Integration of polyoxometalate into defective UiO-66-NH2(Zr/Hf) for visible-light-driven hydrogen photogeneration

UiO-66 plays a crucial role in photocatalytic systems due to its superior stability and tunability. However, the charge transfer from organic ligands to metals is rarely involved in the photo-excitation of the pristine material. Herein, several Keggin-type Cs2.5H0.5PW12O40 (CsPW) were successfully incorporated into a bimetallic metal-organic framework (MOF) using a one-pot, one-step method, resulting in a series of defective CsPW@UNH(Hf-Zr) as optimized photocatalysts for visible-light-driven hydrogen evolution. Further investigations demonstrate that a Z heterojunction mechanism proceeds in the CsPW@UNH(0.65Hf) heterojunction to boost the charge separation via the chemical interaction between the CsPW and UNH(0.65Hf) components. The hydrogen evolution rate for 5 %CsPW@UNH(0.65Hf) is nearly two orders of magnitude greater than that of the bare UNH(Zr). The coexistence of Hf3+ and Zr3+ was observed in defective polyoxometalate-encapsulated MOF (POM@MOF) for the first time during photocatalysis, confirming the successful conjugated pi electrons transition from the amine-containing ligand to bimetallic cluster. This study offers a novel guideline for exploring efficient MOF-based photocatalysts through defect engineering.