散性良好和超顺磁性的特点,在药物靶向输运和肿瘤热疗中有潜在的应用.

Synthesis and superparamagnetism of Fe3O4 hollow nano-microspheres

Fe₃O₄ nanomaterials have received great attention due to their many applications in tumor diagnosis and tumor heat therapy based on their good biocompatibility, magnetic targeting ability and superparamagnetic properties to avoid magnetic reunion in the process of magnetic targeting. Most of superparamagnetic nanoparticles obtained by traditional methods exhibit lower saturation magnetization (MS), because of their small particle sizes. Enlarging the particle size is favorable to increase the MS of magnetic particles. However, the superparamagnetism of the particle could be lost with the increase of particle size. This is not favorable to the targeting delivery of magnetic particles. For this purpose, in this paper, novel Fe₃O₄ nano-microspheres with mesoporous hollow structure are successfully synthesized by a facile hydrothermal method from the FeCl₃6 H₂O, sodium citrate, urea, and polyacrylamide as additive, the reaction temperature is 200℃ and reaction time is 12 h. The crystal structure and purity of the resulting products are examined by powder X-ray diffraction (XRD). The morphologies of the products are studied by using scanning electron microscopy (SEM) and transmission electron microscopic (TEM). The magnetic properties of Fe₃O₄ nano-microspheres are evaluated with a vibrating sample magnetometer. The morphology evolution process and possible formation mechanism of Fe₃O₄ nano-microspheres are investigated. The findings are as follows:all XRD peaks of the hollow Fe₃O₄ nano-microspheres could be assigned to the spinel-type Fe₃O₄. The SEM and TEM images reveal that the products are mesoporous hollow Fe₃O₄ nano-microspheres and possess hierarchical structure, in which large microspheres (160 nm) are self-assembled by smaller Fe₃O₄ initial crystals (18 nm). It is found that the synthetic time of Fe₃O₄ nano-microspheres is considerable for the formation of the Fe₃O₄ hierarchical structure, and that the dispersion and sphericity of Fe₃O₄ nano-microspheres are the best when reaction time is 12 h. The formation of hierarchical hollow structure is believed to be due to the Ostwald ripening process, in which the initial crystals redissolve and regrow. Furthermore, the magnetic measurement results show that as-prepared hollow Fe₃O₄ nano-microspheres exhibit typical superparamagnetic properties whose initial crystal size is in the range of superparamagnetic region. Meanwhile, MS is about 73.3 emu/g at room temperature, which is significantly greater than that of traditional small superparamagnetic nanoparticles and compact solid nano-microspheres. The high saturation magnetization of hollow Fe₃O₄ nano-microspheres originates from a high crystallinity with primary grain, lager size and hierarchical structure. The results indicate that the as-prepared Fe₃O₄ hollow nano-microspheres are dispersed, water-soluble, homogeneous in particle diameter, and superparamagnetic, and can be used in targeted anticancer drug delivery and tumor heat therapy.