Coexisting single-atomic Fe and Fe2O3 on nitrogen-deficient g-C3N4 with enriched Fenton-like oxidation and photocatalytic performances for tetracycline degradation: DFT calculation, degradation mechanism and toxicity evaluation

The regulation of heterogeneous material properties to strengthen the peroxymonosulfate activation to destroy refractory pharmaceuticals remains a challenge. Herein, a promising nitrogen-deficient catalyst (FeCN) with single atom Fe and Fe2O3 nanoparticles dispersing on g-C3N4 matrix was synthesized and applied as a competent peroxydisulfate (PDS) activator for tetracycline (TC) degradation under visible light. The K-edge X-ray absorption fine structures and 57Fe Mössbauer measurements confirmed the unique configuration of Fe2O3 and single atom Fe active sites (pyrrolic and pyridinic FeN4) induced by the neighbouring nitrogen vacancies. The theory calculations and experiments provided a deep insight into the PDS activation and TC degradation via radical and non-radical pathways. The pyrrolic FeN4 active sites dominated the electron transfer, while the pyridinic FeN4 and Fe2O3 decomposed PDS to produce free radicals. The synergistic effect between the Fenton-like oxidation and photocatalysis is responsible for efficient TC degradation. This study offers a new strategy by integrating novel catalysts and advanced oxidation technology for effective wastewater purification.