Hierarchical Porous Zr-Based MOFs Synthesized by a Facile Monocarboxylic Acid Etching Strategy

A new monocarboxylic acid etching (MAE) strategy was developed for transforming chemically stable Zr-based metal-organic frameworks (MOFs) of UiO-66 to their hierarchical porous counterpart. The key design element was based on the incomplete replacement of bridging ligands in MOFs by monocarboxylic acids (MAs), leading to the departure of partial ligands and metal clusters to create mesopores in MOFs. A series of MAs with different acidity and carbon chain length were tested, and propionic acid (PA) was screened to be the suitable choice. The textural features including pore size distribution, specific surface area, and pore volume of the obtained products can be controlled by adjusting the MA concentration and reaction temperature. The obtained hierarchical porous MOFs inherited excellent stability from their parent materials. Additionally, the MAE strategy was universal to construct hierarchical porous Zr-based MOFs, and it was expanded to etch UiO-66 derivatives. The excellent adsorption behavior of the resultant hierarchical porous Zr-based MOFs over two enzymes with different size was also successfully exemplified, demonstrating their application potentials with bulky molecules involved.