Schiff Base Ligands Immobilized on a Nanosized SiO₂–Al₂O₃ Mixed Oxide as Adsorbents for Heavy Metals

Abstract

Three adsorbents have been synthesized by immobilization of Schiff base ligands on the surface of SiO 2 ÀAl 2 O 3 mixed oxides and evaluated for the removal of Cd(II) and Pb(II) from aqueous solutions. The contact time to attain equilibrium for maximum adsorption was 120 min. These heterogeneous Schiff base ligands were found to be effective adsorbents for the removal of heavy metal ions from solution, with Si/Al-pr-N=salicylaldehyde having a high adsorption capacity for Cd(II) ions and Si/Al-pr-N=pyridine-2-carbaldehyde having a high adsorption capacity for Pb(II) ions. The adsorption of heavy metal ions has been studied in terms of pseudo-first-order and pseudo-second-order kinetics, and the Freundlich, Langmuir, and LangmuirÀFreundlich isotherm models have also been applied to the equilibrium adsorption data.

Adsorption of Pb(II) and Hg(II) ions from aqueous single metal solutions by using surfactant-modified ostrich bone waste

“…The effect of pH plays an important role on the active sites of bio-adsorbents as well as the metal speciation during the adsorption reaction [48]. To evaluate the influence of pH on the adsorption capacity of the bone samples, experiments were performed at initial concentration of 2 and 10.0 mg L −1 , and pH range 1.5-11 (Fig.…”

“…The experimental adsorption equilibrium data of HMs on the bone samples were fitted by applying the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models, which are usual models for aqueous-phase adsorption [48]. These adsorption models give a representation of the adsorption equilibrium between an adsorbate in solution and the surface active sites of the adsorbent.…”

“…The constant n gives an idea of the grade of heterogeneity in the energetic centers distribution and is related to the magnitude of the adsorption driving force [48]. High values on n indicate a relative uniformity in the surface.…”

“…However, the initial rapid adsorption gives away a very slow approach to equilibrium. In fact, the fast adsorption at the initial stage is probably due to the increased concentration gradient between the adsorbate in solution and adsorbate in adsorbent as there must be increased number of vacant active sites available in the beginning [24,48]. In order to determine and interpret the mechanisms of metal adsorption processes and major parameters governing sorption kinetics, kinetic sorption data obtained empirically were fitted to the pseudo-first-order, pseudo-second-order, and intraparticle diffusion models shown as Eqs.…”

“…(5)- (7). Each of them has been widely used to describe metal and organic sorption on different sorbents [22,23,48]. From the linear form of these three models, equations can be written as follows: Pseudo-first-order equation : q t ¼ q e ½1 À expðÀk 1 tÞ (5) Pseudo-second-order equation…”