Biomass ash-derived Fe self-doped zeolites for PMS mediated oxytetracycline degradation: Mechanism, pathways and...

The increasing accumulation of biomass power plant ash and widespread antibiotic pollution in water urgently demand sustainable treatment technologies. Herein, an endogenous Fe self-doped zeolite catalyst ANA-2.0 was successfully synthesized from biomass ash and the naturally occurring residual Fe in the ash, and applied to activate peroxymonosulfate (PMS) for oxytetracycline (OTC) degradation. The ANA-2.0/PMS system achieved 95.2% OTC removal at 20 mg/L within 60 min. It displays stable catalytic properties over a broad pH range (3-12), OTC removal efficiency remains above 84.7% in the presence of common anions and humic acid, and the removal efficiency remained at 74.1% after five cycles. Mechanistic analysis revealed a dynamic Fe²⁺/Fe³⁺ redox cycle during the PMS activation, and the simultaneous generation of reactive oxygen species (ROS), including SO₄^•-, •OH, O₂^•- and ¹O₂, where ¹O₂ and O₂^•- dominated, indicating a coupled radical/non-radical oxidation pathway. DFT calculation and LC-MS analysis demonstrated that oxygen-containing functional groups, dimethylamine substituents and their adjacent conjugated carbon atoms in OTC molecules are the most vulnerable sites for ROS attack. Toxicity prediction and wheat seed cultivation experiments substantiated the toxicity of the OTC solution was reduced. The fixed bed and hydrogel bead columns maintain stable OTC removal for 600 min, with efficiencies of 80.3% and 69.8%, respectively. Biomass ash-derived zeolite offers a cost-effective strategy for biomass ash valorization and antibiotic-contaminated water treatment.