High-valent Sn4+ modulated FeSn bimetallic MOF-on-MOF S-scheme heterojunctions for efficient photocatalytic nitrogen fixation

Sn 4+ modulated FeSn bimetallic MOF-on-MOF S-scheme heterojunctions are fabricated. • pH and Sn 4+ synergistically control catalyst morphology and composition distribution. • Optimized NM-FeSn exhibits superior N 2 photoreduction activity and stability. • Sn 4+ doping modulates Fe redox state and optimizes interfacial charge kinetics. • In-situ DRIFTS identifies the full NRR pathway on NM-FeSn heterostructure. Solar-driven photocatalytic nitrogen fixation (PNF) represents a sustainable and eco-friendly alternative to the energy-intensive Haber–Bosch process. Nevertheless, its practical implementation is greatly restricted by sluggish N N bond activation, rapid photogenerated carrier recombination, and insufficient multi-electron/proton transfer kinetics. Herein, dual-phase MOF-on-MOF S-scheme heterojunctions with well-tuned Fe Sn bimetallic active sites (NM-FeSn) are rationally constructed by introducing high-valent Sn 4+ via a facile one-pot solvothermal strategy. Benefiting from the unique 4d 10 5s 0 5p 0 electronic configuration, the incorporated Sn 4+ effectively modulates the electronic structure of the NH₂-MIL framework, optimizes the Fe 2+ /Fe 3+ redox ratio, and improves the structural and chemical stability of the catalyst. The optimal NM-FeSn delivers a prominent NH 3 evolution rate of 2.85 mmol L −1  g −1  h −1 and a high apparent quantum yield of 2.49% at 420 nm, which outperforms previously reported Sn-doped MOF-5 and ZIF-8 photocatalysts. On the basis of systematic photoelectrochemical tests, multi-spectroscopic characterizations, and in-situ DRIFTS measurements, the intrinsic S-scheme charge transfer mechanism and Fe Sn bimetallic synergistic effect are unambiguously revealed. Such synergistic effects significantly accelerate interfacial spatial charge separation, suppress photogenerated carrier recombination, and prolong carrier lifetime. This work systematically clarifies the electronic modulation mechanism of high-valent Sn 4+ doping and provides a versatile structural regulation strategy for the rational design of high-efficiency MOF-based heterojunction catalysts toward artificial nitrogen fixation and other energy conversion applications. Download: Download high-res image (106KB) Download: Download full-size image