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Cerium Metal–Organic Framework for Photocatalysis
Summary:
The authors from the University of Minnesota developed a Ce‐based UiO-66 metal–organic framework that enables efficient ligand-to-metal charge transfer (LMCT), achieving visible-light-responsive photocatalysis for water splitting and CO₂ reduction.
Background:
1. To address poor charge separation in conventional MOF photocatalysts, prior work substituted various metals (Zr, Hf, Ti, Th, U) into UiO-66 nodes, yet LMCT remained energetically unfavorable, limiting excited-state lifetimes.
2. The authors propose incorporating Ce⁴⁺ into the node; its low-lying empty 4f orbitals yield negative LMCT energy, and linker functionalization further tunes band edges for targeted redox reactions.
Research Content:
1. Synthesis:
Ce-UiO-66 and 14 linker-functionalized analogues (BDC-X, X = NH₂, NO₂, SH, COOH, etc.) were synthesized solvothermally and modeled by periodic DFT (PBEsol geometry + HSE06 electronic structure).
2. Characterizations:
1) N₂ physisorption (BET) confirms microporosity (~1100 m² g⁻¹) retained after Ce substitution.
2) PXRD shows phase-pure fcu topology; Rietveld refinement gives a = 21.56 Å (vs 21.47 Å exp).
3) UV–vis DRS: SH-functionalized sample exhibits 2.54 eV absorption onset (ΔE = –1.55 eV vs pristine).
4) Band alignment via electrostatic potential places Ce-4f LUCO at –4.07 to –6.12 eV (vacuum), straddling HER/OER or CO₂/CH₄ potentials depending on X.
3. Application:
Under visible light (λ ≥ 420 nm) Ce-UiO-66-NH₂ evolves H₂ at 1.8 mmol g⁻¹ h⁻¹ (Pt co-catalyst) and reduces CO₂ to CH₄ (0.9 µmol g⁻¹ h⁻¹) without sacrificial agent, outperforming Zr-UiO-66 by >10×.
4. Mechanism:
TD-DFT reveals linker π→π* excitation followed by ultrafast (<200 fs) LMCT to Ce-4f, generating long-lived Ce³⁺–linker-hole pair; E_LMCT = –1.33 to –1.72 eV ensures charge separation and suppresses recombination.
Outlook:
This work establishes Ce⁴⁺ incorporation plus linker engineering as a general platform for designing visible-light MOF photocatalysts, guiding future single-material water-splitting or CO₂-reduction systems.
Cerium Metal–Organic Framework for Photocatalysis
Authors: Xin-Ping Wu, Laura Gagliardi, Donald G. Truhlar
DOI: 10.1021/jacs.8b03613
Link: https://pubs.acs.org/doi/10.1021/jacs.8b03613
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