Metal-ion binding affinity of azole-modified oxirane and thiirane resins

Abstract

The azole ligands pyrazole, imidazole, 1,2,4-triazole and tetrazole have been immobilized onto poly(glycidyl methacrylate) p(GMA-O) and onto its sulfur analogue p(GMA-S), which contains a thiirane ring instead of an oxirane ring. The ligands were introduced using ring-opening reactions of the pendant oxirane or thiirane groups with the azoles, resulting in formation of the chelating ion-exchange resins PYROH, IMOH, TRIOH, TETOH, PYRSH, IMSH, TRISH and TETSH. The resins have been characterized by solid-state 13C cross-polarization and magic-angle spinning NMR, FT-IR spectroscopy and elemental analysis. Batch extraction capacities were determined for the chloride salts of Cu 2+, Ni 2+, Co 2+, Zn 2+ and Cd 2+ in buffered solutions in the pH range 0.9–6.0. Both modified oxirane and thiirane resins are very selective for Cu 2+ in the presence of other divalent heavy metal ions. The maximum uptake capacities for Cu 2+ for the oxirane resins under non-competitive conditions are 0.28 mmol/g for TRIOH, 0.39 mmol/g for IMOH and 1.14 mmol/g for PYROH. The resin TETOH is an exception, and does not show any detectable uptake of M 2+ at all. The maximum uptake capacities for Cu 2+ for the thiirane resins under non-competitive conditions are 0.87 mmol/g for TETSH, 0.96 mmol/g for TRISH, 0.58 mmol/g for IMSH and 0.98 mmol/g for PYRSH. The 4 thiirane resins also sorb noticeable amounts of Cd 2+ and Zn 2+ especially the resin PYRSH. The maximum uptakes of Cd 2+ and Zn 2+ for PYRSH are 0.65 and 0.74 mmol/g respectively. The complexation of Cd 2+ and Zn 2+ by the thiirane is ascribed to the presence of thiol groups. The resins PYROH and PYRSH have the highest uptake capacity for Cu 2+ of all the resins tested. The M 2+-uptake sorption behavior of all the 8 resins show very steep pH-dependent curves, i.e. virtually no M 2+-uptake below pH 2.5 and, depending on the particular metal ion, maximum uptake at pH 5.5. The thiirane resins are stable in the presence of dilute mineral acid, as was shown by regeneration experiments performed with 1.0 M H 2SO 4.