中文摘要：

以气泡为模板,通过简单的一步水热法合成了尖晶石型MⅡFe2O4（M=Fe,Ni）纳米空心微球,并采用柠檬酸对其表面进行了修饰。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、红外光谱（IR）和振动样品磁强计（VSM）对修饰前后纳米空心微球的形貌、结构和磁性能进行了表征。结果表明,MⅡFe2O4（M=Fe,Ni）纳米空心微球的尺寸在300～600nm,前躯体溶液的pH值大于9或反应时间小于12h都不能生成空心结构。此外,MⅡFe2O4（M=Fe,Ni）纳米空心微球呈现较好的超顺磁性,但与纳米Fe3O4实心微粒相比较,Fe3O4纳米空心微球的饱和磁化强度却有所降低。

英文摘要：

MⅡFe2O4（M=Fe,Ni） hollow nanospheres were prepared by a facile hydrothermal method in the presence of ammonium acetate（NH4·AC） as the structure-directing agent without adding any template or surfactant.Then,the citrate was added to coat on the surfaces of MⅡFe2O4（M=Fe,Ni） hollow nanospheres by physical absorption.The structural properties of these hollow nanospheres（nonmodified and modified by adsorption of citrate（CA）） were characterized by X-ray diffractometry（XRD）,scanning electron microscopy（SEM） and infrared（IR） spectroscopy.The results show that the sizes of the MⅡFe2O4（M=Fe,Ni） hollow nanospheres are between 300 to 600 nm,the products are not hollow structures until the reaction time is longer than 12h and pH of reaction is less than 9.IR results reveal that the citrate is successfully grafted onto the hollow ferrite nanospheres.The modification using citrate does not result in a phase change via XRD analysis.The magnetic property investigation shows that all the ferrites carry out the superparamagnetic characterization according to the magnetic hysteresis curve measured by using a vibrating sample magnetometer（VSM） at room temperature.Moreover,compared to the bulk solid Fe3O4 nanospheres,the Ms value of the hollow Fe3O4 nanospheres is lower.This work provides a simple and environmentally friendly route for the synthesis of other metal oxide hollow nano-and micro-scale structures.