Construction of local coordination environment of iron sites over g-C3N4/PCN-222(Fe) composite with high CO2 photoreduction performance

Photocatalytic conversion of CO 2 to usable fuels provides a new strategy for solving energy problems and the greenhouse effect. Porphyrin-based metal-organic frameworks (MOFs) are promising in photocatalysis due to their remarkable light harvesting ability, and the metal active site and its coordination environment can be further adjusted to achieve the high activity. In this work, g-C 3 N 4 /PCN-222 composites with different porphyrin metal centers were fabricated and the g-C 3 N 4 /PCN-222(Fe III ) catalyst showed the highest photocatalytic CO 2 reduction performance than that of g-C 3 N 4 /PCN-222(Fe II ) and other g-C 3 N 4 /PCN-222( M , M = Co, Ni, Cu, Zn) composites. Experimental studies and theoretical calculations showed that the axial coordination in g-C 3 N 4 /PCN-222(Fe III ) distorts the square planar field (Fe-N4) to quasi-octahedral coordination, which led to the moderate adsorption ability of CO 2 reduction intermediate (*CO), resulting in the high photocatalytic activity.