Chen Wei, Huang Ling, Yi Xianfeng, Zheng Anmin
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
Phys Chem Chem Phys. 2018 Feb 28;20(9):6487-6499. doi: 10.1039/c7cp07686j.
Lithium modification, especially quantitative and oriented doping, is an effective way to enhance the adsorption properties of covalent organic frameworks (e.g., CO and H). Two-dimensional squaraine-bridged covalent organic polymers (SQ-COPs), with quantitative and oriented Li-doped open oxygen sites of the squaric-acid unit, are investigated for their CO capture properties by using first-principles calculation combined with grand canonical Monte Carlo (GCMC) simulation. It is found that owing to the strong affinity of Li atoms to the squaraine units of SQ-COPs, the gas adsorption capacity in SQ-COP-Li increased to 3 times more than those of the pristine SQ-COPs. In particular, since the Li-O bonds between squaraine units and Li atoms can enhance the electrostatic interaction between the framework and CO, the adsorption amount of CO in SQ-COP-Li reaches an extremely high capacity of 83.4 and 202.0 mmol g at 298 K and 100 bar for 1-Li (SQ-COP-1-Li) and 3-Li (SQ-COP-3-Li), respectively. Such a high CO uptake means that 3-Li outperforms the best 3D COF (COF-05) materials so far reported, and is even twice that of MOF-177 and IRMOF-10. Even at 30 bar and 298 K, the CO uptake values of 49.2 mmol g of 1-Li and 61.5 mmol g of 3-Li are far higher than 29.7 mmol g of Li-doped COF-102 and 42.0 mmol g of Li-doped COF-105. Moreover, the selectivity of CO/H and CO/CH in 1-Li reaches 19 and 5.4 at 273 K, and 10.3 and 3.6 at 298 K, respectively. Therefore, such Li-doped SQ-COPs might be an environmentally friendly candidate for high CO capture. Furthermore, the possible synthesis pathways of SQ-COP-Li are investigated, and it is indicated that the use of lithium di-isopropylamide and lithium naphthalene as dopants is energetically favorable. The findings in this work are expected to provide new ideas for metal doping and extended applications of functionalized materials.
锂修饰，特别是定量和定向掺杂，是增强共价有机框架（如CO和H）吸附性能的有效方法。通过第一性原理计算结合巨正则蒙特卡罗（GCMC）模拟，研究了具有定量和定向锂掺杂的方酸单元开放氧位点的二维方酸桥连共价有机聚合物（SQ-COPs）的CO捕获性能。研究发现，由于锂原子与SQ-COPs的方酸单元具有很强的亲和力，SQ-COP-Li中的气体吸附容量比原始SQ-COPs提高了3倍。特别是，由于方酸单元与锂原子之间的Li-O键可以增强框架与CO之间的静电相互作用，在298K和100bar下，1-Li（SQ-COP-1-Li）和3-Li（SQ-COP-3-Li）中CO的吸附量分别达到了极高的83.4和202.0mmol/g。如此高的CO吸收量意味着3-Li优于迄今为止报道的最佳3D COF（COF-05）材料，甚至是MOF-177和IRMOF-10的两倍。即使在30bar和298K下，1-Li的49.2mmol/g和3-Li的61.5mmol/g的CO吸收值也远高于锂掺杂的COF-102的29.7mmol/g和锂掺杂的COF-105的42.0mmol/g。此外，1-Li中CO/H和CO/CH的选择性在273K时分别达到19和5.4，在298K时分别达到10.3和3.6。因此，这种锂掺杂的SQ-COPs可能是一种用于高CO捕获的环境友好型候选材料。此外，还研究了SQ-COP-Li可能的合成途径，结果表明使用二异丙基氨基锂和萘锂作为掺杂剂在能量上是有利的。这项工作的发现有望为功能化材料的金属掺杂和扩展应用提供新思路。
