Removal of anionic dyes from aqueous solution by adsorption onto amino-functionalized magnetic nanoadsorbent

The amino-functionalized magnetic nanoadsorbent Fe3O4@SiO2-NH2 was prepared and it was characterized by X-ray powder diffraction, transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The adsorption of anionic dyes including Acid Orange II (AO II) and Reactive Brilliant Red X-3B (X-3B) onto Fe3O4@SiO2-NH2 was investigated. The results showed that Fe3O4@SiO2-NH2 exhibited efficient adsorption for these anionic dyes under acidic conditions, and it was proposed to proceed via electrostatic attraction and hydrogen bonding between the positively charged protonated amino groups (–NH3+) on the adsorbent surface and the negatively charged sulfonate groups (–SO3-) of the dyes. The mechanism was supported by density functional theory (DFT) calculations. The adsorption kinetics for AO II and X-3B on Fe3O4@SiO2-NH2 followed the pseudo-second-order kinetic model, and the adsorption equilibrium data fitted well with Langmuir isotherm model. The maximum adsorption capacities for AO II and X-3B at pH 2 under room temperature were 132.2 and 233.1 mg g−1, respectively. Desorption of dyes and regeneration of the adsorbent were carried out using aqueous solution at pH 10. The adsorbent Fe3O4@SiO2-NH2 could be easily recovered by external magnet and it exhibited good recyclability and reusability for three cycles use.