Cation-exchanged MZSM-5 for CO₂ adsorption: interplay of interaction potential and adsorption configuration

In this study, the CO₂ adsorption behavior of ion-exchanged MZSM-5 (M = Li, Na, K, Cs, Ni and Ba) was investigated to elucidate the adsorption mechanism of CO₂ on cation sites. Among the ion-exchanged ZSM-5 samples, KZSM-5 showed the highest CO₂ adsorption capacity (2.01 mmol/g) approximately twice that of unmodified ZSM-5 (1.12 mmol/g). Fitting of the adsorption isotherms revealed that CO₂ adsorption on MZSM-5 followed the dual-site Langmuir model, with a correlation coefficient (R²) ≥ 0.9999. Further thermodynamic analysis showed that field gradient-quadrupole interactions dominating the adsorbate-adsorbent potential energy. In addition, the angle between the field gradient direction of the K⁺ site in KZSM-5 and the central axis of CO₂ was the smallest (38.1°), indicating that CO₂ adsorption at this site adopted a more favorable configuration. These findings offer a new paradigm for optimizing CO₂ adsorption, emphasizing the interplay of interaction potential and adsorption configuration in adsorbent design.