Abstract: Solar-driven photocatalytic reduction of CO2 into high-value-added chemicals (e.g., formic acid, methanol) represents a cutting-edge strategy for mitigating the greenhouse effect and achieving carbon resource recycling. A series of ligand-functionalized X-MIL-101(Fe) MOFs catalytic materials were prepared by introducing functional groups such as -NH2, -OCH3, -Br and -NO2 by one-pot solvothermal method. The morphology, structure and optoelectronic properties of the catalysts were characterized by X-ray diffractometer (XRD), Element analyzer (EA), scanning electron microscope (FE-SEM), ultraviolet-visible absorption spectroscopy (UV-Vis), photocurrent response spectroscopy (it), electrochemical impedance spectroscopy (EIS) and fluorescence emission spectroscopy (PL). The study demonstrates that the electronic properties of functional groups significantly modulate the light absorption, band structure, and charge carrier behavior of material: electron-donating groups (-NH2, -OCH3) enhance light response and promote charge separation; Electron-withdrawing groups (-Br, -NO2) suppress light absorption and electron transfer. The -NH2 group exhibits a stronger electron-donating ability than the -OCH3 group bonded to the benzene ring. Consequently, under simulated sunlight, amino-modified NH2-MIL-101(Fe) demonstrated optimal CO2 reduction performance, exhibiting the strongest photocurrent response and highest charge separation efficiency. In pure water, its formic acid production rate reached 28.13 μmol g?1 h?1. This rate further increased to 42.61 μmol g?1 h?1 with the addition of a sacrificial agent, representing a 3.45-fold improvement over unmodified MIL-101(Fe). The material also demonstrated excellent reusability, maintaining 93.92% of its activity after four cycles. This study provides theoretical foundations and experimental references for designing highly efficient and stable MOF-based CO2 photoreduction catalysts from the perspectives of the ligand structure.

Key words: Metal-organic frameworks, Ligands, Photocatalyst, Carbon dioxide reduction