Enhancement of visible-light-driven CO₂ reduction performance using an amine-functionalized zirconium metal-organic...

By employing a conjugated amine-functionalized dicarboxylic ligand (H₂L = 2,2'-diamino-4,4'-stilbenedicarboxylic acid, H₂SDCA-NH₂), we have successfully synthesized and characterized a porous and visible light responsive zirconium metal-organic framework ([Zr₆O₄(OH)₄(L)₆]·8DMF, denoted as Zr-SDCA-NH₂). This Zr-MOF showed good chemical stability and broad visible light absorption with an absorption edge at about 600 nm. When used as a photocatalyst, Zr-SDCA-NH₂ exhibits visible-light activity for CO₂ reduction with a formate formation rate of 96.2 μmol h^-1 mmol_MOF^-1, which is higher than the series of reported amine-functionalized Zr-MOFs. Mott-Schottky measurements, photoluminescence study and photocatalytic experiments demonstrated that the Zr₆ oxo cluster through the LMCT process and the organic ligand both contributed to the CO₂ photoreduction. This study indicates that the combination of amino groups and highly conjugated molecules is a feasible and simple strategy to extend light absorption of the organic ligand, which is beneficial for designing a visible light responsive MOF photocatalyst.