Self-assembled 3D flower-like hierarchical Fe3O4/KxMnO2 core-shell architectures and their application for removal of dye pollutants

A simple method for fabricating hierarchical composite structures consisting of K-birnessite (KxMnO2) nanosheets on Fe3O4 microspheres was reported in this paper. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements indicated that the size of the three-dimensional (3D) flower-like hierarchical microspheres was about 420 +/- 5 nm and the shell was composed of nanosheets with a thickness of about 5 nm. The experimental parameters such as reaction time, reaction temperature and the concentration of KMnO4 used in the solution were investigated for the growth of the core-shell hierarchical structures. These core-shell composites exhibited excellent removal efficiency (over 98% for rhodamine B (RB) and 94% for methylene blue (MB)) and rapid separation from aqueous solution by an external magnetic field, taking advantage of the combined benefits of hierarchical structured KxMnO(2) nanosheets and magnetic microspheres. In addition, the adsorption behavior of this new adsorbent fitted well with both Langmuir and Freundlich isotherms and the pseudo-second-order kinetic model. All the results demonstrate that the core-shell composites are effective adsorbents for the removal of dye pollutants and thus could provide a new platform for dye decontamination.