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

Authors: 
Xia, Q., South China University of Technology
Chen, Y., South China University of Technology
Li, Z., South China University of Technology
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.