Green synthesis of gum Arabic-activated magnetite–nickel nanoparticles for selective removal of Cd(<scp>ii</scp>) and Cu(<scp>ii</scp>) from complex aqueous systems

Despite the growing interest in biofunctionalized magnetic nanocomposites, there is limited research on integrating nickel with gum Arabic (GA) to enhance selectivity and stability for heavy metal removal in complex aqueous systems. A green, biofunctional magnetite-nickel nanocomposite (GA-NiMMPs) was synthesized <i>via</i> a modified co-precipitation method using GA as a natural stabilizer and surface modifier. Cadmium and copper were selected as target contaminants because they are among the most hazardous and prevalent heavy metals in industrial effluents, frequently co-existing in electroplating, mining, and metal-finishing wastewaters. GA-NiMMPs exhibited a surface area of 29.32 m² g^-1, a pore diameter of 1.91 nm, and a zeta potential of -22.5 mV, favoring the adsorption of divalent metal ions and enabling their simultaneous removal. Batch adsorption experiments were conducted using 50 mg per L initial concentrations, varying pH, dosage, and contact time. High removal efficiencies of 93.5% for Cd(ii) and 89.0% for Cu(ii), with maximum capacities of 30.4 and 27.7 mg g^-1, respectively, were obtained with optimal performance at pH 6.0, 4.0 g per L dosage, and 240 min contact time. Kinetics follow a pseudo-second-order model, while isotherms fit Langmuir and Sips models, indicating monolayer chemisorption as described by the Langmuir model, alongside surface heterogeneity captured by the Sips model. The material showed higher affinity for Cd(ii), achieving 64% selectivity in binary and 58% in multicomponent systems. These results underscore GA-NiMMPs as a promising bio-derived adsorbent for sustainable Cd(ii) and Cu(ii) remediation in complex waters.