采用共沉淀法合成了Fe3O4磁性纳米颗粒, 进一步以柠檬酸三钠还原法制备出了具有SERS活性的Fe3O4/Ag磁性包覆修饰材料, 用紫外可见吸收光谱、 能谱及透射电镜对结构与形貌进行表征, 发现所制备的Fe3O4/Ag纳米材料粒径约为30～60 nm, 形貌规整接近球形, 经测试Fe3O4/Ag材料很容易被磁铁收集, 能够满足分散萃取再收集的需要。 根据密度泛函理论(DFT)对杀线威(Oxamyl)、 Oxamyl-Ag和Oxamyl-Ag4进行了理论结构优化计算, 得到了杀线威的理论拉曼光谱和与Ag表面增强拉曼光谱及其谱峰的归属, 结合表面增强拉曼光谱(SERS)测定, 研究了杀线威在Fe3O4/Ag表面的吸附行为和增强效应, 测算得到杀线威在Fe3O4/Ag表面上的增强因子为208×105。 研究表明: 理论计算的杀线威拉曼光谱与测定的拉曼光谱具有较好的一致性, DFT理论计算中发现研究分子与活性Ag原子作用越多, 与实测值常规拉曼NRS越接近； 杀线威以双键侧N原子和S原子与Fe3O4/Ag表面吸附作用为主； 双键侧N优先与Ag吸附成键后, 整个分子靠近Ag表面, 最终使得双键侧N原子与S原子共同吸附在Ag表面； Fe3O4/Ag磁性纳米复合材料具有显著的富集吸附和拉曼增强作用； 可利用其作为拉曼基底, 以实现SERS光谱法对杀线威农残的快速分析检测。

In this paper, Fe3O4 magnetic nanoparticles were firstly synthesized with co-precipitation method and the Fe3O4/Ag magnetic coating modified material which has high SERS activity was further prepared by reducing sodium citrate. The structure and morphology were characterized with UV-Visible absorption spectroscopy, energy spectroscopy and transmission electron microscopy. It was found that Fe3O4/Ag material with regular morphology and the nanoparticle diameter is about 30~60 nm. Fe3O4/Ag material can easily be collected by magnets to meet the requirements of dispersion, extraction and re-enrichment under magnetic testing. Then, the theoretical and experimental Raman spectra and assignments of oxamyl on Ag surface are obtained by complexes of Oxamyl, Oxamyl-Ag and Oxamyl-Ag4 molecular structure calculation optimization based on density functional theory (DFT). Surface-enhanced Raman spectroscopy (SERS) is used to investigate the adsorption behavior and enhancement effect of oxamyl on Fe3O4/Ag and the enhancement factor of oxamyl on Fe3O4/Ag surface is calculated as 208×105. The results show that Raman spectra of the determination and the theoretical calculation have good consistency, with more Ag atoms bonded to oxamyl when closer to the NRS. Then, oxamyl is absorbed on Fe3O4/Ag by double bond side N atom and S atom. The double bond side N atom is adsorbed on the Ag surface preferentially, then the whole molecule near the Ag surface. At last the double bond side N atom and S atom adsorbed on the Ag surface together. The proposed Fe3O4/Ag magnetic nanocomposites have significant absorption enrichment and Raman enhancement effect, so Fe3O4/Ag can be used as SERS substrate to achieve rapid analysis and detection of pesticide residues oxamyl.