Comparative Study of Selective CO₂ Adsorption in the Presence of Moisture by UiO-66 and MIL-53(Al) Metal-Organic Frameworks Using Molecular Dynamics Simulation

This study presents a comparative molecular dynamics investigation of the CO₂ capture performance of UiO-66 and MIL-53(Al) metal-organic frameworks (MOFs) under humid flue gas conditions. Simulations across a wide range of relative humidity (0-100% RH) at 313 K reveal that UiO-66 achieves superior and stable performance, characterized by a high CO₂/H₂O selectivity of 12.5 at 50% RH, which is more than three times that of MIL-53(Al) (3.8). This advantage is fundamentally attributed to UiO-66's exceptional structural stability, which prevents framework degradation and preserves active adsorption sites in the presence of water. In contrast, MIL-53(Al) undergoes a pronounced breathing transition above 75% RH, leading to a ~35% unit cell volume collapse and a drastic reduction in CO₂ uptake capacity. Kinetic analysis further demonstrates the operational superiority of UiO-66, which reaches 90% of its equilibrium CO₂ capacity within 12 minutes, compared to over 35 minutes for MIL-53(Al). This rapid kinetics is supported by a CO₂ self-diffusivity in UiO-66 (2.1 × 10⁻⁹ m²/s) that is nearly five times higher than in MIL-53(Al). The results unequivocally identify structural hydrostability as the critical parameter for effective CO₂ capture in humid environments, establishing UiO-66 as a highly promising and robust candidate for post-combustion carbon capture technologies in real-world industrial applications.