Microwave-Assisted Synthesis of SDS-Functionalized Maghemite Nanoparticles with Enhanced Efficiency for the Adsorptive Removal of Methylene Blue Dye

The performance in adsorptive removal of the methylene blue (MB) dye onto three magnetite derivatives nanoparticles was investigated in a batch system. The produced powders consisted of ultrasmall (~ 9–10 nm) nanoparticles of magnetite (Magn), maghemite (Magn-calc.) and sodium dodecyl-functionalized maghemite (Magh@SDS). Magh@SDS was synthesized using microwave-assisted method. The produced powders were characterized for their purity, structure, microstructure, surface functionality and chemical and thermal stability using various techniques. A clear superiority of Magh@SDS nanoparticles for the removal of MB as compared to the pristine nanoparticles was observed. For Magh@SDS the adsorption capacity was found to be highly dependent on the pH of the MB solution, the highest removal efficiency was observed for pH ~ 11.6. The adsorption rate followed a pseudo-second-order kinetic model. While, the experimental equilibrium data were more consistent with the isotherm Freundlich model. Based on Freundlich model a high adoption capacity was calculated, it is of ~ 400 mg g⁻¹ for an adsorbent dosage of 0.25 g L⁻¹ and pH ~ 11.6. The plausible adsorption mechanism of the dye MB onto Magh@SDS nanoparticles was proposed. It involves both chemisorption and physisorption bindings. Additionally, the effect of various coexisting ions was investigated and no significant negative effect on the adsorption capacity of Magh@SDS was observed. Besides, a good reusability performance was observed after repeating seven consecutive adsorption–desorption-regeneration-reuse cycles. A comparative study of Magh@SDS nanoadsorbent with various types of adsorbents for the adsorptive uptake of MB was conducted and Magh@SDS was among the few most performant adsorbents.