Heterogeneous catalysts with low cost, little hazardous, high effective and facile separation from aqueous solution are highly desirable. In this study, magnetic Fe3O4-MnO2 core-shell nanocomposites with various Fe/Mn weight ratios were synthesized through a facile one pot method and then characterized. These as-synthesized solids were applied to activate the peroxymonosulfate (PMS) for 4-chlorophenol degradation. The sample 3 with a Fe/Mn molar ratio of 4:1, which can be separated conveniently through external magnetic field, exhibited higher activity than other Fe3O4-MnO2 nanocomposites, pure MnO2 and physical mixture of Fe3O4 and MnO2. The effects of operational parameters on the catalytic activity of sample 3, including initial Oxone and pollutant dosage, pH and catalyst dosage, were assessed. The catalyst had high stability and good reusability according to five successive repeated reaction. The reactive radicals generated in the PMS/Fe3O4-MnO2 nanocomposites system were sulfate radical (SO4-center dot) and hydroxyl radical (center dot OH). The enhancement of the nanocomposites may be attributed to the interaction of Fe3O4 with MnO2 on the basis of the in situ ATR-FTIR analysis and XPS spectrum. (C) 2014 Elsevier B.V. All rights reserved.