Degradation of organic pollutants using a ternary heterojunction catalyst (CoS2/CoCo2O4–MnFe2O4) for activating peroxymonosulfate with magnetic separation, anti-ion interference, and low ion leaching

Abstract

Activating persulfate to generate reactive oxygen species (ROS) for the effective degradation of toxic organic compounds is an important research topic in environmental management. However, designing a catalyst that meets the key requirements of low ion leaching, magnetic separation, anti-ion interference, and efficient activation has proven challenging. Here, a triple-phase heterojunction catalyst consisting of cobalt sulfide (CoS₂), cobalt oxide (CoCo₂O₄), and manganese iron oxide (MnFe₂O₄) was successfully synthesized. It was utilized to activate peroxymonosulfate (PMS), achieving efficient degradation of tetracycline hydrochloride (TC), with a removal rate of 84.8% in 60 min under the initial conditions of 100 mg L⁻¹ catalyst and 1 mM PMS. Additionally, the CoS₂/CoCo₂O₄–MnFe₂O₄ heterojunction resulted in high removal rates of other organic pollutants over treatment times as short as 5 min [levofloxacin (LFX): 91.8%, metronidazole (MNZ): 61.6%, rhodamine B (RhB): 100%, crystal violet (CV): 100%, respectively]. The presence of iron (Fe), cobalt (Co), and manganese (Mn) as metal elements provided numerous active sites and accelerated the rate of electron transfer. Additionally, the synthesized CoS₂/CoCo₂O₄–MnFe₂O₄-2 composite exhibited excellent interference resistance, with the catalytic effect remaining over 73% in the presence of 10 mM inorganic ions (Cl⁻, NO₃⁻, and H₂PO₄⁻). The incorporation of MnFe₂O₄ into the catalyst greatly reduced the leaching of Co²⁺ ions (from 15.27 mg L⁻¹ to 3 mg L⁻¹) and enabled it to exhibit strong magnetism. This magnetic property (the saturated magnetization reached 50.79 emu g⁻¹) enabled easy separation of the catalyst from the treated solution using magnets. Moreover, the catalyst demonstrated good reusability and stability. The ternary heterojunction catalyst designed not only effectively reduced the use of toxic ions, but also suppressed the leakage of toxic ions, and had an efficient magnetic separation activity, which has resulted in promising application prospects in actual water bodies.