Modulating the d-band center of NNU-55(Fe) for enhanced CO2 adsorption and photocatalytic activity

Photocatalytic reduction of carbon dioxide (CO₂) has emerged as an effective technology to transform CO₂ into valuable chemicals. Metal-organic frameworks (MOFs) show great promise due to their adjustable structures, huge specific surface areas, excellent catalytic properties, and remarkable photo responsiveness. Herein, the MOF material NNU-55(Fe) was employed for the photocatalytic transformation of CO₂ into carbon monoxide (CO). Through electronic modulation of the active metal center (Fe–N4) via inorganic anionic ligand tuning, the photocatalytic performance of NNU-55(Fe) MOFs can be easily regulated. Notably, NO₃⁻-coordinated NNU-55(Fe) demonstrated superior catalytic performance compared to SO₄²⁻- and Cl⁻-coordinated catalysts, achieving a CO production of 124 ​μmol·g⁻¹ within 3 ​h. The stronger electron donation capacity of NO₃⁻ leads to an improved electron density of Fe centers, which lowers the Fe d-band center and enhances the bonding orbital occupancy in the adsorption system, thereby increasing the adsorption strength of CO₂ and reduction activity. This study highlights a simple strategy for altering the catalytic activity and electrical structure of MOFs by altering the coordinated inorganic ligands of metal sites, offering a novel approach to developing efficient photocatalytic materials.