Simultaneous Activation of Peroxydisulfate and Hydrogen Peroxide by Sulfidated Nanoscale Zero-Valent Iron for Efficient MTBE Degradation: Significant Role of Oxygen Vacancy

Nanoscale zero-valent iron (nZVI)-based advanced oxidation processes (AOPs) are limited by the rapidly formed surface layer of iron (oxyhydr) oxides. This restriction can be broken by the simultaneous activation of H2O2 and peroxydisulfate (PDS, S2O82-) over sulfidated nanoscale ZVI (S-nZVI), which displayed a synergistic effect to alleviate the drawbacks of the oxidants used alone. In this work, a biochar-supported S-nZVI (noted as S-nZVI@BC) was employed to simultaneously activate PDS and H2O2 for methyl tert-butyl ether (MTBE) degradation, and the rate constant for S-nZVI@BC/Bi-ox (Bi-ox, bi-oxidant at 1:1 molar ratio of PDS and H2O2) was 3.7-, 4.5-, and 12.8-fold higher than that of nZVI@BC/Bi-ox, S-nZVI@BC/PDS, and S-nZVI@BC/H2O2. According to electron paramagnetic resonance (EPR), X-ray photoelectric spectroscopy (XPS), and in-situ oxygen detection analyses, oxygen vacancies were generated over the shell of S-nZVI@BC during PDS activation, and the oxygen vacancy-contained surface layers promoted H2O2 adsorption and dissociation to produce surface-bound center dot OH (center dot OHads), thus significantly improving H2O2 utilization efficiency and accelerating MTBE degradation. These findings provide promising S-nZVI-based AOPs by combining H2O2 and peroxydisulfate activation for environmental remediation and bring insights for the creation of oxygen vacancy-containing materials for peroxide activation.