Electrostatic Rejection Research Articles

Polysulfide Rejection Strategy in Lithium-Sulfur Batteries Using an Ion-Conducting Gel-Polymer Interlayer Membrane.

Lithium-sulfur batteries (LiSBs) are emerging as promising alternative to conventional secondary lithium-ion batteries (LiBs) due to their high energy density, low cost, and environmental friendliness. However, preventing polysulfide dissolution is a great challenge for their commercial viability. The present work is focused on preparing a lithium salt and ionic liquid (IL) solution (SIL) impregnated ion (lithium ion)-conducting gel-polymer membrane (IC-GPM) interlayer to prevent polysulfide migration toward the anode by using an electrostatic rejection and trapping strategy. Herein, we introduce an SIL-based freestanding optimized IC-GPM70 (70 wt % SIL) interlayer membrane with high lithium-ion conductivity (2.58 × 10-3 S cm-1) along with excellent thermal stability to suppress the migration of polysulfide toward the anode and prevent polysulfide dissolution in the electrolyte. Because of the coulombic interaction, the anionic groups, -CF2 of the β-phase polymer host PVdF-HFP, TFSI- anion of IL EMIMTFSI, and anion BOB- of LIBOB salt, allow hopping of positively charged lithium ions (Li+) but reject negatively charged and relatively large-sized polysulfide anions (Sx-2, 4 <x <8). The cationic group EMIM+ of the IL is electrostatically able to attract and trap the polysulfides in the interlayer membrane. Since the shuttle effect of lithium polysulfides in LiSBs has been suppressed by the prepared IC-GPM70 interlayer, the resulting lithium-sulfur cell exhibits significantly higher cycling stability (1200 cycles), rate performance (1343, 1208, 1043, 875, and 662 mAh g-1 at 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively), and structural integrity during cycling than its counterpart without the IC-GPM70 interlayer. The interlayer membrane has been found to improve the performance and durability of LiSBs, thus making them a viable alternative to conventional LiBs.

Technology selection and process development for enhancing water recovery from mine tailing water: A case study

ABSTRACT A mining operation uses mechanical vapor recompression to treat mine tailings water for discharge to the environment. To maintain the mine’s operations, the removal of an additional 1 MLD of water is required. The water has a high TDS, is supersaturated, and a low pH. A range of water treatment technologies were reviewed and assessed. It was determined that a membrane system was the best option to deploy, and an NF/RO system was recommended for further evaluation. However, because the tailings water pH is in the vicinity of most membrane isoelectric points (~3-4), electrostatic rejection would be greatly affected, allowing excessive ion transmission to the permeate. It was hypothesized that a membrane with an isoelectric point >4 would provide enhanced rejection. Two acid resistant NF polymeric membranes with isoelectric points at approximately pH 5 were tested at laboratory scale. The volume recovery was restricted due to supersaturation chemistry limitations, not osmotic pressure or the operating pressure of the selected membranes. An overall system recovery of ~50% was achievable. An integrated flowsheet was developed for a system that required significantly less capital and energy that an additional thermal evaporation process.

Cross-Linked Ionomer Gel Separators for Polysulfide Shuttle Mitigation in Magnesium–Sulfur Batteries: Elucidation of Structure–Property Relationships

Cross-linked ionomer networks of varying poly(ethylene glycol) diacrylate cross-linker chain length, ionic comonomer chemistry, and comonomer ratio have been studied for their use as polysulfide shuttle inhibiting separators in magnesium–sulfur (Mg–S) batteries. Through the use of X-ray scattering, polysulfide diffusion experiments, conductivity measurements, and Mg–S cell cycling, it was determined that inclusion of tethered anions in polymer networks mitigates the polysulfide shuttle effect. Polysulfide crossover through networks into a bulk electrolyte can be reduced by absorption into the polymer gel, steric rejection, and electrostatic rejection, with the predominance of these mechanisms dictated by polymer composition and structure. The best network composition allowed an initial Mg–S cell discharge capacity of 522 mAh/g compared to a discharge capacity of 365 mAh/g using a literature standard glass fiber separator. The ionomer cell saw 67% capacity retention after three cycles, whereas the glass fi...

Electro-Conductive Composite Gold-Polyethersulfone-Ultrafiltration-Membrane: Characterization of Membrane and Natural Organic Matter (NOM) Filtration Performance at Different In-Situ Applied Surface Potentials.

Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 107 S m−1 was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L−1). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (−1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.

Coordinative Layer-by-Layer Assembly of Thin Films Based on Metal Ion Complexes of Ligand-Substituted Polystyrene Copolymers and Their Use as Separation Membranes

Polystyrene copolymers containing either 4′-vinyl-2,2′:6′,2″-terpyridine (P1) or 2,6-bis(1-methyl-1H-benzo[d]imidazol-2-yl)pyridin-4-yloxy)-methacrylate (P2) as comonomers are prepared and studied on metal ion coordination in solution and coordinative sequential assembly of films and membranes. Permeation and separation of ions and neutral aromatic molecules across the membranes are investigated. UV–vis titration of P1 with zinc acetate in chloroform/methanol (25:1) indicates formation of 2:1 ligand:metal bis-complexes, while titration of P2 led to 1:1 monocomplexes. It is demonstrated that coordinative interactions between the ligand groups and metal ions such as Zn(II) or Cu(II) can be used for layer-by-layer assembly of ultrathin films on solid quartz supports and porous supporting membranes. Formation of coordination polymer assemblies is characterized using UV-spectroscopy, quartz crystal microbalance measurements, scanning electron microscopy, and thickness measurements. Coordinative films prepared on porous polyacrylonitrile/polyethylene terephthalate supporting membranes exhibit a selective transport of ions and small molecules. Ion transport in aqueous and alcoholic solution is controlled by a sieving effect and by electrostatic rejection at the ligand–metal ion complexes in the membrane. The transport of organic aromatic molecules is only controlled by the sieving effect. Separation factors α(NaCl/BaCl2) up to 4.2 and α(naphthalene/perylene) up to 4.8 are found.

Electroconductive and electroresponsive membranes for water treatment

Abstract In populated, water-scarce regions, seawater and wastewater are considered as potable water resources that require extensive treatment before being suitable for consumption. The separation of water from salt, organic, and inorganic matter is most commonly done through membrane separation processes. Because of permeate flux and concentration polarization, membranes are prone to fouling, resulting in a decline in membrane performance and increased energy demands. As the physical and chemical properties of commercially available membranes (polymeric and ceramic) are relatively static and insensitive to changes in the environment, there is a need for stimuli-reactive membranes with controlled, tunable surface and transport properties to decrease fouling and control membrane properties such as hydrophilicity and permselectivity. In this review, we first describe the application of electricity-conducting and electricity-responsive membranes (ERMs) for fouling mitigation. We discuss their ability to reduce organic, inorganic, and biological fouling by several mechanisms, including control over the membrane’s surface morphology, electrostatic rejection, piezoelectric vibrations, electrochemical reactions, and local pH changes. Next, we examine the use of ERMs for permselectivity modification, which allows for the optimization of rejection and control over ion transport through the application of electrical potentials and the use of electrostatically charged membrane surfaces. In addition, electrochemical reactions coupled with membrane filtration are examined, including electro-oxidation and electro-Fenton reactions, demonstrating the capability of ERMs to electro-oxidize organic contaminates with high efficiency due to high surface area and reduced mass diffusion limitations. When applicable, ERM applications are compared with commercial membranes in terms of energy consumptions. We conclude with a brief discussion regarding the future directions of ERMs and provide examples of several applications such as pore size and selectivity control, electrowettability, and capacitive deionization. To provide the reader with the current state of knowledge, the review focuses on research published in the last 5 years.

PH and ion strength modulated ionic species loading in mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSN) have emerged as appealing host materials to accommodate guest molecules for biomedical applications, and recently various methods have been developed to modulate the loading of guest molecules in the silica matrix. Herein, it was demonstrated that pH and ion strength showed great influence on the loading of charged species into the nanoparticles, taking MCM-41 as a host MSN model and methylviologen (MV2+) and 1,5-naphthalene disulfonate (NDS2−) as typical charged ionic guest molecules. As the pH increased from 3.0 to 8.0, the loading amount of MV2+ increased gradually, while on the contrary, it decreased gradually for NDS2−, for the solution pH changed the electrostatic interaction between the silica matrix and the ionic guest molecules. Additionally, the adding of NaCl reduced the electrostatic interaction, which resulted in a decreasing of the electrostatic rejection and electrostatic accumulation for the molecules carrying the same and the opposite charge to the particle respectively. Thus, pH and ion strength can be employed as simple approaches to modulate the loading of charged molecules and permselectivity in MSN. This work has a definite guidance function for molecule loading, transport modulation, controlled release as well as sensors based on MSN.

Cathode membrane fouling reduction and sludge property in membrane bioreactor integrating electrocoagulation and electrostatic repulsion

Applying minute electric field on conductive membrane cathode and Fe anode effectively reduced membrane fouling in eMBR (electric field attached membrane bioreactor) by integrating electrocoagulation (EC) with electrostatic rejection of the foulants. The effect and the mechanism of electric currents on the anode corrosion and release of ferrous iron, sludge activity and fouling reduction were investigated in EC-eMBR. Comparative tests were carried out using four reactors, fed with the same influent, but operated under different electric current, constantly at 0mA, 1mA, 3mA and 5mA. Without electric current (0mA), the membrane filtration lasted 34days, when 3times membrane cleaning were conducted (average 11days/cycle). With 1mA current, the filtration lasted 48days with only 2times membrane cleaning (average 24days/cycle), indicating an optimal balanced effect of EC and electrostatic rejection on foulants. Under higher currents at 3mA and 5mA, 3times membrane cleaning were required during 54days and 47days lasting filtration (18days or 16.3days/cycle), respectively. The integration of EC and electrostatic rejection extended the filtration cycle and reduced the cleaning frequency. High currents EC tends to counteract and reduce the electrostatic rejection effect of high currents electric field on foulants. The positive effects of EC included the increase in sludge activity, the decrease of both the extracellular polymeric substance (EPS) and the specific filtration resistances.

Seeding-free synthesis of dense zeolite FAU membranes on 3-aminopropyltriethoxysilane-functionalized alumina supports

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite FAU membranes using 3-aminopropyltriethoxysilane (APTES) as covalent linker between the FAU layer and the alumina support. APTES acts as molecular linker for anchoring the FAU precursors onto the support surface to promote the nucleation and the formation of a thin, well intergrown FAU membrane. Additionally, at the pH of zeolite FAU crystallization (about 11), the zeta potential of the alumina support is changed by APTES-treatment from strongly negative to neutral, which will be helpful to reduce the electrostatic rejection between the negatively charged precursor species and the alumina support. The SEM and XRD characterizations indicate that a relative thin but dense and phase-pure FAU zeolite membrane with a thickness of about 2.5 μm can be formed on the α-Al 2O 3 support after crystallization at 75 °C for 24 h, and no cracks, pinholes or other defects are visible in the membrane layer. The zeolite FAU membranes prepared on APTES-modified Al 2O 3 supports display higher separation selectivities than those prepared on non-modified Al 2O 3 support. For binary mixtures at 100 °C and 1 bar, the mixed gas separation factors of H 2/CO 2, H 2/N 2, H 2/CH 4 and H 2/C 3H 8, are found to be 6.5, 6.0, 4.0 and 11.1, respectively, which are higher than the corresponding Knudsen coefficients. Further, relative high H 2 permeances of about 4.0 × 10 −7 mol m −2 s −1 Pa −1 can be obtained through the FAU membrane due to the thin layer and the relative wide pores of 0.74 nm.

Resistive-Pulse Detection of Short dsDNAs Using a Chemically Functionalized Conical Nanopore Sensor

To develop nanopore resistive-pulse sensors for the detection of short (50 base-pair [bp] and 100 bp) DNAs. Conically shaped nanopores were chemical etched into polyethylene terphthalate membranes. The as-etched membrane had anionic carboxylate sites on the pore walls. Neutral and hydrophilic ethanolamine functional groups were attached to these carboxylate sites using well-established EDC (1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride) chemistry. The ethanolamine-functionalized pores were used to detect 50 and 100 bp DNAs via the resistive-pulse method. The resistive-pulse signature produced by the 50 bp DNA could be distinguished from that of the 100 bp DNA with these sensors. Attachment of ethanolamine to the carboxylate groups on the pore wall lowered the anionic charge density on the wall. This mitigated the problem of electrostatic rejection of the anionic DNAs from the pore and enabled the detection of these DNA analytes.

Mechanism of Electrostatic Gating at Conical Glass Nanopore Electrodes

The mechanism of molecule-based electrostatic gating of redox fluxes at conical glass nanopore (GNP) electrodes has been investigated using finite-element simulations. The results demonstrate that the fluxes of cationic redox molecules through the nanopore orifice can be reduced to negligibly small values when the surface charge of the nanopore is switched from a negative to a positive value. Electrostatic charge reversal can be affected by ionization of surface-bound moieties in response to environmental stimuli (e.g., photoionization or acid protonation), but only if the negative charge of the glass is included in the analysis. Numerical simulations of the responses of GNP electrodes are based on a simultaneous solution of the Poisson and Nernst-Planck equations and are in excellent agreement with our previously reported experimental results for electrostatic gating of the fluxes of Ru(NH 3) 6 (3+) and Fe(bpy) 3 (2+) at GNP electrodes with orifice radii between 15 and 100 nm. The gating mechanism is discussed in terms of three components: (1) migration of ionic redox species in the depletion layer adjacent to the electrode surface; (2) migrational transport along the charged pore walls; (3) electrostatic rejection of charged molecules at the pore orifice. The numerical results indicate that all three components are operative, but that ion migration along the pore walls is dominant.

Net-based force-directed macrocell placement for wirelength optimization

We propose a net-based hierarchical macrocell such that placement dictates the cell placement. The proposed approach has four phases. 1) Net clustering and net-level floorplanning phase: a weighted net dependency graph is built from the input register-transfer-level netlist. Clusters of nets are then formed by clique partitioning and a net-cluster level floorplan is obtained by simulated annealing. The floorplan defines the regions where the nets in each cluster must be routed. 2) Force-directed net phase: a force-directed net is performed which yields a coarse net-level without consideration for the cell placement. 3) Iterative net terminal and cell phase: a force-directed net and cell is performed iteratively. The terminals of a net are free to move under the influence of forces in the quest for optimal wire length. The cells with high net length cost may jump out of local minima by ignoring the rejection forces. The overlaps are reduced by employing electrostatic rejection forces. 4) Overlap removal and input/output (I/O) pin assignment phase: Overlap removal is performed by a grid-based heuristic. I/O pin assignment is performed by minimum-weight bipartite matching. Placements generated by the proposed approach are compared with those generated by Cadence Silicon Ensemble and the O-tree floorplanning algorithm. On average, the proposed approach improves both the total wire length and longest wire length by 18.9% and 28.3%, respectively, with an average penalty of 5.6% area overhead.

Selective removal of cobalt species using nanofiltration membranes.

Selective removal of cobalt species from simulated nuclear liquid waste was investigated with different nanofiltration (NF) membranes at various solution pH levels, initial cobalt concentrations, and background ion concentrations. This study provides insight into the understanding of the relationships between rejections of a target compound (cobalt) and chemical equilibria of various species in the feed solution during NF. Particularly, the ratio of electrostatic rejection to steric rejection for different membranes used was quantitatively evaluated to find outthe relative significance in NF. Substantial cobalt rejection by NF was achieved along with partial separation of monovalent ionic species, although it depended on the level of liquid pH and the presence of background species. Greater cobalt rejection at increased pH was attributed to the precipitation of CoCO3(s) associated with natural carbonates originating from atmospheric CO2 gas rather than that of Co(OH)2(s). A loose NF membrane (e.g., NTR7410) gave as high a rejection as other tighter ones due to the stronger influence of electrostatic rejection, particularly at low pH where no cobalt precipitation was occurring. The decrease of cobalt rejection with the addition of boric acid was found to occur due to the formation of complexes between cobalt and boric acid, which was verified by the analyses of solution turbidity and near-infrared spectroscopy.

Integration of charged membrane into perstraction system for separation of amino acid derivatives

The integration of a charged membrane into a perstraction system for high selective separation is reported. A mixture of N-(benzyloxycarbonyl)-L-aspartic acid (ZA), L-phenylalanine methyl ester (PM), and N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methyl ester (ZAPM) was used as the model solution. The aqueous phase containing ZA, PM, and ZAPM was adjusted to pH 6 and was contacted with tert-amyl alcohol through a charged membrane. Seven different ion-exchange membranes and two different microfiltration membranes were tested for the separation system. Only ZAPM could permeate into the organic phase through SELEMION AMV and ASV. The separations between ZA and ZAPM and between PM and ZAPM were performed by biphasic extraction and electrostatic rejection, respectively. The permeabilities of ZAPM were higher than those of PM for all experiments using the ion-exchange membranes, although the molecular weight of ZAPM is larger than that of PM. The membrane that had a smaller pore size showed higher ZAPM selectivity. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 162-167, 1997.

New selective perstraction system with charged membrane

A new perstraction system using a charged membrane was developed in order to obtain high selectivity by liquid-liquid equilibrium and electrostatic rejection effects. A mixture of N- beenzyloxycarbonyl)- l-aspartic acid (ZA), l-phenylalanine methyl ester (PM) and N- (benzyloxycarbonyl)- l-phenylalanine methyl ester (ZAPM) was used as the model solution. The aqueous phase was adjusted to pH 6 and using a positively charged membrane, only ZAPM was extracted into the organic phase. The separations between ZA and ZAPM, and between PM and ZAPM were performed by bi-phasic extraction and electrostatic rejection, respectively. The utility of this hybrid separation system, combining perstraction with charged membrane separation is demonstrated.

A simple miniature magnetic probe with inherent electrostatic rejection

A modification of a basic center-tapped magnetic probe design has been developed wherein subtraction of capacitive signals is carried out by the probe itself. The electrostatic rejection of this probe is compared with other typical designs.

Characterization of the morphological modification induced by long term operations on phosphoric acid fuel cell (PAFC) electrodes

The modification of the morphological and adhesive binding of PAFC electrodes has been studied by electron spectroscopy and electron microscopy with regard to their endurance and preparative treatments. The corrosion of the electrodes has been found to dramatically affect the electrical and adhesive contact between PTFE (polytetrafluoroethylene) and active carbon. This has been detected in X-ray photoelectron spectroscopy (XPS) by the ‘charging’ shift seen for F 1 s due to the loss in electronic contact between these components. In addition, the adhesive character of the contact between the SiC matrix and the gas diffusion electrodes has been revealed by the XPS spectral characteristics. Here a major difference between the anode and the cathode has been observed with the cathode having a greater deadhesion. Extensive physical characterization by pore volume and size distribution, wetting, and weight loss has been performed. These results have been correlated with the XPS results to give a complete model of the deterioration of this technologically important system. A possible explanation for the observed loss of PTFE from the surface of the cathode based on an electrostatic rejection model of the delaminated PTFE particles is also suggested.

SHORT-RANGE ORDER IN AMORPHOUS GeTe FILMS

Thin films of amorphous (stoichiometric) GeTe have been examined by direct recording of electron diffraction, and intensity profiles across the diffuse diffraction pattern have been recorded with electrostatic rejection of inelastically scattered electrons. Radial distribution analysis of these curves shows that the local order is not characteristic of the distorted rocksalt structure of bulk GeTe, i.e., nearest-neighbor distance of 2.99 Å and nearest-neighbor coordination of 6. Instead it is found that the nearest-neighbor distance is 2.65 Å with coordination of approximately 4. This result is of significance for the interpretation of the electronic properties of amorphous films.