CO2 adsorption on alpha-CALF-20 using Monte Carlo simulation

Efficient carbon capture is important for reducing greenhouse gas emissions. Among adsorbents, nanoporous materials, such as metal-organic frameworks, have shown considerable potential. In this work, we investigated the adsorption isotherms of CO2 on alpha-CALF-20 using Grand-Canonical Monte Carlo simulations. The RASPA 2.0 software was used for the simulations, modeling CO2 molecules with a transferable force field, and a rigid framework. Two force fields, the Universal Force Field and DREIDING, were used to describe guest-host interactions, with the objective of exploring their influence on predicted adsorption behavior. Atomic framework charges were assigned using the REPEAT method. The results showed that the force field influences the adsorption capacity, but not the shape of the isotherms. Quantitatively, DREIDING force field predicted a maximum uptake of approximately 5.1 mmol/g at 1 bar and 273 K; Universal Force Field estimated an uptake of about 4.8 mmol/g at the same conditions. A similar trend was observed in other isotherms, indicating consistent differences between the two force fields. Both force fields reproduced the expected Type I isotherm behavior, characteristic of nanoporous materials, with minor differences observed in adsorption strength and framework-adsorbate interactions. These findings emphasize the need for careful selection of force fields to improve the quantitative agreement with experimental data, which is essential for a reliable prediction of adsorption capacities in practical applications.