Ni₂P‐Modified Ta₃N₅ and TaON for Photocatalytic Nitrate Reduction

Abstract Self‐sustaining photocatalytic NO₃⁻ reduction systems could become ideal NO₃⁻ removal methods. Developing an efficient, highly active photocatalyst is the key to the photocatalytic reduction of NO₃⁻. In this work, we present the synthesis of Ni₂P‐modified Ta₃N₅ (Ni₂P/Ta₃N₅), TaON (Ni₂P/TaON), and TiO₂ (Ni₂P/TiO₂). Starting with a 2 mM (28 g/mL NO₃⁻−N) aqueous solution of NO₃⁻, as made Ni₂P/Ta₃N₅ and Ni₂P/TaON display as high as 79% and 61% NO₃⁻ conversion under 419 nm light within 12 h, which correspond to reaction rates per gram of 196 μmol g⁻¹ h⁻¹ and 153 μmol g⁻¹ h⁻¹, respectively, and apparent quantum yields of 3–4%. Compared to 24% NO₃⁻ conversion in Ni₂P/TiO₂, Ni₂P/Ta₃N₅ and Ni₂P/TaON exhibit higher activities due to the visible light active semiconductor (SC) substrates Ta₃N₅ and TaON. We also discuss two possible electron migration pathways in Ni₂P/semiconductor heterostructures. Our experimental results suggest one dominant electron migration pathway in these materials, namely: Photo‐generated electrons migrate from the semiconductor to co‐catalyst Ni₂P, and upshift its Fermi level. The higher Fermi level provides greater driving force and allows NO₃⁻ reduction to occur on the Ni₂P surface.