Metal uptake by didentate and tridentate pyrazole-containing ligands immobilized onto poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)

Abstract

The pyrazole-containing ligands 2-(3,5-dimethyl-l-pyrazolyl)ethylamine and bis(2-(3,5-dimethyl-l-pyrazolyl)ethyl)amine have been anchored to poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate), using ring opening reactions of the pendant epoxy groups with the amines (abbreviations of the modified polymers are GN6/4 and GD6/4, respectively). Both resins have been characterized by solid-state 13C cross-polarization and magic-angle spinning NMR and i.r. spectroscopy and elemental analysis. Batch extraction capacities were determined for the chloride salts of Cu 2+, Ni 2+, Zn 2+, Co 2+, Cd 2+ and Ca 2+ in the pH range 0.9–6.0. GN6/4 shows a high metal-uptake capacity for Cu 2+ (0.68 mmol/g) and low uptake capacities for the other divalent metal ions around pH 6. GD6/4 shows a totally different uptake pattern, i.e. around pH 6 it shows also a surprisingly high Ni 2+ uptake (0.30 mmol/g), even higher than for Cu 2+ (0.20 mmol/g). However, competitive experiments, performed with solutions containing a mixture of metal chloride salts and acetate buffer, showed high selectivity for Cu 2+ for both resins. Distribution coefficients determined for both resins and the metal ions Cu 2+ and Ni 2+ indicate that the Cu 2+ complexes, formed on the polymers, are more stable than the Ni 2+ complexes. Kinetic experiments showed that the uptake of Cu 2+ by both GN6/4 and GD6/4 is rapid; t 1/2 = 13 min for both resins. The Ni 2+ uptake by GD6/4 is considerably slower than the Cu 2+ uptake; t 1/2 = 30 min. Regeneration (stripping) of Cu 2+- and Ni 2+-loaded GN6/4 or GD6/4 with 0.5 M H 2SO 4 is also rapid; t 1/2 = 1 min for both resins. The capacity for Cu 2+ was found to stay at the same level after several cycles of consecutive loading and stripping, while the Ni 2+ capacity slightly increases after each cycle. The uptake of Cu 2+ and Ni 2+ by GD6/4 is influenced by the presence of various anions such as Cl −, NO 3 −, BF 4 − and OAc −. This effect was most clearly demonstrated by the results of the Ni 2+ capacity measurements: the uptake of Ni 2+ is considerably higher in the presence of acetate or nitrate anions.