含水离子液体/金属界面结构的SERS研究

利用表面增强拉曼光谱(SERS)研究了不同含水量下离子液体及水分子在银电极上随电位变化吸附方式的改变,通过水的O-H伸缩振动谱峰频率变化特征,详细探究了水在离子液体/电极界面上的存在形式及作用方式以及体系零电荷电位与水含量的关系.水含量较低时O-H伸缩振动的Stark系数值较低,随水含量的增加O-H伸缩振动的谱峰位置逐渐向高波数方向移动,同时O-H伸缩振动的Stark系数也逐渐增大,1molL-1BMIM]Br水溶液中达到76cm-1V-1,且体系的零电荷电位正移,这些差异与水在离子液体中所形成氢键的程度及水分子的存在形式密切相关,在水的含量较低时水与离子液体阳离子通过氢键作用而存在于界面层中,当水的含量增加时,水分子间氢键的作用增强,水与电极表面直接作用的可能性增大.

Structure of water at ionic liquid/Ag interface probed by surface enhanced Raman spectroscopy

The potential dependent adsorption behavior of water and ionic liquid was probed by surface-enhanced Raman spectroscopy （SERS） at Ag electrode surface in the ionic liquids containing water with different concentration. The configuration of water at ionic liquid/electrode interface and the relationship between the potential of zero charge （pzc） and the molar fraction of water was deduced through the changes in the vibrational frequency of OH stretching mode. Small Stark effect value was determined in the system with lower molar fraction of water. With the increase of the water concentration,the OH stretching vibrational frequency gradually shift to the high wavenumber region,the pzc was also moved positively and the Stark effect value of OH stretching vibrational mode increased. It reached to about 76 cm^-1/V in the 1 mol dm^-3 BMIM] Br aqueous solution. These differences were mainly contributed by hydrogen bonding and the configuration of water in the ionic liquid solution. In solution with lower water content,water molecules existed at the interface layer through hydrogen bonding with cation,while in higher content solution,the intermolecular hydrogen bonding between water molecules was strengthened and the possibility of the direct interaction between the water molecule and electrode surface increased.