Supported liquid membranes ionic carriers

The ability of calixarenes to bind large metal ions with high kinetic stability is important in the search for complexants for radionuclides such as Cs (ti/2 = 30.2 yr) and Sr (ti/2 = 65 d) from the reprocessing of exhausted nuclear fuel. There has been considerable interest in caesium-complexed calix[4]-bis-crowns as selective Cs-carriers. Transport isotherms of trace level Cs through supported liquid membranes containing calix[4]-bis-crowns have been determined as a function of the ionic concentration of the aqueous feeder solutions, and l,3-calix[4]-bis-o-benzo-crown-6 appears to be much more efficient in decontamination than mixtures of crown ethers and acidic exchangers, especially in highly acidic media. " ... 

Kubota and Goto s group studied the selective permeatimi of dysprosium and neodymium against ferric ion by an ionic liquid-based supported liquid membrane (SLM) using DODGAA as the mobile carrier (Baba et al., 2011) because the DODGAA is soluble in ionic liquids such as l-octyl-3-... 

Depending on their structure, symmetric membranes can be catalogued as porous and non-porous or dense (polymeric swollen-network), while asymmetric membranes for desalting applications (NF and RO, basically) consist of a dense and thin active layer and a thick porous sublayer for mechanical stability (usually an UF membrane). Moreover, supported liquid membranes (SLMs), and aetivated membranes (AMs), which basically consist in the immobilization of speeifie agents (organic solvent, carrier or ionic liquid at room temperature) in the pores/structure of a support membrane, have been developed for selective separation of valuable/contaminant compoimds [8-11]. 

Polymer inclusion membranes (PIMs) are a relatively novel type of self-supporting liquid membranes for the extraction and separation of metallic and non-metallic ionic species and small organic molecules from dilute aqueous solutions. PIMs entrap a solute-selective extraction reagent, often referred to as the carrier, in a base polymer matrix, which consists of a base polymer and in some cases may contain plasticizers and chemical modifiers. When the PIM is placed in contact with the dilute aqueous solution, the extractant reactively couples with the solute of interest and transfers it into or through the membrane. 

Carrier-assisted transport through supported liquid membranes is one of the important applications of supramolecular chemistry. Carriers for the selective transport of neutral molecules, anions, cations or zwitter ionic species have been developed. The transport can be described by subsequent partitioning, complexation and diffusion. Mechanistic studies are mainly focussed on diffusion limited transport, in which diffusion of the complex through the membrane phase is the rate-limiting step of the transport. Recently, kinetic aspects in membrane transport have been elucidated with new carriers for which the rate of decomplexation determines the rate of transport. In this chapter, recent mechanistic aspects for carrier-assisted transport through supported liquid membranes are reviewed. 

Calix[4]-W5-crowns 1-7 are used as selective cesium-carriers in supported liquid membranes (SLMs). Application of the D esi diffusional model allows the transport isotherms of trace level Cs through SLMs (containing calix[4]-6/5-crowns) to be determined as a function of the ionic concentration of the aqueous feed solutions. Compound 5 appears to be much more efficient than mixtures of crown ethers and acidic exchangers, especially in very acidic media. Decontamination factors greater than 20 are obtained in the treatment of synthetic acidic radioactive wastes. Permeability coefficient measurements are conducted for repetitive transport experiments in order to determine the SMLs stability with time. Very good results (over 50 days of stability) and high decontamination yields are observed with l,3-calfac[4]-Aw-crowns 5 and 6. 

Fontas, C, Palet, C., Salvado, V. Hidalgo, M. (2000). A hollow fiber supported liquid membrane based on Aliquat 336 as a carrier for rhodium(III) transport and preconcentration. Journal of Membrane Science, 178,1-2,131-139, ISSN 0376-7388 Frade, R. F. M., Rosatella, A. A., Marques, C. S., Branco, L. C., Kulkarni, R S., Mateus, N. M. M, Afonso, C. A. M. Duarte, C. M. M. (2009). Toxicological evaluation on human colon carcinoma cell line (CaCo-2) of ionic liquids based on imidazolium, guanidinium, ammonium, phosphonium, pyridinium and pyrrolidinium cations. Green Chemistry, 11,10,1660-1665, ISSN 1463-9262 Fraser K. J. MacFarlane D. R. (2009). Phosphonium-based ionic liquids An overview. 

Since the concept of supported ionic liquid membranes (SILMs) is quite similar to that of conventional SLMs, it seems logical that the same membrane configurations used in the latter will be useful when ILs are used as carriers in supported membrane operation. Between these different configurations, we can find the following. 

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