Nitrogen-oxygen defect engineering enhanced intrinsic electric field in CoFe₂O₄/g-C₃N₄ heterojunctions for photocatalytic tetracycline degradation and H₂ evolution

A range of efficient g-C₃N₄/CoFe₂O₄ heterojunction with nitrogen deficiencies (NDs) and oxygen deficiencies (ODs) were successfully synthesized through doping-melting and hydrothermal methods. Nitrogen-oxygen defect engineering effectively enhanced the active sites on the catalyst surface and regulated the optical bandgap, band structure, and work function (Φ) of g-C₃N₄ and CoFe₂O₄, regulating the strength of the intrinsic electric field (IEF) and promoting the separation of photo-generated carriers at the heterojunction interface. Among the series of samples, CH-H2@CFO-A5 (properly oxalate-doped g-C₃N₄/CoFe₂O₄ heterojunctions treated with prolonged annealing) demonstrated remarkable optical properties due to its narrowest optical band gap, while the strongest IEF and redox potential make it has strong carrier dynamics and photocatalytic efficiency. Under visible light, the mineralization rate of tetracycline (TC) on CH-H2@CFO-A5 and the photocatalytic hydrogen production rate were 4.51 times and 2.72 times higher than that of unmodified CN-H0@CFO-A1, respectively. This study aimed to provide an efficient strategy for regulating the IEF within the heterojunction, by altering the Fermi level through multi-element defect engineering.