Degradation of enrofloxacin by a novel Fe–N–C@ZnO material in freshwater and seawater: Performance and mechanism

Abstract

In this study, we investigated the doping of Fe–N–C with ZnO (Fe–N–C@ZnO) to enhance its performance in the reduction of biological toxicity and degradation of enrofloxacin (ENR) in seawater. The steady-state/transient fluorescence analysis and free radical quenching test indicated an extremely low electron–hole recombination rate and the generation of reactive oxygen species in Fe–N–C@ZnO, leading to an improvement in the energy efficiency. We compared the ENR degradation efficiencies of Fe–N–C@ZnO and ZnO using both freshwater and seawater. In freshwater, Fe–N–C@ZnO exhibited a slightly higher degradation efficiency (95.00%) than ZnO (90.30%). However, the performance of Fe–N–C@ZnO was significantly improved in seawater compared to that of ZnO. The ENR degradation efficiency of Fe–N–C@ZnO (58.87%) in seawater was 68.39% higher than that of ZnO (34.96%). Furthermore, the reaction rate constant for ENR degradation by Fe–N–C@ZnO in seawater (7.31 × 10−3 min−1) was more than twice that of ZnO (3.58 × 10−3 min−1). Response surface analysis showed that the optimal reaction conditions were a pH of 7.42, a photocatalyst amount of 1.26 g L−1, and an initial ENR concentration of 6.56 mg L−1. Fe–N–C@ZnO prepared at a hydrothermal temperature of 128 °C and heating temperature of 300 °C exhibited the optimal performance for the photocatalytic degradation of ENR. Based on liquid chromatography–mass spectrometry analysis, the degradation processes of ENR were proposed as three pathways: two piperazine routes and one quinolone route.