Abstract
The Schiff base chelating ligands; (E)-2-(3,3-dimethoxy-2-oxa-7,10-diaza-3-silaundec-10-en-11-yl)phenol(L1), (E)-N-(2-((pyridine-2ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L2) and (E)-N-(2-((thiophen-2-ylmethylene)amino)ethyl)-3-(trimethoxysilyl)propan-1-amine (L3)were immobilized on Fe₃O₄ magnetic nanoparticles (MNPs) and utilized in the extraction of Cr(VI), Cd(II) and Pb(II) metal cations from aqueous solutions. The compounds synthesized, denoted as L1@Fe₃O₄-L3@Fe₃O₄, were characterized using FT-IR spectroscopy, TEM-SEM, VSM, and BET/BHJ techniques for analysis of functional groups, surface morphology, magnetic properties and degree of porosity of the adsorbents respectively. BET/BHJ technique confirmed the mesoporous nature of the compounds as their pore diameters ranged between 15-17 nm. The initial optimization conditions of pH, adsorbent dosage, initial metal concentration and contact time on adsorption were studied using L1@Fe₃O₄. The optimum efficiencies recorded were 68% and 46% for Cr(VI) and Cd(II) respectively, obtained at pH 3, and a metal concentration of 20 ppm while an efficiency of 99% was recorded for Pb(II) cations at pH 7 and a metal concentration of 100 ppm. Compounds L2@Fe₃O₄ and L3@Fe₃O₄ were also used in the extraction of metal cations from aqueous solution and gave efficiencies of 22%, 56%, 78% for L2@Fe₃O₄ and 19%, 90%, 59% using L3@Fe₃O₄ for Cr(VI), Cd(II), and Pb(II), respectively. The maximum adsorption capacities of L1@Fe₃O₄ for Cr(VI), Cd(II), and Pb(II) cations were obtained from the Langmuir isotherm as 32.84, 41.77, and 450.45 mg/g, respectively. The experimental data was analyzed using pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich kinetic models. Both linear and non-linear forms of kinetic isotherms; Langmuir, Freundlich, Redlich-Peterson, and Temkin were utilized to investigate the nature of adsorption on L1@Fe₃O₄. The mechanistic studies deduced that the Langmuir isotherm and pseudo-second-order kinetic model better described the adsorption process with high correlation coefficient values (R²>0.98).