Feng Mingbao, Qu Ruijuan, Wei Zhongbo, Wang Liansheng, Sun Ping, Wang Zunyao
State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, P. R. China.
Sci Rep. 2015 May 7;5:9859. doi: 10.1038/srep09859.
The thermal decomposition of Nafion N117 membrane, a typical perfluorosulfonic acid membrane that is widely used in various chemical technologies, was investigated in this study. Structural identification of thermolysis products in water and methanol was performed using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS). The fluoride release was studied using an ion-chromatography system, and the membrane thermal stability was characterized by thermogravimetric analysis. Notably, several types of perfluorinated compounds (PFCs) including perfluorocarboxylic acids were detected and identified. Based on these data, a thermolysis mechanism was proposed involving cleavage of both the polymer backbone and its side chains by attack of radical species. This is the first systematic report on the thermolysis products of Nafion by simulating its high-temperature operation and disposal process via incineration. The results of this study indicate that Nafion is a potential environmental source of PFCs, which have attracted growing interest and concern in recent years. Additionally, this study provides an analytical justification of the LC/ESI-MS/MS method for characterizing the degradation products of polymer electrolyte membranes. These identifications can substantially facilitate an understanding of their decomposition mechanisms and offer insight into the proper utilization and effective management on these membranes.
本研究对广泛应用于各种化学技术的典型全氟磺酸膜Nafion N117膜的热分解进行了研究。采用液相色谱-电喷雾电离-串联质谱法（LC/ESI-MS/MS）对水和甲醇中热解产物进行结构鉴定。使用离子色谱系统研究氟化物释放情况，通过热重分析表征膜的热稳定性。值得注意的是，检测并鉴定出了包括全氟羧酸在内的几种全氟化合物（PFCs）。基于这些数据，提出了一种热解机理，即自由基攻击导致聚合物主链及其侧链断裂。这是通过模拟Nafion的高温运行和焚烧处置过程，对其热解产物进行的首次系统性报告。本研究结果表明，Nafion是PFCs的潜在环境来源，近年来PFCs已引起越来越多的关注。此外，本研究为采用LC/ESI-MS/MS方法表征聚合物电解质膜降解产物提供了分析依据。这些鉴定结果可极大地促进对其分解机理的理解，并为这些膜的合理利用和有效管理提供见解。
