One-step fabrication in aqueous solution of a granular alginate-based hydrogel for fast and efficient removal of heavy metal ions

Granular alginate-based hydrogels were prepared in situ in an aqueous solution via grafting and crosslinking reactions among sodium alginate (SA), acrylic acid (AA), polyvinylpyrrolidone (PVP), and gelatin (GE). Fourier transform infrared spectra, elemental analysis, and scanning electrical microscopy revealed that AA monomers were grafted onto an SA backbone, and that PVP and GE were present in the hydrogel network as linear interpenetrating components. The grafting polymerization and crosslinking reaction between only SA and AA yielded a bulk gel, but the introduction of PVP and GE into the reaction mixture led to the formation of granular products. Electrostatic and hydrogen-bonding interactions among SA, PAA, PVP, and GE were the main driving forces for the formation of granular products. The adsorption isotherms and adsorption kinetics were evaluated for the adsorption of model heavy-metal ions on one of the hydrogels. The results indicated that the hydrogel has satisfactory adsorption capacities (3.028 mmol/g, Ni2+; 3.146 mmol/g, Cu2+; 2.911 mmol/g, Zn2+; 2.862 mmol/g, Cd2+), adsorption rates, and recovery capacities for the target metal ions. In addition, competitive adsorption results suggested that the hydrogel has a stronger affinity for Cu2+ ion than for the other ions.