LAUSR

Abstract Generation of SO4•- anchored on metal oxides via radical transfer from •OH to surface SO42- functionality (•OH → SO4•-) is singular, unraveled recently, and promising to decompose aqueous refractory contaminants. The core in furthering supported SO4•- production is to reduce the energy required to accelerate the rate-determining step of the •OH → SO4•- (•OH desorption), while increasing the collision frequency between the •OH precursors (H2O2) and H2O2 activators (Lewis acidic metals) or between SO42--attacking radicals (•OH) and supported SO4•- precursors (SO42-). Herein, Mn-substituted Fe3O4 oxo-spinels (MnXFe3-XO4; MnX) served as reservoirs to accommodate the Lewis acidic Fe/Mn and SO42-, whose properties were tailored by altering the metal compositions (X). The production of supported SO4•- via the •OH → SO4•- was of high tangibility, as confirmed by their electron paramagnetic resonance spectra coupled with those simulated. A concave trend was observed in the plot of the Lewis acidic strength of Fe/Mn versus X of MnX with the minimum at X∼ 1.5. Hence, Mn1.5 could expedite •OH liberation from the surface most proficiently and therefore exhibited the greatest initial H2O2 scission rate, as corroborated by its lowest energy barrier needed for activating the •OH → SO4•-. Meanwhile, a volcano-shaped trend was found in the plot of SO42- concentration versus X of MnX (other than Mn3). This could tentatively increase the collision frequency between •OH and SO42- on the surface of Mn1.5, as partially substantiated by its second largest pre-factor among the catalysts. Therefore, Mn1.5 exhibited the highest phenol consumption rate (-rPHENOL, 0) among the catalysts, which was ∼20-fold larger than those for SO42--modified Fe2O3 and NiO, which we reported previously. Mn1.5 also outperformed other catalysts in recycling phenol degradation, fragmenting another pollutant (aniline), and mineralizing phenol/aniline.