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Two-Phase System Utilizing Hydrophobic Metal–Organic Frameworks (MOFs) for Photocatalytic Synthesis of Hydrogen Peroxide
Summary:
The authors from Osaka University developed hydrophobic MIL-125-Rn MOFs via post-synthetic alkylation, achieving enhanced photocatalytic H₂O₂ production and spontaneous product separation in a benzyl alcohol/water two-phase system.
Background:
1. Prior studies utilized MIL-125-NH₂ for photocatalytic H₂O₂ synthesis, yet suffered from catalyst degradation in acidic media and energy-intensive product separation.
2. This work proposes hydrophobization of MIL-125-NH₂ to confine the MOF in the organic phase, simultaneously protecting the framework and enabling phase-selective reaction chemistry.
Research Content:
1. Synthesis:
MIL-125-NH₂ was alkylated with C₄ or C₇ anhydrides (acetic, valeric, octanoic) at 80 °C in acetonitrile to yield MIL-125-Rn (n = 4, 7).
2. Characterizations:
- BET: Surface area dropped from 1500 m² g⁻¹ (pristine) to 500–560 m² g⁻¹ after alkylation.
- SEM/TEM: 200–300 nm disk-like particles retained crystallinity post-modification.
- Water contact angle: Increased from 30° to 124°, confirming hydrophobicity.
- UV-Vis: LCCT band blue-shifted slightly but visible absorption preserved.
3. Application:
Under visible light (λ > 420 nm) in BA/H₂O biphasic media, MIL-125-R7 produced 2.5 mmol L⁻¹ H₂O₂ in 3 h (vs 1 mmol L⁻¹ for pristine) while benzaldehyde remained in the BA phase; activity further doubled at pH 0.3 or in saturated NaCl.
4. Mechanism:
Photo-excited MIL-125-Rn oxidizes benzyl alcohol to benzaldehyde in the BA phase; generated O₂⁻ migrates to aqueous phase where acidic/Na⁺ conditions accelerate disproportionation to H₂O₂, spatially separated from the catalyst to suppress H₂O₂ decomposition.
Outlook:
Hydrophobic MOF engineering coupled with biphasic reaction design realizes efficient, selective and robust solar-driven H₂O₂ production, offering a blueprint for stabilizing water-sensitive photocatalysts and simplifying downstream separation.
Two-Phase System Utilizing Hydrophobic Metal–Organic Frameworks (MOFs) for Photocatalytic Synthesis of Hydrogen Peroxide
Authors: Yusuke Isaka, Yudai Kawase, Yasutaka Kuwahara, Kohsuke Mori, Hiromi Yamashita
DOI: 10.1002/anie.201901961
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.201901961
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