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

Abstract

A simple method for fabricating hierarchical composite structures consisting of K-birnessite (K_xMnO₂) 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 K_xMnO₂ 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.