A morphology modulation strategy to construct Z-scheme WO3/Fe-W18O49 heterojunctions with tunable nanowire size for efficient photocatalytic nitrogen fixation

Abstract

Ammonia occupies a vital position in the development of human society. The synthesis of NH₃ depends primarily on the Haber–Bosch process, in which N₂ and H₂ are reacted at high temperatures, high pressures, and in the presence of a catalyst. The adoption of renewable solar energy as a reaction power source contributes to the goal of transforming the energy mix. In this work, we prepared a Z-scheme heterojunction, WO₃/Fe-W₁₈O₄₉, by morphology modulation, and Fe-W₁₈O₄₉ nanowires were uniformly adhered to the surface of disc-like WO₃, which consisted of micrometer bands stacked together. The change in the proportionality between WO₃ and Fe-W₁₈O₄₉ in the heterojunction could further optimize the size of Fe-W₁₈O₄₉ nanowires. The smaller size structure of Fe-W₁₈O₄₉ nanowires resulted in relatively more corresponding defect structures outside of them. The abundant OVs in Fe-W₁₈O₄₉ would accomplish the adsorption of N₂, and the presence of Fe with a transformable valence facilitated the electron transfer between W₁₈O₄₉ and N₂. Under the excitation of the full spectrum, 0.10WO₃/Fe-W₁₈O₄₉ presented the most outstanding N₂ fixation activity with an ammonia generation rate of 153.8 μmol g⁻¹ h⁻¹. The ammonia synthesis rate of 0.10WO₃/Fe-W₁₈O₄₉ was 16.4 and 2.1 times higher than that of WO₃ and Fe-W₁₈O₄₉. However, the ammonia generation rate of the 0.10WO₃/Fe-W₁₈O₄₉ composite photocatalyst microrods was only 113.6 μmol g⁻¹ h⁻¹. The formation of a Z-scheme heterojunction accelerated the separation of photogenerated carriers and optimized the redox capacity of electron–hole pairs. The synergistic effect generated by the morphology modulation and Z-scheme heterojunction together promoted the photocatalytic performance. This work provided a theoretical basis for exploring the technological development of WO₃/Fe-W₁₈O₄₉ in the field of photocatalytic nitrogen fixation.