1 research outputs found
Enhancement of CO<sub>2</sub> Uptake and Selectivity in a Metal–Organic Framework by the Incorporation of Thiophene Functionality
The complex [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco] (H<sub>2</sub>tdc = thiophene-2,5-dicarboxylic
acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase
in carbon dioxide (CO<sub>2</sub>) uptake and CO<sub>2</sub>/dinitrogen
(N<sub>2</sub>) selectivity compared to the nonthiophene analogue
[Zn<sub>2</sub>(bdc)<sub>2</sub>dabco] (H<sub>2</sub>bdc = benzene-1,4-dicarboxylic
acid; terephthalic acid). CO<sub>2</sub> adsorption at 1 bar for [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco] is 67.4 cm<sup>3</sup>·g<sup>–1</sup> (13.2 wt %) at 298 K and 153 cm<sup>3</sup>·g<sup>–1</sup> (30.0 wt %) at 273 K. For [Zn<sub>2</sub>(bdc)<sub>2</sub>dabco], the equivalent values are 46 cm<sup>3</sup>·g<sup>–1</sup> (9.0 wt %) and 122 cm<sup>3</sup>·g<sup>–1</sup> (23.9 wt %), respectively. The isosteric heat of adsorption for
CO<sub>2</sub> in [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco] at zero coverage
is low (23.65 kJ·mol<sup>–1</sup>), ensuring facile regeneration
of the porous material. Enhancement by the thiophene group on the
separation of CO<sub>2</sub>/N<sub>2</sub> gas mixtures has been confirmed
by both ideal adsorbate solution theory calculations and dynamic breakthrough
experiments. The preferred binding sites of adsorbed CO<sub>2</sub> in [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco] have been unambiguously
determined by in situ single-crystal diffraction studies on CO<sub>2</sub>-loaded [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco], coupled with
quantum-chemical calculations. These studies unveil the role of the
thiophene moieties in the specific CO<sub>2</sub> binding via an induced
dipole interaction between CO<sub>2</sub> and the sulfur center, confirming
that an enhanced CO<sub>2</sub> capacity in [Zn<sub>2</sub>(tdc)<sub>2</sub>dabco] is achieved without the presence of open metal sites.
The experimental data and theoretical insight suggest a viable strategy
for improvement of the adsorption properties of already known materials
through the incorporation of sulfur-based heterocycles within their
porous structures