Dual-metal strategy in sodium-cadmium MOFs: Achieving excellent CO2 uptake and long-term stability

초록

A major challenge in post-combustion carbon capture is creating MOFs that achieve high CO2 capture efficiency while being recyclable and stable in real-world operating conditions. In this study, we implemented a dual-metal strategy in the Sodium Cd MOF by substituting Cd2+ with Cu2+ or Ca2+ via rapid microwave irradiation, eliminating the need for extended solvent-exchange processes. While managing cadmium-based frameworks requires caution, this system serves as a high-precision model for developing a methodological blueprint for bimetallic site modulation. Optimized Sodium (Cd, Cu)-2 and Sodium (Cd, Ca)-2 variants achieved CO2 capacities of 2.35 and 2.60 mmol/g (15 kPa, 298 K) with IAST selectivities of 852 and 892, respectively, significantly outperforming the pristine MOF (1.77 mmol/g; 781). To establish robust validation boundaries, the performance of the lead material, Sodium (Cd, Ca)-2, was verified by a Henry's Law selectivity of 110 and an experimental breakthrough selectivity of similar to 312. These tiered metrics confirm a significant separation advantage under both theoretical and practical conditions. This improvement results from substituting Cd with Cu2+ and Ca2+ ions, which modify the surface electronic environment and generate extra adsorption sites. These results were further supported by improved porosity and strengthened CO2-MOF interactions, as evidenced by in situ DRIFTS and isosteric heat of adsorption. The designed materials retained > 94% of their initial adsorption capacity over 100 adsorption-desorption cycles and after 30 days of exposure to a humid environment. Moreover, excellent adsorption capacities under realistic flue-gas concentrations (both dry and humid) highlight a robust balance between adsorption performance and hydrolytic stability.

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