Synthesis of oxidized Dioscorea dumentorum starch nanoparticles for the adsorption of lead(II) and cadmium(II) ions from wastewater

The search for efficient adsorbents for the treatment of wastewater has led to the exploration of derivatized starches. Here, Dioscorea dumentorum starch was isolated, oxidized and acid-hydrolyzed in a dual-modification approach. The native starch (NTS) and the resulting oxidized starch nanoparticles (Oxy-SNPs) were characterized by FTIR, SEM, XRD and TGA, and then applied in removing Pb2+ and Cd2+ ions from simulated wastewater. Investigation of the functional properties of the starches as well as their characterization confirmed the success of the modification and the suitability of the Oxy-SNPs as adsorbent for metal-ions removal. Adsorption of Pb2+ and Cd2+ ions increased with augmentation of initial metal-ions concentration. Metal removal peaked and flattened after 90 min. Freundlich isotherm gave a superior fitting of experimental data above the Langmuir and Dubinin-Radushkevich (D-R) isotherms, indicating energetically heterogeneous Oxy-SNPs surface. Kinetic data followed the pseudo-second-order model with R2 values of 0.9934 and 0.9989 for Pb2+ and Cd2+ ions, respectively, signifying that the valency forces caused sharing or exchange of electrons during the interactions. Thermodynamic parameter showed that the processes were feasible, exothermic and occurred with decrease disorderliness. Energy values calculated from D-R model (35.36 kJ/mol for Pb2+; 28.87 kJ/mol for Cd2+), the good fitting of Elovich model and the magnitude of ΔHº being <29 kJ/mol all suggest chemical adsorption.