2D WO3–x Nanosheet with Rich Oxygen Vacancies for Efficient Visible-Light-Driven Photocatalytic Nitrogen Fixation

Oxygen vacancy modulation holds great promise for enhancing the photocatalytic activity for efficient nitrogen fixation under mild conditions. In this work, the two-dimensional WO_3-x nanosheets with rich oxygen vacancies were prepared using solvothermal synthesis. The WO_3-x nanosheets (rich oxygen vacancies) display nice photocatalytic activity for N₂ reduction to ammonia with a high yield rate of 82.41 μmol·g_cat^-1·h^-1 under irradiation of visible light (420 nm), which is 3.59 times higher than that of the WO_3-x nanoparticles (poor oxygen vacancies). Electron spin resonance (ESR), N₂ adsorption-desorption isotherms, and transient photocurrent responses in the N₂ or Ar atmosphere experiments proved that the rich oxygen vacancies, which are induced by the nanosheet structure, could serve as active sites for the chemisorption of N₂ and facilitate the electron transfer from unsaturated sites to activated N₂. Moreover, based on the analysis of banding energy, the oxygen vacancies not only boosted the ability of visible light harvesting but also elevated the defect energy level to the Fermi level, further inhibiting the defect relaxation effect. The findings offer an insight into the design of the efficient photocatalysts via structure engineering and defect engineering for photocatalytic N₂ fixation.