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Design and control of gas diffusion process in a nanoporous soft crystal

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Science  25 Jan 2019:
Vol. 363, Issue 6425, pp. 387-391
DOI: 10.1126/science.aar6833

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Flexibility in gas absorption

Soft materials such as porous coordination polymer (PCP) can exhibit temperature-dependent flexible motions of their internal pores that can assist in gas separation and storage. Gu et al. designed a copper-based PCP with a ligand that contains phenothiazine-5,5-dioxide. The entrances to the porous cages changed size with temperature, when these functional groups underwent flipping motions. The change in gate size could lead to high selectivity for gas absorption and enabled the separation of oxygen from argon and of ethylene from ethane as well as long-term gas storage under ambient conditions.

Science, this issue p. 387

Abstract

Design of the gas-diffusion process in a porous material is challenging because a contracted pore aperture is a prerequisite, whereas the channel traffic of guest molecules is regulated by the flexible and dynamic motions of nanochannels. Here, we present the rational design of a diffusion-regulatory system in a porous coordination polymer (PCP) in which flip-flop molecular motions within the framework structure provide kinetic gate functions that enable efficient gas separation and storage. The PCP shows substantial temperature-responsive adsorption in which the adsorbate molecules are differentiated by each gate-admission temperature, facilitating kinetics-based gas separations of oxygen/argon and ethylene/ethane with high selectivities of ~350 and ~75, respectively. Additionally, we demonstrate the long-lasting physical encapsulation of ethylene at ambient conditions, owing to strongly impeded diffusion in distinctive nanochannels.

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