Bipyridine Derivatives: Design, Synthesis And Heavy Metal Ions Extraction In Supercritical Carbon Dioxide

Based on theoretical analysis and study of the relation between ligand structure and chelating behavior, fluorinated and ether-oxide bipyridine derivatives were desigined and synthesized as chelating ligands and their structure were determined. Solubility tests in supercritical CO₂ were carried out at different temperatures and pressures and the measured data were correlated using a semiempirical model and the calculated results showed satisfactory agreement with experimental data. Meanwhile, eight kinds of heavy metal ions(Cu²⁺,Co²⁺,Ni²⁺,Fe²⁺,Pb²⁺,Cd²⁺,Mn²⁺,Zn²⁺ ) in-situ extraction in supercritical CO₂ was carried out from spiked filter paper. Firstly, in order to find the optimum condition of metal ions extraction in supercritical CO₂, the effects of pressure, temperature, extraction time and the amount of ligands on the extraction efficiency of Cu²⁺ were systematically investigated. Secondly, based on the extraction research of Cu²⁺ from supercritical CO₂, the optimum conditions obtained were 25MPa, 333K, 60min and [Cu²⁺]:[Ligand] = 1:50, respectively, for the three fluorinated ligands. Without the perfluoro-1-octanesulfonic acid tetraethylammonium salt (PFOAT) as co-extractant, the extraction efficiencies were not satisfactory, indicating that the chelating ligand might form complexes with metal ions but either equilibrium constant might be very small or the complexes'solubilities in supercritical CO₂ were low. In order to increase the extraction efficiency, PFOAT was added to the system. As expected, the extraction efficiencies of metal ions had increased for all the ligands. The extraction efficiencies for Ni²⁺ and Cu²⁺ were higher than the other metal ions. Finally, the mixed metal ions extraction was tested. With PFOAT or without PFOAT, the Ni²⁺ and Cu²⁺ extraction were the highest among metal ions, indicating that the fluorinated bipyridine ligands had good selectivity for Ni²⁺ and Cu²⁺.The optimum extraction condition were obtained at 25MPa, 313K, 90min and [Cu²⁺]:[Ligand] = 1:10, respectively, for the three ether-oxide bipyridine ligands. The extraction conditions were similar to the fluorinated bipyridine ligands. Without the co-extractant PFOAT, the efficiencies were very low. But after adding PFOAT to the system, the extraction efficiencies increased.