(757c) Heat-Treatment of Defective Uio-66 from Modulated Synthesis:Adsorption and Stability Studies

Metal-organic frameworks (MOFs) are well-known for their diversity in terms of pore size, geometry and functionality. Recently, defect engineering in MOFs has drawn intense research interest for both fundamental and practical reasons. However, in the area of defective MOFs, studies evaluating adsorption performance of large molecules and elucidating the influence of defect on material stability are relatively sparse. In this work, two versions of defective UiO-66 structures containing supermicropores or micro-mesopores have been prepared through a joint of modulated synthesis and post-synthetic heat treatment at 200 °C and 320 °C under vacuum, respectively. The effect of defects inside UiO-66 on guest interaction is evaluated using several molecule physisorption with different sizes, including N₂, SO₂, benzene, and cyclohexane. Gas uptake experiments as well as GCMC isotherm calculations show that the defective UiO-66 (200 °C) with the incorporation of trifluoroacetate groups displays a significant increase in large size molecules, specifically cyclohexane. In addition to adsorption properties, we also systematically studied defect concentration and its correlation with deviation in stability from pristine UiO-66 in water and acidic environments. We propose a potential degradation pathway for both pristine and defective UiO-66 upon water attack for stability analysis. Interestingly, both experimental and computational results demonstrate that the defective UiO-66 (200 °C) with the incorporation of trifluoroacetate groups displays excellent stability upon exposure to water and acidic environments.