Metal doping in cerium metal-organic frameworks for visible-response water splitting photocatalysts

Cerium metal-organic frameworks (Ce-MOFs) show great promise for photocatalytic water splitting as they have low-lying unoccupied 4f orbitals with energies lower than the unoccupied linker orbitals to drive the ligand-to-metal charge transfer (LMCT) of the photo-generated electron at the linker to separate the photo-excited charges. Nevertheless, the large and negative LMCT energies of Ce-MOFs are often accompanied by high photon-absorption energies, which then limit the application of Ce-MOFs as visible-light-driven water splitting photocatalysts. In this work, we propose that metal (Zr or Ti) doping can raise the very negative LMCT energies of Ce-MOFs, consequently leading to the decrease of the absorption energy and promoting the response of Ce-MOFs to visible light. By functionalizing the linker of the mixed-metal MOFs, we found two possible visible-response photocatalysts for water splitting using a single photocatalyst.