Fabrication of MIL-101(Cr/Al) with flower-like morphology and its catalytic performance

The morphology and structure of metal organic frameworks (MOFs) are closely related to their properties. Herein, a flower-like morphology MOF (named as MIL-101(Cr/Al)A-f) was rationally designed in a acid-free environment and the Al3+ was transformed into the framework by the substitution process of cation exchange. During the preparation process of MIL-101(Cr/Al)A-f, we found that the acidity of the reaction mixture could regulate the morphology of MIL-101(Cr/Al)A-f by adjusting the coordination of the metal clusters and the ligand chains. The catalytic performance of MIL-101(Cr/Al)A-f was evaluated by the hydroxyalkylation of phenol with formaldehyde. Due to the larger surface area and high-density sites, MIL-101(Cr/Al)A-f showed a higher catalytic activity than the octahedron morphology MIL-101(Cr/Al)A-0.5 which was prepared with traditional method in acidic environment. In approximately equal Al3+ content, the MIL-101(Cr/Al)A-f showed a remarkably high yield (97.1%) and a excellent selectivity (98.3%) to bisphenol F at 60 °C for 30 min. Finally, a possible mechanism for the synthesis of bisphenol F was proposed and the hydroxyalkylation of phenol with formaldehyde to bisphenol F was fitted by the Langmuir-Hinshelwood kinetic model.