Hydrophilic magnetic nanoparticles have been widely applied in biological sciences. In this work, we proposed a convenient method to synthesize surface carboxylic magnetic nanoparticles. Firstly, hydrophobic magnetic nanoparticles coated with oleic acid were prepared from ferric chloride and ferrous chloride by co-precipitation method, with oleic acid as surfactant. Then the C =C bond of oleic acid coated on the surface of particles was oxidized into -COOH by KMnO4 solution in situ, thereby hydrophobic magnetic nanoparticles functioned by monolayer carboxylic groups were obtained. The magnetic nanoparticles were characterized by transmission electron microscopy(TEM) , X-ray diffraction ( XRD ) , Fourier transform infrared ( FTIR) , ther-mogravimetric analysis( TGA) , vibrating sample magnetometry ( VSM) and Zeta potential analyzer and so on. The results showed that magnetic nanoparticles surface was successfully carboxyl-functioned. The average diameter and the saturation magnetization of the nanoparticles were about 9 nm and 64. 5 A · M2/kg, respectively. The remnant magnetization and coercivity of the nanoparticles were nearly to be 0, which demonstrated it was classic superparamagnetic. The carboxyl-functioned magnetic nanoparticles could be dispersed into water to form ferrofluid, which were stable for more than 42 d without precipitation at pH values of 7-10.%提出了一种快速对磁性纳米粒子表面羧基化的方法.以氯化铁和氯化亚铁为原料,油酸为表面活性剂,通过共沉淀法制得油酸包覆的亲油性Fe3O4磁性纳米粒子,然后用高锰酸钾进行原位氧化,将覆盖在粒子表面油酸中的C=C键氧化成-COOH,从而得到单层羧基功能化的亲水性磁性纳米粒子.利用透射电子显微镜(TEM),X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、热重分析仪(TGA)、振动样品磁强计( VSM)和Zeta电位分析仪等对其进行了表征.结果表明,磁性纳米粒子的表面被成功羧基化,粒子的平均直径约为9 nm,饱和磁化值为64.5 A·m2/kg,剩磁和矫顽力近似为零,具有典型的超顺磁性.羧基化磁性纳米粒子可在pH =7～10的水溶液中形成稳定分散的磁流体,保存42 d后无沉淀出现.
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