Asymmetric membranes with modified gold films as selective gates for metal ion separations

McCleskey, T. Mark; Ehler, Deborah S.; Young, Jennifer S.; Pesiri, David R.; Jarvinen, Gordon D.; Sauer, Nancy N.

doi:10.1016/s0376-7388(02)00387-3

Cited by 17 publications

(21 citation statements)

References 22 publications

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“…Metal ion separations require recognition to achieve selectivity . A molecular-level investigation of the selectivity layer is important to understand the driving forces for extraction and hence to design membrane structures with specific ionic recognition properties.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of the Structure and Thermodynamics of Carrier-Assisted Uranyl Ion Extraction

Jayasinghe

Beck

2009

J. Phys. Chem. B

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We present molecular dynamics simulations of interfaces relevant to the selective chemical extraction of uranyl ions from aqueous solution. These molecular-level simulations model ion transfer in the PUREX process and in synthetic, selective membranes. We first present simulations of water/oil interfaces modified by incorporation of tributyl phosphate (TBP) into the oil phase (hexane). A range of concentrations is examined, from a single TBP molecule to values close to those utilized in the PUREX process. The TBP molecules exhibit strong interfacial activity, and the interface broadens relative to the water/oil case with increasing TBP concentrations. Additional structural features, including radial distribution functions and orientational distributions, are examined to elucidate the molecular ordering at the interface; the interface structure changes substantially with increasing TBP concentration. Finally, free-energy profiles are computed for (1) a single TBP molecule and a single uranyl nitrate complex [UO2(NO3)2] across the water/oil interface and (2) a UO2(NO3)2.TBP2 complex across both water/oil and water/(oil+TBP) interfaces. The UO2(NO3)2 complex is strongly repelled from the water/oil interface, while the UO2(NO3)2.TBP2 complex exhibits interfacial activity that decreases with increasing TBP concentration. The UO2(NO3)2.TBP2 complex displays a net free-energy driving force for partitioning into the oil phase that increases with increasing TBP concentration.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of the Structure and Thermodynamics of Carrier-Assisted Uranyl Ion Extraction

Jayasinghe

Beck

2009

J. Phys. Chem. B

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“…6b it is clearly seen that the pores of the film remain open after sputtering. 42 Following the Au film sputtering through a mask, Fig. 7a, a 1.5 Â 0.6 cm square of membrane is cut out, Fig.…”

Section: Resultsmentioning

confidence: 99%

Functionalized nanoporous track-etched β-PVDF membrane electrodes for lead(ii) determination by square wave anodic stripping voltammetry

et al. 2011

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Track-etched functionalized nanoporous -PVDF membrane electrodes, or functionalized membrane electrodes (FME), are thin-layer cells made from track-etched, poly(acrylic acid) (PAA) functionalized nanoporous -poly(vinylidene fluoride) (-PVDF) membranes with thin Au films sputtered on each side as electrodes. The Au film is thin enough that the pores of the membranes are not completely covered. The PAA functionalization is specifically localised in the walls of the nanoporous -PVDF membrane by radio grafting. The PAA is a cation exchange polymer that adsorbes metal ions, such as Pb 2+ , from aqueous solutions thus concentrating the ions into the membrane. After a calibrated time the FME is transferred to an electrochemical cell for analysis. A negative potential is applied to the Au film of the FME for a set time to reduce the adsorbed ions onto the Au film working electrode. The other metalized side of the FME functions as a counter electrode. Finally, square-wave anodic stripping voltammetry (SW-ASV) is performed on the FME to determine the metal ion concentrations in the original solution based on calibration. The calibration curve of charge versus log concentration has a Temkin isotherm form. The FME membranes are 9 m thick and have 40 nm diameter pores with a density of 10 10 pores/cm 2. This high pore density provides a large capacity for ion adsorption. Au ingress in the pores during sputtering forms a random array of nanoelectrodes. Like surface modified electrodes for adsorptive stripping voltammetry, the pre-concentration step for the FME is performed at open circuit. The zero current intercept of the calibration for Pb 2+ is 0.13 ppb (g/L) and a detection limit of 0.050 ppb based on 3S/N from blank measurements. Voltammetry (CV) and chronoapmerometry (CA) were used to characterize the system. The apparent diffusion coefficient (D) for Pb 2+ in the PAA functionalized pores was determined to be 2.44 x 10-7 cm 2 /s and the partition coefficient (pK M) was determined to be 3.08. The maximum allowable levels for toxic metals in water are now set at low ppb (g/L) levels. The maximum levels of Pb 2+ in potable water established the European Environmental Agency (EEA) the United States Environmental Protection Agency (EPA) and recommendations from the World health Organisation (WHO) are 7.2, 15.0, and 10.0 ppb respectively and the goal of the United States EPA is zero. 1-3 Reliable quantification of these low concentrations is difficult time consuming and expensive. Also, the analysis equipment is not portable so the samples have to be sent a centralised lab which typically involves a 24 hour turn around time, which means that pollution events can be missed, or detected too late. Electrochemical analysis techniques, such as anodic stripping voltammetry (ASV), are generally inexpensive, rapid and portable. The electrode of choice for measuring trace levels of toxic metal ions by ASV has been the dropping mercury electrodes (DME). 4 DMEs and mercury film electrodes are very sensitive, due to their high capa...

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“…Pd and Ag mix completely in all proportions [28,29] and there is no reason to assume this mixing does not occur within the pores of the support. Therefore, analogous to the work of Pesiri et al [25] and McCleskey et al [30] on the penetration of physical vapour deposited (PVD) Au in alumina Anodisc TM membranes, the penetration depth of Pd into the ␣-alumina support is studied with RBS. The Pd penetration also has important ramifications for the membrane performance, i.e., on the adhesion strength of the metal layer to the support and on the hydrogen permeability.…”

Section: Introductionmentioning

confidence: 99%

Improving the control of the electroless plating synthesis of Pd/Ag membranes for hydrogen separation using Rutherford backscattering

Witjens

Bitter

Dillen

et al. 2005

Journal of Membrane Science

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Rutherford backscattering (RBS) was used to determine the thickness and composition of several micrometers thick electroless-plated Pd/Ag alloy layers deposited on porous ␣-alumina. To determine the composition of the alloy, the thickness of the Pd layer after the first synthesis step and the thickness of the Pd/Ag sandwich structure after the second synthesis step were determined. The error in the determined thicknesses (±5%) is much smaller than for the commonly used techniques, i.e., the weight difference and the scanning electron microscopy (SEM) cross-section method. RBS allows accurate determination of plating rates and an even more accurate value for the composition, since the error in the thickness is mainly systematic. This enables one to tune the synthesis parameters for layer thickness and alloy composition.A further and very important advantage of RBS is that pore filling of the support can be studied. Results showed that Pd penetrates into the alumina support during plating, with RBS it could be detected up to 1.4 m deep. It is estimated that the equivalent of 0.1 m bulk Pd is present in the pores of the support of typical electroless-plated samples.

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Asymmetric membranes with modified gold films as selective gates for metal ion separations

Cited by 17 publications

References 22 publications

Molecular Dynamics Simulations of the Structure and Thermodynamics of Carrier-Assisted Uranyl Ion Extraction

Molecular Dynamics Simulations of the Structure and Thermodynamics of Carrier-Assisted Uranyl Ion Extraction

Functionalized nanoporous track-etched β-PVDF membrane electrodes for lead(ii) determination by square wave anodic stripping voltammetry

Improving the control of the electroless plating synthesis of Pd/Ag membranes for hydrogen separation using Rutherford backscattering

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