Flower-like Fe3O4@manganese dioxide@tannic acid core-shell structure for efficient adsorption of dyes and Mn (VII) in water

It causes water pollution mainly from textile wastewater and industrial wastewater in large quantities, which causes irreversible harm to the environment. In this study, a novel composite adsorbent (Fe₃O₄@MnO₂@TA) was synthesized by integrating tannic acid (TA) with Fe₃O₄ and MnO₂ via a hydrothermal method. The adsorption performance of the composite toward methylene blue (MB), malachite green (MG), crystal violet (CV), and Mn (VII) in aqueous solution was systematically investigated. The Fe₃O₄@MnO₂@TA composites were characterized by SEM, TEM, XRD, FTIR, TGA and BET. The magnetic magnitude of Fe₃O₄@MnO₂@TA composites was 5.06 emu g⁻¹, which provided a magnetic basis for the recovery of the composites. Considering the target range of various influencing factors during the adsorption process, the effects of such variables as adsorbent type, initial concentration, adsorption time, and adsorption temperature on pollutant adsorption efficiency were investigated. The adsorption behavior of MB, MG, CV, and Mn (VII) was analyzed using several kinetic and isotherm models, with the Fe₃O₄@MnO₂@TA composites satisfied the pseudo-second-order kinetic model and Langmuir isotherm models. The interactions existing between the conformal materials and MB, MG, CV and Mn (VII) were simulated by Density Functional Theory (DFT) calculations, and the results of the simulations can be matched with the experimental data. The adsorption mechanisms are mainly related to electrostatic interactions, n-π/π-π interactions, and hydrogen bonding interactions. In conclusion, Fe₃O₄@MnO₂@TA composites are adsorbents with potential applications for the removal of ions and dyes from wastewater.