Enhanced CO2 Uptake in Cobalt-Based MOFs via Textural Optimization and Water-Induced Flexibility

Developing metal-organic frameworks (MOFs) that combine high CO2 uptake, ultramicroporosity, and stability under humid conditions remains a challenge for practical carbon capture. Here, a rational and optimized synthetic strategy allows to eliminate Co(OH)(2) impurities, unlocking previously inaccessible ultramicroporosity in a robust cobalt-based MOF, constructed from Co(II) nodes and the multitopic 3,6 N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (trz(2)An) linker. This protocol increases the accessible surface area of 50% while preserving a narrow pore size distribution centered at 3.6 & Aring;, critical for CO2:N-2 selectivity. Static CO2 adsorption measurements reveal uptake values of 5 and 4 mmol g(-1) at 0 and 30 degrees C, respectively. Dynamic breakthrough experiments with 5-10% CO2:N-2 mixtures demonstrate excellent separation performance and stability over 15 cycles, with mild regeneration in N-2 at room temperature. Notably, the optimized material exhibits a 24% and 46% increase in CO2 uptake at 10 and 25 degrees C, respectively, compared to the nonoptimized analogue. In addition, and notably in contrast to most CO2 adsorbents, CO2 uptake further increases under humid conditions, reaching a 65% enhancement, highlighting a beneficial role of water in the adsorption process. This increase is reasonably attributed to transient pore opening due to guest-induced linker flexibility, allowing ultramicropore accessibility without compromising structural integrity. These findings demonstrate how targeted synthetic control can activate latent porosity in rigid ultramicroporous MOFs, offering a viable pathway toward CO2 capture under realistic operating conditions.