Regulating photocatalysis by external-stimuli manipulation of the microenvironment in europium–organic frameworks

Abstract

Although catalysis is highly dependent on the catalytically active site, accurately regulating the microenvironment around the active site is an important way to improve the overall performance of catalysts. Herein, an Eu-based MOF with a rod-shaped secondary building unit (SBU) was obtained through a self-assembly strategy, and named Eu-MOF-T (T = temperature). Eu-MOF-T can absolutely and kinetically transform into another structure, Eu-MOF-S (S = solvent), under a stimulus in different solvents. Interestingly, Eu-MOF-S can convert into Eu-MOF-T absolutely and thermodynamically upon temperature stimulation. These transformations are mainly caused by microenvironmental changes, including the ligand torsion angle and cavity volume in the structure, and take place in the form of single-crystal-to-single-crystal. Incredibly, Eu-MOF-S exhibits a halved cavity volume due to the bending of the ligand, yet demonstrates a superior photocatalytic CO₂RR capacity of 7886.1 μmol g⁻¹ h⁻¹, while Eu-MOF-T, which possesses a larger cavity porosity, has a capacity of only 599.7 μmol g⁻¹ h⁻¹. Theoretical calculations further reveal that Eu-MOF-S is more favorable for the formation of COOH* and promotes its further conversion into CO during the CO₂RR.