Pore engineering inducing defects-neighbored Fe single site with high spin configuration for ultrafast fenton-like catalytic degradation of tetracycline hydrochloride with singlet oxygen-dominated pathway

A mesoporous N-doped carbon bearing atomically dispersed Fe (Fe 1 -N-Cv) was created that uniquely couples carbon-vacancy and pore engineering to switch the electron spin state of highly accessible Fe sites from low-spin (t 2 g 5 e g 0 ) to high-spin (t 2g 3 e g 2 ), thereby unlocking superior Fenton-like activity. The material was synthesized by pyrolyzing Fe-encapsulated ZIFs under negative pressure, whereby the built-in pressure gradient simultaneously enlarged pores and generated carbon vacancies. Fe 1 -N-Cv degrades pollutants 3.89-fold faster than conventional Fe 1 -N-C, maintains > 99 % tetracycline removal and > 95 % mineralization during 240 min of continuous flow operation, operates over a pH range of 3.0–9.0, and shows stable recyclability and strong resistance to coexisting matrix constituents. Mechanistic analysis identifies a non-radical regime dominated by singlet oxygen, assisted by high-valent Fe-oxo and electron-transfer pathways, while DFT calculations show that carbon defects accelerate interfacial charge transfer and lower the free-energy barrier for PMS activation. Synergistic engineering of carbon vacancies and pores thus emerges as a powerful lever to modulate both the geometric accessibility and electronic spin state of single-atom Fe centers, directly translating into markedly enhanced Fenton-like performance. This strategy offers a promising approach for boosting single-atom-catalyst activity and robustness, advancing their practical deployment in continuous environmental remediation technologies.