Low-pressure-RF plasma modification of UiO-66 and its application in methylene blue adsorption

Defect engineering of metal-organic frameworks has attracted increasing attention in recent years for potential applications in gas storage and catalysis. In this study, defective UiO-66 is obtained by Ar and H₂ plasma treatments. Compared with the pristine UiO-66, a new aperture with a size of ~4 nm appears for a sample with the plasma modification, indicating the formation of mesopores within UiO-66 framework. Characterization results demonstrate that the pore volume, surface area and the number of Lewis and Brönsted acid sites can be easily tuned by varying the discharge parameters. The adsorption performance of UiO-66 is evaluated for the adsorption of methyl blue. In comparison to the pristine UiO-66 and the sample with H₂ plasma treatment, the Ar plasma modified sample shows excellent adsorption activity due to the suitable pore size and volume. Equilibrium adsorption capacity as high as 40.6 mg·g^-1 is achieved for the UiO-66 (Ar) sample.