The self-assembly stacked ladder-like CoFe₂O₄ in the peroxymonosulfate activation for antibiotic degradation

The morphology and size play an important role in the catalytic activity. In this study, a stacked ladder-like CoFe₂O₄ catalyst (T-CFO) was prepared by hard template method, which was used to activate peroxymonosulfate (PMS) to degrade ciprofloxacin (CIP). The formation of CoFe₂O₄ with an average particle size of 44 nm and high surface energy was realized by SiO₂ template, resulting in the stepped CoFe₂O₄ aggregation with low crystallinity, high specific surface area and oxygen vacancy defects through hierarchical self-assembly. Quenching experiments and electron paramagnetic resonance analysis showed that the morphology affected the types of the main reactive oxygen species (ROS) in the catalytic system. Both free radical SO₄^∙− and non-free radical ¹O₂ in T-CFO/PMS system contributed to the oxidative degradation of CIP. Under optimized reaction conditions, T-CFO had the highest CIP removal efficiency (99.9 %) than spherical CoFe₂O₄ (73.1 %) and Non-template CoFe₂O₄ (28 %) within 40 min. The reaction kinetic constants (k_obs) of T-CFO, S-CFO and N-CFO were 0.1464, 0.03376 and 0.0085 min⁻¹, respectively. In addition, the source of ¹O₂ was also explored, revealing that ¹O₂ was mainly due to the existence of oxygen vacancy except for the weak part derived from O₂^∙−. Theoretical density functional theory (DFT) calculation verified that oxygen vacancy was not only conducive to the adsorption of PMS, but also could reduce reaction energy barrier of O-O bond breaking, accelerating the generation of ¹O₂.