Exploring enthalpies of CO2 and N2 adsorption on Zn- and Co-based zeolitic frameworks at varying temperatures and pressures

• Zn/Co-ZIFs exhibit large microporous surface areas (∼2000 m²/g) and pore volumes (∼0.6 cm³/g). • CO 2 and N 2 adsorption were analyzed using Freundlich-Langmuir, Clausius-Clapeyron, and Virial models across 268–323 K and up to 3000 kPa. • ZIFs reveals higher CO 2 adsorption capacity (7 – 11 mmol/g) compared to N 2 (1–3 mmol/g). • Isosteric enthalpies for CO 2 and N 2 are -22 ± 5 and -15 ± 2 kJ/mol, respectively, indicating physisorption. • Co-ZIF shows enhanced CO 2 selectivity over N 2 compared to Zn-ZIF at lower temperatures and pressures. This study investigates the thermodynamics of CO 2 and N 2 adsorption on zeolitic imidazolate frameworks (ZIFs), focusing on the effects of metal ions under varying temperatures and pressures. Zn- and Co-based ZIFs were synthesized using 2-methylimidazole and characterized by XRD, FT-IR, Raman spectroscopy, and BET isotherms, confirming high microporosity. Gas adsorption experiments were performed at pressures up to 3000 kPa and temperatures between 268 and 323 K. The CO 2 adsorption capacities vary from 274 to 157 cm³/g, while N 2 ranged from 67 to 29 cm³/g as temperature increased. The synergistic dynamics of temperature and pressure enhanced CO 2 diffusion and induced pore structure changes via a gate-opening mechanism. Isosteric enthalpy (ΔH ads ) values, determined using Freundlich-Langmuir/Clausius-Clapeyron and virial fits, were -22 ± 5 kJ/mol for CO 2 and -15 ± 2 kJ/mol for N 2 , confirming that physisorption is the dominant mechanism. Gibbs free energy (ΔG ads ) for CO 2 ranged from -12 to -18 kJ/mol, and entropy (ΔS ads ) from -0.01 to -0.03 kJ/mol/K, suggesting spontaneous and thermodynamically favorable CO 2 adsorption, though spontaneity decreased with rising temperature. ZIFs containing Zn exhibited high CO 2 adsorption capacity, while those with Co showed better CO 2 selectivity over N 2 , highlighting their potential for efficient CO 2 capture under various temperature and pressure conditions.