Chelating resins VII: studies on chelating resins of formaldehyde and furfuraldehyde-condensed phenolic Schiff base derived from 4,4′-diaminodiphenylsulphone and o-hydroxyacetophenone

Abstract

The synthesis, characterization and capacity studies of two chelating resins having multiple functional groups capable of coordinating to several metal ions are reported. The resins were synthesized by condensing phenolic Schiff bases derived from 4,4′-diaminodiphenylsulphone and o-hydroxyacetophenone with formaldehyde/furfuraldehyde. The polymeric Schiff bases were found to form complexes readily with several transition metal ions. The resins were completely soluble in dimethyl sulphoxide, tetrahydrofuran, partially soluble in CHCl 3, CCl 4, and insoluble in water. On formation of the polychelate with transition metal ions such as Cu(II) and Ni(II), the solubility sharply decreased. The Schiff bases, resins and the polychelates were characterized by FTIR, FT 1H-NMR, 13C-NMR and XRD studies, and thermal analyses like TGA and DSC. From FTIR studies the phenolic oxygen and the imine nitrogen of the resins were found to be the coordination sites. The 1H-NMR data indicated the presence of bridging methylene and terminal methylol functions in the formaldehyde-condensed Schiff base. The thermal stability of the resins and the polychelates was compared by analysing TG data which provided the various kinetic parameters like activation energy, frequency factor and entropy changes associated with the thermal decomposition. The DSC and XRD data indicated that the incorporation of the metal ions significantly enhanced the degree of crystallinity. The adsorption characteristics of the resins towards Cu(II) and Ni(II) in dilute aqueous solutions were followed spectrophotometrically. Cu(II) was seen to undergo preferential adsorption in a mixture of Cu(II) and Ni(II). The effects of contact time, pH, temperature, the size of the sorbents and the concentration of the metal ions in solution on the metal uptake behavior of the resins were studied.