Tailoring Lewis acidic metals and SO4 2?functionalities on bimetallic Mn-Fe oxo-spinels to exploit supported SO4?? in aqueous pollutant fragmentation

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.

Automated summary

The generation of SO4?? anchored on metal oxides through radical transfer is promising for decomposing refractory contaminants in water. By adjusting the metal compositions and Lewis acidic strength, the production of SO4?? can be optimized to increase the degradation rate of pollutants.