Abstract
A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.
Highlights
The current energy crisis produced by the imminent depletion of non-renewable energy sources has prompted the scientific community to carry out numerous investigations with the aim of finding inexhaustible and environmentally friendly alternative energy forms [1,2,3]
It was efficiently anchored onto EthanePMO via a grafting procedure, obtaining the EthanePMO@NCOFeFe material with an iron loading of 0.235 mmol Fe/g periodic mesoporous organosilica (PMO)
The photocatalytic hydrogen production system was adequately optimized in the homogeneous phase using the FeFeOH complex as the catalyst, [Ru(bpy)3 ]2+ as the photosensitizer, and ascorbic acid as the electron donor in a water/acetonitrile mixture (11.8 vol%)
Summary
The current energy crisis produced by the imminent depletion of non-renewable energy sources has prompted the scientific community to carry out numerous investigations with the aim of finding inexhaustible and environmentally friendly alternative energy forms [1,2,3]. In this area, solar energy applied to the chemical decomposition of an abundant substrate such as water is constantly on the rise as a key strategy for obtaining hydrogen [4,5,6,7,8]. Regarding [2Fe2S] active sites, the structural modifications through ligand replacement in the first coordination sphere or incorporation of functionalities via the dithiolate-bridged group in the second coordination sphere have provided some interesting characteristics to the diiron complex
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