Enabling highly concentrated tetracycline degradation with tailored FeCo nanocrystals in porous graphitic carbon fiber

Eliminating highly concentrated antibiotic wastewater by transition metal catalyst-assisted AOPs is challenging. Herein, by varying the metal precursor composition (Co/Fe ratios of 1/1, 1.5/2/3), alloyed Co₇Fe₃ nanocrystals or spinel-like CoFe₂O₄ can be switched and both confined within the porous N-doped graphitic carbon fibers by electrospinning and controlled graphitization. Impressively, iron precursors played a dual role in working as reactive centers and main activators for the creation of porous carbon networks affording improved accessibility to catalytic sites and easy tetracycline (TC) diffusion effect. The catalytic activity of the resulting materials was closely related to surface metal valence and composition. Notably, the CoFe₂O₄ exhibited a significant improvement in peroxymonosulfate (PMS) adsorption and activation, explained by the present electron-deficient Co and Fe synergetic sites together with the interesting Jahn–Teller effect. Fe₁Co₂/CNF demonstrated the highest efficiency in degrading TC, achieving a reaction rate constant of 0.4647 min⁻¹ with a low activation energy of 9.3 kJ·mol⁻¹, nearly a 7.5-fold enhancement compared to Fe₁Co₃/CNF (0.062 min⁻¹). The reaction mechanism and the role of reactive oxidative species revealed a synergy of ·SO₄⁻, ·OH, ·O₂⁻ and ¹O₂. Wherein, ·O₂⁻ plays a more dominant role in the degradation of TC than other reactive species. Additionally, a reinforced electron-transfer pathway in the Fe₁Co₂/CNF system during PMS interaction was demonstrated. Furthermore, the degradation routes of TC were unraveled, and the toxicity of various intermediate by-products was assessed. Importantly, our continuous flow-type TC degradation process and light-driven photothermal strengthened reaction process demonstrated consistent performance, thereby offering a promising approach for tackling highly concentrated antibiotic wastewater.