Amorphization and defect engineering in constructing ternary composite Ag/PW10V2/am-TiO2−x for enhanced photocatalytic nitrogen fixation

Abstract

Photo-driven nitrogen fixation involves the activation and hydrogenation processes of molecular nitrogen in producing ammonia at the photocatalyst surface. Herein, significant enhancement of the catalytic efficiency is achieved via constructing a ternary Ag/PW₁₀V₂/am-TiO_2−x composite (the optimal PW₁₀V₂ and Ag NPs loadings are 14.5 wt% and 1.5 wt%, respectively) with high specific surface area of 513 m² g⁻¹. The well-designed Z-scheme heterojunction between divanadium substituted phosphotungstic acid (PW₁₀V₂) and amorphous TiO_2−x (am-TiO_2−x) combined with localized surface plasmon resonance (LSPR) of Ag NPs endowed the ternary Ag/PW₁₀V₂/am-TiO_2−x composite with superior oxidation–reduction performance. Accommodated by amorphization and defect engineering, enriched surface oxygen vacancies (OVs) were produced. In the absence of a sacrificial agent, high NH₃/NH₄⁺ productions of 424.9 μmol g_cat⁻¹ were achieved under a nitrogen atmosphere when irradiating under simulated sunlight for 2 h. The results show that the enhancement of catalytic efficacy is well correlated with a Z-scheme heterojunction and Ag–am-TiO_2−x interface with factors of 1.2–1.4 and 1.4–1.8, respectively. The roles of the surface OVs and amorphous structure are emphasized when compared with anatase TiO_2−x and Ag/PW₁₀V₂/anatase-TiO_2−x. In addition to the excellent photocatalytic activity, the composite demonstrates high photochemical stability with negligible activity decay. This work also gives some inspiration to prepare polyoxometalates-based photocatalysts with high activity for photocatalytic nitrogen fixation.