Ultraviolet light assisted heterogeneous Fenton degradation of tetracycline based on polyhedral Fe3O4 nanoparticles with exposed high-energy {110} facets

Polyhedral Fe3O4 nanoparticles (NPs) with exposed high-energy {110} facets were synthesized by hydro-thermal method using ferrous sulfate and sodium thiosulfate as precursor at 140 °C. The as-synthesized catalysts were characterized via X-ray powder diffraction (XRD), electro impedance spectra (EIS), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) at room temperature. The well-defined Fe3O4 NPs with exposed high-energy {110} facets distributed a wide size, and the percentage of {110} facets was approximately 38.5% for single Fe3O4 NPs crystal. The synergistic effect of UV irradiation and the polyhedral Fe3O4 NPs improved the photodegradation efficiency of tetracycline (TC). The degradation efficiency of polyhedral Fe3O4 NPs catalyzing UV-Fenton system reached 96.7% after 60 min reaction, which was more substantial than polyhedral Fe3O4/H2O2 system (40%) and spherical Fe3O4 NPs catalyzing UV-Fenton system (28%) after 60 min reaction. The TOC degradation efficiency reached 56.5% for polyhedral Fe3O4 NPs catalyzing UV-Fenton after 120 min reaction, while UV/H2O2 system and spherical Fe3O4 NPs catalyzing UV-Fenton was 36.0% and 22.1% respectively after 120 min reaction. Moreover, polyhedral Fe3O4 NPs catalyzing UV-Fenton system exhibited an extremely wide pH range (from 3.0 to 9.0) for efficient degradation of TC. Simultaneously, the extraordinary high degradation efficiency was based on 10 mM H2O2 concentration, which had low requirement for H2O2. Further, the polyhedral Fe3O4 NPs could be reused for five consecutive cycles while still achieving at 91.7% of its original degradation efficiency and recycled under a magnetic field along with excellent chemical stability. Ultraviolet light assisted heterogeneous Fenton in the polyhedral Fe3O4 NPs system improved the OH and O2− production efficiency and Fe(III)/Fe(II) redox cycle, which consequently achieved an excellent degradation efficiency.