Synthesis, characterization and structure effects on selectivity properties of silica gel covalently bonded diethylenetriamine mono- and bis-salicyaldehyde and naphthaldehyde Schiff ,s bases towards some heavy metal ions

Abstract

Four silica gel-immobilized new metal chelate Schiff ,s bases were synthesized (I–IV). Silica gel chemically bonded diethylenetriamine mono-naphthaldehyde and mono-salicyaldehyde Schiff's bases (phases I and III) were produced via the interaction of silica gel-modified diethylenetriamine with naphthaldehyde and salicylaldehyde, respectively. However, phases II and IV arose through the interaction of bis-naphthaldehyde and bis-salicylaldehyde Schiff ,s bases of diethylenetriamine with 3-chloropropyltrimethoxysilane modified silica gel. The characterization of such new phases, their capabilities towards selective extraction or separation of Fe(III), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) ions were studied and evaluated by both batch and column techniques as a function of pH and time of contact. Phases III and I showed high performance towards Cu(II) extraction, where their Cu(II) sorption determined to be 0.957 and 0.940 mmol g −1, respectively. However, for phases IV and II, the great affinity was devoted to Fe(III) extraction followed by Cu(II) ions. The reactivity of metal ion sorption was discussed in the light of effects of bulkiness as well as orientation of immobilized chelate on sorbent reactivity. Donor sites of phases III and I (diethylenetriamine and azomethene nitrogens along with phenolic hydroxyl group oxygen) are fully active, whereas phases IV and II are partially active with only participation of oxygen and azomethene nitrogen. The order of increasing thermal stability (IV<II<I<III) and fastness of metal uptake equilibration process coincides satisfactorily with decreasing bulkiness of the chelate. Results of separation under dynamic conditions of binary mixtures containing Cu(II) with Ni(II), Zn(II), Cd(II) and Pb(II) using phase III are in accordance with its selectivity towards Cu(II) retention relative to the other coexisting ions.