Removal of methylene blue dye from water with Fe3O4/poly(HEMA-co-AMPS) magnetic hydrogels

In this research, a novel magnetic hydrogel (MHG) adsorbent based on Fe3O4/poly(2-hydroxyethylmethacrylate-co-2-acrylamido-2-methylpropanesulfonic acid) Fe3O4/poly(HEMA-co-AMPS) was synthesized by in situ co-precipitation of Fe3O4 magnetic particles inside poly(HEMA-co-AMPS) hydrogels. This adsorbent was used to adsorb the organic cationic dye methylene blue (MB) from aqueous solutions. The properties of the adsorbent were characterized by FT-IR, TGA, XRD, VSM, and EDX-SEM techniques. The degree of swelling was recorded in water, acidic medium (HCl 0.01 M), and basic medium (NaOH 0.01 M). The results confirmed that Fe3O4 particles were successfully synthesized within the poly(HEMA-co-AMPS) hydrogel structure. Magnetic hydrogels have higher swelling and reach equilibrium faster than hydrogels. The magnetic hydrogel prepared with 3 % crosslinker and 10 % AMPS (MHG3(10)) showed better potential to remove MB dye, adsorption capacity Qmax = 445.35 mg/g, this was obtained under the best conditions at pH 6.5, dose of 1 g/L, and contact time of 10 min. Over the test pHpzc, the surface of the MHG3(10) is predominantly negative at pH values higher than 2.47. The adsorption process of MHG3(10) for MB removal follows the Langmuir model and obeys pseudo-second-order kinetics. In addition, thermodynamic studies performed show that the adsorption process is endothermic (ΔH0 = 75.946 kJ/mol) and spontaneous with a positive value of entropy (ΔS0 = 263.562 J/mol·K). Regeneration experiments showed that MHG3(10) can be reused several times as its removal efficiency is still 94 % after 10 adsorption–desorption cycles. Therefore, the magnetic hydrogel MHG3(10) proved to be a promising adsorbent for the removal of the pollutant MB dye from aqueous media.