Facet-controlled activation of persulfate by magnetite nanoparticles for the degradation of tetracycline

Abstract

Three kinds of magnetite nanoparticles (MNPs) with different exposed crystal facets were synthesized by hydrothermal methods to investigate the effects of exposed facets on the catalytic performance. Under the heterogeneous activation of persulfate (PS), MNPs exposed with {111} facet exhibited better catalytic performance than that exposed with {110} or {100} facet in the degradation of tetracycline, and catalytic performance followed the order of MNPs{111} > MNPs{100} > MNPs{110}. The degradation efficiency of PS/MNPs{111} system reached 74.38% in 4 h, which was much higher than PS/MNPs{110} (19.29%) or PS/MNPs{100} (33.79%) system. Hydroxide, physically adsorbed H2O on the MNPs surface and transformations of Fe(II)/Fe(III) were the main factors to determine the high catalytic performance of MNPs{111} for PS, as illustrated by the X-ray photoelectron spectroscopy (XPS) analysis. The corresponding catalytic oxidation mechanism has been proposed on the basis of attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR), electron paramagnetic resonance (EPR) spectroscopy and quenching tests. SO4− and OH were the main radicals in catalytic degradation of tetracycline. Density functional theory (DFT) analysis suggested that the difference of {110}, {111} and {100} facets of magnetite determine the electron density and the density of states on the surface of catalysts. In addition, relatively low concentration of humic acid promoted the removal of tetracycline, and higher concentration of humic acid inhibited the tetracycline removal.