Novel magnetic gel composite based on sodium alginate crosslinked by Yttrium(III) as biosorbent for efficient removal of direct dyes from aqueous solution

Abstract

A novel magnetic gel composite Fe3O4@SA/Y was synthesized by synergistic cross-linking reaction of sodium alginate (SA) and Yttrium(III) ions with Fe3O4 and characterized by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Fourier Transform-Infrared (FTIR), Vibrating Sample Magnetometer (VSM), X-ray Photoelectron Spectroscopy (XPS) and BET specific surface area test method, respectively. The magnetic composite was used for the removal of three dyes, Direct Blue 86 (DB-86), Direct Green 6 (DG-6) and Direct Brown 2 (DB-2) from water. Batch adsorption studies show that the ultra-high removal efficiency of 98.8, 97.2 and 95.6% for DB-86, DG-6 and DB-2 adsorption onto Fe3O4@SA/Y in 120 min of contact time at pH 2.0 decreases slightly with the pH increase from 2.0 to 10.0 at 298 K. The adsorption process of each dye completely accords with the pseudo-second order rate model. Equilibrium data of DB-86 conform to the Langmuir model well, while the adsorption behavior of DG-6 and DB-2 can be better described by the Freundlich model. The saturated adsorption capacity can reach 370, 435 and 1250 mg/g for DB-86, DG-6 and DB-2 at 328 K, respectively. The thermodynamic studies revealed the spontaneous and endothermic nature of adsorption reaction. The dye adsorption by Fe3O4@SA/Y mainly involved electrostatic adsorption, hydrogen bonding and complexation. An eco-friendly Fe3O4@SA/Y biosorbent with high-cost performance and easy separation through magnetic properties has promising application for the efficient removal of dark color for dye effluent with a very wide pH range.