Improved hydrolytic robustness and catalytic performance of flexible lanthanide-based metal-organic frameworks: A matter of coordination environments

Abstract

Due to the flexible structures and vulnerable coordination bonds, hydrolytic stability of metal-organic frameworks (MOFs) is a critical issue for practical use. Besides the collapse of MOF structures by water intrusion, herein, we found that phase transformation among MOF isomers (viz., t-Ln-BTC, m-Ln-BTC, and c-Ln-BTC) can be triggered by water/organic solvent soaking. In isostructural Ln-BTC, different Ln cations (Ce3+, Y3+, or their combination) affected the hydrolytic robustness of the frameworks by altering the bonding strength of Ln-O. In addition, the Ln-BTC isomers can serve as host materials to immobilize AuPd alloy nanoparticles for the catalytic benzyl alcohol oxidation reaction in aqueous solution, wherein, the catalytic performance increased in the order of m-Ln-BTC/Au-Pd < c-Ln-BTC/Au-Pd < t-Ln-BTC/Au-Pd. Nevertheless, the poor recyclability of t-Ln-BTC/Au-Pd was caused by the phase transformation of t-Ln-BTC to less porous m-Ln-BTC during the catalytic reaction. Strikingly, the hydrolytic robustness and catalytic recyclability of c-Y-BTC/Au-Pd were even better than the carbon-coating samples using thermal treatment (a routine strategy reported in the literature). Our results have demonstrated that the coordination environments between lanthanide ions and ligands have a significant effect on the structural stability, which can prevent the attack of water molecules and consequently protect the constituent metal-ligand bonds.