Proton mobility in sulfonic acid functionalized mesoporous materials studied by MAS PFG NMR diffusometry and impedance spectroscopy
Proton mobility in sulfonic acid functionalized mesoporous materials studied by MAS PFG NMR diffusometry and impedance spectroscopy
复制标题
通过 MAS PFG NMR 扩散测定法和阻抗谱研究磺酸功能化介孔材料中的质子迁移率
DOI：
10.1016/j.micromeso.2017.07.029
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发表时间：
2018
影响因子：
5.2
通讯作者：
J. Haase
中科院分区：
文献类型：
--
作者：
N. Dvoyashkina;C.F. Seidler;M. Wark;D. Freude;J. Haase
用阻抗谱和MAS PFG核磁共振扩散法研究了磺酸功能化介孔分子筛MCM-41、MCM-48和KIT-6中的质子迁移率。在140C时，MCM-41、MCM-48和KIT-6的质子电导率最高，分别为S−1的19倍、S的0.48倍和S的37倍。水分子在功能化的MCM-41和KIT-6中的自扩散系数小于本体水的扩散系数，而官能化的MCM-48的水分子的自扩散系数则较大。为了进行比较，我们利用能斯特-爱因斯坦方程从电导值计算了载流子的扩散系数。结果表明，对于MCM样品，核磁共振水扩散系数包含了粒子间的贡献，并且比电荷载流子扩散系数高出一个数量级。这是因为水分子在扩散观测时间(20-100ms)内的平方根位移大于介孔颗粒尺寸，对于MCM材料而言，其大小为1-4μm。相比之下，对于由高达50μm的较大颗粒组成的KIT-6，可以检测到材料颗粒内的颗粒内扩散，因为物种的平方根位移小于颗粒的大小。可以观察到核磁共振扩散系数的双组分行为，较慢的组分描述了粒子内的自扩散。观察到的粒子内核磁共振扩散系数与电荷载流子扩散系数是一致的。由此可以得出结论，核磁共振技术可以观察到氢离子或Zundel离子的载流子扩散率，而不会出现水的波动。因此，我们认为功能化介孔材料的粒内质子传导是一种无水涨落的“填充酸机制”。
The proton mobility in sulfonic acid functionalized mesoporous MCM-41, MCM-48 and KIT-6 was studied by impedance spectroscopy and MAS PFG NMR diffusometry. Highest proton conductivities were found at 140 °C as 19 S m−1, 0.48 S m−1, and 37 S m−1, for MCM-41, MCM-48 and KIT-6, respectively. The self-diffusion coefficients of water molecules in functionalized MCM-41 and KIT-6 were found to be smaller than the diffusivity of the bulk water, however, for functionalized MCM-48 they appeared to be larger. For comparison, we calculated diffusion coefficients of the charge carrier from the conductivity values by means of the Nernst-Einstein equation. It turned out that for MCM samples the NMR water diffusivity includes inter-particle contributions and succeeds the charge carrier diffusivity by some order of magnitudes. The reason is that the root-square displacement of the water molecules within the diffusion observation time (20–100 ms) is larger than the mesoporous particle size, which amounts 1–4 μm for the MCM materials. In contrast, for KIT-6 consisting of larger particles of up to 50 μm, it became possible to detect the intra-particle diffusion within the material particles, because the root-square displacement of the species is smaller than the size of the particles. A two-component behavior of the NMR diffusivity can be observed, and the slower component describes the self-diffusion within the particles. The observed intra-particle NMR diffusivity is in agreement with the charge carrier diffusivity. From this, one may conclude that the NMR technique observes the charge carrier diffusivity of hydroxonium or Zundel ions without water fluctuations. Therefore, we claim that the intra-particle proton conduction in functionalized mesoporous materials is a “packed-acid mechanism” without water fluctuation.
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DOI：
10.1039/ap9933000055
发表时间：
1993
期刊：
--
影响因子：
--
作者：
M. Holz;S. R. Heil;A. Sacco
通讯作者：
M. Holz;S. R. Heil;A. Sacco
DOI：
--
发表时间：
2016
期刊：
影响因子：
--
作者：
Christoph Seidler
通讯作者：
Christoph Seidler
DOI：
--
发表时间：
1999
期刊：
影响因子：
--
作者：
M. Spaeth;K. Kreuer;J. Maier;C. Cramer
通讯作者：
C. Cramer
207Pb NMR 检测 MAS 转子中旋转引起的温度梯度。
影响因子：
3.2
作者：
T. Mildner;H. Ernst;D. Freude
通讯作者：
D. Freude