Thermal-swing Extraction of Cadmium(II) by Thermosensitive Polymer Gel Crosslinked with Encapsulating Hexadentate Ligand

Abstract

Thermal-swing extraction of CdII with a thermosensitive gel, poly(N-isopropylacrylamide) (NIPA) crosslinked with an encapsulating ligand, N,N,N′,N′-tetrakis(4-propenyloxy-2-pyridylmethyl)ethylenediamine (TPPEN), was examined. CdII was extracted in the gel swollen at 5 °C and released from the gel shrunken at 40 °C. The difference in the distribution ratios of CdII between these temperatures was more than 30 times.

Thermoresponsive extraction of cadmium(II) ions by poly(TPEN–NIPA) gels. Effect of chain length and branched spacer structure on gel formation and extraction behavior

“…Syntheses of pyridine derivatives bearing allyloxy moieties 3a-6a and TPEN derivative 1a were previously reported. [5][6][7] Reactions affording 3b-d, 4b-d, 5b-d and 6b-d were conducted in similar manners. Although the reaction of 2-methyl-4-nitropyridine-1-oxide with allylic alcohol 2a or 2d proceeded smoothly, harsh conditions were necessary to afford 3b and 3c.…”

“…The gel was shown to extract Cd II at low temperatures, whereas little extraction was observed at elevated temperatures. [5][6][7][8] N,N,N¢,N¢-(tetrakis-2-pyridylmethyl)ethylenediamine is recognized as a hexadentate ligand with six nitrogen donors and has been shown to chelate a variety of soft metal ions such as Hg, Cd, Au and Pd. [9][10][11][12][13] It was also shown to be effective for the chelation of f-block metals; the separation of minor actinides from high-level radioactive waste is a pressing issue.…”

Thermosensitive gels incorporating polythioether units for the selective extraction of class b metal ions

“…Some copolymers of various ratios of ATH to NIPAAm were synthesized successfully. In several studies, researchers used the combination of NIPAAm and ligands which contained N-donor atoms or O-donor atoms [8][9][10]. In such cases, it was difficult to determine the ratio of NIPAAm and those ligands, because the NIPAAm unit itself has N and O atoms.…”

“…Therefore, the combination of poly-N-isopropylacrylamide and a selective extractant may change such thermoresponsive polymer extraction. Takeshita et al examined the separation of Americium(III) and Europium(III) using the copolymer of N-isopropylacrylamide and N-donor atom containing ligand [8][9][10]. On the other hand, thioether chemistry has been developed since 1970 [11][12][13][14][15][16][17][18].…”

“…It would be possible to investigate the relationship between the change of the ratio of ATH vs. N-isopropylacrylamide and the property change of the polymer. It was impossible to determine the ratio of N-donor ligand in the polymer [8][9][10] the polymer solution was determined spectrophotometrically by the relative absorbance change at 750 nm via temperature of the polymer solution. Metal ion extraction using the copolymer with appropriate counter anions such as picrate, nitrate or perchlorate ion was examined.…”