Extra Unsaturated Metal Centers of Zirconium-Based MOFs: a Facile Approach towards Increasing CO₂ Uptake Capacity at Low Pressure

Developing adsorption materials to capture CO₂ at low pressure has attracted great attention due to the low CO₂ partial pressure in fuel gases. Herein, zirconium-based metal–organic frameworks (PCN-X) are successfully synthesized and open metal sites (Fe³⁺ and Al³⁺) are incorporated into the PCN-X MOFs. The results indicate that the CO₂ adsorption capability is enhanced through the strong interaction between extra open metal centers and CO₂ molecules at low pressure. Meanwhile, the CO₂ adsorption capacity of PCN-X with incorporated Al³⁺ is higher than with incorporated Fe³⁺, which can be attributed to the higher isosteric heat of CO₂ adsorption. The adsorption kinetics further indicate the faster CO₂ transmission on PCN-X with extra Al³⁺ than with extra Fe³⁺. Besides, modified PCN-X, treated by some inorganic acids, exhibits favorable chemical stability, which is suitable for CO₂ capture from acidic fuel gases.