Selective and efficient removal of emerging contaminants by sponge-like manganese ferrite synthesized using a solvent-free method: Crucial role of the three-dimensional porous structure.

Ubiquitous macromolecular natural organic matter (NOM) in wastewater seriously influences the removal of emerging small-molecule contaminants via heterogeneous advanced oxidation processes because this material covers active sites and quenches reactive oxygen species. Here, sponge-like magnetic manganese ferrite (MnFeO-S) with a three-dimensional hierarchical porous structure was prepared via a facile solvent-free molten method. Compared with the particle-like structure of MnFeO-P, the sponge-like structure of MnFeO-S presents an enlarged specific surface area (112.14 m·g vs. 58.73 m·g) and a smaller macropore diameter (68.2-77.2 nm vs. 946.5 nm). Enlarging the specific surface area increases the exposure of active sites, and adjusting the pore size helps sieve NOM and emerging contaminants. These changes are expected to effectively improve the degradation activity and overcome interference. To confirm the superiority of the sponge-like structure, MnFeO-S was used to activate peroxymonosulfate (PMS) for the degradation of multiple emerging contaminants, and its ability to degrade bisphenol A with and without humic acid (HA) was compared with that of MnFeO-P. The degradation activity of MnFeO-S was 1.6 times greater than that of MnFeO-P. Moreover, 20 mg·L HA inhibited the degradation activity of MnFeO-S by only 7.1%, which was much lower than that obtained for MnFeO-P (53.4%). In addition, the excellent performance was maintained in multiple water matrices. Notably, under lake water matrices, the degradation activity of MnFeO-P was inhibited by 35.6% while that of MnFeO-S was hardly inhibited. More importantly, the MnFeO-S/PMS system was also applicable to the treatment of actual wastewater and 73.0% and 90.1% of total organic carbon and chemical oxygen demand was removed from bio-treated coking wastewater containing non-biodegradable contaminants and NOM. This study provides an alternative route for the green production of high-activity porous spinel ferrites with environmental anti-interference properties.