摘要
采用共沉淀法合成Fe3O4纳米颗粒,再以柠檬酸三钠还原Ag NO3获得了具有SERS活性的Fe3O4@Ag磁性纳米复合材料。基于密度泛函理论(DFT)的量子化学计算方法和表面增强拉曼光谱(SERS)技术,从理论计算和实验测定表征探讨了2-噻吩甲酸(2-TCA)在Fe3O4@Ag表面的吸附行为和增强效应。结果表明:理论计算得到的拉曼光谱与实际测得的常规拉曼光谱基本一致,而在DFT理论计算中所键连的Ag原子数越多,与实测值就越接近。溶液的浓度和p H对拉曼增强效果有很大的影响,当溶液的p H=3且浓度为1×10-4mol·L-1时有最大拉曼增强效应。峰强随2-TCA浓度的增加呈现先增大后减小的趋势,浓度过大会导致大量2-TCA分子吸附聚集在Ag表面形成局部"拥堵",阻碍了激发光尤其是光谱信号的散射通过,从而减弱了拉曼增强效应。p H的变化使溶液中2-TCA分子形态发生改变,结构形态不同,其在Ag表面的吸附方式也不同。中性C4H3SCOOH分子以环上S:形式垂直吸附键合在Ag表面,形成S—Ag配位键而产生SERS光谱。-1价C4H3SCOO-离子以S—Ag配位和O—Ag共价"双键合"侧卧方式共同吸附在Ag表面而产生SERS光谱。在Ag表面,以单独S—Ag配位键吸附或键合的能力比S—Ag配位和O—Ag共价共同吸附方式要弱,但其产生的SERS信号更强,故2-TCA中性分子比2-TCA-离子更有利于SERS的产生。随着p H值的增加,溶液中的2-TCA由中性分子逐渐转化为-1价的C4H3SCOO-离子,因而在p H>3以后,拉曼增强效应逐步减弱。
Fe3O4magnetic nanoparticles were firstly synthesized by co-precipitation method,and Fe3O4@ Ag magnetic material which has improved SERS effect was further prepared by reduction of Ag NO3 using sodium citrate. Both density functional theory( DFT) and surface-enhanced Raman scattering( SERS) spectroscopy technique were used to investigate the adsorption behavior and enhancement effect of 2-thiophene carboxylic acid( 2-TCA) on the Fe3O4@ Ag surface. The results show that Raman spectra of the theoretical calculation and the determination are basically identical,and the more Ag atoms are introduced in theoretical calculation,the closer the measured value is tothe theoretical value. The concentration and p H of the solution have great influence on the Raman enhancement effect,and the solution of 1 × 10- 4mol·L- 1at p H = 3 can present excellent Raman signal response. The SERS effect increases initially and decreases afterwards with the increasing of concentration,which can be inferred that a lot of 2-TCA molecules are adsorbed and gathered on the Ag surface to form a local 'congestion'and interfere the transmission of the excitation light,especially spectroscopic signal scattering. 2-TCA molecule morphology is changed with the increasing of p H,and the adsorption mode is influenced by the molecule morphology. The neutral C4H3 SCOOH is vertically adsorbed on the Ag surface by the formation of S—Ag coordination bond. However,C4H3SCOO-anion is adsorbed on Ag surface with S—Ag coordinate bond and O—Ag covalent bond which is named as'double-bonged'side pattern. Although the adsorption of S—Ag coordinate bond is weaker than 'double-bonged'side pattern,the SERS signal is stronger,because the neutral 2-TCA molecules are more beneficial to the generation of SERS signal comparing with 2-TCA-anion.The neutral 2-TCA molecules are gradually transformed into C4H3SCOO-anion with the increasing of p H,which leads to the decreasing of SERS effect gradually after p H > 3.
出处
《发光学报》
EI
CAS
CSCD
北大核心
2015年第12期1477-1484,共8页
Chinese Journal of Luminescence
基金
浙江省公益性技术应用研究(分析测试)计划(2015C37068)
浙江省科技计划(2013C1152)资助项目
