Modulating band structure of g-C3N4 by doping oxygen to transform FeCo2O4/g-C3N4 heterojunction from type-II to S-scheme for enhancing photo-Fenton-like reaction

Constructing S-scheme heterojunctions is a highly prevalent approach in enhancing the activation efficiency of peroxymonosulfate (PMS). However, the two semiconductors that have the potential to form S-scheme heterojunction (such as FeCo2O4 and carbon nitride) typically tend to form type-II heterojunction. In this study, through oxalic acid assisted oxygen atom doping in carbon nitride, followed by the utilization of oxygen-doped carbon nitride (O-CN) as precursors in combination with cobalt chloride and iron chloride, the final synthesis of a novel composite catalyst is achieved. The introduction of oxygen atoms into the graphite carbon nitride can lead to an overall reduction in the band structure, facilitating the controlled transformation of a type-II heterojunction to an S-scheme heterojunction. This transformation is confirmed through density functional theory (DFT) calculations and electron spin resonance (ESR) tests. In the photo-Fenton-like system, the 15% FeCo2O4/Oxygen doped-C3N4 (FCOCN) catalyst demonstrated a remarkable degradation efficiency of 93.5% for tetracycline hydrochloride (TCH). This efficiency surpassed that of O-CN (47.8%) and FeCo2O4 (60.3%). Furthermore, the degradation efficiency of the 15% FCOCN catalyst was significantly higher than that of photocatalysis (2.04 times greater) and Fenton-like treatment (1.11 times greater). Remarkably, within a short period of 14 min, the emerging contaminants, including sulfamethoxazole (SMX), bisphenol A (BPA), and carbamazepine (CBZ), were completely degraded. Atrazine (ATZ) showed a remarkable degradation rate of 77.1%. This study offers valuable insights into the construction of S-scheme heterojunction through the manipulation of band structure in type-II heterojunction by oxygen doping.