Iron-Based Metal-Organic Frameworks (MOF) as Photocatalysts for Radical and Cationic Polymerizations under Near UV and Visible LEDs (385–405 nm)

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Summary:
The authors from IS2M-UHA, Aix-Marseille Université, and Institut Lavoisier developed iron(III)-based MOFs (MIL-53, MIL-88A/B, MIL-100, MIL-127) as photocatalysts for LED-driven radical/cationic polymerizations, achieving 58 % epoxy conversion and 37 % acrylate conversion under air or laminate conditions.

Background:
1. Previous work on photoredox initiators relied on soluble dyes or rare-metal complexes; limited stability, toxicity, and high cost remain issues.
2. The authors proposed using porous, eco-friendly iron-carboxylate MOFs combined with diphenyliodonium salt (Iod) and N-vinylcarbazole (NVK) to create efficient, visible-light-active photoinitiating systems.

Research Content:
1. Synthesis
   MIL-53, MIL-88A/B, MIL-100 (nano & micro), and MIL-127 were hydro/solvothermally synthesized with the corresponding linkers (terephthalic, fumaric, trimesic, azobenzenetetracarboxylic acids).
2. Characterizations
   1) BET: MIL-100 2400 m² g⁻¹, MIL-127 1400 m² g⁻¹; others closed porosity.
   2) SEM: particle sizes 50 nm–9 µm depending on MOF.
   3) UV–vis: broad Fe-ligand absorption 385–435 nm matching LED@385/405 nm; ESR spin-trapping confirmed Ph• and Ph-NVK• radicals.
3. Application
   Formulations MIL/Iod/NVK (0.2/2/3 wt %) were irradiated with LEDs (365/385/405 nm). Under air, MIL-53 achieved 58 % EPOX conversion (405 nm); in laminate, MIL-100 reached 37 % TMPTA conversion (405 nm).
4. Mechanism
   Photo-excited MOF reduces Iod to Ph• and oxidizes NVK to Ph-NVK•; radicals propagate polymerization while MOF is regenerated via reductive/oxidative cycles.

Outlook:
This work pioneers MOF-based photoinitiators for low-energy LED curing, opening routes to MOF-reinforced polymer composites with enhanced mechanics and sustainability.

Iron-Based Metal-Organic Frameworks (MOF) as Photocatalysts for Radical and Cationic Polymerizations under Near UV and Visible LEDs (385–405 nm)
Authors: Jing Zhang, Frederic Dumur, Patricia Horcajada, Carine Livage, Pu Xiao, Jean Pierre Fouassier, Didier Gigmes, Jacques Lalevée
DOI: 10.1002/macp.201600352
Link: https://onlinelibrary.wiley.com/doi/full/10.1002/macp.201600352

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