Removal of aqueous Zn(II) and Ni(II) by Schiff base functionalized PAMAM dendrimer/silica hybrid materials

Abstract Schiff base modified PAMAM dendrimer/silica hybrid materials (SG-G0-SA, SG-G1.0-SA, and SG-G2.0-SA) were synthesized and used for removing aqueous Zn(II) and Ni(II). The influence of solution pH, time, temperature, and the concentration of metal ion on the removal effect were investigated. The regeneration of the adsorbents was evaluated. The interaction mechanism between adsorbents and metal ions was revealed by density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS) analysis. Results show the as-prepared adsorbents display comparable adsorption property for Zn(II) and Ni(II). The optimum solution pH for Zn(II) and Ni(II) removal are 6.0 and 5.0. The adsorption kinetic follows pseudo-second-order (PSO) model, while the adsorption isotherm obeys Langmuir model. The adsorption was carried out with monolayer adsorption in chemical mechanism. 0.5 mol·L−1 HNO3–5% thiourea solution can be used as efficient eluent to regenerate the adsorbents that upload metal ions. Adsorption mechanism indicates the imino N atoms and carbonyl O atoms that play the main role in the adsorption process.