Synthesized structure of Mg-MOF-74 decorated on ZIF-8 as solid adsorbent for CO2 capture

• A hierarchical ZIF-8/Mg-MOF-74 composites was successfully synthesized for effective CO₂ capture in flue gas and direct air. • ZIF-8/Mg-MOF-74 composites remains efficient and excellent reusability for CO₂ capture after 5 cycles. • Tunable design of ZIF-8/Mg-MOF-74 composites enable optimization for sustainable carbon capture technologies. In this study, a ZIF-8/Mg-MOF-74 composite was synthesized using a simple post-modification method. Mg-MOF-74 was grown directly on ZIF-8, forming a hierarchical structure that combines molecular sieving and enhanced adsorption capabilities. The Mg-MOF-74 outer layer, rich in open metal sites (OMS), enables strong CO 2 interactions. The optimized composite, prepared with a Mg 2+ /H 4 dhtp molar ratio of 1:1, exhibited a remarkable surface area of 823.61 m²/g and a pore volume of 0.76 cm 3 /g. It achieved exceptional CO 2 capture, with 4.09 mmol/g in 12 % CO 2 (simulated flue gas) and 0.066 mmol/g from ambient air at 30 °C and 60 % relative humidity. These findings demonstrate the efficacy of simple synthesis techniques in enhancing MOF-based CO 2 capture. This work emphasizes the potential of integrating MOFs for efficient CO 2 adsorption, offering promising strategies to address carbon emissions and environmental challenges.