One-step nitrogen defect engineering of polymeric carbon nitride for visible light-driven photocatalytic O₂ reduction...

Polymeric carbon nitride (PCN) is an important metal-free photocatalyst for visible light-driven hydrogen peroxide (H₂O₂) production from O₂ reduction. Herein, we synthesized the DPCN catalysts possessing nitrogen defects by one-step thermal polymerization of urea in N₂ stream. As compared to the PCN conventionally synthesized in static air, X-ray photoelectrons spectroscopy (XPS) characterization disclosed that there are more pyridinic N defects in the DPCN catalysts, which is attributed to the removal of a proportion of NH₃ released from urea pyrolysis by flowing N₂. UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Mott-Schottky, steady-state and time-resolved photoluminescence (PL), and electrochemical impedance spectroscopy (EIS) characterizations revealed that the introduction of the nitrogen defects narrows down the band gap, improves the density of the photoexcited charge carriers, prolongs the lifetime of the charge carriers, and enhances the charge transfer efficiency. In visible light-driven photocatalytic O₂ reduction to H₂O₂, the optimal DPCN catalyst afforded an activity of 4.35 times that of the PCN catalyst and a H₂O₂ concentration of 2.83 mmol L^-1 after 10 h of visible light irradiation. This one-step thermal polymerization approach is valid when replacing N₂ stream with Ar and He streams.