Directed Assembly of Cuprous Oxide Nanocatalyst for
CO<sub>2</sub> Reduction Coupled to Heterobinuclear ZrOCo<sup>II</sup> Light Absorber in Mesoporous Silica
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Abstract
Hierarchical assembly of an oxo-bridged
binuclear ZrOCo<sup>II</sup> light absorber unit coupled to a cuprous
oxide nanocluster catalyst
for CO<sub>2</sub> reduction on mesoporous silica support is demonstrated.
The proper positioning of the Cu oxide cluster was achieved by photodeposition
of a [Cu(NCCH<sub>3</sub>)<sub>4</sub>]<sup>2+</sup>precursor by visible
light excitation of the ZrOCo charge transfer chromophore, followed
by mild calcination at 350 C. Illumination of the Cu<sub><i>x</i></sub>O<sub><i>y</i></sub>-ZrOCo unit so formed in the
presence of a diethylamine electron donor resulted in the reduction
of surface Cu centers to Cu<sup>0</sup> as demonstrated by the characteristic
infrared band of adsorbed <sup>13</sup>CO probe molecules at 2056
cm<sup>–1</sup>. For analogous Cu<sub><i>x</i></sub>O<sub><i>y</i></sub>-TiOCo<sup>II</sup> units, the oxidation
state makeup of the surface Cu centers was dominated by Cu<sup>I</sup>, and the Cu<sup>0</sup>, Cu<sup>I</sup>, and Cu<sup>II</sup> composition
was found to depend on the wavelength of MMCT excitation. The observed
strong dependence of the CO<sub>2</sub> photoreduction yield on the
oxidation state of the surface Cu centers directly proves that CO<sub>2</sub> is reduced on the Cu<sub><i>x</i></sub>O<sub><i>y</i></sub> surface, thus establishing that the ZrOCo<sup>II</sup> unit functions as light absorber, donating electrons to the Cu<sub><i>x</i></sub>O<sub><i>y</i></sub> catalyst on
whose surface CO<sub>2</sub> is reduced