Abstract
Photocatalytic reduction of CO2 is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)2 clusters as connecting nodes and Ru(phen)3-derived ligands as linkers is constructed to catalyze visible-light-driven CO2 reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}2 active sites, which can selectively reduce CO2 to formate in a two-electron process with a remarkable rate of 321.9 μmol h−1 mmolMOF−1. The electron transfer from Ru metalloligands to Eu(III)2 catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.
Highlights
Photocatalytic reduction of CO2 is a promising approach to achieve solar-to-chemical energy conversion
Single-crystal X-ray crystallographic study with synchrotron radiation reflected that the EuRu(phen)3−Metal-organic frameworks (MOFs) crystallize in a orthorhombic crystal system with space group of I222
There are two types of interconnected channels in the Eu-Ru3-MOF structure: one is a continuous channel along the [011] direction, with window dimensions of 15 × 20 Å, and the other one with smaller aperture is along the [111] direction (Supplementary Fig. 9)
Summary
Photocatalytic reduction of CO2 is a promising approach to achieve solar-to-chemical energy conversion. Photoexcited electron transfer from ligands to catalytic centers is observed These previous studies lead us to hypothesize that integrating Ru-polypyridine photosensitizers into Eu cluster-based MOFs will be a promising strategy to enhance the catalytic activities on CO2 reduction under visiblelight irradiation. The Eu-Ru (phen)3-MOF exhibits visible-light-driven selective CO2 photoreduction to formate with a remarkable rate of 321.9 μmol h−1 mmolMOF−1 Such a self-assembled Eu-Ru(phen)3MOF is the solitary example that exhibits a high efficiency for selective CO2 photo-reduction in the family of Ln-MOFs. Timeresolved photoluminescence (PL) spectroscopy combined with femtosecond transient optical absorption spectroscopy confirms that charge transfers from Ru photocenters to Eu-O cluster on a time scale of 1 to 300 ns. In situ electron paramagnetic resonance (EPR) study clearly indicates that after accepting of photoexcited electrons from metalloligand, the Eu(III)[2] clusters become active catalytic centers for the photoreduction of CO2
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