Removal of azo dyes by eco-friendly rare-earth cross-linked sodium alginate polymer gel spheres: Equilibrium isotherms, kinetics and regeneration performance

To produce efficient green adsorbent materials, neodymium alginate (SA/Nd) gel spheres were prepared by crosslinking sodium alginate with rare earth ions using the droplet polymerization method. The prepared materials were characterized and analysed by SEM–EDS, XRD, TGA, FT–IR, UV–Vis, BET–BJH and XPS, and the adsorption performance of the SA/Nd for two azo dyes in water was investigated. The results show that the SA/Nd has a pleated structure with abundant oxygen-containing functional groups. The maximum adsorption capacities for the dyes reached 1325 and 1175 mg/g under the optimal conditions. The adsorption process is consistent with the pseudo-second-order kinetic model and is accomplished by a combination of physical and chemical adsorption. The Langmuir isotherm model better reflects the adsorption equilibrium, and surface monolayer-dominated adsorption occurs. After seven cycles of desorption and recycling of the adsorbent material, the removal rate of the two azo dyes remained above 80%. The SA/Nd promotes the efficient adsorption of dyes mainly through electrostatic interactions, hydrogen bonding and complexation. These results provide reference data for the treatment of printing and dyeing wastewater.