Magnetic Double-Crosslinked Nanocomposite Hydrogel Beads for Methylene Blue Removal

A magnetic double-crosslinked nanocomposite hydrogel beads that can be used for water treatment were prepared through the construction of ionic bonds and borate bonds, using sodium alginate, poly(vinyl alcohol) and graphene oxide/ferroferric oxide nanocomposites (GO/Fe3O4) as raw materials. The characterization studies of the prepared hydrogel beads were performed by XRD, FTIR, XPS, SEM, and TGA. The adsorption process was investigated by varying the dye, GO/Fe3O4 contents, pH, adsorbent dosage and initial dye concentration. The highest removal efficiency of cationic dye methylene blue by the prepared hydrogel beads could reach 95.2%. The adsorption kinetics experimental results confirmed that the adsorption of methylene blue on the prepared hydrogel beads was mainly chemisorption, and the intraparticle diffusion was the only rate-controlling. After five cycles of use, the prepared hydrogel beads could still remove >94% of methylene blue in solution. The mechanism analysis based on FTIR and XPS measurements illustrated that the excellent removal efficiency of the hydrogel beads was mainly due to the hydrogen bonding and electrostatic attraction between hydrogel beads and methylene blue molecules. This investigation revealed that a low-cost, high-efficiency, magnetically separable adsorption material has been successfully prepared, which has potential application value for the removal of cationic compounds in wastewater.