Hierarchically Porous\nStructured Adsorbents with Ultrahigh\nMetal–Organic Framework Loading for CO<sub>2</sub> Capture

Metal–organic frameworks (MOFs) have emerged as\npromising\ncandidates for CO<sub>2</sub> adsorption due to their ultrahigh-specific\nsurface area and highly tunable pore-surface properties. However,\ntheir large-scale application is hindered by processing issues associated\nwith their microcrystalline powder nature, such as dustiness, pressure\ndrop, and poor mass transfer within packed beds. To address these\nchallenges, shaping/structuring micron-sized polycrystalline MOF powders\ninto millimeter-sized structured forms while preserving porosity and\nfunctionality represents an effective yet challenging approach. In\nthis study, a facile and versatile strategy was employed to integrate\nmoisture-stable and scalable microcrystalline MOFs (UiO-66 and ZIF-8)\ninto a poly(acrylonitrile) matrix to fabricate readily processable,\nmillimeter-sized hierarchically porous structured adsorbents with\nultrahigh MOF loadings (∼90 wt %) for direct industrial carbon\ncapture applications. These structured composite beads retained the\nphysicochemical properties and separation performance of the pristine\nMOF crystal particles. Structured UiO-66 and ZIF-8 exhibited high\nspecific surface areas of 1130 m<sup>2</sup> g<sup>–1</sup> and 1431 m<sup>2</sup> g<sup>–1</sup>, respectively. The\nstructured UiO-66 achieved a CO<sub>2</sub> adsorption capacity of\n2.0 mmol g<sup>–1</sup> at 1 bar and a dynamic CO<sub>2</sub>/N<sub>2</sub> selectivity of 17 for a CO<sub>2</sub>/N<sub>2</sub> gas mixture with a 15/85 volume ratio at 25 °C. Furthermore,\nthe structured adsorbents exhibited excellent cyclability in static\nand dynamic CO<sub>2</sub> adsorption studies, making them promising\ncandidates for practical application.