Hierarchical porous nanosheets of Co-Mn bimetallic oxide from deep eutectic solvent for highly efficient peroxymonosulfate activation

The development of highly active catalysts is the key to the successful application of sulfate radical (SO₄^·−)-based advanced oxidation processes (AOPs) to wastewater treatment. Herein, bimetallic oxide CoMn₂O₄ hierarchical porous nanosheets (CoMn₂O₄ HPNSs) were constructed using glucose/urea deep eutectic solvent (DES) as sustainable solvent and self-formed sacrificial carbon templates. The prepared CoMn₂O₄ HPNS exhibited outstanding peroxymonosulfate (PMS) activation performance, achieving the rapid degradation of refractory organic compounds in wastewater, including 5-sulfosalicylic acid (100%), acetaminophen (100%), oxtetracycline (100%), and sulfamethoxazole (91%) within 20 min. This excellent performance was attributed not only to the synergistic catalytic effect of Co-Mn bimetals, but also to the hierarchical porous structure which exposes more active sites and accelerates the migration of PMS and organic pollutants. In addition, CoMn₂O₄ HPNS also showed excellent reusability and high stability in multiple cycles of degradation. The active species quenching results and electron paramagnetic resonance measurements revealed that SO₄^·− greatly contributed to organic degradation, while ¹O₂ and ·OH also involved. Moreover, a series of other transition metal oxides (Co₃O₄, Fe₂O₃, Mn₃O₄, NiO, and CoFe₂O₄) with hierarchical porous nanosheet structures were successfully fabricated with this method. This study provides a simple, general, and low-cost strategy for fabricating hierarchical porous transition metal oxides, which are promising for the environmental remediation or many other applications in the future.