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Issue 9, 2018
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Lithium doping on 2D squaraine-bridged covalent organic polymers for enhancing adsorption properties: a theoretical study

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Abstract

Lithium modification, especially quantitative and oriented doping, is an effective way to enhance the adsorption properties of covalent organic frameworks (e.g., CO2 and H2). 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 CO2 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 CO2, the adsorption amount of CO2 in SQ-COP-Li reaches an extremely high capacity of 83.4 and 202.0 mmol g−1 at 298 K and 100 bar for 1-Li (SQ-COP-1-Li) and 3-Li (SQ-COP-3-Li), respectively. Such a high CO2 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 CO2 uptake values of 49.2 mmol g−1 of 1-Li and 61.5 mmol g−1 of 3-Li are far higher than 29.7 mmol g−1 of Li-doped COF-102 and 42.0 mmol g−1 of Li-doped COF-105. Moreover, the selectivity of CO2/H2 and CO2/CH4 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 CO2 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.

Graphical abstract: Lithium doping on 2D squaraine-bridged covalent organic polymers for enhancing adsorption properties: a theoretical study

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Publication details

The article was received on 15 Nov 2017, accepted on 31 Jan 2018 and first published on 31 Jan 2018


Article type: Paper
DOI: 10.1039/C7CP07686J
Citation: Phys. Chem. Chem. Phys., 2018,20, 6487-6499
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    Lithium doping on 2D squaraine-bridged covalent organic polymers for enhancing adsorption properties: a theoretical study

    W. Chen, L. Huang, X. Yi and A. Zheng, Phys. Chem. Chem. Phys., 2018, 20, 6487
    DOI: 10.1039/C7CP07686J

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