Heterogeneous Fenton-like degradation of tetracyclines using porous magnetic chitosan microspheres as an efficient catalyst compared with two preparation methods

The construction of heterogeneous Fenton-like catalyst with high efficiency is crucial for wastewater treatment. In this study, magnetite nanoparticles were successfully embedded into chitosan beads to form a porous structure (Fe3O4-Cs) by in-situ or two-step method, and it was put forward as a kind of Fenton-like catalyst to degrade tetracyclines for the first time. SEM, TEM, XRD, FT-IR, XPS, TG and BET technologies were used to characterize its properties. After comparing the tetracycline hydrochloride (TC) degradation efficiencies of two prepared beads, the in-situ method was selected for subsequent studies. The influential factors of TC degradation efficiency were investigated, including iron content, pH value, the amount of H2O2, reaction temperature, catalyst dosage and initial TC concentration. The results showed that under the optimal conditions, about 96.0% of TC (48.09 mg/L) and 68.3% of total organic carbon (TOC) were degraded within 20 min and 120 min, respectively. The degradation efficiencies for the other two tetracyclines: oxytetracycline (OTC) and doxycycline hyclate (DOTC), have been explored as well. And the degradation process followed pseudo first order kinetic equation. In addition, these Fe3O4-Cs beads with saturated magnetization could be easily reused for 6 cycles without significantly reducing catalytic activity. High degradation performance of beads was attributed to the stable porous structure, abundant active sites and possible synergistic effects between two components, which promoted the formation of hydroxyl radicals (HO center dot) for TC degradation. The possible reaction pathways and mechanism on TC degradation were discussed technically. In short, these results indicated that macroscopic Fe3O4-Cs beads (3-4 mm) with high efficiency, excellent stability and reusability exhibited a superior Fenton-like process on the removal of tetracyclines for future application.