Utilization of Nigella sativa seed biomass for copper (II) adsorption from aqueous solutions and wastewater: performance evaluation, kinetics, thermodynamics, and theoretical insights

In this study, sodium alginate (SA) and sodium alginate/graphene oxide (SA/GO) beads were used to remove copper ions (Cu²⁺) from aqueous solutions. The adsorption experiments were conducted under optimized conditions: pH 5, a contact time of 240 min, an adsorbent dose of 2 g/L, and an initial Cu²⁺ concentration of 100 mg/L. The adsorption kinetics were best described by the pseudo-second-order model, suggesting chemisorption as the rate-limiting step. The adsorption isotherm followed the Langmuir model, with a maximum adsorption capacity of 83.33 mg/g for SA/GO beads. Thermodynamic studies indicated the process was spontaneous and endothermic. The SA/GO beads demonstrated enhanced copper removal efficiency compared to SA beads, with a removal efficiency of 93.5% at 200 mg/L Cu²⁺ concentration. Computational studies, including density functional theory (DFT), confirmed strong interactions between Cu²⁺ ions and the functional groups on the adsorbent surface. The novelty of this study lies in the synergistic effect of GO incorporation into SA beads, offering a promising and efficient approach for heavy metal removal from wastewater.