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

Abstract

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.