Urea-tailored biochar activated peroxydisulfate for carbazole degradation: An electron transfer process from in-plane to out-of-plane

Carbazole (CBZ) is a ubiquitous and toxic N-heterocyclic contaminant in water and soil, posing substantial environmental risks. Current remediation strategies for CBZ struggle with low efficiency, high energy consumption, or strict operational conditions, making persulfate-based advanced oxidation a promising alternative. Herein, we synthesized a series of urea-tailored biochars (UBCs) via low-temperature co-pyrolysis. Among them, UBC5 featuring an extremely high N content (21.4%) showed optimal peroxydisulfate (PDS) activation for CBZ degradation. The UBC5/PDS system achieved ∼90% CBZ removal within 1 h across pH 3-9, and exhibited strong resistance to inorganic anions (Cl − , SO 4 2− , H 2 PO 4 − ) and humic acid. Furthermore, the system effectively degraded CBZ in soil (71-82% within 1 h), with residual concentrations falling below safety thresholds for industrial land after 12 h. Quenching experiments, electron paramagnetic resonance, and electrochemical analyses revealed a non-radical degradation pathway: UBC5-PDS∗ mediated electron transfer, with a minor contribution from 1 O 2 . Characterizations and density functional theory calculations elucidated a unique “in-plane to out-of-plane electron transfer” mechanism. The degradation intermediates exhibited reduced toxicity, with negligible adverse effects on soybean growth. Notably, UBC5 has lower production cost ($9.52 kg −1 ) and carbon emissions (18.38 kg CO 2 e kg −1 ) than typical activators. This study provides new insight for the design of carbon-based persulfate activators and an efficient, sustainable approach for the remediation of CBZ-contaminated water and soil.