58 research outputs found
Preparation and use of calixarene acetamido derivativesfor selective removal of strontium from aqueous solutions
No full textPreparation of calix[4]arene crown ethers for selective extraction of cesium and actinides from aqueous wastes
No full textC.A. 122: 23973
Selective Extraction of Cesium at Tracer Level Concentration From a Sodium Nitrate Solution with Calix Crowns: Molecular Modeling Study of the Cs+/Na+ Selectivity
No full textCalix[4]arene mono- and bis-crown6 in the 1,3 alternate conformation are highly selective extractants for cesium towards sodium in an acidic liquid waste. Extraction and selectivity are related to complexation properties which can be studied by Molecular Dynamics techniques. In this paper, we describe the results of Molecular Dynamics simulations in an explicit water phase for four complexes of 1,3-alternate mono- and bis-crown-calix[4]arenes. The structural features obtained are interpreted on the basis of cation/ligand complementarity and can explain the relative performances in Na+ and Cs+ extraction for the compounds simulated
I calixareni nel trattamento dei rifiuti radioattivi
No full textRiassunto
Molecole a forma di calice (calixareni) sono state utilizzate come macrocicli di partenza per la realizzazione di nuovi ionofori altamente efficienti e selettivi nella rimozione di cationi radioattivi dai rifiuti liquidi provenienti da centrali nucleari. Calix[4]areni contenenti funzioni chelanti bidentate (CMPO) estraggono tutti gli attinidi, mentre i calix[4]crowns sono in grado di complessare il 137Cs con una selettività eccezionale. I risultati ottenuti hanno portato, in alcuni casi, allo sviluppo di processi industriali di separazione.
Abstract
Calix shaped macrocycles, and therefore named calixarenes, were used as building blocks for the synthesis of new ionophores highly efficient and selective in the extraction of radioactive cations from waste resulting from the reprocessing of exhausted nuclear fuel. Calix[4]arenes with bidentate chelating units such as CMPO extract all actinides, while calix[4]crowns are able to complex 137Cs with an outstanding selectivity. In some cases, the results obtained allowed to develop an industrial separation process
New Efficient Calixarene Amide Ionophores for the Selective Removal of Strontium Ion from Nuclear Waste: Synthesis, Complexation, and Extraction Properties
No full textThree novel lower rim hexamide derivatives 5(6), 7(6), and 9(6) of p-hydroxycalix[6]arene and four octamides 5(8), 7(8)-9(8) derived from the corresponding p-hydroxycalix[8]arene were synthesized, and their potential as extractants in radioactive waste treatment was evaluated, in comparison with upper rim analogues 12(6) and 12(8) and other existing selective neutral ionophores currently used in radioactive waste treatment. Extraction of alkali and alkaline earth metal picrates from water to dichloromethane, and of the corresponding nitrates from acidic water solution simulating radioactive waste. to 2-nitrophenyl hexyl ether (NPHE), showed that the lower rim amides extract divalent cations much better than monovalent ones. The upper rim hexa-12(6) and octamide 12(8) are very inefficient ligands, hardly extracting any cation. In all cases, p-alkoxy octamides are more efficient and selective extractants than the corresponding hexamides. In the case of simulated waste solutions, the distribution coefficients for strontium removal by octamides (6.5 < D-Sr < 30) are much higher than the corresponding value (Ds,) found for dicyclohexyl-18-crown-6 (DC18C6), and the same applies for the strontium/sodium selectivity, which is 6500 < D-Sr/D-Na < 30 000 for octamides and 47 for DC18C6. ESI-MS, UV-vis, and X-ray crystal structure studies give consistent results and indicate the formation of 2:1 (cation/ligand) strontium complexes for all octamides tested. Stability constants were determined in homogeneous methanol solution for alkali metal (log beta (11) less than or equal to 2), calcium (4.3 less than or equal to log beta (11) less than or equal to 6.0; 9.4 less than or equal to log beta (21) less than or equal to 12.0), and strontium (5.6 less than or equal to log beta (11) less than or equal to 12.3) ions using a UV-vis competition method with 1-(2-pyridylazo)-2-naphthol (PAN). They confirm the high efficiency and high divalent/monovalent selectivity found in metal ion extraction experiments for the new octamide ligands. Evidence for a positive cooperative effect between the two metal ion binding sites was obtained in the case of the Ca2+ complex of octamide 1(8)
New Calix[4]arene-monobenzo- and -dibenzo-crown-6 as Cesium Selective Ionophores in the Radioactive Waste Treatment: Synthesis, Complexation and Extraction Properties
No full textCesium possesses two long lived isotopes Cs-135 and Cs-137 and the first one has a very long (2.3 x 10(6) y) half life and is one of the most mobile nuclides in a repository. Calix[4]arene-crowns-6 in the 1,3-alternate conformation are emerging as a new class of ionophores exhibiting a very high efficiency and selectivity in the complexation of cesium ion and its removal from highly acidic ([HNO3] = 3-4 M) radioactive waste having also high sodium nitrate concentration ([NaNO3] = 2-4 M). In order to improve both efficiency and cesium selectivity we have synthesised the novel calix[4]arene dibenzo-crowns-6 1 and 2 and the calix[4]arene-monobenzocrown-6 3 in 1,3-alternate conformation and evaluated their complexation properties towards alkali metal cations in homogeneous solution and in two phase systems, together with their performance in radioactive waste treatment. All data confirm the higher Cs/Na selectivity of the 1,3-alternate calix[4]crown-6 1-3 containing aromatic rings in the polyether loop, in comparison to previously synthesised compounds of the same series
1,3-Dialkoxycalix[4]arenecrown-6 in 1,3-Alternate Conformation: Cesium-Selective Ligands that Exploit Cation-Arene Interactions
No full textExceptionally high selectivity for cesium ions (α(Cs/Na) > 33000) is displayed by calix[4]arenecrowns-6 in the 1,3-alternate conformation. They also remove 137Cs quantitatively (>96%) from radioactive waste that is 1 M in HNO3. The complexation properties result from the simultaneous operation of several effects: the size of the crown ether ring, the polarity of the calix conformation, and the strength of the cation/π-electron interactions. The latter interaction was evident in the X-ray crystal structure of the cesium complex (shown on the right)
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