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

Abstract

Fe⁰@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 Fe⁰ and FeS for contaminants removal was found in experimental results. The removal rates of Cr(VI) and phenol by ball milled Fe⁰@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(VI) inhibited phenol degradation. Acidic conditions were beneficial to Cr(VI) and phenol removal. Scan electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) analysis suggested that surface morphology and element valence of ball milled Fe⁰@FeS hybrids changed after reaction. Radicals quenching experiment and EPR (electron paramagnetic resonance) results illustrated that SO₄•⁻ and HO• 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 Fe⁰@FeS hybrids, providing useful perspective for applying ball milled Fe⁰@FeS hybrids for complex wastewater treatment.