Optimal synthesis of a direct Z-scheme photocatalyst with ultrathin W₁₈O₄₉ nanowires on g-C₃N₄ nanosheets for solar-driven oxidation reactions

Constructing Z-scheme photocatalysts is an effective approach to enhance the conversion efficiency of solar to chemical energy. Herein, W₁₈O₄₉/g-C₃N₄ heterostructures have been synthesized by growing W₁₈O₄₉ ultrathin nanowires on g-C₃N₄ nanosheets via a convenient solvothermal process. Various characterizations were performed on the materials to understand the structure-performance relationship. The photocatalytic properties of the W₁₈O₄₉/g-C₃N₄ heterostructures were evaluated by the two oxidation reactions, phenol degradation and oxidative NC coupling of benzylamines, under a simulated sunlight (360 ≤ λ ≤ 780 nm). With tuning the W₁₈O₄₉/g-C₃N₄ mass ratio, the optimal photocatalyst of W₁₈O₄₉(30)/g-C₃N₄ containing 30 wt% W₁₈O₄₉ nanowires exhibited the highest activity in both the photocatalytic reactions. The generations and contributions of the active species in the photocatalytic reactions were identified by electron spin resonance (ESR) spectra and active-species-eliminating experiments. Accordingly, the photocatalytic mechanism of W₁₈O₄₉/g-C₃N₄ heterostructures has been expounded based on the direct Z-scheme electron transfer between the two semiconductors as well as the synergistic actions of active sites on W₁₈O₄₉ nanowires and g-C₃N₄ nanosheets. This work demonstrates a rational paradigm to construct 1D/2D semiconductor heterostructures and provides further insights into Z-scheme photocatalytic mechanism for boosting solar-driven pollutant degradation and organic transformation.