Visible-Light Driven Oxidation of Water as Catalyzed
by Co-APO‑5 in the Presence of Ru Sensitizer
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Abstract
Cobalt aluminum phosphate with AFI
zeolitic structure (Co-APO-5) catalyzes light-driven water oxidation
(WO) when both the ruthenium complex [Ru(bpy)<sub>3</sub>]<sup>2+</sup>, as photosensitizer, and persulfate species S<sub>2</sub>O<sub>8</sub><sup>2–</sup>, as sacrificial electron acceptor, are present.
Measurements have been run in a flow reactor, allowing the amount
of oxygen evolved to be evaluated and, in particular, the initial
rate of WO reaction to be measured. The latter has been studied as
a function of chemical composition, and some kinetic features have
been established. Competitive reactions occur extensively, causing
the oxidation of the Ru complex to the detriment of oxygen production.
The initial rate of WO increases with the amount of catalyst until
turbidity of the suspension sets in. A reaction order close to −1
with respect to persulfate was found, which indicates the occurrence
of surface processes involving Co centers at the outer layer of Co-APO-5
particles (accessed by the bulky [Ru(bpy)<sub>3</sub>]<sup>2+</sup> species, at variance with Co species in the core), for the adsorption
onto which competition takes place between the Ru complex and persulfate
species. A less pronounced negative order (ca. −0.4) for the
sensitizer was also observed, for which an interpretation is proposed