Electronic structure engineering of Co-Fe dual single-atom sites on carbon aerogel for enhanced visible-light-assisted peroxymonosulfate activation

Single-atom catalysts (SACs) for peroxymonosulfate (PMS) activation are often constrained by the limited electronic tunability of isolated mono-metal centers, which weakens oxidant adsorption and interfacial charge transfer. Herein, we overcome this limitation by constructing a Co-Fe dual single-atom catalyst anchored on a nitrogen-doped carbon aerogel (Co–Fe/NCNA) for visible-light-assisted tetracycline degradation. Spectroscopic and synchrotron analyses confirm that atomically dispersed Co-N₃ and Fe-N₄ sites coexist within a hierarchically porous three-dimensional carbon framework, ensuring high active-site accessibility and rapid mass transport. The Co–Fe/NCNA system achieves 97.7% ± 2.6% tetracycline (TC) removal within 15 min (k = 0.22 min⁻¹), dramatically outperforming single-metal and metal-free analogues. Density functional theory calculations indicate that the coupled Co-Fe sites reconstruct the local electronic structure, elevate the d-band center, strengthen PMS adsorption, and reduce the activation barrier for PMS conversion to 0.30 eV. The TC degradation proceeds through a cooperative radical/nonradical oxidation network, in which h⁺-mediated oxidation acts as the primary apparent pathway, while ¹O₂, ·O₂⁻, ·OH, SO₄·⁻, and possible high-valent metal-oxo-like species contribute synergistically or serve as auxiliary pathways. Notably, a fixed-bed continuous-flow reactor sustains ∼95% tetracycline removal over 120 h, and outstanding activity is retained under natural sunlight. This work establishes electronic structure engineering of dual single-atom sites as a powerful strategy to boost visible-light-driven PMS activation for sustainable water remediation.