Novel UiO‐66‐NH ₂ /W ₁₈ O ₄₉ Photocatalyst for Enhanced Nitrogen Fixation to Ammonia Under Visible Light: Improved Efficiency and New Mechanisms

Converting atmospheric nitrogen (N 2 ) into ammonia (NH 3 ) by sustainable methods presents a significant challenge in green chemistry. Photocatalytic N 2 fixation under visible light offers a promising solution, provided efficient catalysts can effectively weaken the strong N≡N bond. In this study, we present a composite photocatalyst composed of the metal–organic framework (MOF) UiO‐66‐NH 2 and substoichiometric tungsten oxide (W 18 O 49 ). The oxygen vacancies in W 18 O 49 extend its visible light absorption, while UiO‐66‐NH 2 provides a high surface area and amine‐functionalized linkers that enhance light harvesting. We synthesized UiO‐66‐NH 2 /W 18 O 49 composites with varying UiO‐66‐NH 2 contents (30%, 50%, and 70% by weight) and evaluated their photocatalytic performance under visible‐light irradiation. The 50% UiO‐66‐NH 2 /W 18 O 49 composite exhibited the highest NH 3 production rate of 420.8 μmol g −1 h −1 , which is 27.2 times higher than that of pure UiO‐66‐NH 2 and 10.9 times higher than that of W 18 O 49 . This enhancement is attributed to the synergistic heterojunction between UiO‐66‐NH 2 and W 18 O 49 , where the MOF provides a large surface area and efficient light absorption, while W 18 O 49 contributes plasmon‐generated hot electrons and abundant oxygen vacancies. The composite demonstrates broadened visible‐light absorption, efficient charge separation, and rapid charge transfer, thus suppressing electron–hole recombination. These results highlight the potential of the UiO‐66‐NH 2 /W 18 O 49 composite as an effective photocatalyst for solar‐driven ammonia production under mild conditions.