Carbon vacancies modulated confined Fe single-atoms on loofah-derived biochar for Fenton-like process via non-radical PAA activation

Efficient activation of peracetic acid (PAA) via electron transfer pathway (ETP) is attractive for water treatment, yet flexibly tuning the host electronic environment of single-atom sites while retaining scalability remains challenging. Herein, the concentration of carbon defects (CDs) surrounding Fe–N₅ centers in loofah-derived biochar is tuned by varying the CaCO₃ dosage during one-step carbonization. CaCO₃ concurrently acts as a spacer, in-situ etchant, and CO₂-blowing agent, generating a hierarchically porous framework that exposes Fe–N₅ sites and preserves mechanical integrity. The resulting LP-FeSAC achieves rapid bisphenol A (BPA) removal with k obs  = 1.61 min −1 within 9 min across pH 3–11. Increasing CDs density boosts PAA oxidation over the Fe single-atom catalyst, with broad tolerance to water matrices via a non-radical ETP (97.9%). DFT calculations reveal that CDs-induced Fe N bond compression reorganizes the Fe-3d crystal-field manifold (t₂g/eg), upshifts the d-band center, and lowers the interfacial barrier for ETP. In continuous flow, an LP-FeSAC-functionalized hollow-fiber module sustains ≈90% BPA removal for 600 min with minimal Fe leaching (≤12 μg L −1 ). This work establishes defect-guided hierarchical porosity and Fe–N₅ as an accessible co-catalytic anchor for designing ETP-selective, non-radical advanced oxidation, providing a scalable waste-to-resource route toward remediation of emerging aqueous pollutants.