Synthesis, characterization, and sorption properties of silica gel-immobilized Schiff base derivatives

Abstract

In this study, two Schiff base ligands were synthesized and characterized by Elemental analysis, infrared spectroscopy and nuclear magnetic resonance, respectively. The silica gel surface was, respectively immobilized with Schiff base derivatives, 4-(4-(4-[1-methyl-3-oxobutidenamino]fenil] fenilimino)-2-pentanon (BAA) and 4-{5-[1-methyl-3-oxobutylideneamino]-1-naphthylimino}-2-pentanone (NAA), after surface modification by 3-aminopropyltrimethoxysilane (APTS) to prepare new adsorbents. Characterization of the surface modification was confirmed through elemental analysis, thermogravimetry and scanning electron microscopy. The immobilized silica gels (Si–APTS–BAA and Si–APTS–NAA) were used for sorption of Cu(II) ion in aqueous solution. The influence of the pH, amount of adsorbent, ion concentration, time, and temperature was investigated. The characteristics of the sorption process were evaluated by using the Langmuir and Freundlich sorption isotherms. The sorption of Cu(II) metal ion onto modified silica gels correlated well with the Langmuir type sorption isotherm and sorption capacities were found to be 28.57 mmol g−1 (BAA) and 25.31 mmol g−1 (NAA) for Cu(II) metal ion. Thermodynamic parameters such as the standard free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated to explain the nature of sorption process. Various kinetic models including pseudo-first-order and pseudo-second-order were investigated to determine the mechanism of sorptions. The experimental data fitted the pseudo-second-order well for both Schiff base ligands.