Cerium Metal–Organic Framework for Photocatalysis

Ligand-to-metal charge transfer (LMCT) can bring about the separation of photogenerated charges. Here we calculate the electronic structures of metal-organic frameworks (MOFs) having the UiO-66 architecture and M₆O₄(OH)₄ inorganometallic nodes with M = Zr, Hf, Th, Ti, U, or Ce. We find that LMCT is favorable only in the Ce case, where it is promoted by the low-lying empty 4f orbitals of Ce⁴⁺. We therefore propose that incorporating Ce⁴⁺ into the node is an effective way to facilitate LMCT in a MOF. In addition, we show that by functionalizing the linker, it should be possible to engineer the electronic structure of the Ce-MOF for a desired reaction (e.g., water splitting) while preserving favorable LMCT. We also find that linker functionalization with electron donating or withdrawing groups allows tuning of the LMCT energy, and increasing the number of functional groups on each linker enhances the tuning; these findings are encouraging for applying Ce-MOFs for visible-response photocatalytic water splitting.