Synergistic and Competitive Adsorption of Methylene Blue and Rhodamine B on Core-shell Magnetic Manganese Dioxide Nanocomposites

Background: Although pristine and modified manganese oxides were used as adsorbent for dyes removal from aqueous solutions, their applications were limited to the removal of single dye components. From the practical viewpoint, it is necessary to investigate the adsorption behavior of dyes on manganese oxide adsorbents in multi-component systems. Herein, the present work investigated the performance of core-shell magnetic manganese dioxide (Fe3O4/C/MnO2) nanocomposites as an adsorbent to remove methylene blue (MB) and rhodamine B (RhB) in single and binary dye solutions. Method: Fe3O4/C/MnO2 microspheres were prepared using the redox reaction of KMnO4 to MnO2 in alkaline solution on the surface of carbon-coated magnetite (Fe3O4/C). The effect of pH and adsorbent amount on adsorption was examined, and the adsorption isotherms and kinetics of MB and RhB in single and binary dye solutions were studied. Results: In single dye solutions, the adsorption isotherms of both MB and RhB fitted well with the Langmuir model. In binary dye solution, the adsorption amount of MB increased because of the synergetic effect, while the adsorption amount of RhB decreased due to competitive effect. The adsorption isotherms of MB and RhB in binary dye solution followed the Sheindorf-Rehbun-Sheintuch (SRS) and extended Langmuir model, respectively. Both MB and RhB adsorption could be expressed by the pseudo-second-order kinetic model in single or binary dye solutions. Conclusion: Fe3O4/C/MnO2 nanocomposites exhibited an excellent adsorption property to MB and RhB and high magnetic separability. Keywords: Fe3O4/C/MnO2 nanocomposites, methylene blue, rhodamine B, adsorption, redox reaction, binary dye solutions.