Synthesis, characterization and performance evaluation of lignosulfonate-graft-(Net-poly(acrylamide-co-(acrylic acid)-co-N,N′ methylenebisacrylamide)), for the removal of Pb2+ and Cu2+ from water

A composite material synthesized by conventional graft copolymerization of lignosulfonate (Ls), acrylic acid (AA), acrylamide (AM), and N,N-methylbisacrylamide (NNMBA) is reported. The presence of NNMBA, a crosslinker, causes the grafts to have a polymer network structure. The hydrogel material was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It was then tested for Pb²⁺ and Cu²⁺ adsorption, demonstrating a maximum removal efficiency of 90 % and 40 %, respectively. Furthermore, kinetic models revealed that the pseudo-second-order model fitted well the data for both metals. The Langmuir model provided a better fit for Pb⁺² adsorption, while the Freundlich model was more suitable for Cu²⁺ adsorption. The maximum adsorption capacities were found to be 111.94 mg/g for Pb²⁺ and 31.82 mg/g for Cu²⁺. Estimated pore radii calculated from swelling experimental data correlated well with the adsorption capacities of Pb²⁺ and Cu²⁺, offering new insights about the role of the polymer network structure on heavy metal removal.