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 N 2 reduction and H 2 O oxidation reactions at the molecular level for photocatalytic N 2 fixation remains a challenge. Herein, MnO x and Pt nanoparticles (NPs) were decorated onto amine-functionalized metal organic framework NM-Fe {NH 2 -MIL-101(Fe)}, attempting to promote photoredox reactions simultaneously. Benefiting from the synergy of redox reactions, the optimized Pt@NM-Fe/MnO x exhibits an NH 3 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. 15 N isotope labeling experiments demonstrates that the N in the nitrogen reduction reaction (NRR) originated exclusively from N 2 . The performance improvement can be attributed to the spatial synergy of N 2 reduction and H 2 O oxidation reactions on the Pt@NM-Fe/MnO x composite photocatalyst. More specifically, MnO x acts as the H 2 O oxidation site by capturing holes to generate H +, while NM-Fe serves as the N 2 reduction center by accepting electrons. MnO x captures holes to oxidize H 2 O into H +, while Pt NPs activate the generated H + into *H for photocatalytic N 2 fixation. Density functional theory calculations indicate that the breakage of the O–H bond in the H 2 O oxidation process is synchronized with the formation of *NNH in N 2 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.