Directing the Structural Features of N2‐Phobic Nanoporous Covalent Organic Polymers for CO2 Capture and Separation |
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Authors: | Dr Hasmukh A Patel Sang Hyun Je Dr Joonho Park Prof Yousung Jung Prof Ali Coskun Prof Cafer T Yavuz |
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Institution: | 1. Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305–701 (Republic of Korea);2. Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305–701 (Republic of Korea) |
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Abstract: | A family of azo‐bridged covalent organic polymers (azo‐COPs) was synthesized through a catalyst‐free direct coupling of aromatic nitro and amine compounds under basic conditions. The azo‐COPs formed 3D nanoporous networks and exhibited surface areas up to 729.6 m2 g?1, with a CO2‐uptake capacity as high as 2.55 mmol g?1 at 273 K and 1 bar. Azo‐COPs showed remarkable CO2/N2 selectivities (95.6–165.2) at 298 K and 1 bar. Unlike any other porous material, CO2/N2 selectivities of azo‐COPs increase with rising temperature. It was found that azo‐COPs show less than expected affinity towards N2 gas, thus making the framework “N2‐phobic”, in relative terms. Our theoretical simulations indicate that the origin of this unusual behavior is associated with the larger entropic loss of N2 gas molecules upon their interaction with azo‐groups. The effect of fused aromatic rings on the CO2/N2 selectivity in azo‐COPs is also demonstrated. Increasing the π‐surface area resulted in an increase in the CO2‐philic nature of the framework, thus allowing us to reach a CO2/N2 selectivity value of 307.7 at 323 K and 1 bar, which is the highest value reported to date. Hence, it is possible to combine the concepts of “CO2‐philicity” and “N2‐phobicity” for efficient CO2 capture and separation. Isosteric heats of CO2 adsorption for azo‐COPs range from 24.8–32.1 kJ mol?1 at ambient pressure. Azo‐COPs are stable up to 350 °C in air and boiling water for a week. A promising cis/trans isomerization of azo‐COPs for switchable porosity is also demonstrated, making way for a gated CO2 uptake. |
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Keywords: | adsorption carbon dioxide gas selectivity microporous materials polymers |
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