Predicting flue gas component adsorption in CALF-20: A molecular dynamics study anchored by experimental CO2 capture

This study investigates the efficacy of the zinc-triazole-oxalate-based metal-organic framework (MOF), CALF-20, for carbon dioxide (CO2) capture, combining experimental analysis and molecular dynamics (MD) simulations. The CALF-20 adsorbent was successfully synthesized and characterized using XRD, FTIR, FESEM, and N2 adsorption-desorption techniques, confirming its crystalline structure, chemical integrity, and mesoporous nature. Experimental adsorption studies at temperatures and pressures revealed a CO2 uptake of approximately 4.72 mmol/g at 298 K and 1 bar. Isotherm and kinetic modeling indicated that adsorption is well described by the Freundlich and fractional-order kinetic models, suggesting a complex mechanism on a heterogeneous surface. Thermodynamic analysis confirmed the process is spontaneous and exothermic (ΔH° = −10.024 kJ/mol), characteristic of physisorption. MD simulations used the DREIDING force field in LAMMPS for the CALF-20 framework and single-component (CO2, N2), binary (CO2N2), and ternary (CO2N2H2O) simulations. Complementary ternary simulations in RASPA used DREIDING for CO2 and N2, but employed the TIP4P water model for H2O to improve the accuracy of water-adsorption predictions (hydrogen bonding and electrostatics). These simulations confirmed CALF-20′s higher affinity for CO2 than for N2 and provided mechanistic insight into moisture effects—competitive H2O uptake that modestly reduces CO2 adsorption at higher pressures, while overall CO2 selectivity is preserved. IAST-predicted selectivity for a CO2N2 mixture (12.5:87.5 %) reached ∼140 at 298 K and 0.1 bar. CALF-20 also exhibited excellent cyclic stability, with negligible loss in capacity over 10 adsorption-desorption cycles. These integrated findings underscore the potential of CALF-20 as a robust, selective, and reusable adsorbent for post-combustion CO2 capture applications.