Metal Ion Flux Research Articles

Electrochemically controlled ion transport across polypyrrole/multi-walled carbon nanotube composite membranes

Polypyrrole (PPy) films doped with acid-treated multi-walled carbon nanotubes (CNTs) were prepared by galvanostatic polymerisation of pyrrole (Py) dissolved in aqueous dispersions of CNTs, which served as the background electrolyte. Morphological characterization of PPy(CNT) films showed a random deposition of the polymer on the surface of the support material, with the former creating a porous, interconnecting three-dimensional network structure. The porous nature of PPy(CNT) films favours movement of large amounts of water in and out of the films during redox cycling, which also causes extensive volume changes. Raman spectroscopy, the electrochemical quartz crystal microbalance method and scanning electron microscopy were used to explore the properties of PPy(CNT) films. In addition, the factors influencing the electrochemically controlled transport of metal ions across composite membranes composed of polypyrrole doped with acid-treated multi-walled carbon nanotubes (PPy(CNT)) were studied. The factors examined were: The polymerization conditions (current density and time), the type of support material on which the polypyrrole films were deposited, and the use of single layer or bilayer type polypyrrole films. The flux of metal ions across the composite membranes was able to be electrochemically controlled when Nucleopore® track-etched membranes were used as the support material, while the flux was controlled by the concentration gradient present when polyvinylidene difluoride (PVDF) was used as the support material for PPy(CNT) films. However, electrochemically controlled movement of metal ions across PVDF-supported membranes was achieved when a bilayer type PPy film (PPy(pTS)/PPy(CNT)) was used (pTS=toluene-4-sulfonic acid). Increasing the thickness of the PPy(CNT) layer in the composite membrane was found to enhance the membranes permeability towards K+.

Improving the quality of barrier/seed interface by optimizing physical vapor deposition of Cu Film in hollow cathode magnetron

The quality of physical vapor deposition (PVD) grown barrier/seed interface in Cu interconnect metallization was significantly improved by enhancing Cu nucleation on the Ta barrier surface. This was accomplished through filtering of nonenergetic species from the deposition flux, increasing the fraction of Cu ions, improving metal ion flux uniformity, and minimizing gas ion bombardment of the growing film. The self-sputtering ability of Cu was combined with a magnetically confined high-density plasma in the Novellus hollow cathode magnetron (HCM®) PVD source. Spatial profiles of plasma density and temperature, as well as ion flux, metal ion fraction, and ion energy, were measured by planar Langmuir probes, quartz crystal microbalances, and gridded energy analyzers, all located at the wafer level. Multiple criteria, such as seed step coverage and roughness, the seed layer’s resistance to agglomeration, and its stability in the plating bath, have been used to evaluate interface quality. As a result, a new and improved Cu PVD process which demonstrates superior stability during subsequent process steps and ensures successful electrofill performance with a more than 50 % reduction in minimal requirement of field thickness as well as sidewall thickness has been developed.

Innovative approach to enhance uranium ion flux by consecutive extraction via hollow fiber supported liquid membrane

The enhancement of liquid membrane performance in this study, by consecutive extraction using a synergistic extractant, is the first to demonstrate that the synergistic extractant, normally employed in the solvent extraction process, can also be extended to extraction applications via a liquid membrane. The study focuses on increasing the flux of metal ions using a consecutive extraction reaction which occurs inside the liquid membrane phase. Uranium ions in trisodium phosphate solution, a by-product of monazite processing, are the specie of interest in this experiment. The feed solution is trisodium phosphate containing uranium ions, whereas the stripping solution is nitric acid. The extractant is Aliquat336 mixed with TBP in kerosene. The results demonstrate that when Aliquat336 is mixed with TBP, the flux of uranium ions is synergistically increased because of a consecutive extracting reaction in the liquid membrane phase. The highest flux is 3600 mg m −2 s −1 with 0.06 M TBP and 0.6 M Aliquat336. Synergistic extraction is also obtained because the flux is much higher than that obtained using a single extractant.

Application of experimental design approach and artificial neural network (ANN) for the determination of potential micellar-enhanced ultrafiltration process

In this study, micellar-enhanced ultrafiltration (MEUF) was applied to remove zinc ions from wastewater efficiently. Frequently, experimental design and artificial neural networks (ANNs) have been successfully used in membrane filtration process in recent years. In the present work, prediction of the permeate flux and rejection of metal ions by MEUF was tested, using design of experiment (DOE) and ANN models. In order to reach the goal of determining all the influential factors and their mutual effect on the overall performance the fractional factorial design has been used. The results show that due to the complexity in generalization of the MEUF process by any mathematical model, the neural network proves to be a very promising method in compared with fractional factorial design for the purpose of process simulation. These mathematical models are found to be reliable and predictive tools with an excellent accuracy, because their AARE was ±0.229%, ±0.017%, in comparison with experimental values for permeate flux and rejection, respectively.

Zinc availability regulates exit from meiosis in maturing mammalian oocytes

Cellular metal ion fluxes are known in the case of alkali and alkaline earth metals but not well documented for transition metals. Here, we describe major changes in the zinc physiology of the mammalian oocyte as it matures and initiates embryonic development. Single-cell elemental analysis of mouse oocytes by synchrotron-based x-ray fluorescence microscopy (XFM) revealed a 50% increase in total zinc content within the 12-14 hour period of meiotic maturation. Perturbation of zinc homeostasis with a cell-permeable small molecule chelator blocked meiotic progression past telophase I. Zinc supplementation rescued this phenotype when administered prior to this meiotic block. However, following telophase arrest, zinc triggered parthenogenesis, suggesting that exit from this meiotic step is tightly regulated by the availability of a zinc-dependent signal. These results implicate the zinc bolus acquired during meiotic maturation as an important part of the maternal legacy to the embryo.

Transport of metal ions across an electrically switchable cation exchange membrane based on polypyrrole doped with a sulfonated calix[6]arene

The conducting polymer polypyrrole, PPy, was used as the active component of a cation exchange membrane for transferring a range of metal ions between two solutions by electrical modulation of the polymer between its conducting and non-conducting states. The cation exchange membranes consisted of platinum sputter-coated polyvinylidene difluoride (PVDF) which had been coated with polypyrrole doped with sulfonated calix[6]arene (PPy(C6S)). It was shown that applying a constant potential in the range −0.4 to +0.6 V did not result in any metal ion flux across the PVDF/Pt-PPy(C6S) membrane. However, a gradual but steady increase in metal ion concentration was detected in the receiving cell when −0.8 V was applied to the membrane. To investigate the effect of film thickness on the permeability of metal ions, transport experiments were performed with composite membranes containing 2.0, 3.3, and 5.6 μm thick PPy(C6S) films. The permeability of the metals across the membrane increased as the PPy(C6S) film thickness decreased and was found to decrease in the following order: Ca 2+ > K + > Mn 2+ ≫ Co 2+, when the receiving cell contained deionised water. The PVDF/Pt-PPy(C6S) composite membrane showed significant permeability towards metal ions such as Ca 2+, K + and Mn 2+, with the flux for Ca 2+ higher than that seen for this metal ion with any previously studied PPy films containing other complexing dopants.

Flux of multiple charged metal ions of high energy from plasma produced by a moderate energy laser pulse

Studies of the energy spectrum and charge state distribution of ions produced from an Al target irradiated with a laser pulse of moderate energy (90 mJ) and light intensity (4.2 × 1012 W cm−2) and of 27 ps pulse duration are presented. It is established that highly charged ions of the target material up to Al11+ are emitted from the laser produced plasma and evidence of the presence of Al12+ ions is also established. The maximum of the bulk of ion energy distributions approaches 7 keV/Z, which exceeds the values typically observed earlier in plasma produced by laser radiation of the intensity mentioned above. Theoretical examination of the experimental results reveals that the relatively high ion energies can be explained by the specific conditions of the experiments, namely the relatively large diameter of focal spot of the laser beam, appropriate length of the laser pulse, and so on.

In situ plasma diagnostics study of a commercial high-power hollow cathode magnetron deposition tool

Using a newly designed and built plasma diagnostic system, the plasma parameters were investigated on a commercial 200mm high-power hollow cathode magnetron (HCM) physical vapor deposition tool using Ta target under argon plasma. A three dimensional (3D) scanning radio frequency (rf)-compensated Langmuir probe was constructed to measure the spatial distribution of the electron temperature (Te) and electron density (ne) in the substrate region of the HCM tool at various input powers (2–15kW) and pressures (10–70mTorr). The Te was in the range of 1–3eV, scaling with decreasing power and decreasing pressure. Meanwhile, ne was in the range of 4×1010–1×1012cm−3 scaling with increasing power and decreasing pressure. As metal deposits on the probe during the probe measurements, a self-cleaning plasma cup was designed and installed in the chamber to clean the tungsten probe tip. However, its effectiveness in recovering the measured plasma parameters was hindered by the metal layer deposited on the insulating probe tube which was accounted for the variation in the plasma measurements. Using a quartz crystal microbalance combined with electrostatic filters, the ionization fraction of the metal flux was measured at various input power of 2–16kW and pressure of 5–40mTorr. The metal ionization fraction reduced significantly with the increasing input power and decreasing gas pressure which were attributed to the corresponding variation in the ionization cross section and the residence time of the sputtered atoms in the plasma, respectively. Both the metal neutral and ion flux increased at higher power and lower pressure. The 3D measurements further showed that the ionization fraction decreased when moving up from the substrate to the cathode.

In Situ Imaging of Metals in Cells and Tissues

In Situ Imaging of Metals in Cells and Tissues

Determination of optimal conditions for separation of metal ions through membrane dialysis using statistical experimental methods

Statistical experimental methods were used to optimize the variable conditions of membrane dialysis process with a complex agent. Permselectivity of metal ions has been investigated in a two-compartment dialyzer with reflux flow. Cu+2-Ni+2 ion system was chosen for the experimental investigation. Oxalic, malonic acid, acid and citric acid were selected as a complex agent used in the investigated solution in order to increase the discrepancy between transport fluxes of metal ions. The concentration ratio of complex agent to metal ions (X1), pH value of investigated solution (X2) and concentration of metal ions (X3) were conducted to be optimized. The Box-Behnken design and response surface methodology were employed in the design of experiments and the analysis of results. The experimental results indicated that oxalic acid is a better complex agent in this study. For the case of oxalic acid as complex agent, the maximal permselectivity of metal ions was obtained when concentration ratio of complex agent to...

Laterally resolved ion-distribution functions at the substrate position during magnetron sputtering of indium-tin oxide films

During the magnetron sputtering from an indium-tin oxide (ITO) target (76mm diameter) we measured the ion-distribution functions (IDFs) of energetic ions (argon, indium, and oxygen ions) at the substrate surface using a combination of a quadrupole mass spectrometer and an electrostatic energy analyzer. We obtained the IDFs for argon sputtering pressures in the range from 0.08to2Pa and for dc as well as rf (13.56MHz) plasma excitation with powers from 10to100W. The IDF measurements were performed both over the target center at a target-to-substrate distance of 65mm and at different positions along the target radius in order to scan the erosion track of the target. The mean kinetic energies of argon ions calculated from the IDFs in the dc plasma decreased from about 30to15eV, when the argon pressure increased from 0.08to2Pa, which is caused by a decrease of the electron temperature also by a factor of 2. Indium atoms exhibit higher mean energies due to their additional energy from the sputtering process. The total metal ion flux turns out to be proportional to the discharge power and the pressure, the latter dependence being due to Penning ionization of the metal atoms (In and Sn). From the scans across the target surface the lateral distributions of metal, oxygen, and argon ions were derived. In the dc discharge the position of the erosion track is reproduced by increased ion intensities, while it is not the case for the rf excited plasma. The lateral variations of the observed species do not influence the lateral resistivity distributions of the deposited ITO films.

Preferential transport behaviors of ternary system cupric–nickel–zinc ions through cation-exchange membrane with a complexing agent by dialysis

Abstract Preferential transport behaviors of ternary metal ion system were studied in a stirred batch cation-exchange membrane dialyzer. Cu 2+ –Ni 2+ –Zn 2+ system was chosen for investigation. Malonic acid, oxalic acid and citric acid were employed, respectively, as a complexing agent in order to enhance the discrepancy in transport fluxes of metal ions. The results show that the effective order of complexing agents is malonic acid > oxalic acid > citric acid. The stoichiometric ratio of complexing agent to metal ions and the pH value of the feed solution are the primary factors on the preferential transport behaviors of metal ions. The optimal dimensionless permeation flux ratio of P Zn–Na / P Ni–Na / P Cu–Na is obtained about 5.3/3.6/0.7. On the basis of the Nernst–Planck equation and interface equilibrium, a theoretical model of the system is established. The predicted results obtained by theoretical model are in good agreement with the experimental results.

Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

An electrochemical membrane reactor with three compartments (anolyte, catholyte and central compartment) based on in-house-prepared cation- and anion-exchange membrane was developed to achieve in situ separation and recovery of chromic acid and metal ions. The physicochemical and electrochemical properties of the ion-exchange membrane under standard operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of chromate and dichromate of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that metal ion migrated through the cation-exchange membrane from central compartment to catholyte and OH− formation at the cathode leads to the formation of metal hydroxide. Simultaneously, chromate ion migrated through the anion-exchange membrane from central compartment to the anolyte and formed chromic acid by combining H+ produced their by oxidative water splitting. Thus a continuous decay in the concentration of chromate and metal ion was observed in the central compartment, which was recovered separately in the anolyte and catholyte, respectively, from their mixed solution. This process was completely optimized in terms of operating conditions such as initial concentration of chromate and metal ions in the central compartment, the applied cell voltage, chromate and metal ion flux, recovery percentage, energy consumption, and current efficiency. It was concluded that chromic acid and metal ions can be recovered efficiently from their mixed solution leaving behind the uncharged organics and can be reused as their corresponding acid and base apart from the purifying water for further applications.

Polymer inclusion membranes: The concept of fixed sites membrane revised

The mechanism of facilitated transport of metal ions across polymer inclusion membranes (PIMs) is revised on the basis of transport flux measurements and of new data brought by techniques sensitive to local inter-molecular interactions and molecular diffusion. Cellulose triacetate (CTA) membranes built with two types of inclusion carriers: a liquid one Aliquat 336 and a crystalline one Lasalocid A, both able to carry metal ions across PIMs and supported liquid membranes (SLMs) made of the same components, have been compared. Both PIM systems show similar effects for what concern the need of a carrier threshold concentration for the occurrence of a transport flux across PIM as revealed by flux and fluorescence correlation spectroscopy (FCS) measurements, and the dependence of the chemical nature of plasticizers on the metal ion flux. These systems also present similar Raman and far IR signatures of structural evolution of PIMs with the increase of the carrier concentration within the CTA matrix. All the presented data are interpreted as concern PIMs, according to an evolution of chemical interactions between components of the polymeric membrane able to lead to a phase transition. This phase transition type of the carrier-plasticized polymer system is induced by the increase of carrier concentration in the polymer chains. The PIM progressively organizes itself like a liquid SLM because of the enhancement of preferential solvent interactions between the carrier and the plasticizer. The main conclusion of this study is that the classically adopted “hopping” transport mechanism between fixed carrier sites in a PIM does not apply to such carrier chemically unbound to polymer membrane systems.

Facilitated transport of Zn(II), Cd(II) and Pb(II) ions through polymer inclusion membranes with calix[4]-crown-6 derivatives

Competitive transport of an equimolar mixtures of Zn(II), Cd(II), and Pb(II) ions from aqueous nitrate source phase ( c Me = 0.001 M, each) through polymer inclusion membranes (PIMs) using calix[4]crown-6 derivatives, as ion carriers, has been investigated. The influence of the group attached type to the calix[4]-crown-6 molecule on the selectivity and efficiency of Zn(II), Cd(II), and Pb(II) transport across polymer inclusion membranes containing cellulose triacetate as the support was studied. The transport selectivity orders for the PIM with 4 and 5 was: Pb(II) > Zn(II) > Cd(II), whereas for 3 was: Pb(II) > Zn(II) ≥ Cd(II). The metal cations transport results can be explained by their tendency as the Lewis acids in chemical interaction with the bases. The selectivity coefficients of Pb(II)/Zn(II) and Pb(II)/Cd(II) decrease with the hydrochloric acid concentration increase in receiving phase. Also the influence of the plasticizers nature, i.e. o-nitrophenyl pentyl ether ( o-NPPE), o-nitrophenyl octyl ether ( o-NPOE), and bis(2-ethylhexyl)adipate (DOA) on the ion transport through PIMs is presented. The initial flux of metal ions insignificantly increases in the following order: DOA < o-NPOE < o-NPPE, i.e. with decrease of plasticizers viscosity. The stability of PIM with calix[4]crown-6 derivatives was confirmed in replicate experiments.

Roles of Metal Ion Complexation and Membrane Permeability in the Metal Flux through Lipophilic Membranes. Labile Complexes at Permeation Liquid Membranes

The various physicochemical factors that influence the flux of carrier-transported metal ions through permeation liquid membranes (PLM) are studied systematically. Understanding PLM behavior is important (i) to optimize the application of PLM as metal speciation sensors in environmental media and (ii) because PLM may serve as bioanalogical devices that help to elucidate the environmental physicochemical processes occurring at the surface of biological membranes. Diffusion of free and complexed metal ions in solution, as well as diffusion of the metal carrier complex in the membrane, is considered. The respective roles of diffusion layer thickness, ligand concentration, complex stability, carrier concentration, and membrane thickness are studied experimentally in detail and compared with theory, using various labile complexes, namely, Pb(II)-diglycolate, Cu(II)-diglycolate, and Cu(II)-N-(2-carboxyphenyl)glycine. Conditions where either membrane diffusion or solution diffusion is rate limiting are clearly discriminated. It is shown in particular, that, by tuning the carrier concentration or membrane thickness, either the free metal ion concentration or the total labile metal species are measured. PLM can thus be used to determine whether models based on the free ion activity in solution (such as BLM or FIAM models) are applicable to metal uptake by microorganisms in a real natural medium.

Transport of Zn(II), Cd(II), and Pb(II) across CTA plasticized membranes containing organophosphorous acids as an ion carriers

In this work a competitive transport of an equimolar mixtures of Zn(II), Cd(II), and Pb(II) across polymer inclusion membranes (PIMs) is presented. In PIMs di-2-ethylhexylphosphoric acid (D2EHPA) as well as commercial extractants, i.e. Cyanex ® 272, 301, and 302 were used as ion carriers. The influence of nature extractants on cation transport selectivity and efficiency has been explored. Cyanex ® 301 and 302 used as ionic carriers for competitive transport of Zn(II), Cd(II) and Pb(II) give preferential selectivity order: Pb(II) > Cd(II) > Zn(II). The selectivity coefficients for Pb(II)/Cd(II) and Pb(II)/Zn(II) for transport with Cyanex ® 302 have been found, they were equal to 2 and 4.4, respectively. To understand the influence of plasticizers nature on Zn(II), Cd(II), Pb(II) ions transport through PIM, membranes with different compounds, i.e. dioctyl phthalate (DOP), o-nitrophenyl octyl ether (ONPPE), bis(2-ethylhexyl) adipate (DOA), and tris(2-etylhexyl) phosphate (TOF) were prepared. The initial fluxes of metal ions increase in the following order of plasticizers: DOA < TOF < ONPOE, i.e. with their viscosity decrease, whereas DOP proved to be equally effective as ONPOE. The addition of 3,7-dinonyl-naphthalene-1-sulfonic acid into PIM with Cyanex ® 302 plays a role of a synergetic factor in the membrane process. A long-term experiment was carried out to demonstrate the durability of PIMs. The application of PIM transport process for 92% and 96% removal of lead(II) and cadmium(II), respectively, from technological sludge eluates is also shown.

Investigation of high power impulse magnetron sputtering pretreated interfaces for adhesion enhancement of hard coatings on steel

In order to improve the adhesion of hard coatings such as CrN, a surface pretreatment by the novel high power impulse magnetron sputtering (HIPIMS) technique followed by reactive unbalanced d.c. magnetron sputtering deposition was performed using a Cr target. The HIPIMS plasma comprising a high metal ion-to-neutral ratio consisting of single- and double-charged metal species identified by mass spectrometry increased the metal ion flux to the substrate. When applying a negative substrate bias U b the adhesion was enhanced due to sputter cleaning of the surface and metal ion intermixing in the interface region. This intermixing, resulting in a gradual change of the composition, is considered to enhance the adhesion of the hard coatings on steel substrates. The pretreatment was carried out in an inert gas atmosphere at a pressure of p Ar = 1 mTorr, the duration was varied between 25 and 75 min, whereas the negative substrate bias was varied between 400 V and 1200 V. The adhesion was found to depend on the substrate bias as well as on the target power and, for low substrate bias, on the duration of the pretreatment. For CrN the critical load of failure determined by scratch test could be increased in comparison to the values reported for specimens pretreated by conventional Ar etching. The influence of the target peak voltage, the substrate bias as well as pretreatment time on the constitution and morphology of the interface after the pretreatment is discussed applying analytical transmission electron microscopy.

Donnan Effects in the Steady-State Diffusion of Metal Ions through Charged Thin Films

The steady-state diffusion of metals ions through thin films with fixed charged groups was investigated using diffusive gradients in thin films (DGT) measurements. Copolymers of acrylamide and sodium acrylate cross-linked with N,N'-methylenebisacrylamide were used as diffusive gels. The rate of diffusion of cadmium ions through the gels was measured by determining the mass of cadmium bound to a backing chelex resin after a known deployment time. Variation of the ionic strength as well as the fixed charge density and the thickness of the gel layer allowed evaluation of the impact of the Donnan partitioning and the diffusion layer in solution on the observed steady-state flux of ions through the layer. The results underscore that, as the Donnan partitioning increases, the impact of the diffusion layer in solution becomes more significant. At modest Donnan potentials, Donnan partitioning controls the net flux of metal ions, whereas at conditions of increasing Donnan potential, i.e., at decreasing ionic strength, the flux is increasingly limited by diffusion in solution. An analytical expression is developed to describe the influence of Donnan partitioning on the observed steady-state flux of metal ions.

LIX ®-loaded polymer inclusion membrane for copper(II) transport : 2. Optimization of the efficiency factors (permeability, selectivity, and stability) for LIX ® 84-I

Polymer inclusion membrane transport of copper(II) in chloride and sulfate medium is studied using CTA (support), tris(2- n-butoxyethyl)phosphate (plasticizer), LIX ® 84-I (carrier), and ethanol (additive). An optimization in the aqueous phases (pH, type of anions and buffer concentration) and membrane compositions (extractant and plasticizer concentrations) was performed and the efficiency factors (permeability, selectivity, and stability) of the system evaluated. It was observed that besides the improvement in metal ion flux and reduction in metal accumulation in the membrane by the incorporation of the additive in the casting solution, an increase in membrane stability is also attained. A transport model for the system in sulfate medium is proposed. Values for the aqueous and organic resistances ( Δ a = 10 4.7 and Δ o = 10 8.0 s m −1, respectively), true organic diffusion coefficient and membrane diffusion coefficient of the Cu(II)–carrier complex in the membrane phase ( D b,o = 10 −13 and D o = 10 −12.2 m 2 s −1, respectively) were calculated assuming that a carrier–diffusion mechanism is mainly responsible for ion transport, as suggested for the transport profiles, and the value of the conditional extraction constant ( log K ′ ext = − 5.6 ) determined in an independent form by solid–liquid extraction experiments. A highly selective separation of Cu(II) from Zn(II) and Fe(III) was achieved as well.