亚甲基蓝在胶体银表面的吸附——表面增强拉曼光谱和密度泛函理论计算  

Adsorption of Methylene Blue on Colloidal Silver—A Surface-Enhanced Raman Spectroscopy Study Combined with Density Functional Theory Calculations

作　　者：钟亮[1] 胡勇军[1] 邢达[1] 谷怀民[1] 

机构地区：[1]华南师范大学激光生命科学研究所教育部重点实验室,广东广州510631

出　　处：《光谱学与光谱分析》2010年第1期90-94,共5页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金面上项目(30870676);广东省自然科学基金项目(7117865;07005823);华南师范大学激光生命科学研究所教育部重点实验室开放课题基金资助

摘　　要：获得了不同浓度下亚甲基蓝(methylene blue,MB)溶液在银溶胶中的表面增强拉曼光谱。结果表明:亚甲基蓝分子与银纳米粒子高浓度下物理吸附为主,低浓度下化学吸附为主;不同浓度下存在不同的吸附取向,即高浓度下为"直立"取向,低浓度为"平躺"取向。通过观察低浓度下MB在银胶中吸附时间对谱图的影响,得知低浓度下吸附取向不随时间发生变化。应用密度泛函(DFT)方法在B3LYP/6-31+G~*和LANL2DZ基组水平上对亚甲基蓝阳离子(MB^+)及MB^+与Ag原子形成的不同构型体系进行了结构优化和频率计算。实验与理论计算结果表明,MB^+有可能通过N—Ag和S—Ag与Ag原子形成两种较强的吸附构型。电荷布居分析表明,与S原子相比,芳香环上的N原子更易与Ag发生相互作用。还对实验观察到的部分谱峰及它们的振动模式作出了初步归属和讨论。Surface-enhanced Raman spectra of methylene blue （MB） at different concentrations in silver colloid were obtained. The results indicate that the physical adsorption is dominant at high concentration while the chemical adsorption is the main fashion at relatively low concentration; there are different adsorption orientations at different concentration： MB^＋ molecule is perpen dicular to the surface of silver nanoparticle at high concentration and adopts a parallel orientation on the surface of nanoparticle atlow concentration. The effect of adsorbing time of MB molecule in Ag colloid was investigated and the adsorption dynamics study shows that the parallel orientation at low concentration does not change with the adsorbing time increasing. Density functional theory （DFT） calculations at the level of B3LYP/6-311＋G ^＊ （for C, S, N, H）/LANL2DZ （for Ag） were employed to optimize the structures and predict Raman frequencies of MB^＋ and various MB^＋-Ag complexes. The results of experiments and calcula-tions suggest that the silver atom prefers to be bound to N and S atoms in the aromatic ring, and thus two different complexes are formed, i.e. conformer N-Ag and conformer S-Ag. Moreover, the Mulliken charge population analysis indicates that N atom in the aromatic ring prefers to interact with Ag than S atom does. Finally, the Raman frequencies observed in the experiments and their vibrational modes were tentatively assigned and discussed.

关 键 词：亚甲基蓝 表面增强拉曼散射 密度泛函理论 吸附取向 

分 类 号：O657.3[理学—分析化学]