Page 9 - Shimadzu Journal vol.4 Issue1

New Energy

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OER specie of fac-[Re(bpy)(CO) 3 (MeCN)] desorbs monodentate
ligands readily. In contrast, the OER specie of
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fac-[Re{4,4'-(MeO) 2 bpy}(CO) 3 -{P(OEt) 3 }] is stable and has a strong
reducing power due to the electron-releasing methoxy group attached
to the 4,4' position of the bpy ligand. Using a reaction system with a
mixture of these complexes at a mole ratio of 1:24 achieved a
quantum yield of 0.59 for the CO 2 reduction (ΦCO) photocatalyst .
(2)
To further strengthen the system's function, we developed a system
using a ring-shaped Re(I) polynuclear complex as the photosensitizer,
which shows strong absorption of visible light and offers high
quantum yield for OER specie generation. This resulted in a ΦCO of
0.81, which is the highest efficiency for a photocatalyst system
(4)
reported thus far .
Fig. 5 Hybrid Semiconductor Photocatalyst
Ru(II)-Re(I) Supramolecular Complex Photocatalyst Photocatalyst with a Light Capturing Function

Using a tris(diimine)ruthenium(II) complex with strong absorption in Periodic mesoporous silica (PMO) is a group of substances with a highly
the visible region as a photosensitizer and linking it to an Re(I) ordered mesoporous structure with pores on the order of a few nm in
complex catalyst by means of a bridging ligand, we developed a diameter. They exhibit unique optical functions depending on the
(5)
highly efficient CO2 reduction photocatalyst driven by visible light . In skeleton organic groups that form the mesopore walls. Acd-PMO (Fig. 1),
particular, when a Ru(II)-Re(I) binuclear complex linked by two alkyl which contains the acridone group (Acd), has been reported to absorb
chains was exposed to visible light in the presence of a sacrificial visible light and efficiently transfer its excitation energy to organic
(9)
reducing agent BIH, it efficiently and nearly selectively generated CO pigments immobilized inside the mesopores . Therefore, we decided to
(5)
(according to the equation below) . This resulted in very good perform a detailed study of the CO 2 reduction function of a new
photocatalytic properties, with a quantum yield of CO generated by composite material produced by introducing a Ru(II)-Re(I) supramolecular
(10)
irradiation of visible light of 59 %, over 3000 CO molecules (TN) photocatalyst into the Acd-PMO mesopores . We synthesized a
generated per photocatalyst molecule, and over 35 catalytic turnovers polynuclear Ru(II)-Re(I) complex with phosphonate groups (-PO 3 H 2 )
per minute (TF). attached to ligand terminals as anchors (RuRe, Fig. 1). When the
substance was added to acetonitrile, together with Acd-PMO and stirred,
a composite material was formed with RuRe immobilized in the
Acd-PMO mesopores. Then using the 400 nm excitation light, which is
the primary wavelength absorbed by the Acd-PMO material, the light
emission characteristics of the composite were studied in detail. The result
indicated that introducing RuRe efficiently quenched light emission from
the Acd group and a new light emission was observed from the Ru
photosensitizer. This result shows that excitation energy from the
photoexcited Acd group was transferred to the Ru photosensitizer.
This type of polynuclear complex used to serve multiple functions with
a single molecule is referred to as a supramolecular photocatalyst. This composite was suspended in a DMF-triethanolamine solution
containing benzimidazoline derivatives (BIH) as a reducing agent. When it
Supramolecular photocatalysts with the Re(I) catalyst portion swapped was exposed to 405 nm monochromatic light in a CO 2 atmosphere, the
with a Ru(II) carbonyl complex are able to selectively reduce CO 2 to CO 2 was efficiently reduced to selectively generate CO. This achieved 590
formic acid with high efficiency and high endurance . CO turnovers during 36 hours of light exposure (using the introduced
(6)
RuRe as a reference). Compared to a composite material (RuRe/MCM41)
created by introducing RuRe to mesoporous silica (MCM41) that does not
Metal Complex - Semiconductor Composite Photocatalysts absorb 405 nm light or have other light-capturing functions, using the
RuRe/Acd-PMO composite generated about 2.4 times more CO. These
We succeeded in developing an artificial Z-scheme composite
results clearly show that the light-capturing effect of Acd-PMO can
photocatalyst that combines an supramolecular photocatalyst with a
enhance photocatalyst properties by efficiently collecting light in RuRe.
(7)
semiconductor catalyst (Fig. 5) . On the surface of a TaON
semiconductor substrate supporting silver microparticles, the
Ru(II)-Ru(II) supramolecular photocatalyst was secured to
methylphosphonate groups introduced as anchors. When the
semiconductor catalyst and the supramolecular complex photocatalyst
photosensitizer successively absorbed visible light, reduction of CO 2 to
formic acid at the catalyst portion of the supramolecular catalyst and
oxidization of methanol on the TaON substrate occurred
simultaneously.

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