Heterogeneous Fenton degradation of ciprofloxacin by RM-Co PBA prepared with red mud as iron source and carrier

Loading catalysts onto carriers to prepare supported catalysts is an important strategy for improving dispersion, stability and catalytic performance. In this study, we synthesized a supported red mud (RM)-based Fe-Co Prussian blue analogue (RM-Co PBA) catalyst using RM as iron source and carrier by acid dissolution-reduction-coprecipitation method to activate H₂O₂ for the degradation of ciprofloxacin (CIP). The RM-Co PBA obtained under the synthesis conditions of HCl concentration of 2.4 M and potassium cobalt cyanide addition of 4 mM exhibited the best dispersibility and regular shape, resulting in high catalytic performance. The degradation efficiency of RM-Co PBA/H₂O₂ system reached 75.79% in 10 min, which was 10.54 times and 1.21 times of that of RM/H₂O₂ system and Fe-Co PBA/H₂O₂ system, respectively. The RM-Co PBA/H₂O₂ system was almost unaffected by pH and was suitable for treating low concentration CIP wastewater. Additionally, the system can be reused well and possessed certain resistance to inorganic anions. The results showed that superoxide radical (⋅O₂^-) was the main ROS attacking CIP, which accumulated continuously in the cycling process of Co(III)/Fe(III) and Co(II)/Fe(II). On the other hand, the presence of a large number of oxygen vacancies in RM-Co PBA enhanced the production of ⋅O₂^- by endowing it with good electron transfer performance. Finally, we proposed possible CIP degradation pathways and demonstrated the toxicity reduction of each pathway by a quantitative structure-activity relationship analysis. This study provides guidance for the resource utilization of RM and the efficient treatment of antibiotic wastewater.