Magnetic Core–Shell Fe3O4@polypyrrole@4-vinylpyridine Composites for the Removal of Multiple Dyes

Although adsorption materials demonstrate a great potential in adsorbing dye molecules, fabricating an adsorbent that can adsorb multiple dyes at the same times has met with limited success. Here, magnetic core–shell Fe3O4@PPy@4-VP composites are successfully fabricated for the treatment of a variety of dyes including methylene blue (MB), malachite green (MG), rhodamine B (RhB), and alizarin red (AR). The effects of concentration of dyes, temperature, and time on the adsorption performances are studied. The adsorption properties are further elucidated by adsorption kinetics, isotherm, and adsorption thermodynamic models in detail. The results show that the fitted adsorption kinetic curves for the four dyes (MB, MG, RhB, and AR) fit better to the proposed pseudo-second-order model. The adsorption process for MB, MG, RhB, and AR is in accordance with the Langmuir model, and the adsorption process for AR is in accordance with the Freundlich isotherm model. The Boyd film diffusion model and intraparticle diffusion model are used to explore the diffusion process of adsorption. Meanwhile, the discussion of adsorption thermodynamics indicates that the adsorption process of four dyes shows a spontaneous endothermic behavior. In addition, the removal amounts q after five adsorption–desorption cycles are 98.98, 97.37, 97.87, and 39.49% for MB, MG, RhB, and AR, respectively, and the losses are less than 1%. The prepared adsorbent is not only capable of adsorbing various dyes simultaneously, but it, with a saturation magnetization value of 33.84 emu g–1, can be rapidly separated from solution, thus offering a wide range of applications in the field of separation and adsorption.