Complexed Semiconductor Cores Activate Hexaniobate Ligands as Nucleophilic Sites for Solar-Light Reduction of CO2 by Water

Abstract

Although pure and functionalized solid-state polyniobates such as layered perovskites and niobate nanosheets are photocatalysts for renewable-energy processes, analogous reactions by molecular polyoxoniobate cluster-anions are nearly absent from the literature. We now report that under simulated solar light, hexaniobate cluster-anion encapsulated 30-Ni^II -ion "fragments" of surface-protonated cubic-phase-like NiO cores activate the hexaniobate ligands towards CO₂ reduction by water. Photoexcitation of the NiO cores promotes charge-transfer reduction of Nb^V to Nb^IV , increasing electron density at bridging oxo atoms of Nb-μ-O-Nb linkages that bind and convert CO₂ to CO. Photogenerated NiO "holes" simultaneously oxidize water to dioxygen. The findings point to molecular complexation of suitable semiconductor "fragments" as a general method for utilizing electron-dense polyoxoniobate anions as nucleophilic photocatalysts for solar-light driven activation and reduction of small molecules.

Keywords: CO2 Reduction; Hexaniobate Anion; Molecular Complex; Nickel Oxide; Photocatalysis.