表面增强拉曼光谱研究银电极/乙腈界面微量水的吸附行为

Investigations on the Adsorption Behavior of Water on Ag Electrode/Acetonitrile Interface by Using Surface-enhanced Raman Spectroscopy

利用表面增强拉曼散射技术研究了含微量水的乙腈溶液中银电极 /乙腈界面水分子的吸附行为 ,详细考察了随电极电位的改变及微量水浓度对其的影响 .研究表明 ,银电极双电层中存在多种吸附模式下的水分子结构 .在较正电位下 ,水分子主要与乙腈形成弱的氢键共吸附于电极表面上 ,ν(O— H)伸缩振动出现在3 487cm- 1左右 ,一定范围内增加体相水的浓度对其影响较小 ;在较负电位下 ,随着乙腈解离反应的进行 ,水分子转为与表面配合物 [Ag(CN) n]( n- 1 ) - 作用而共吸附于电极表面 ,其有序性地增加导致 ν(O— H)频率出现在更高的波数 3 5 83 cm- 1 .增加水的浓度加强了界面水分子间的氢键作用 ,致使 ν(O— H)红移 ;在极负电位下 ,水分子发生解离 ,ν(O— H)的振动主要来自 Li OH微晶 ,其波数为 3 665 cm- 1 .随着体相水含量的增加 ,电极表面进一步形成水合 Li OH· H2 O,特征 ν(O— H)的波数为 3 5 63 cm- 1 .

The surface-enhanced Raman scattering(SERS) spectrum of the trace amount of water on the silver/acetonitrile interface was investigated as a function of the applied potential and the concentration of water. The results show that several adsorption modes of water exist in the electrochemical double layer of silver. At relatively positive potentials, the water molecule was co-adsorbed with acetonitrile through weak hydrogen bond, which was hardly affected by the increase of the concentration of water. The frequency of ν(O-H) appears at 3 487 cm -1. When the scanning potentials were negative values, the water molecule turned to interact with the surface complex (n-1)- produced by the dissociation reaction of the solvent acetonitrile. The frequency of ν(O-H) centered at ca. 3 583 cm -1 which red-shifted with the increase of the concentration of water. At more negative potentials, the hydrogen evolution reaction of water occurs seriously, and the quantity of OH - produced led to the formation of the crystallite LiOH which had the vibration of ν(O-H) locating at 3 665 cm -1. The formation of LiOH·H 2O, in which the frequency of ν(O-H) was at 3 563 cm -1, becomes possible when increasing the quantity of water to 1.0 mol/L in the bulk solution.