Tailoring defect-type and ligand-vacancies in Zr(iv) frameworks for CO2 photoreduction

Abstract

The nature and degree of defects can fine-tune the light absorption energy (E_abs) and charge transfer energy (E_LMCT) of metal–organic frameworks (MOFs), which are important for photocatalytic reactions. Herein, a series of UiO-66-NH₂ with missing-linker (ML)/missing-cluster (MC) defects and different degrees of ligand vacancies were synthesized and utilized to explore their photocatalytic performance of CO₂ reduction. The photocatalytic CO yield of UiO-66-NH₂-ML-100 with ML defects reaches 21.3 μmol g⁻¹ h⁻¹, which is 2.2 times that of UiO-66-NH₂-MC-150 with MC. Both experiments and density functional theory (DFT) calculations demonstrate that the nature of MC defects enlarges E_abs, while the ligand vacancy changes the coordination environment of Zr(IV) and lowers E_LMCT. More ligand vacancies per metal node lead to smaller E_LMCT, which is beneficial for the CO₂ photoreduction reaction. This work provides a pathway to boost photocatalytic performance by tailoring the defects of MOFs.