MgAlFe-Mixed Metal Oxides Derived from Layered Double Hydroxides Enhanced Peroxydisulfate Activation for Ciprofloxacin Degradation via an Electron Transfer Mechanism

Advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) dominated by the nonradical pathway have aroused great concern in organic pollutant degradation due to the high tolerance to interference. However, secondary pollution caused by leached metal ions remains a scientific challenge for PDS activators that are mainly composed of transition metals. To develop efficient and green metal catalysts for PDS activation, we proposed a coprecipitation combined with calcination approach to prepare MgAlFe-mixed metal oxides (MMOs). MMO-700 obtained by calcination at 700 °C possesses a large specific surface area (213.14 m2/g) and atomically dispersed active sites, which synergistically facilitated the enrichment of abundant ciprofloxacin (CIP) and PDS on the catalyst surface, thereby providing a prerequisite step for PDS activation. This featured system selectively generated the MMO-700/PDS* complex, resulting in an efficient degradation efficiency of 79.7% for CIP with almost no leaching of Fe detected. Impressively, MMO-700 also exhibited excellent environmental adaptability and desirable catalytic efficiency in the PDS* complex-mediated electron transfer process. In addition, CIP degradation involved three possible pathways including the opening and oxidation of the piperazine ring, the opening of the cyclopropyl ring, and the transformation of the quinolone group. This study provides a new strategy for developing efficient and green catalysts to achieve PDS nonradical activation and contribute to wastewater treatment.