Novel Fe3O4@lignosulfonate/phenolic core-shell microspheres for highly efficient removal of cationic dyes from aqueous solution

The application of green adsorbents from renewable biomass for dye wastewater treatment has received wide attention in recent years. In this work, novel lignin-based Fe3O4@lignosulfonate/phenolic core-shell micro spheres were fabricated for the first time to remove cationic dyes from aqueous solutions. The emulsion polymerization using p-toluenesulfonic acid as a curing agent was employed to synthesize the microspheres at a moderate temperature. Detailed characterizations were conducted to provide a broad evaluation of the micro spheres followed by batch experiments to analyze the methylene blue (as a model cationic dye) adsorption performance. Results showed that lignosulfonate/phenolic shell coated uniformly on the Fe3O4 core to form a well-defined core-shell microsphere. Due to cross-linking by phenolic resin, the lignosulfonate coated on the microspheres is highly insoluble in aqueous solutions at a wide pH range, which is prerequisite for an effective dye adsorption from wastewater. The adsorption study showed that the endothermic adsorption process was completed in 40 min and the adsorption kinetics followed a pseudo-second-order model. The equilibrium data were consistent with the Langmuir equation and the maximum monolayer capacity was 283.6 mg/g, which was much higher than those of most lignins and lignin-rich biomass. After adsorption, the microspheres were recycled and a fast regeneration ( < 10 min) was achieved using ethanol as a methylene blue extraction solvent. Overall, these results indicate that the novel Fe3O4@lignosulfonate/phenolic microspheres offer a great potential for removing cationic dyes from wastewater in practical applications.