Effective adsorption of Cd(II), Cr(VI) and Pb(II) ions from aqueous solutions using silica immobilized (pyridine)/(phenoxy)imine chelating agents

Mesoporous silica materials, MCM-41 and SBA-15, were used to modify the Schiff base ligands: N-(pyridin-2-ylmethyl)-3-(triethoxysilyl)propan-1-amine ( L1 ) and 2-(((3-(triethoxysilyl)propyl)amino)methyl)phenol ( L2 ) to give the respective immobilized chelating agents L1@SBA-15 , L2@SBA-15 , and L2@MCM-41 . The immobilized chelating agents were characterized using various techniques, including FT-IR, ¹H NMR, SEM, EDX, TEM, PXRD, BET, VSM, and TGA-DTA/DSC. The adsorption capacities of L1@SBA-15 , L2@MCM-41 , and L2@SBA-15 of Cr(VI), Pb(II), and Cd(II) ions from aqueous solutions were assessed under different pH, contact times, initial concentrations, and chelating agent dosages. Adsorption capacities of 9.85 mg/g, 14.42 mg/g, and 13.38 mg/g for Cr(VI) anion (pH of 3) and Pb(II) and Cd(II) at pH 9 were obtained using L2@MCM-41 . Using L2@SBA-15 , an optimum pH of 3 for Cr(VI) and Pb(II) (120 min) and 9 for Cd(II) (480 min) were obtained, affording adsorption capacities of 9.84 mg/g, 14.99 mg/g, and 14.61 mg/g, respectively. Furthermore, L2@SBA-15 exhibited optimal dosages of 0.1 mg for Cd and Pb(II) cations and 10 mg for Cr(VI) anion and initial concentrations of 10 ppm, 20 ppm, and 80 ppm for Cr(VI), Pb(II), and Cd(II) ions, respectively. The adsorption kinetics followed a pseudo- second-order model, and the Freundlich adsorption isotherm best described the equilibrium data. • N^N and N^O chelating agents synthesized and immobilized silica materials. • Immobilized chelating agents use in the removal of Cd(II), Pb(II) and Cr(VI) metal ions from water. • Adsorption efficiencies of 97 % Cd(II) and Pb(II) and 67 % for Cr(VI) anions observed. • Materials showed improved adsorption efficiencies of mixed metal ions. • The adsorbents were used in three cycles with minimal loss in adsorption efficiencies.