Self-diffusion of pure and mixed gases in mixed-linker zeolitic imidazolate framework-7-8 by high field diffusion NMR
Self-diffusion of pure and mixed gases in mixed-linker zeolitic imidazolate framework-7-8 by high field diffusion NMR
复制标题
通过高场扩散核磁共振研究纯气体和混合气体在混合连接剂沸石咪唑酯骨架-7-8中的自扩散
DOI：
10.1016/j.micromeso.2019.109603
复制
发表时间：
2019
影响因子：
5.2
通讯作者：
Vasenkov, Sergey
中科院分区：
文献类型：
--
作者：
Berens, Samuel;Hillman, Febrian;Jeong, Hae-Kwon;Vasenkov, Sergey
用脉冲梯度场核磁共振技术研究了二氧化碳、甲烷、乙烯、乙烷、氙气等纯气体以及选定的两组分混合物在杂化分子筛咪唑骨架-7-8(ZIF-7-8)晶体中的自扩散行为。该材料由2-甲基咪唑(ZIF-8连接体)和较大体积的苯并咪唑(ZIF-7连接体)在同一骨架中混合而成。将在混合连接剂ZIF-7-8中测得的晶内扩散数据与母材料ZIF-8中的相应数据进行了比较。结果表明，在相同或相似的实验条件下，ZIF-7-8合金的晶内气体扩散总是比ZIF-8合金慢。这一观察结果与ZIF-7-8中预期的比ZIF-8中更小的孔径尺寸是一致的。同时，乙烷/乙烯在两种ZIF中的扩散选择性是相似的。还观察到，对于大于二氧化碳的纯研究气体，在所有加载压力下，ZIF-8和ZIF-7-8中的扩散系数比并不随气体尺寸的增加而增加。所有这些数据都归因于ZIF-7-8比ZIF-8具有更大的框架灵活性效应。由于连接体的柔韧性，在存在大的吸附剂时，这种效应表现为孔尺寸的扭曲和/或增大。
Self-diffusion of pure gases including carbon dioxide, methane, ethylene, ethane, and xenon as well as selected two-component mixtures was studied in hybrid zeolitic imidazolate framework-7-8 (ZIF-7-8) crystals using pulsed field gradient (PFG) NMR. This material was formed by mixing 2-methylimidazolate (ZIF-8 linker) and bulkier benzimidazolate (ZIF-7 linker) in the same framework. The intracrystalline diffusion data measured in mixed-linker ZIF-7-8 was compared with the corresponding data in the parent ZIF-8 material. It was found that under the same or comparable experimental conditions the intracrystalline gas diffusion was always slower in ZIF-7-8 than in ZIF-8. This observation is consistent with the expected lower pore aperture size in ZIF-7-8 than in ZIF-8. At the same time, the ethane/ethylene diffusion selectivity was found to be similar in both ZIFs. It was also observed that for the pure studied gases larger than carbon dioxide the diffusivity ratios in ZIF-8 and ZIF-7-8 do not increase with increasing gas size at all loading pressures used. All these data are attributed to greater framework flexibility effects in ZIF-7-8 than ZIF-8. Such effects manifest themselves in a distortion and/or increase in the aperture size in the presence of large sorbates due to linker flexibility.