Exploring Electron Transfer Mechanism in Synergistic Interactional Reduced Polyoxometalate-Based Cu(I)–Organic Framework for Photocatalytic Removal of U(VI)

Abstract

Photocatalytic reduction of U(VI) is a promising method for removing uranium containing pollutants. However, using polyoxometalate-based metal-organic frameworks (POMOFs) for photoreduction of U(VI) is rare, and the relevant charge transfer pathway is also not yet clear. In this article, we demonstrate a highly efficient strategy and revealed a clearly electron transfer pathway for the photoreduction of U(VI) with 99% removal efficiency by using a novel POMOF, [Cu(4,4'-bipy)]₅·{AsMo₄^VMo₆^VIV₂^VO₄₀(V^IVO)[V^IVO(H₂O)]}·2H₂O (<b>1</b>), as catalyst. The POMOF catalyst was constructed by the connection of reduced {AsMo₁₀V₄} clusters and Cu(I)-MOF chains through Cu-O coordination bonds, which exhibits a broader and stronger light absorption capacity due to the presence of reduced {AsMo₁₀V₄} clusters. Significantly, the transition of electrons from Cu(I)-MOF to {AsMo₁₀V₄} clusters (Cu → Mo/V) greatly inhibits the recombination of photogenerated carriers, thereby advancing electron transfer. More importantly, the {AsMo₁₀V₄} clusters are not only adsorption sites but also catalytically active sites. This causes the fast transfer of photogenerated electrons from Mo/V to UO₂²⁺(Mo/V → O → U) via the surface oxygen atoms. The shorter electron transmission distance between catalytic active sites and UO₂²⁺ achieves faster and more effective electron transport. All in all, the highly effective photocatalytic removal of U(VI) using the POMOF as a catalyst is predominantly due to the synergistic interaction between Cu(I)-MOFs and reduced {AsMo₁₀V₄} clusters.