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Abstract
<p class="first" id="P3">Selective, visible-light-driven conversion of CO
<sub>2</sub> to CO with a turnover frequency of 20 s
<sup>−1</sup> under visible light irradiation at 25 °C is catalyzed by an aqueous
colloidal system
comprising a pseudoternary complex formed among carbon monoxide dehydrogenase (CODH),
silver nanoclusters stabilized by polymethacrylic acid (AgNCs-PMAA), and TiO
<sub>2</sub> nanoparticles. The photocatalytic assembly, which is stable over several
hours and
for at least 250000 turnovers of the enzyme’s active site, was investigated by separate
electrochemical (dark) and fluorescence measurements to establish specific connectivities
among the components. The data show (a) that a coating of AgNCs-PMAA on TiO
<sub>2</sub> greatly enhances its ability as an electrode for CODH- based electrocatalysis
of
CO
<sub>2</sub> reduction and (b) that the individual Ag nanoclusters interact directly
and dynamically
with the enzyme surface, most likely at exposed cysteine thiols. The results lead
to a model for photocatalysis in which the AgNCs act as photosensitizers, CODH captures
the excited electrons for catalysis, and TiO
<sub>2</sub> mediates hole transfer from the AgNC valence band to sacrificial electron
donors.
The results greatly increase the benchmark for reversible CO
<sub>2</sub> reduction under ambient conditions and demonstrate that, with such efficient
catalysts,
the limiting factor is the supply of photogenerated electrons.
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