Adsorption behaviors of heavy metal ions by different hydrazone-modified sodium alginate in aqueous medium: Experimental and DFT studies

Herein the hydrazone-modified sodium alginate, being prepared with aldimine condensation through dihydrazide and dialdehydes sodium alginate, possessed extremely effective and selective removal of Pb2+, Cd2+, and Cu2+. Equilibrium adsorption data of biphthalate dihydrazidemodified sodium alginate was obeyed the Freundlich isotherm and pseudo-second-order kinetics models, which reflected that the adsorption process was mainly via the chemisorption, and the maximum adsorption capacities for Pb2+, Cd2+, and Cu2+ were found to be 668.42, 472.37, and 200.10 mg g−1, respectively. The thermodynamic parameter for the sorption demonstrated the process was endothermic and spontaneous. Fourier Transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses revealed combination of chelation interactions coordination and ion exchange of nitrogen and oxygen atoms with heavy metal ions, and the density functional theory (DFT) calculations confirmed that heavy metal ions formed a stable five membered ring coordination structure with the nitrogen and oxygen atoms in hydrazone groups. Moreover, the adsorption efficiency was not significantly reduced after 10 adsorption–desorption recycles. To sum up, this study provides a new strategy for the removal of heavy metal ions by hydrazone-modified sodium alginate with great potential for wastewater treatment.