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 one 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 the unexpectedly high CO2/N2 adsorption selectivity (ca. 41), far surpassing all other previously reported UiO-66 (< ca. 25). Both 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 work at the molecular level confirms that the unexpectedly high CO2 heat of adsorption can be attributed to the surface heterogeneity, specifically the local distribution of defective sites with different terminations.