共聚焦拉曼光谱研究Mg2+和SO42-缔合平衡作用

硫酸镁溶液是一种应用很广的电解质溶液，Mg2+和SO42-缔合平衡的特征与规律一直是人们关注的热点，具有重要的现实意义。本文利用拉曼光谱法并结合高斯-洛伦兹去卷积分峰拟合程序分析了不同浓度的MgSO4溶液在不同温度下Mg2+和SO42-缔合结构特征，计算了其缔合平衡常数KR值，并对标准状态下Mg2+与SO42?离子缔合反应及其生成的接触式离子对CIP′的表观热力学参数进行了推测计算。实验结果表明：MgSO4溶液中SO42－浓度与ν1-SO42?特征峰的峰面积和峰强度之间均存在较好的线性相关关系。自由态SO42?是ν1-SO42?特征峰的主要结构。随着溶液温度的升高，1.5和2.0mol/LMgSO4溶液ν1-SO42?特征峰的峰面积和峰强度有减小的趋势，峰位发生红移，峰的对称性发生变化，其中自由态SO42?结构比例呈下降趋势，而单齿接触式离子对结构比例相应增加，双齿接触式离子对和SO42?离子团簇结构比例变化规律不明显。Mg2+和SO42-的缔合平衡随温度升高向右移动，KR值逐渐增大。在较稀MgSO4溶液中，几乎没有双齿接触式离子对和SO42?离子团簇结构，ν1-SO42?特征峰缔合结构及KR值随温度变化没有明显规律。相同温度条件下，KR值随MgSO4溶液浓度的升高呈现指数降低的趋势。

Studies on association equilibrium of Mg2+ and SO42-by confocal Raman spectroscopy

Magnesium Sulfate solution is an important electrolyte solution which is widely used in many fields. The characteristics and the association equilibrium of Mg2+ and SO42- have been the focus of attention, which has important application values. In this paper, the characteristic of ion association structure of Mg2+ and SO42- in different concentration MgSO4 solutions at different temperature were studied by Raman Spectroscopy combined with Gauss-lorentz peak fitting program. Furthermore, the ion association equilibrium constant KR of MgSO4 solutions were calculated. Furthermore, the apparent thermodynamic parameters of the associated reaction of Mg2+ and SO42? and the product of the contact ion pair CIP′under standard state were inferred. The spectra experiments results showed that the peak area and peak intensity of the ν1-SO42? characteristic peaks in MgSO4 solution were linearly associated with the concentration of SO42?. The free SO42- ion was the main structure of ν1-SO42? characteristic peaks. During the process of the temperature increasing for high concentration of 1.5mol/L and 2.0mol/L MgSO4 solution, the peak area and peak intensity of the ν1-SO42? characteristic peaks decreased, red shift phenomenon occurred in the peak position, and the symmetry of the peak changed. Accordingly, the content of free SO42- ions decreased, the chance of monodentate contact ion pairs (CIPs) increased, but the content of bidentate CIPs and SO42- groups structure changed irregularly. Likewise, the ion association equilibrium constant KR of MgSO4 solution increased which showed that the ion association equilibrium moved to the right with the temperature increasing for 1.5mol/L and 2.0mol/L MgSO4 solution, thus more CIPs generated. In dilute MgSO4 solutions, there were almost no bidentate CIPs and SO42- groups structure detected, the ion association structure of ν1-SO42? characteristic peaks and KR value changed irregularly. At the same temperature, the KR value decreased exponentially with the increasing of the concentration of MgSO4 solution.