Yuan Yue, Dong Xiuqin, Chen Yifei, Zhang Minhua
Key Laboratory for Green Synthesis and Conversion of China Education Department, R&D Center for Petrochemical Technology, Tianjin University, Tianjin, China.
Phys Chem Chem Phys. 2016 Aug 17;18(33):23246-56. doi: 10.1039/c6cp02156e.
Iodine capture is of great environmental significance due to the high toxicity and volatility of I2. Here we conduct a systematic computational investigation of iodine adsorption in zeolitic imidazolate frameworks (ZIFs) by adopting the grand canonical Monte Carlo (GCMC) simulation and the density functional theory (DFT) method. The results confirm the vital structural factors for iodine adsorption at 298 K and moderate pressures including metal sites, organic linkers, symmetry, and topology types. The uptake will be enhanced by active metal sites, the simple imidazolate linker and single asymmetric linkers with polar functional groups. The symmetry effect is stronger than the surface properties. Meanwhile low steric hindrance is more beneficial than polar functional groups to iodine adsorption. The specific topology types like mer bringing large surface areas and large diameter cages result in high iodine capacities. Iodine molecules tend to locate in cages with large diameters and aggregates along the sides of cages. In contrast, water prefers small diameter cages. In hydrophilic materials, water has a negative impact on iodine uptake due to its similar adsorption sites to iodine. The selectivity of iodine over water increases with increasing water content due to the large diameter cages of ZIFs. This work proves that ZIFs can be identified as efficient and economical adsorbents with high diversity for iodine in a water-containing system. Furthermore, it provides comprehensive insights into key structural factors for iodine uptake and separation in silver-free porous solids.
由于碘的高毒性和挥发性，碘捕获具有重大的环境意义。在此，我们采用巨正则蒙特卡罗（GCMC）模拟和密度泛函理论（DFT）方法，对碘在沸石咪唑酯骨架（ZIFs）中的吸附进行了系统的计算研究。结果证实了在298K和中等压力下碘吸附的关键结构因素，包括金属位点、有机连接体、对称性和拓扑类型。活性金属位点、简单的咪唑酯连接体以及带有极性官能团的单不对称连接体可增强碘的吸附量。对称性效应比表面性质更强。同时，低空间位阻比极性官能团对碘吸附更有利。特定的拓扑类型，如具有大表面积和大直径笼状结构的mer，导致碘容量高。碘分子倾向于位于大直径的笼状结构中，并沿笼壁聚集。相比之下，水更喜欢小直径的笼状结构。在亲水性材料中，由于水与碘具有相似的吸附位点，水对碘的吸附有负面影响。由于ZIFs的大直径笼状结构，碘对水的选择性随着含水量的增加而增加。这项工作证明，ZIFs可被视为在含水体系中对碘具有高吸附多样性的高效且经济的吸附剂。此外，它还提供了对无银多孔固体中碘吸附和分离的关键结构因素的全面见解。
