基于活性金电极上硫代水杨酸自组装单分子层的电化学表面增强拉曼光谱

采用原位电化学表面增强拉曼光谱(EC-SERS)研究了硫代水杨酸(TSA)吸附在活性Au电极表面的自组装单分子层(SAMs).TSA在活性Au表面的化学吸附及不同酸碱度下的TSA浸饰单层膜的SERS光谱,表明随pH值的增加,峰强呈现2个不同的下降阶段.通过EC-SERS考察不同电富集时间和电位的影响,显示在酸性介质和0.7 V及70 s富集时间下,可以获得最大EC-SERS信号,并随着电位负移,信号逐渐减弱,直至基本消失,表明TSA分子在Au表面排布状态会随外加条件的改变而发生变化.通过计算TSA在不同pH值下的分布分数以及探针分子在不同电位下的增强因子(EF),结合SERS和EC-SERS的变化走势对比,得出TSA在活性Au表面自组装形成单分子层/膜的机理,指出由于TSA不同的电化学吸附取向,以及高负电位下的还原/脱附作用,使得Au表面拉曼活性降低,造成EF显著减小,不可逆地失去了SERS的活性.

Electrochemical SERS of Self-Assembled Monolayer of Thiosalicylic Acid Adsorbed on Activated Gold Electrodes

Amonolayer film of thiosalicylic acid (TSA) adsorbed on activated gold electrodes was investigated by using in situ electrochemical surface-enhanced Raman scattering (EC-SERS). In the SERS spectra of selfassembled monolayers in solutions with different pH values, two peaks with Raman intensities that decreased with increasing pH were observed. The optimum EC-SERS signals were obtained at 0.7 V and 70 s, and it was found that the intensities became weaker, and the peaks eventually disappeared, when the potential was negatively shifted. This showed that the alignments of TSA assembled on the gold surface changed in response to changes in the external conditions. The absorption mechanism of the TSA monolayer was investigated by calculating the distribution fraction of TSA at different pH values and the enhancement factor (EF) at different potentials, using a combination of SERS and EC-SERS. As a result of different electrochemical absorption orientations of TSA and its reduction/desorption behavior at high negative potentials, the Raman enhanced effect of TSA on gold was significantly reduced and the SERS activity was irreversibly lost.