Hierarchically Porous Structured Adsorbents with Ultrahigh Metal-Organic Framework Loading for CO₂ Capture

Metal-organic frameworks (MOFs) have emerged as promising candidates for CO₂ adsorption due to their ultrahigh-specific surface area and highly tunable pore-surface properties. However, their large-scale application is hindered by processing issues associated with their microcrystalline powder nature, such as dustiness, pressure drop, and poor mass transfer within packed beds. To address these challenges, shaping/structuring micron-sized polycrystalline MOF powders into millimeter-sized structured forms while preserving porosity and functionality represents an effective yet challenging approach. In this study, a facile and versatile strategy was employed to integrate moisture-stable and scalable microcrystalline MOFs (UiO-66 and ZIF-8) into a poly(acrylonitrile) matrix to fabricate readily processable, millimeter-sized hierarchically porous structured adsorbents with ultrahigh MOF loadings (∼90 wt %) for direct industrial carbon capture applications. These structured composite beads retained the physicochemical properties and separation performance of the pristine MOF crystal particles. Structured UiO-66 and ZIF-8 exhibited high specific surface areas of 1130 m² g^-1 and 1431 m² g^-1, respectively. The structured UiO-66 achieved a CO₂ adsorption capacity of 2.0 mmol g^-1 at 1 bar and a dynamic CO₂/N₂ selectivity of 17 for a CO₂/N₂ gas mixture with a 15/85 volume ratio at 25 °C. Furthermore, the structured adsorbents exhibited excellent cyclability in static and dynamic CO₂ adsorption studies, making them promising candidates for practical application.