Metal-ion extraction by immobilised aza crown ethers

The immobilisation of [15]aneNO(4), [15]aneN(2)O(3), and [18]aneN(2)O(4) onto the oxirane and thiirane containing copolymers p(GMA-O) and p(GMA-S) resulted in six aza crown ether containing polymers with interesting metal-ion affinities, The pendent hydroxy or thiol groups, originating from the polymeric backbones, appeared to play an important role in the observed metal-ion affinities. The metal-ion affinity of p(GMA-O)-[15]aneN(2)O(3) for a range of cations was found to decrease with decreasing ionic radius: Ag+ > Pb2+ > Cd2+ > Cu2+. The thiol-containing analogue of this polymer, p(GMA-S)-[15]aneN(2)O(3), showed a reversed Cd2+/Cu2+ selectivity. This illustrates the capability of pendent hydroxy groups to seriously reduce the stability of complexes of small cations compared to those of large cations. All the modified oxirane resins tested were found to be Ag+-selective in the presence of a range Of divalent (heavy) transition-metal ions. The difference in ring size between [15]aneN(2)O(3) and [18]aneN(2)O(4) was found to have a significant effect on the uptake values of Cu2+ and Zn2+, as these ions are too small to fit into the ligand cavity of [18]aneN(2)O(4). The uptake values for the larger Ag+ and Pb2+ were found to be similar for both resins, Loaded resins were successfully regenerated (with an efficiency of 99%) by treatment with 2.0 m acid solutions (Pb2+ and Cd2+) or with a 3.35 m NH3 + 2.0 m NH4NO3 solution (Ag+).