Environmentally friendly synthesis and morphology engineering of mixed-metal MOF for outstanding CO₂ capture efficiency

Fossil fuels are a major source of energy, but they significantly contribute to CO₂ emissions, exacerbating climate change. In this study, a sustainable CO₂ adsorbent based on Mixed-Metal MOF-74 was developed using cobalt (Co) and nickel (Ni), demonstrating superior adsorption performance. To address the environmental concerns associated with conventional synthesis methods that often rely on toxic solvents and salts, a green synthesis approach was employed, utilizing environmentally friendly solvents. The synthesized material, engineered to adopt a rod-like morphology, demonstrates an enhanced surface area-to-volume ratio, thereby providing a greater number of accessible active sites for CO₂ molecules. Comprehensive characterization confirmed the porous nature of the material. Among the compositions tested, the CoNiMOF-74 (1:1) exhibited the highest CO₂ adsorption capacity, reaching 7.55 mmol/g at 25 °C and 9.36 mmol/g at 5 °C, demonstrating a strong interaction with CO₂ (isosteric heat of adsorption: 40.7 kJ/mol). The experimental data were well represented by established adsorption models, including the Hill isotherm and fractional-order kinetic models, with R² values above 0.95 for all metal compositions. Under simulated flue gas conditions, the adsorbent displayed excellent selectivity for CO₂ over N₂ (selectivity values: 25–28). DFT calculations revealed significant interaction with CO₂, with an adsorption energy of −0.25 eV, underscoring the potential of material for effective CO₂ capture. The material also demonstrated robust stability over ten adsorption–desorption cycles, indicating its suitability for industrial applications in CO₂ capture.