Cost-effective microwave-assisted synthesis of diatomite-supported MOF-74 for CO2 capture toward potential net-negative emissions

Green microwave-assisted synthesis of composite using methanol/water. • Natural diatomite support reduces cost and suppresses MOF-74(Ni) aggregation. • DRIFTS and Molecular Simulation reveal CO 2 binding at unsaturated Ni 2+ sites. • Life cycle assessment indicates potential net-negative CO₂ emissions. Developing cost-effective and efficient adsorbents is essential for practical CO 2 capture. Herein, a hierarchical MOF-74(Ni)/diatomite composite is prepared via a microwave-assisted in situ growth strategy, using natural diatomite as a low-cost porous support and a methanol/water system as a relatively benign solvent medium. Rapid crystallization is achieved at 100 °C within 20 min, providing an energy-efficient route for constructing mineral-supported MOF adsorbents. Structural characterization confirms the uniform anchoring of MOF-74(Ni) crystals on the porous diatomite scaffold without compromising the intrinsic crystallinity of the framework. The diatomite scaffold not only promotes the dispersion of MOF-74(Ni) but also constructs interconnected micro-/ meso -/macroporous transport channels, thereby enhancing gas diffusion and mass transfer. The optimized composite delivers a CO 2 uptake of 4.86 mmol·g −1 at 298 K and 1 bar, an IAST-predicted CO 2 /N 2 selectivity of 76, and a dynamic CO 2 capacity of 4.37 mmol·g −1 . It also retains over 97% of its initial capacity after 50 adsorption–desorption cycles and exhibits stable CO 2 uptake under humid and multicomponent simulated flue gas conditions. In situ DRIFTS and molecular simulations reveal that CO 2 adsorption occurs primarily at coordinatively unsaturated Ni 2+ sites through electrostatic interactions and weak coordination. ZLC analysis further confirms enhanced intraparticle diffusion and improved CO 2 desorption kinetics in the composite. Life cycle assessment estimates emissions of 308 kg CO 2 -eq per ton of CO 2 captured, indicating the potential for net-negative emissions and highlighting the promise of mineral-supported MOF adsorbents for sustainable carbon capture. Download: Download high-res image (307KB) Download: Download full-size image