Molten salt-assisted synthesis of nitrogen-vacancy crystalline graphitic carbon nitride with tunable band structures for efficient photocatalytic overall water splitting

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2023-02, Vol.454, p.140123, Article 140123
• Main Authors: Shao, Yifan, Hao, Xuqiang, Lu, Shunda, Jin, Zhiliang
• Format: Article
• Language: English
• Subjects: Co3O4 nanorods; Crystalline g‐C3N4; Interfacial charge separation; Nitrogen-vacancy; Photocatalytic overall water splitting
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2022.140123

Nitrogen-vacancy crystalline g-C3N4 nanosheets with tunable band structures were successfully prepared by alkali-molten salt-assisted method. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 which loaded Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a notable quantum efficiency of 11.94% at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48%. [Display omitted] •Nitrogen-vacancy crystalline g-C3N4 was prepared via molten-salt-assisted method.•Vacancy and highly-crystalline can efficiently promote charge separation.•Matching of HER/OER via Pt and Co3O4 NRs further improve charge carrier separation.•g-C3N4-D2/3%Co3O4 has high H2 evolution rate with marked AQE (11.94 %) and STH (1.48 %).•Pt/g-C3N4-D2/3%Co3O4 possesses outstanding overall water splitting activity. The photocatalytic overall water splitting performance of graphitic carbon nitride (g-C3N4) has still been restricted by its inefficient charge separation efficiency. Herein, nitrogen-vacancy crystalline g-C3N4 nanosheets (g-C3N4-D) with tunable band structures were successfully prepared by the alkali-molten salt-assisted method for efficient photocatalytic overall water splitting. Among them, g-C3N4-D2 not only combines the advantages of the amorphous and crystalline state of two-dimensional g-C3N4 nanosheets, but also introduces nitrogen vacancy to adjust the bandgap structures of crystalline g-C3N4 by an alkali etching, thus improving the light energy utilization and charge separation efficiency. TEM and EPR spectrum prove the existence of N defects in the crystalline g-C3N4. The excellent and stable photocatalytic overall water splitting activity with H2 and O2 evolution rate of 49.60 μmol g−1 h−1 and 24.71 μmol g−1 h−1 was obtained over g-C3N4-D2 with Pt and Co3O4 nanorods as cocatalysts (Pt/g-C3N4-D2/3%Co3O4 NRs) under AM 1.5G simulated light irradiation. In the half-reaction experiments, the maximum H2 evolution rate of Pt/g-C3N4-D2/3%Co3O4 NRs is 3.78 mmol g−1 h−1 with a significant quantum efficiency of 11.94 % at 400 nm, and the solar-hydrogen conversion efficiency (STH) is 1.48 %. The photocatalytic water oxidation activity of Pt/g-C3N4-D2/5%Co3O4 NRs is 42.34 μmol g−1 h−1.