硫代水杨酸在银表面的化学吸附及其表面增强拉曼光谱研究

采用电化学法对Ag电极粗糙活化，进而对含巯基基团的硫代水杨酸(TSA)进行表面增强拉曼光谱(SERS)研究。研究表明，溶液浓度与pH对增强效应影响显著，1×10-3 mol·L-1与pH 4分别为增强效应的最佳浓度与酸度。浓度增大由于空间位阻等因素影响而增强效应急速下降。由TSA化学吸附所产生的S—Ag峰位基本不随pH改变;但pH对峰强度有显著影响。经对TSA在不同pH下的分布和机理研究表明，TSA是通过中性C₆H₄(COOH)SH分子中的硫醇端基脱H后与活化的Ag表面进行吸附，形成S—Ag化学键而产生SERS光谱。在较强碱性条件下负一价的C₆H₄(COO-)SH 可能与OH- 形成竞争吸附而不易产生SERS;同时吸附基团巯基对羧基振动谱峰的变化以及对苯环共轭体系中的电子云分布有很大影响。

Chemical Adsorption of Thiosalicylic Acid on Silver Surface Investigated by Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) of thiosalicylic acid (TSA) with sulfydryl group was investigated on the surface of electrochemically roughed silver electrode. The result shows that SERS enhancement effect was relative to the concentration and pH, and 1×10-3 mol·L-1 and pH 4 were the optimal condition. While the concentration increased, the enhancement effect decreased quickly because of steric hindrance. S—Ag peak position by the absorption of TSA was basically consistent, but pH significantly affected its intensity. The distribution and mechanism of TSA at different pH were further investigated. It was showed that TSA was adsorbed on the active silver surface via the sulfydryl group without H of neutral C₆H₄(COOH)SH molecule. Competitive adsorption of negative valence C₆H₄(COO-)SH and OH- may bring non-SERS under the strong base condition. At the same time, the sulfydryl group significantly influenced the carboxyl vibration peak’s change and the distribution of electron cloud of benzene ring conjugate system.