Metal‐Organic Frameworks (MOFs) recently emerged as a new platform for the realization of integrated devices for artificial photosynthesis. However, there remain few demonstrations of rational tuning of such devices for improved performance. Here, a fast molecular water oxidation catalyst working via water nucleophilic attack is integrated into the MOF MIL‐142, wherein Fe3O nodes absorb visible light, leading to charge separation. Materials are characterized by a range of structural and spectroscopic techniques. New, [Ru(tpy)(Qc)(H2O)]+(tpy = 2,2′:6′,2″‐terpyridine and Qc = 8‐quinolinecarboxylate)‐doped Fe MIL‐142 achieved a high photocurrent (1.6 × 10−3A·cm−2) in photo‐electrocatalytic water splitting at pH = 1. Unassisted photocatalytic H2evolution is also reported with Pt as the co‐catalyst (4.8 µmol g−1min−1). The high activity of this new system enables hydrogen gas capture from an easy‐to‐manufacture, scaled‐up prototype utilizing MOF deposited on FTO glass as a photoanode. These findings provide insights for the development of MOF‐based light‐driven water‐splitting assemblies utilizing a minimal amount of precious metals and Fe‐based photosensitizers.
Synthesized iron‐terephthalate metal–organic frameworks (MOFs), MIL‐101 and MOF‐235, with contrasting morphologies are examined to elucidate the role of structural arrangement in catalytic aqueous pollutant degradation. MIL‐101 demonstrates a larger pseudo‐first order rate constant than MOF‐235 (3.5 ± 0.2 molFe−1
- PAR ID:
- 10440756
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- AIChE Journal
- Volume:
- 69
- Issue:
- 12
- ISSN:
- 0001-1541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Isostructural Cr and Fe nanoporous MIL-101, synthesized without mineralizing agents, are investigated for styrene oxidation utilizing aqueous hydrogen peroxide to yield valuable oxygenates for chemical synthesis applications. Styrene conversion rates and oxygenate product distributions both depend on metal identity, as MIL-101(Fe) is more reactive for total styrene oxidation and is more pathway selective, preferring aldehyde (benzaldehyde) formation at the α-carbon to the aromatic ring, where MIL-101(Cr) sustains epoxide (styrene oxide) production at the same α-carbon. These pathways often involve hydrogen peroxide derived radical intermediates (O, –HOO˙, –HO − ˙) and metallocycle transition states. We postulate that the higher reactivity of one of these surface intermediates, Fe( iv )O relative to Cr( iv )O, leads to higher styrene oxidation rates for MIL-101(Fe), while higher electrophilicity of Cr( iii )–OOH intermediates translates to the higher styrene oxide selectivity observed for MIL-101(Cr). Secondary styrene oxide and benzaldehyde conversions are observed over both analogs, but the former is more prevalent over MIL-101(Fe) due to higher Lewis/Brønsted acid site density and strength compared to MIL-101(Cr). Recyclability experiments combined with characterization via XRD, SEM/EDXS, and FT-IR and UV-vis spectroscopies show that the nature of MIL-101(Fe) sites does not change significantly with each cycle, whereas MIL-101(Cr) suffers from metal leaching, which impacts styrene conversion rates and product distribution. Both catalysts require active site regeneration, though MIL-101(Fe) sites are more susceptible to reactivation, even under mild conditions. Finally, examination of styrene conversion for three unique synthesized phases of MIL-101(Cr) rationalizes that nodal defects are largely responsible for observed reactivity and selectivity but predispose the framework to metal leaching as a predominant deactivation mechanism.more » « less
