A multipath peroxymonosulfate activation process over supported by magnetic CuO-Fe3O4 nanoparticles for efficient degradation of 4-chlorophenol

Heterogeneous catalysts with low cost, environmentally friendly, highly effective and ready separation from aqueous solution are highly desirable. Magnetic CuO-Fe3O4 nanoparticles, a type of non-toxic bimetallic transition metal oxide, is a promising heterogeneous catalyst for activation of peroxymonosulfate (PMS) to generate reactive oxygen species (ROS) that has not been previously investigated. In this study, the activation of PMS by CuO-Fe3O4 nanoparticles was evaluated using the degradation of 4-chlorophenol as a model reaction. Several critical factors such as pH, catalyst dosage and PMS concentration were investigated. CuO-Fe3O4/PMS system demonstrated a wide effective pH range to degrade 4-chlorophenol, namely 5.5 to 9.5. With the increase of the catalyst dosage, the degradation efficiency of 4-chlorophenol appeared to increase first and then decrease, that the inflection point was 0.5 g/L. Elevated PMS concentration obviously improved the decomposition of 4-chlorophenol; however, the plateau was reached when the PMS concentration was 8 mM. Further increase in PMS concentration would not significantly improve the removal efficiency. Through examining the effects of scavengers and electron spin resonance (ESR) analyses, CuO-Fe3O4 nanoparticles were proven to activate PMS through a non-radical and radical pathway to generate singlet oxygen, sulfate radicals and hydroxyl radicals. Based on results, CuO-Fe3O4 nanoparticles were effective, environmentally friendly and low cost catalysts for efficient activation of PMS. These features make CuO-Fe3O4 nanoparticles a readily available heterogeneous catalyst to activate PMS for refractory organic pollutants degradation in advanced oxidation processes (AOPs).