Preparation and characterization of magnetic sodium alginate-modified zeolite for the efficient removal of methylene blue

A magnetic sodium alginate (SA)-modified zeolite (SA/zeolite/Fe3O4) composite was prepared using the precipitation method to remove methylene blue (MB) from wastewater. SA was deposited on the surface of zeolite through CaCl2 cross-linked precipitation. Meanwhile, Fe3O4 nanoparticles were coated by SA and precipitated onto the surface of zeolite. The carboxyl group was introduced through SA modification, which enhanced the cationic adsorption capacity of the SA/zeolite/Fe3O4 composite compared with that of zeolite. Characterization analysis indicated that SA and Fe3O4 were successfully loaded onto the surface of zeolite. The effect of initial pH and results of co-existing cation adsorption experiments showed that the adsorption of MB molecules on the surface of the SA/zeolite/Fe3O4 composite mainly relied on electrostatic attraction. Infrared spectroscopic and X-ray photoelectron spectroscopic analyses proved that the mechanism underlying the adsorption between MB molecules and the SA/zeolite/Fe3O4 composite was ion exchange. Results of the adsorption model fitting showed that the adsorption process was well described by pseudo-second-order kinetics and the Langmuir isothermal line model. Adsorption thermodynamic studies suggested that the adsorption was a spontaneous exothermic process, and Langmuir analysis revealed that the theoretical maximum adsorption capacity was 181.85 mg/g. In addition, the regeneration study indicated that the adsorption was suitable for four cycles. This study suggests that the SA/zeolite/Fe3O4 composite is an ideal adsorbent for the removal of cationic dyes from an aqueous medium.