Photocatalytic CO 2 Reduction by Ternary Heterostructures of Sb 2 VO 5 Nanorods, CdS Quantum Dots, and a Zinc(II) Porphyrin Complex

We synthesized ternary heterostructures of Sb2VO5 nanorods, CdS quantum dots (QDs), and zinc(II) 5-(3-carboxyphenyl)-10,15,20-(triphenyl)porphyrin (Zn3MCP), hereafter referred to as Sb2VO5/CdS-Zn3MCP triads, and evaluated their performance as CO2-reduction photocatalysts. The photocatalytic CO2-reduction reaction (CO2RR), which converts CO2 to fuels and feedstocks, is challenging because it competes with the hydrogen evolution reaction (HER) and because it can proceed through several different multielectron, multiproton mechanisms. We hypothesized (a) that, within Sb2VO5/CdS-Zn3MCP triads, photoexcited CdS QDs would transfer electrons to Zn3MCP and holes to midgap electronic states of Sb2VO5, (b) that charge separation would enable subsequent redox half-reactions, and (c) that Zn3MCP would selectively catalyze CO2RR. To evaluate these hypotheses, we characterized excited-state mechanisms and photocatalytic reactivity of Sb2VO5/CdS-Zn3MCP triads, as well as CdS-Zn3MCP dyads and Sb2VO5/CdS heterostructures as two-component analogues. Within CdS-Zn3MCP dyads, photoexcited CdS QDs transferred energy to Zn3MCP. In photochemical experiments, CdS-Zn3MCP dyads promoted both CO2RR, to yield CO and CH4, and HER. Sb2VO5/CdS heterostructures likewise promoted both CO2RR and HER but with H2 as the primary photoproduct. Remarkably, Sb2VO5/CdS-Zn3MCP triads promoted photocatalytic CO2RR, to yield CO and CH4, with 100% selectivity for CO2RR over HER. As the loading of Zn3MCP increased, the yield of CH4, the 8-electron, 8-proton CO2RR product, increased, suggesting cooperativity between porphyrin centers. This photocatalytic reactivity is consistent with the targeted charge-separation mechanism. Our results reveal that Sb2VO5/CdS-Zn3MCP triads are promising CO2-reduction photocatalysts and, more generally, that light-initiated mechanisms of heterostructures can be tuned with composition and interfacial properties to engender new reactivity and selectivity in photocatalysis.