What question did this study set out to answer?

The research aims to develop a novel urea-tailored biochar for effective degradation of carbazole in contaminated environments.

March 7, 2026Open Access

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

Key Points

The research aims to develop a novel urea-tailored biochar for effective degradation of carbazole in contaminated environments.
Synthesis of urea-tailored biochars via low-temperature co-pyrolysis
Activation of peroxydisulfate for carbazole degradation
Characterization and analysis of electron transfer processes
Assessment of toxicity of degradation intermediates
Achieved ∼90% carbazole removal within 1 hour at pH 3-9
Successfully degraded carbazole in soil with 71-82% removal
Identified a non-radical degradation pathway mediated by electron transfer
Reduced toxicity of degradation intermediates with no adverse effects on soybean growth

Abstract

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. • Low-temperature urea doping enables the pyrolyzed biochar with ultra-high N content. • Doped in-plane and out-of-plane protonated pyridinic NH on UBC5 respectively immobilize CBZ and PDS. • UBC5/PDS system degrades CBZ primarily via non-radical pathways of ETP and 1 O 2. • CBZ potential degradation pathway, mechanism and toxicological alteration by UBC5/PDS system are proposed.

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

Key Points

Abstract

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