纳米TiO2增强阴离子导电膜中碱性离子液体的稳定性研究

Study on Stabilization of Alkaline Ionic Liquids in Anion-Conducting Membranes Reinforced by Nano-TiO2

摘要:

首先，以N-甲基吡咯烷为原料，通过两步法合成碱性甲基吡咯烷离子液体（[DMPy]OH）。然后，通过物理掺杂方式在聚乙烯醇（PVA）膜基质中引入[DMPy]OH碱性离子液体和纳米二氧化钛（TiO2），最后引入戊二醛（GA）交联PVA，制得PVA-[DMPy][OH]-TiO2复合膜。利用纳米二氧化钛（Nano-TiO2）表面分布的未配位饱和的Ti4+、O2-与[DMPy]OH中阴阳离子间的自组装效应，以及戊二醛（GA）交联PVA形成半互穿结构来降低膜内碱性离子液体的流失率，增加膜内“阳离子活性点位”数量，加快OH-的迁移速率，提高电导率。借助X射线衍射(XRD)和Mapping测试证实了Nano-TiO2和[DMPy]OH间自组装作用的存在，同时对复合膜的机械性能、热稳定性能、电导率、耐碱性等指标进行测试。结果表明，该系列复合膜，形貌平整、均一；当离子液体添加量为25wt%，Nano-TiO2添加量为1wt%时，80℃下PVA-[DMPy][OH]-TiO2复合膜的电导率为2.78×10-3 S.cm-1，室温下浸渍于水中12h后，离子液体流失率为23.2%；与未添加Nano-TiO2的PVA-[DMPy][OH]膜相比，电导率提高了19.4%，离子液体流失率降幅约为34.3%；室温下，3M KOH中耐碱性测试120h后，电导率和初始值相比并无明显变化，表现出优异的耐碱稳定性。热稳定性测试结果表明，该膜分解温度高于200℃，具有良好的热稳定性。

Abstract:

A new pyrrolidonium ionic liquid ([DMPy]OH) was synthesized with 1-Methylpyrrolidine via two-step procedure. Additionally, [DMPy]OH and nano-TiO2 were introduced into the polyvinyl alcohol (PVA) as matrix by physical doping, and then glutaraldehyde (GA) was used to cross-link PVA to obtain PVA-[ DMPy] [OH]-TiO2 composite membrane. The self-assembly effect of non-coordinating Ti4+, O2- on the surface of Nano-TiO2 and anion-cation in [DMPy]OH, and the semi-interpenetrating structure formed by GA cross-linked PVA can reduce the loss rate of ionic liquid in the membrane and increase the number of \"cationic active site\", speed up OH- migration rate, increase anionic conductivity. The existence of self-assembly between Nano-TiO2 and [DMPy]OH was confirmed by X-ray diffraction (XRD) and Mapping. The mechanical properties, thermal stability, conductivity, alkali resistance, and other properties of the composite membrane were also tested. The result indicates that PVA-[DMPy]OH]-TiO2 composite membrane has uniform morphology, the introduction of Nano-TiO2 can reduce the loss rate of IL, enhance the conductivity and mechanical properties. The experiment results show that when the [DMPy]OH mass fraction were 25wt% and Nano-TiO2 were 1wt%, the conductivity is 2.78×10-3 S.cm-1 at 80℃, the ionic liquid loss rate is 23.2% at room temperature, conductivity was 19.4% higher than that without Nana-TiO2 addition, and the loss rate of ionic liquid was also greatly decreased (about 34.3%). No obvious variety in conductivity is observed for the composite membrane after immersing in 3M KOH solution at room temperature, show that membrane has excellent alkali stability. TGA shows that membrane has good thermal stability; the initiate decomposition temperature is higher than 200oC.