The impact of metal leaching in MOF materials on the evaluation of photocatalytic CO2 reduction activity – A case study

Most photocatalyzed CO₂ reduction systems employed visible light photosensitizer, metal-containing CO₂ reduction catalyst and sacrificial reagent, demonstrating excellent efficiency and high selectivity. However, the influence of metal ion leached from decomposition of trace amounts of metal-containing catalyst has rarely been discussed. Here, we discovered that leaching Fe ion from Fe-MOF during the catalyzed CO₂ reduction process was the crucial species for efficient CO₂ reduction in our system which utilized [Ru(bpy)₃]Cl₂·6H₂O as photosensitizer, tri-isopropanolamine (TIPA) as sacrificial reagent and Fe-MOF as CO₂ reduction catalyst. FeCl₃ was tested as CO₂ reduction catalyst instead of Fe-MOF and provided 73,750 μmol g⁻¹ h⁻¹ of CO in MeCN, 329,500 μmol g⁻¹ h⁻¹ in N,N-Dimethylformamide after 4 h of visible light irradiation. Additionally, we investigated other metal chlorides (Na, Cr, Mn, Ni et, al.) to study the effect of Fe ion. Both Fe³⁺, Co²⁺ and Ni²⁺ provided satisfactory catalytic efficiency which indicated that the effect of metal ion leaching in Metal-organic frameworks (MOFs) contained photocatalytic CO₂ reduction systems should be appreciated. Furthermore, the concentration of Cl⁻ also played a beneficial role and enhanced the catalysis process.