Chelating resin containing hybrid calixpyrroles: New sorbent for noble metal cations

Novel chelating resins containing macrocyclic ligand calix[4]pyrrole[2]thiophene 6 immobilized on a cross-linked vinylbenzyl chloride/divinylbenzene copolymer are reported. The modification of the polymeric support by the macrocycle was followed by elemental and IR spectral analysis, indicating a significant degree of modification (up to 0.29 mmol of the macrocyclic ligand per gram resin after 7 days of modification - Resin 4). This material has shown a marked preference for cations of noble metals (Au(III), Ag(I), Pt(IV), Pd(II)) in static sorption studies over other metal cations, including Cu(II), Pb(II) or Cd(II). The affinity of the resin for noble metal cations is a result of the presence of “soft” electron pair donor atoms (sulfur) in the macrocycle, as well as the fact that the size of the macrocyclic receptor and metal cations are comparable. Langmuir-type isotherms were observed for platinum, palladium and silver on Resin 4, but the uptake of gold is probably driven by the reduction of Au(III) to metallic gold on the surface of the resin, therefore considerably high values of uptake were observed in this case (up to 335 mg/gresin). Gold was also found to be preferably sorbed and reduced in the presence of other noble metals cations; the selectivity coefficient in gold/silver binary mixture was 130.