Silicate-Enhanced Heterogeneous Flow-Through Electro-Fenton System Using Iron Oxides under Nanoconfinement

Herein, a silicate-enhanced flow-through electro-Fenton system with a nanoconfined catalyst was rationally designed and demonstrated for the highly efficient, rapid, and selective degradation of antibiotic tetracycline. The key active component of this system is the Fe₂O₃ nanoparticle filled carbon nanotube (Fe₂O₃-in-CNT) filter. Under an electric field, this composite filter enabled in situ H₂O₂ generation, which was converted to reactive oxygen species accompanied by the redox cycling of Fe³⁺/Fe²⁺. The presence of the silicate electrolyte significantly boosted the H₂O₂ yield by preventing the O-O bond dissociation of the adsorbed OOH*. Compared with the surface coated Fe₂O₃ on the CNT (Fe₂O₃-out-CNT) filter, the Fe₂O₃-in-CNT filter demonstrated 1.65 times higher k_L value toward the degradation of the antibiotic tetracycline. Electron paramagnetic resonance and radical quenching tests synergistically verified that the dominant radical species was the ¹O₂ or HO· in the confined Fe₂O₃-in-CNT or unconfined Fe₂O₃-out-CNT system, respectively. The flow-through configuration offered improved tetracycline degradation kinetics, which was 5.1 times higher (at flow rate of 1.5 mL min^-1) than that of a conventional batch reactor. Liquid chromatography-mass spectrometry measurements and theoretical calculations suggested reduced toxicity of fragments of tetracycline formed. This study provides a novel strategy by integrating state-of-the-art material science, Fenton chemistry, and microfiltration technology for environmental remediation.