Solvent-modulated and polyacrylate-confined ultramicroporous MOF nanocrystals for humidity-tolerant low-concentration CO2 capture

Structured adsorbents capable of combining strong low-pressure CO 2 affinity, high selectivity, and humidity tolerance are highly desired for low-concentration CO 2 capture, yet remain difficult to realize because shaping often compromises porosity and mass transport. Here, we report a solvent-directed and nanoconfined crystallization strategy to construct millimeter-sized polyacrylate (PA)-supported Zn 2 (Mtz) 2 Ox-EG sphere (Zn 2 (Mtz) 2 Ox-EG@PA). Ethylene glycol modulates the ultramicroporous environment of Zn 2 (Mtz) 2 Ox, enhancing its low-pressure CO 2 affinity, while the confined macroporous network of the PA matrix promotes heterogeneous nucleation and suppresses free crystal growth, sharply reducing the size of the micrometer-scale MOF bulk crystals by nearly 100-fold. The resulting Zn 2 (Mtz) 2 Ox-EG@PA composite exhibits a high CO 2 uptake for 1.68 mmol g −1 at 0.05 bar and 313 K, while N 2 and CH 4 adsorption are strongly suppressed. Consequently, high IAST selectivities of 3447 for CO 2 /N 2 and 1275 for CO 2 /CH 4 are achieved at a 5/95 gas ratio. The hydrophobic MOF framework and PA matrix endow the composite with excellent hydrothermal durability, retaining framework integrity after hot-water treatment at 403 K for 7 days. Dynamic breakthrough experiments further demonstrate efficient CO 2 /N 2 separation from a 5 vol% CO 2 stream at 90% RH, highlighting the potential of nanoconfined MOF crystallization for robust structured adsorbents under humid dilute-CO 2 conditions.