Ni 2 P‐Modified Ta 3 N 5 and TaON for Photocatalytic Nitrate Reduction

Self‐sustaining photocatalytic NO 3 − reduction systems could become ideal NO 3 − removal methods. Developing an efficient, highly active photocatalyst is the key to the photocatalytic reduction of NO 3 − . In this work, we present the synthesis of Ni 2 P‐modified Ta 3 N 5 (Ni 2 P/Ta 3 N 5 ), TaON (Ni 2 P/TaON), and TiO 2 (Ni 2 P/TiO 2 ). Starting with a 2 mM (28 g/mL NO 3 − −N) aqueous solution of NO 3 − , as made Ni 2 P/Ta 3 N 5 and Ni 2 P/TaON display as high as 79% and 61% NO 3 − 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% NO 3 − conversion in Ni 2 P/TiO 2 , Ni 2 P/Ta 3 N 5 and Ni 2 P/TaON exhibit higher activities due to the visible light active semiconductor (SC) substrates Ta 3 N 5 and TaON. We also discuss two possible electron migration pathways in Ni 2 P/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 Ni 2 P, and upshift its Fermi level. The higher Fermi level provides greater driving force and allows NO 3 − reduction to occur on the Ni 2 P surface.