NH 2 -MIL-101(Fe) Functionalized with MnO x and Pt Nanoparticles for Photocatalytic Nitrogen Fixation: Synergistic Enhancement of Oxidation and Reduction Processes via Co-Catalysts

Precisely modulating the synergistic effect of N2 reduction and H2O oxidation reactions at the molecular level for photocatalytic N2 fixation remains a challenge. Herein, MnOx and Pt nanoparticles (NPs) were decorated onto amine-functionalized metal organic framework NM-Fe {NH2-MIL-101(Fe)}, attempting to promote photoredox reactions simultaneously. Benefiting from the synergy of redox reactions, the optimized Pt@NM-Fe/MnOx exhibits an NH3 production rate of ca. 340 μmol g–1 h–1, which is 4.5 times that of NM-Fe, along with an apparent quantum efficiency (AQE) of 0.33% at 420 nm. 15N isotope labeling experiments demonstrates that the N in the nitrogen reduction reaction (NRR) originated exclusively from N2. The performance improvement can be attributed to the spatial synergy of N2 reduction and H2O oxidation reactions on the Pt@NM-Fe/MnOx composite photocatalyst. More specifically, MnOx acts as the H2O oxidation site by capturing holes to generate H+, while NM-Fe serves as the N2 reduction center by accepting electrons. MnOx captures holes to oxidize H2O into H+, while Pt NPs activate the generated H+ into *H for photocatalytic N2 fixation. Density functional theory calculations indicate that the breakage of the O–H bond in the H2O oxidation process is synchronized with the formation of *NNH in N2 reduction, lowering the energy barrier. The present work demonstrates a synergistic integration strategy that overcomes the kinetic mismatch between the two half-reactions through precise spatial modulation of functional sites.