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-C 3 N 4 /CoFe 2 O 4 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-C 3 N 4 and CoFe 2 O 4 , 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-C 3 N 4 /CoFe 2 O 4 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. • Nitrogen/oxygen defects improve interfacial area and active sites for catalysis. • Defects modulate the band structure and work function (Φ) of semiconductors. • g-C 3 N 4 /CoFe 2 O 4 Z-scheme heterojunction retains a higher REDOX potential. • Fermi level (E f ) modulation enhances the internal electric field (IEF).