Surfactant-free porous nano-Mn3O4 as a recyclable Fenton-like reagent that can rapidly scavenge phenolics without H2O2
Current methods that utilize Fenton-like reagents to remove persistent organic pollutants suffer from several limitations, i.e., the reagents may release metal ions into the sludge and cause secondary pollution, the reagents are easily inactivated after use, and the use of additives (e.g., 2KHSO5·KHSO4·K2SO4, Na2S2O8 and H2O2) can be costly but cannot be avoided. In this work, through a one-pot reaction, we prepared surfactant-free porous nano-Mn3O4 as an efficient Fenton-like reagent. Without the addition of external H2O2, it could remove 86.8% and 96.9% of the phenol from an aqueous solution within 1 and 5 min, respectively, and thus outperformed many other reported reagents. The underlying mechanism for the removal of organic pollutants by this Mn3O4 reagent was examined. It was found that the low-valence Mn in Mn3O4 reacted with the dissolved O2 to generate H2O2, and the H2O2 in turn created hydroxyl radicals (HO˙) to degrade organic pollutants. The Mn3O4 was also annealed to generate porous nano-Mn2O3, and a comparison of the performance of Mn3O4 and Mn2O3 in removing organic pollutants revealed that low-valence Mn in the oxides played a critical role in scavenging the pollutants. Note that this novel nano-Mn3O4 could remove pollutants without the addition of external H2O2, and it could be easily reactivated after use through reduction by NaBH4 and thus be recycled. The Mn3O4 can also be successfully applied to complex polluted water containing a mixture of phenolics. These findings pave the way for developing other efficient and environmentally friendly Fenton-like reagents for removing organic pollutants in wastewater.
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