Effective adsorption of methylene blue dye onto magnetic nanocomposites. Modeling and reuse studies

Abstract

In the present study, new adsorbent beads of alginate (A)/maghemite nanoparticles (Y-Fe2O3)/functionalized multiwalled carbon nanotubes (f-CNT) were prepared and characterized by several techniques, e.g., N2 adsorption-desorption isotherms, Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA/DTG), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM) and further tested for the adsorption of the dye methylene blue (MB) from water. The beads (A/γ-Fe2O3/f-CNT) presented a relatively low BET specific surface area value of 59 m2g-1. The magnetization saturation values of A/γ-Fe2O3/f-CNT beads determined at 295 K was equal to 27.16 emu g-1, indicating a magnetic character. The time needed to attain the equilibrium of MB adsorption onto the beads was estimated within 48 h. Thus, several kinetic and isotherm equation models were used to fit the kinetic and equilibrium experimental results. The number of adsorbed MB molecules per active site, the anchorage number, the receptor sites density, the adsorbed quantity at saturation, the concentration at half saturation and the molar adsorption energy were quantified using the monolayer model. The calculated negative ΔG0 and positive ΔH0 values suggested the spontaneous and endothermic nature of the adsorption process. In addition, A/γ-Fe2O3/f-CNT composites can be used at least for six times maintaining their significant adsorptive performance and could be easily separated by using a magnet from water after treatment.