Denkenberger Kerri A, Bowers Ruth A, Jones A Daniel, Mueller Karl T
Department of Chemistry, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Langmuir. 2007 Aug 14;23(17):8855-60. doi: 10.1021/la7004453. Epub 2007 Jul 18.
Solid-state nuclear magnetic resonance (NMR) methods are used to follow the thermal degradation of Krytox 1506, a common perfluoropolyether, following adsorption onto the surfaces of gamma-Al2O3 and a model clay (kaolinite). The alumina studies are complemented with thermogravimetric analysis (TGA) to follow the degradation process macroscopically. Molecular-level details are revealed through 19F magic-angle spinning (MAS), 27Al MAS, and 19F --> 27Al cross-polarization MAS (CPMAS) NMR. The CPMAS results show the time-dependent formation of probable VIAl(O6 - nFn) (n = 1, 2, 3) species in which the fluorine atoms are selectively associated with octahedrally coordinated aluminum atoms. For the alumina system, the changes in peak shapes of the CP spectra over time suggest the early formation of catalytically active degradation products, which in turn lead to the formation of additional perfluoropolyether degradation products. Similar to the alumina system, the kaolinite system also displays new resonances in both the 27Al MAS and 19F --> 27Al CPMAS spectra after thermal treatment at 300 degrees C for up to 20 h but reveals a more distinct species at -15.5 ppm that forms at the expense of an initial species (3 ppm), which is in greater abundance at shorter heating times.
固态核磁共振（NMR）方法用于跟踪Krytox 1506（一种常见的全氟聚醚）在吸附到γ - Al2O3和一种模型粘土（高岭土）表面后的热降解过程。通过热重分析（TGA）对氧化铝进行研究，以从宏观上跟踪降解过程。通过19F魔角旋转（MAS）、27Al MAS和19F→27Al交叉极化MAS（CPMAS）NMR揭示分子水平的细节。CPMAS结果表明可能形成了VIAl(O6 - nFn)（n = 1, 2, 3）物种，其中氟原子选择性地与八面体配位的铝原子结合。对于氧化铝体系，CP谱峰形状随时间的变化表明早期形成了具有催化活性的降解产物，进而导致形成更多的全氟聚醚降解产物。与氧化铝体系类似，高岭土体系在300℃下热处理长达20小时后，27Al MAS和19F→27Al CPMAS谱中也出现了新的共振峰，但在-15.5 ppm处显示出一种更明显的物种，它以初始物种（3 ppm）为代价形成，初始物种在较短加热时间时丰度更高。
