Room-Temperature Synthesis of Fe-Incorporated ZIF-8 for Enhanced Photocatalytic Nitrogen Reduction and Hydrogen Evolution

Photocatalytic nitrogen reduction reaction (PNRR) is a promising alternative to the energy-intensive Haber–Bosch process, but inefficient charge separation, N≡N activation, and poor selectivity limit its practical implementation. To overcome these challenges, herein we report the room-temperature coprecipitation synthesis of Fe-incorporated zeolitic imidazolate framework-8 (ZIF-8) photocatalysts with varying Fe loadings (5–20%) to introduce Fe–Nx active centers within a stable ZIF-8 scaffold. Structural and optical studies confirm that Fe incorporation preserves the crystalline framework, while FTIR analysis reveals a distinct Fe–N stretching band at 628 cm–1, supporting Fe–N coordination within the framework. Fe incorporation also leads to progressive bandgap narrowing from 5.17 to 2.40 eV, substantially extending the visible-light photoresponse. TRPL measurements reveal that Fe incorporation lengthens the average charge-carrier lifetime from 1.01 to 1.34 ns, evidencing suppressed electron–hole recombination through Fe2+/Fe3+ redox cycling. Optimized 15% Fe-ZIF-8 achieves 326 μmol g–1 h–1 NH3 production, with a SCC of 0.117% and an AQE of 0.87% at 340 nm, nearly three times higher than pristine ZIF-8. Isotopic labeling studies confirm that nitrogen originates from the supplied N2 source. The photocatalyst also demonstrates a hydrogen production rate of 254 μmol h–1. Furthermore, machine-learning-assisted analysis supports the structure–activity relationships. Overall, this work demonstrates Fe-ZIF-8 as a promising photocatalyst for MOF-based PNRR systems.