Enhancing photocatalytic CO2-to-CO conversion by iron complexes through 8-hydroxyquinoline ligand regulation

Abstract

Metal complexes, with their well-defined molecular structures and design flexibility, offer an ideal platform for developing CO₂ reduction photocatalysts. While ligand modification is an effective strategy to enhance catalytic performance, it also presents several challenges. In this work, two 8-hydroxyquinoline-based organic ligands bearing different substituents were initially synthesized. Two ligands were subsequently employed in reactions with Fe(III) ion, respectively, generating two distinct molecular complexes, designated 1-Fe and 2-Fe. The binuclear structures of two complexes were unambiguously elucidated by single-crystal X-ray diffraction (SCXRD), and ESI-MS spectra. Under visible-light irradiation, both complexes demonstrated photocatalytic activity for CO₂ reduction to CO in aqueous solution. Notably, complex 1-Fe exhibited a marked improvement in both activity (TON_CO = 3106) and selectivity (Sel_CO = 81 %) compared to the 2-Fe catalyst (TON_CO = 1641, Sel_CO = 61 %). Furthermore, the superior CO₂ photoreduction performance of 1-Fe was comprehensively investigated by electrochemical tests, and photoinduced electron transfer dynamics, as well as in-situ attenuated total reflection infrared fourier transform spectroscopy (ATR-IFTS).