Ball milled Fe0@FeS hybrids coupled with peroxydisulfate for Cr(VI) and phenol removal: Novel surface reduction and activation mechanisms

Fe-0@FeS hybrids were synthesized by ball milling and applied to couple with peroxydisulfate (PS) for Cr(VI) reduction and phenol oxidation. A synergistic effect between Fe-0 and FeS for contaminants removal was found in experimental results. The removal rates of Cr(VI) and phenol by ball milled Fe-0@FeS hybrids coupled with PS were 97% and 88.7% (initial concentrations of Cr(VI) and phenol are 35 and 40 mg/L, respectively), indicating a successful treatment method for industrial wastewater containing metals, metalloids and organic pollutants. Concentrations of Cr(VI) lower than 45 mg/L could promote the degradation of phenol, while high concentration of Cr(Vl) inhibited phenol degradation. Acidic conditions were beneficial to Cr(VI) and phenol removal. Scan electron microscope (SEM), Fourier transform infrared spectroscopy (MR), and X-ray photoelectron spectroscopy (XPS) analysis suggested that surface morphology and element valence of ball milled Fe-0@FeS hybrids changed after reaction. Radicals quenching experiment and EPR (electron paramagnetic resonance) results illustrated that SO4 center dot(-) and HO center dot were major free radical species for phenol degradation. Fe(II) quenching experiment revealed that surface-bound Fe(II) instead of dissolved Fe(II) mainly participated in Cr(VI) reduction and PS activation. This study illustrated novel surface reduction of Cr(VI) and surface activation of PS by ball milled Fe-0@FeS hybrids, providing useful perspective for applying ball milled Fe-0@FeS hybrids for complex wastewater treatment. (C) 2020 Elsevier B.V. All rights reserved.