Squarate-Calcium Metal–Organic Framework for Molecular Sieving of CO₂ from Flue Gas with High Water Vapor Resistance

Abstract

While molecular sieving is a desirable approach for extracting CO2 from flue gas, water vapor in the flue gas often poses significant difficulty in this separation process. To tackle this challenge, we targeted a squarate-calcium metal–organic framework with strong water stability, Ca­(C4O4)­(H2O), for its pore diameter was in the middle of the kinetic diameters of CO2 and N2. Ca­(C4O4)­(H2O) exhibited excellent separation performance for CO2/N2 (15/85 vol) with adsorption selectivity values of 73 at 1 bar and 298 K. This efficient separation was further confirmed by multicomponent breakthrough experiments. Additionally, Ca­(C4O4)­(H2O) showed strong interaction with CO2 based on the very high isosteric heat of 47.7 kJ/mol. The strong affinity between CO2 and Ca­(C4O4)­(H2O) was further explained with density functional theory calculations, which exhibited that CO2 was bound tightly via hydrogen bonds between the oxygen atoms in CO2 and the hydrogen atoms in H2O, as well as π–π interactions between CO2 and the aromatic ligand in the framework. Furthermore, the cyclic adsorption/regeneration experiments under 100% relative humidity, 15 vol % CO2, and balance N2 demonstrated that Ca­(C4O4)­(H2O) is a promising adsorbent for CO2 removal in practical applications due to its excellent tolerance to water vapor and recyclability.

Toward sustainable syntheses of Ca-based MOFs

“…CO2 gas adsorption experiments measured at 298 K of Ca(SQ)(H2O) synthesised from egg shells under aqueous conditions and via ball-milling of commercial calcite had uptake capacities in the range 2.0 -2.5 mmol/g at 1 bar (fig. S20), which is comparable to those reported by Tu and Zhang et al 28 Calcium carbonate and fumaric acid were reacted under the same milling condition with deionised water (20 μL). PXRD (fig.…”

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“…Metal-containing nodes are connected by organic ligand bridges to create metal organic frameworks (MOFs), which are formed by powerful coordination bonds and are a current area of study in crystalline porous materials. , The MOF can be prepared from metal ions or clusters using organic linkers via self-assembly under favorable synthesis conditions, as shown in Figure a. The process parameters (temperature, pressure, and reaction time) and compositional parameters (concentration of metal ions/organic ligands, pH, and solvent) are crucial to the ostracized adsorption properties of MOFs (Figure a) .…”

Recent Advances in the Development of Metal–Organic Frameworks for Propylene and Propane Separation

“…Among all separation mechanisms, molecular sieving is an ideal approach that can achieve high selectivity by allowing only the target component to enter the pore space while rejecting others based on molecular size or shape cutoffs. , However, the highly similar molecular structures of C 3 H 6 and C 3 H 8 add very strict demands on the precise tuning of pore size and shape. To date, only a handful of sieving materials have been reported.…”