中文摘要：

针对传统的管式炉固态还原法对涡旋磁性Fe_3O_4纳米环还原效果有限的问题,采用基于溶液法的新型还原手段,当α-Fe_2O_3纳米环被还原成Fe_3O_4纳米环后,油酸作为表面活性剂包覆在Fe_3O_4纳米环表面,随后通过转水过程形成纳米环水分散体。研究结果表明：溶液法还原能够保持纳米环最初均一的环状形貌,良好的结晶性和边界清晰的涡旋磁畴结构。这种亲水性Fe_3O_4纳米环的表面存在壬二酸,易于抗体或药物连接。这项工作提供了1种将没有表面修饰的纳米环粉末转化成具有涡旋磁畴结构的水溶性纳米环胶体溶液用于各种生物医学领域的简便方法。

英文摘要：

Aiming at the problem of limited reductive effect of the traditional solid-state reduction in tube furnace,a novel reduction method of solution-based reduction process was introduced to convert surfactant-freeα-Fe_2O_3 nanorings（NRs）into water-dispersible Fe_3O_4 NRs.In this process,the uniformα-Fe_2O_3 NRs obtained through hydrothermal synthesis method are firstly thermally reduced to hydrophobic Fe_3O_4 NRs in the presence of hydrophobic oleic acid surfactant and non-polar trioctylamine solvent（under a flow of 5% H2/95% Ar）.Subsequently,oxidative cleavage of oleic acid capping agent using sodium periodate oxidizing agent is imparted to yield water-dispersible Fe_3O_4 NRs.The results show that the obtained Fe_3O_4 NRs using solution-based reduction process can retain its original uniform ring shape with good crystallinity and well-defined magnetic vortex domain.Moreover,with the presence of azelaic acid on the surface of hydrophilic Fe_3O_4 NRs,antibody or drugs can be easily conjugated.This work provides a convenient approach to convert surfactant-free nanoparticle powders into water-dispersible nanoparticles colloidal solutions for various biomedical applications.