(687g) Moisture-Enhanced Feature for Potential CO2 Capture Under Humid Conditions within Microporous PCN-250 Frameworks

Developing metal-organic frameworks (MOFs) with moisture-resistant feature or moisture-enhanced adsorption for the practical applications of CO₂ capture remains a challenge. In this work, we investigate the CO₂ adsorption behavior of two iron-based MOFs materials under humid conditions, PCN-250(Fe₃) and PCN-250(Fe₂Co). An interesting and unusual adsorption behavior is observed that the two materials demonstrate an unusual moisture-enhanced adsorption of CO₂. H₂O molecule eccentrically induces a remarkable increase in CO₂ uptake of the MOFs for the dynamic CO₂ capture from CO₂/N₂ (15: 85) mixture. For PCN-250(Fe₃), its CO₂ adsorption capacity increases by 54% under wet conditions (50% RH) in comparison with that under dry conditions (from 1.18 mmol/g to 1.82 mmol/g). Similarly, PCN-250(Fe₂Co) also exhibits an increase of 69% in CO₂ adsorption capacity, from 1.32 mmol/g to 2.23 mmol/g. Even under the conditions of 90% RH, the CO₂ adsorption capacities of PCN-250(Fe₃) and PCN-250(Fe₂Co) still have increase of 43.7% and 70.2% in comparison of dry conditions, respectively. Molecular simulations indicate that the hydroxyl functional groups (μ-OH) within the framework play a determined role in improving CO₂ uptake in the presence of water vapor. Furthermore, partial substitution of Fe³⁺ by Co²⁺ ions in the PCN-250 framework leads to a significant improvement in CO₂ adsorption capacity and selectivity. These combinational properties including excellent moisture stability (stable in exposing 90% RH humid air for 30 days), superior recyclability and moisture-enhanced feature make PCN-250 materials one of the best adsorbent materials for CO₂ capture under humid conditions. This study provides a new paradigm that the PCN-250 frameworks can not only be moisture-resistant but also subtly convert the common detrimental impact of moisture into a positive impact on improving CO₂ capture performance.