Enhancement of aqueous stability of NH2-MIL-101(Fe) by hydrophobic grafting post-synthetic modification.

The development of water-stable metal-organic frameworks is a critical issue for their photocatalysis applications in water treatment. A phenyl-ethyl side chain with low surface energy was grafted into NH2-MIL-101(Fe) through a post-synthetic modification (PSM) method. As a result, a novel MIL-101(Fe)-1-(4-(ethyl)phenyl)urea (named MIL-101(Fe)-EPU) was synthesized. Basic morphology, crystal structure, and chemical bond features of MIL-101(Fe)-EPU were retained after PSM. Nitrogen X-ray photoelectron spectroscopy analysis confirmed the successful introduction of the phenyl-ethyl side chain, and this transformation increased its hydrophobicity and water stability. Contact angles of MIL-101(Fe)-EPU to water raised from 59.6 to 140.4°. And its structure maintained intact after 72 h water exposure, indicating higher stability than parent NH2-MIL-101(Fe). In the photocatalysis reaction with visible light and oxidant donor (H2O2), MIL-101(Fe)-EPU demonstrated a degradation efficiency of tetrabromobisphenol A with a reaction rate at 0.0313 min-1. The predominant reaction mechanism was OH·oxidation. The acid condition was beneficial for this photocatalysis reaction and high stability was observed. Besides, photocatalysis efficiency, crystal structure, and chemical structures were all retained in different actual water mediums, suggesting high adaptability of MIL-101(Fe)-EPU. In general, hydrophobic group grafting using a PSM method endows MIL-101(Fe)-EPU the potentiality as photocatalyst for organic contaminant elimination from water.