Selective and rapid uptake of copper(II) by a novel chelating resin containing imidazole groups

Abstract

The ligand 4-[(2-aminoethyl)mercaptomethyl]-5-methylimidazole has been anchored to poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) using a ring opening reaction of the pendant epoxy groups with the amine (abbreviation of the modified polymer: GM6/4). The resin has been characterized by solid state 13C cross-polarization and magic angle spinning nuclear magnetic resonance and infrared spectroscopy and elemental analyses. Batch extraction capacities were determined for Cu 2+, Cd 2+, Zn 2+, Ni 2+, Co 2+ and Ca 2+ in the pH range 0.8–5.9, showing a high capacity for Cu 2+ (0.42 mmol Cu 2+/g resin), a moderate capacity for Ni 2+ (0.15 mmol/g), Zn 2+ (0.12 mmol/g) and Cd 2+ (0.10 mmol/g) and a low capacity for Co 2+ (0.03 mmol/g) and Ca 2+ (no detectable uptake) around pH 5. Competitive experiments, which were performed with solutions containing a mixture of metal chloride salts (1.25 g/l of Cu 2+, Cd 2+, Zn 2+ and Ni 2+) showed selectivity for Cu 2+ (pH 5: Cu 2+: 0.35 mmol/g; Cd 2+: 0.02 mmol/g; Zn 2+: 0.02 mmol/g and Ni 2+: 0.01 mmol/g). Kinetic experiments showed that the uptake of Cu 2+ is rapid; t 1 2 = 8–20 min for 0.016 molar solutions. Regeneration (stripping) of Cu 2+-loaded GM6/4 with 1 M and 0.5 M H 2SO 4 was also rapid (typically, t 1 2 = 2 min ). The capacity for Cu 2+ remained at the same level after several cycles of consecutive loading and stripping. To investigate the possible effect of hydroxy-substituents on the coordination mode of the resin, the glycidyl groups of GMA were hydrolyzed with H 2SO 4 to yield 2,3-dihydroxypropyl groups. The resulting resin GOH6/4 was characterized as described for GM6/4. The metal-uptake capacities of GOH6/4 for the metal ions mentioned above were found to be very low, typically 0.01 mmol/g.