Suparna Sodaye

Diffusional Transport of Ions in Plasticized Anion-Exchange Membranes

Diffusional transport properties of hydrophobic anion-exchange membranes were studied using the polymer inclusion membrane (PIM). This class of membranes is extensively used in the chemical sensor and membrane based separation processes. The samples of PIM were prepared by physical containment of the trioctylmethylammonium chloride (Aliquat-336) in the plasticized matrix of cellulose triacetate (CTA). The plasticizers 2-nitrophenyl octyl ether, dioctyl phthalate, and tris(2-ethylhexyl)phosphate having different dielectric constant and viscosity were used to vary local environment of the membrane matrix. The morphological structure of the PIM was obtained by atomic force microscopy and transmission electron microscopy (TEM). For TEM, platinum nanoparticles (Pt nps) were formed in the PIM sample. The formation of Pt nps involved in situ reduction of PtCl(6)(2-) ions with BH(4)(-) ions in the membrane matrix. Since both the species are anions, Pt nps thus formed can provide information on spatial distribution of anion-exchanging molecules (Aliquat-336) in the membrane. The glass transitions in the membrane samples were measured to study the effects of plasticizer on physical structure of the membrane. The self-diffusion coefficients (D) of the I(-) ions and water in these membranes were obtained by analyzing the experimentally measured exchange rate profiles of (131)I(-) with (nat)I(-) and tritiated water with H(2)O, respectively, between the membrane and equilibrating solution using an analytical solution of Ficks second law. The values of D(I(-)) in membrane samples with a fixed proportion of CTA, plasticizer, and Aliquat-336 were found to vary significantly depending upon the nature of the plasticizer used. The comparison of values of D with properties of the plasticizers indicated that both dielectric constant and viscosity of the plasticizer affect the self-diffusion mobility of I(-) ions in the membrane. The value of D(I(-)) in the PIM samples did not vary significantly with concentration of Aliquat-336 up to 0.5 mequiv g(-1), and thereafter D(I(-)) increased linearly with Aliquat-336 concentration in the membrane. The self-diffusion coefficients of water D(H(2)O) in PIM samples were found to be 1 order of magnitude higher than the value of D(I(-)) and varied slightly depending upon the plasticizer present in the membrane. It was observed in electrochemical impedance spectroscopic studies of the PIM samples that diffusion mobility of NO(3)(-) ions was 1.66 times higher than that of I(-) ions, and diffusion mobility of SO(4)(2-) ions was half of that for I(-) ions. The theoretical interpretation of experimental counterions exchange rate profiles in terms of the Nernst-Planck equation for interdiffusion also showed higher diffusion mobility of NO(3)(-) ions in the PIM than Cl(-), I(-), and ClO(4)(-) ions, which have comparable diffusion mobility.

Backscattering spectrometry studies on metal ion distribution in polymer inclusion membranes

Abstract Polymer inclusion membranes based on cellulose triacetate polymer, containing 2-nitrophenyloctyl ether as plasticizer and dinonyl napthalene sulfonic acid as cation exchanger were loaded with Cs+ and Ag+ and were studied by backscattering spectrometry technique to measure the distribution of the metal ions across the membrane using a proton beam. The study showed that the distribution of the metal ions across the membrane is uniform, thereby suggesting the uniform distribution of the cation exchanger. This indicates that the hydrophilic nature of the sulfonic acid group in the cation exchanger does not significantly influence its distribution in the predominantly hydrophobic matrix of cellulose triacetate. However, the microstructure of the membrane, obtained by atomic force microscopy, shows the formation of blobs on the surface of the PIM indicating the inhomogeneity at the sub-micron scale.

Pore-functionalized polymer membranes for preconcentration of heavy metal ions

Functionalized membranes containing carboxylate, phosphate and sulfonate groups were prepared by UV-initiator induced graft polymerization of the functional monomer (acrylic acid, ethylene glycol methacrylate phosphate (EGMP) and 2-acrylamido-2-methyl-1-propane sulfonic acid) with a crosslinker (methylenebisacrylamide) in the pores of poly(propylene) host membranes. The functionalized membranes thus obtained were characterized by gravimetry, FTIR spectroscopy, radiotracers and scanning electron microscopy for the degree of grafting and water uptake, presence of functional groups, ion-exchange capacity, and physical structure of the membranes, respectively. The uptakes of Cs(+), Ag(+), Sr(2+), Cd(2+), Hg(2+), Zn(2+), Eu(3+), Am(3+), Hf(4+) and Pu(4+) ions in the functionalized membranes were studied as a function of acidity of the equilibrating aqueous solution. Among the functionalized membranes prepared in the present work, the EGMP-grafted membrane (with phosphate groups) showed acid concentration dependent selectivity towards multivalent metal ions like Eu(3+), Am(3+), Hf(4+) and Pu(4+). The solvent extraction studies of EGMP monomer in methyl isobutyl ketone (MIBK) solvent indicated that divalent and trivalent metal ions form complexes with EGMP in 1:2 proportion, but the distribution coefficients of trivalent metal ions were significantly higher that for the divalent ions. The uptakes of Eu(3+) ions in monomeric EGMP (dissolved in MIBK) and polymeric EGMP (in the forms of crosslinked gel and membrane) were studied as a function of concentration of H(+) ions in the equilibrating solution. This study indicated that polymeric EGMP has better binding ability towards Eu(3+) as compared to monomeric EGMP. The variation of distribution coefficients of Eu(3+)/Am(3+) in gel and membrane as a function of H(+) ion concentration in the equilibrating aqueous solution indicated that ionic species held in the membrane and gel were not same. These results indicated that proximity of functional groups (phosphate) plays an important role in metal ion binding with polymeric EGMP.

Interdiffusion of exchanging counterions in poly(perfluorosulfonic acid) membrane.

The kinetics of forward (Li+/Na+mem <=> Mn+aq) and reverse (Mn+mem <=> Li+/Na+aq) exchanges of metal ions(Mn+ ) Ag+, Cs+, Ba2+, and Eu3+) in the poly(perfluorosulfonic acid) membrane (Nafion-117) equilibrated with a well-stirred aqueous salt solution were experimentally measured using radioactivity tagged counterions. A numerical solution of the Nernst-Planck (N-P) equation for interdiffusion was used to interpret the kinetics of these exchanges. The experimentally measured kinetics of forward and reverse Na+ ion exchanges with Mn+ ions between the membrane and the equilibrating solution were found to be close to that predicted by the N-P equation. The minor differences between the experimental and predicted exchange rate profiles were attributed to change in water content of the poly(perfluorosulfonic acid) membrane in different ionic forms. The kinetics of Li+ ion exchanges with Na+ and Cs+ ions was found to be unusual as the self-diffusion coefficient D(ion)(m) of Li+ ions in the membrane were quite different in the forward and reverse exchanges. The values of D(ion)(m) for Li+ ion, obtained by the N-P equation, were found to be 2 x 10-6 and 0.2 x 10-6 cm2 s-1in Li+mem <=> Na+/Cs+aq and Na+/Cs+mem <=> Li+aq exchanges, respectively. The drastic differences in diffusion mobility of Li+ ions during forward and reverse exchanges was attributed to weak electrostatic interactions of Li+ ions with the fixed exchange sites as indicated by the reported equilibrium constant Kex of the Li+-exchange reaction in Nafion membrane. D(ion)(m) is high in the forward exchange due to minimum retardation in diffusion mobility of Li+ ions by the electrostatic forces in the membrane. In reverse exchange, Li+ diffusion mobility is retarded due to its slow replacement of counterions from the membrane.

Beam energy dependence of cross sections of projectile like fragments in 19F+89Y reaction

Angular distributions of projectile-like fragments (PLFs) have been measured in 19F+89Y reaction at Elab = 70, 85 and 100 MeV. From the center of mass angular distributions of PLFs, their cross sections have been deduced at these beam energies. Beam energy dependence of the cross sections of PLFs formed in quasi-elastic transfer reactions has been found to be significantly different from those formed in incomplete fusion (massive transfer) reactions. Experimental angular distributions were converted into the plots of the transfer probability versus distance of closest approach to deduce the slope parameter for different transfer channels. Comparison of the slope parameters suggested that the overlap of the projectile and the target nuclei increases with increasing beam energy for a given transfer channel and also with increasing mass transfer at a given beam energy.

Effect of entrance channel parameters on the fusion of two heavy ions: Excitation functions of reaction products in16O +66Zn and37Cl +45Sc reactions

Excitation functions of reaction products formed in16O +66Zn and37Cl +45Sc systems, leading to the same compound nucleus,82Sr, were measured using recoil-catcher technique and off-line γ-ray spectrometry. The contribution of non-compound processes like transfer and incomplete fusion (ICF) reactions to the cross-sections of different evaporation residues were delineated by comparing the experimental data with the predictions of Monte Carlo simulation code PACE2. The results show that non-compound processes become a significant fraction of the total reaction cross-section in16O +66 systems in the beam energy range studied, while37Cl +45Sc gives mainly compound nucleus products. The mass asymmetry dependence of the fusion and non-compound cross-sections have been analysed in terms of the static fusion model and sum rule model

Scintillating adsorptive membrane for preconcentration and determination of anionic radionuclides in aqueous samples

A composite polymer membrane containing liquid anion exchanger and scintillator molecules was developed for preconcentration and quantitative determination of anionic radionuclides like pertechnetate and iodide ions. The radiation emitted by the radionuclides sorbed in the membrane lead to scintillation signals. This scintillating adsorptive membrane was prepared by immobilizing trioctylmethyl ammonium chloride (liquid anion-exchanger) along with 2,5-diphenyl oxazole (primary scintillator), and 4-bis(methylstyryl)benzene (wavelength shifter) in the plasticized polystyrene matrix. The anion selectivity of the membrane follows Hofmeister series i.e. hydrophobic anions are preferentially sorbed in the membrane matrix. It was observed that TcO4− ions were transferred quantitatively to the membrane matrix from equilibrating aqueous solutions having pH 2–8 and multicomponent feed solution like seawater. The amount of TcO4− ions preconcentrated in the membrane was directly quantified by counting the scintillations produced by β-particles in the membrane matrix. The scintillating membrane developed in the present work was optimized in terms of its scintillation efficiency, β-scintillation pulse height, anion-exchange capacity and reusability.

EC decay of 244Bk

Berkelium isotopes have been produced in 11B-induced reaction on 238U. The EC decay of 244Bk → 244Cm has been studied by carrying out the single and coincidence measurements of the γ-rays emitted during the de-excitation of the 244Cm levels. Radiochemical separations have been carried out to minimize the contribution from the fission products and target. The new half-life of 244Bk is obtained as 5.02 ± 0.03 h, which is close to the theoretically calculated value. The relative intensities of the decay γ-rays have been re-evaluated. Based on the coincidence measurements, a tentative partial level scheme for 244Bk → 244Cm decay has been proposed.

Anomalous fission fragment angular distribution in the {sup 11}B+{sup 243}Am reaction at near-barrier energies

Fission fragment angular distributions were measured in {sup 11}B+{sup 243}Am reaction in the beam energy (E{sub lab}) range of 60-72 MeV. Experimental anisotropies in {sup 11}B+{sup 243}Am reaction were found to be higher than the values calculated using the statistical theory indicating contribution from noncompound nucleus fission. For {sup 11}B+{sup 243}Am reaction, entrance channel mass asymmetry is higher than the Businaro-Gallone critical mass asymmetry. Observation of anomalous fission fragment angular distribution in {sup 11}B+{sup 243}Am reaction possibly indicates that the target deformation plays an important role in deciding the contribution from noncompound nucleus fission.