Rapid one-pot microwave-assisted synthesis and defect engineering of UiO-66 for enhanced CO₂ capture

UiO-66 and its derivative consisting of zirconium oxide clusters and terephthalate-based linkers stand out as some of the most extensively studied metal-organic frameworks (MOFs) for various applications owing to their exceptional stability as compared with other MOFs. However, practical applications often require the rapid synthesis of highly crystalline UiO-66 and its derivatives and the facile engineering of their defects. Herein, we present the rapid formation of UiO-66 at ambient pressure under microwave irradiation. More importantly, we control the defectivity of UiO-66 simply by modulating microwave power. Lower microwave power results in more defective UiO-66, exhibiting higher textural properties than theoretical values, attributable to the concurrent increase in the linker and cluster defects in the framework. The most defective UiO-66 in this work exhibits unexpectedly high CO₂/N₂ adsorption selectivity (ca. 41), far surpassing that of all other previously reported UiO-66 (<ca. 25). Both the experimental and computational results confirm that the unusually high CO₂/N₂ selectivity of the most defective UiO-66 is likely due to the relatively high concentration of energetically favorable adsorption sites generated under microwave irradiation. Computational studies at the molecular level confirm that the unexpectedly high CO₂ heat of adsorption is due to surface heterogeneity, specifically the local distribution of defective sites with varying terminations, rather than the overall concentrations of each terminal group in the UiO-66 crystal.