Oxidation State Change of Cerium-based UiO-66 Architecture

Conference: 2022: 72nd ACA Annual Meeting
Ying-Pin Chen Poster Author
Darien, IL 
Tieyan Chang Additional Author
The University of Chicago
Lemont, IL 
Yu-Sheng Chen Additional Author
University of Chicago
Limont, IL 
07/30/2022: 5:30 PM - 7:30 PM
Poster Session 
Portland Marriott Downtown Waterfront 
Room: Exhibit Hall 


Over the past decade, the UiO-66 series, constructed from M6O4(OH)4 nodes (M = Zr, Hf, Th, Ti, Ce) and ditopic carboxylate linkers have aroused attention because of their great stability and diverse applications in the field of metal-organic frameworks (MOFs). Researchers discovered that not all the M-UiO-66s possess similar stimulus-responsive behaviors. The process of photo-excitation via Ligand-to-metal charge transfer (LMCT) is favorable only in the Ce-based UiO-66 crystal. Computational scientists proposed that LMCT is promoted from the empty 4f orbitals of Ce4+.
However, single-crystal X-ray diffraction and Thermogravimetric Analysis (TGA) data revealed that a significant number of missing ligands is present in our Ce-UiO-66 crystals, suggesting that the Ce6 node is likely composed of Ce4+ and Ce3+, instead of pure Ce4+. This result indicates that the performance of photo catalysis using Ce-UiO-66 will be unreliable if the oxidation state of Ce-UiO-66 is incomplete. In this work, we present a method to confirm the oxidation state using single-crystal X-ray diffraction. As a consequence, single-crystal data demonstrated that the Ce-Ce bond length of the Ce6 cluster is shrinking with air exposure time. This finding provides a facile way to rapidly judge the oxidation state of Ce-UiO-66 prior to catalysis use.