Chelating resins VI: Chelating resins of formaldehyde condensed phenolic Schiff bases derived from 4,4 '-diaminodiphenyl ether with hydroxybenzaldehydes - Synthesis, characterization, and metal ion adsorption studies

Phenolic Schiff bases derived from o-, m-, and p-hydroxybenzaldehydes and 4 , 4'-diaminodiphenyl ether were subjected to polycondensation reaction with formaldehyde. The resins were found to form polychelates readily with seve ral metal ions. The materials were characterized by elemental analysis, GPC , IR, W-Vis, H-1-NMR, XRD, and thermal analyses like TG, DTG, and DSC studi es. The H-1-NMR spectra of the resins provided evidence of polycondensation with well-defined peaks for bridging methylene and terminal methylol funct ions. The metal-ligand bonds were registered in the IR spectra of the polyc helates. The thermal analysis data provided the kinetic parameters like act ivation energy, frequency factor, and entropy changes associated with the t hermal decomposition. These data indicated the resins to be more stable tha n the polychelates. The DSC and XRD data indicated that the incorporation o f metal ions significantly enhanced the crystallinity of the polymers. The resins could adsorb several metal ions from dilute aqueous solutions. Adsor ption characteristics of the resins towards Cu(II) and Ni(II) were studied spectrophotometrically both in competitive and noncompetitive conditions. T he effects of pH, contact time, quantity of the sorbent, concentration of t he metal ions in a suitable buffer medium were studied. The resins were fou nd to be selective for Cu(II) leading to its separation from a mixture of C u(II) and Ni(II). (C) 2000 John Wiley & Sons, Inc.