Transport Of Ionic Species Research Articles

Highly Efficient Ionic Photocurrent Generation through WS2 -Based 2D Nanofluidic Channels.

The unique feature of nacre-like 2D layered materials provides a facile, yet highly efficient way to modulate the transmembrane ion transport from two orthogonal transport directions, either vertical or horizontal. Recently, light-driven active transport of ionic species in synthetic nanofluidic systems attracts broad research interest. Herein, taking advantage of the photoelectric semiconducting properties of 2D transition metal dichalcogenides, the generation of a directional and greatly enhanced cationic flow through WS2 -based 2D nanofluidic membranes upon asymmetric visible light illumination is reported. Compared with graphene-based materials, the magnitude of the ionic photocurrent can be enhanced by tens of times, and its photo-responsiveness can be 2-3.5 times faster. This enhancement is explained by the coexistence of semiconducting and metallic WS2 nanosheets in the hybrid membrane that facilitates the asymmetric diffusion of photoexcited charge carriers on the channel wall, and the high ionic conductance due to the neat membrane structure. To further demonstrate its application, photonic ion switches, photonic ion diodes, and photonic ion transistors as the fundamental elements for light-controlled nanofluidic circuits are further developed. Exploring new possibilities in the family of liquid processable colloidal 2D materials provides a way toward high-performance light-harvesting nanofluidic systems for artificial photosynthesis and sunlight-driven desalination.

Photoinduced Directional Proton Transport through Printed Asymmetric Graphene Oxide Superstructures: A New Driving Mechanism under Full‐Area Light Illumination

Abstract2D‐material‐based membranes with densely packed sub‐nanometer‐height fluidic channels show exceptional transport properties, and have attracted broad research interest for energy‐, environment‐, and healthcare‐related applications. Recently, light‐controlled active transport of ionic species in abiotic materials have received renewed attention. However, its dependence on inhomogeneous or site‐specific illumination is a challenge for scalable application. Here, directional proton transport through printed asymmetric graphene oxide superstructures (GOSs) is demonstrated under full‐area illumination. The GOSs are composed of partially stacked graphene oxide multilayers formed by a two‐step direct ink writing process. The direction of the photoinduced proton current is determined by the position of top graphene oxide multilayers, which functions as a photogate to modulate the horizontal ion transport through the beneath lamellar nanochannels. This transport phenomenon unveils a new driving mechanism that, in asymmetric nanofluidic structures, the decay of local light intensity in depth direction breaks the balance of electric potential distribution in horizontal direction, and thus generates a photoelectric driving force for ion transport. Following this mechanism, the GOSs are developed into photonic ion transistors with three different gating modes. The asymmetrically printed photonic‐ionic devices provide fundamental elements for light‐harvesting nanofluidic circuits, and may find applications for artificial photosynthesis and artificial electric organs.

Electroosmotic flow and transport of ionic species through a slit soft nanochannel filled with general electrolytes

A numerical study is presented of the electroosmotic flow (EOF) and transport of ionic species through a slit soft nanochannel filled with general electrolytes. The rigid walls of the undertaken channel are coated with ion and fluid penetrable charged polyelectrolyte layers (PELs). The physicochemical properties of the surface PELs grafted on the lower and upper walls are considered to be either similar or dissimilar in nature. A nonlinear model based on the coupled Poisson–Boltzmann equation for electrostatics and the modified Stokes equation for hydrodynamics is adopted. Based on the Debye–Huckel limit under a low potential approximation a closed form solution for the induced potential and axial velocity is derived. However throughout our present study a sophisticated numerical technique is adopted to consider a wide range of pertinent parameters governing the problem. It is observed that the EOF and transport of ionic species strongly depends on the choice of the PEL-charge and the background electrolyte solution. In addition we have shown that the selectivity of mobile electrolyte ions can be actively tuned by regulating the physicochemical properties of the surface PELs and the background aqueous medium.

Photo-induced ultrafast active ion transport through graphene oxide membranes

Layered graphene oxide membranes (GOM) with densely packed sub-nanometer-wide lamellar channels show exceptional ionic and molecular transport properties. Mass and charge transport in existing materials follows their concentration gradient, whereas attaining anti-gradient transport, also called active transport, remains a great challenge. Here, we demonstrate a coupled photon-electron-ion transport phenomenon through the GOM. Upon asymmetric light illumination, cations are able to move thermodynamically uphill over a broad range of concentrations, at rates much faster than that via simple diffusion. We propose, as a plausible mechanism, that light irradiation reduces the local electric potential on the GOM following a carrier diffusion mechanism. When the illumination is applied to an off-center position, an electric potential difference is built that can drive the transport of ionic species. We further develop photonic ion switches, photonic ion diodes, and photonic ion transistors as the fundamental elements for active ion sieving and artificial photosynthesis on synthetic nanofluidic circuits.

Characterization of transport through polymers for fracking fluid treatment and organic acid concentration in extractive membrane bioreactors

AbstractBACKGROUNDThe water‐intensive practice of hydraulic fracturing produces wastewater containing a variable matrix of organic and inorganic compounds, including ions and ionizable organic compounds. Extractive membrane bioreactors (EMBs) operating with tailored polymer membranes can selectively sequester and/or transport these solutes for biological treatment. Four grades of Hytrel™ tubing were compared for their suitability in EMB systems, based on the polymers' thermodynamic affinity for solutes and their ability to transport or speciate ionic wastewater constituents.RESULTSOf the four Hytrel™ grades compared, high water content types (30% and 54% equilibrated water content) facilitated the transport of ionic species through the tubing, with all monovalent species being transported through both high‐water content grades, and lack of transport through the low‐water content tubing (3% and 5%). Undissociated organic acids were transported through all tubing types and dissociated acids were able to permeate only high‐water content grades. Using this differential ability to transport/not transport an organic acid depending on its dissociation state, a low‐water content Hytrel™ grade of tubing was able to concentrate a dilute butyric acid solution by 220% after 48 h.CONCLUSIONThe use of polymeric tubing for EMB applications for the treatment of hydraulic fracturing wastewater requires knowledge of both solute affinity and water content for complex waste streams, both of which affect the capability to transport organic and ionic species. © 2018 Society of Chemical Industry

Mathematical Modeling of Ion Transport through Nanopores

The study of transport of ionic species through a nanopore is important in determining the underlying behavior of electrolytes on the nanoscale; the understanding of which has important application...

Electroosmotic flow reversal and ion selectivity in a soft nanochannel

This article deals with the modulation of electroosmotic flow (EOF) and transport of ionic species through the parallel plate soft nanochannel. The charged rigid walls of the channel are covered by diffuse polyelectrolyte layer (PEL) which entraps immobile charges. A diffuse distribution of the polymer segment density and charge density is assumed. A nonlinear model based on the Poisson-Nernst-Planck equations coupled with the Darcy-Brinkman equations is adopted. Going beyond the widely employed Debye-H $\ddot {u}$ ckel linearization, we adopt a sophisticated numerical tool to study the effect of pertinent parameters on the modulation of EOF through the soft nanochannel. Several interesting key features including the flow reversal, occurrence of zero flow rate, and perm selectivity are studied by regulating the charges entrapped within the diffuse PEL and the surface charge distributed along the channel wall. The results indicate that the channel can be cation-selective, anion-selective, and non-selective based on the nature of the charges within the PEL and wall charge. We have also identified the parameter range for validity of the linearized model for the case of step-like PEL.

Effect of Electrolyte Pretreatment on the Formation of TiO2 Nanotubes: An Ignored yet Non‐negligible Factor

AbstractTailoring the geometric configuration of anodic TiO2 nanotubes enables their use in various applications. This paper demonstrates that the methods for pretreating electrolyte solutions significantly influence the growth of anodic nanotubes. Pretreatment is usually ignored by studies, but is a crucial and non‐negligible factor in the control of nanotube growth. The results indicate that magnetic stirring and ultrasonic agitation facilitate the dissolution and mass transport of ionic species in the solution, resulting in a homogeneous solution and a high TiO2 nanotube growth rate. Isolation of the solution from wide contact with the atmosphere through simple sealing further increases the growth rate. This is attributed to the hindrance of humidity absorption, which biases the original water content of the solution and thus causes the formation of an initial thick compact oxide layer that prevents ion diffusion. The findings can serve as a guide to electrolyte pretreatment routes for studying nanotube growth mechanisms and for tailoring nanotube features toward different applications.

Diffusional and migrational transport of ionic species affected by electrostatic interactions with an oppositely charged hydrogel layer attached to an electrode surface

The effect of the presence of a charged thin gel layer on the electrode surface on mass transport of electroactive species of opposite charge was investigated. The layer was deposited using the electrochemically-induced free-radical polymerization method. The ferrocenyltrimethylammonium cation (FcN+) served as the electroactive probe. Ionic accumulation of the anodic electrode product was observed in experiments with normal sized electrodes. Microelectrodes were used without supporting electrolyte to study the contribution of migration to the overall mass transport to the modified surface.

Nanoparticles in Concrete: Application in Fresh and Hardened State

The paper summarizes utilization of nanoparticles (NP) in concrete for enhancing its mechanical, transport or other properties. The first part is devoted to review of NPs used in fresh concrete mixtures that have been reported previously in the literature while the second part shows original results from utilization of nanoparticles as healing agents for reparing of existing concrete structures. In the second case, nanoparticles are delivered to concrete via electrokinetic principle by using their surface charge provided in colloidal solutions. Particles are transported in the pore liquid of concrete due to electric field applied between the concrete surface and steel reinforcement. In this way, distressed concrete can be repaired, cracks sealed and risk of corrosion diminished. The injection of NPs can be complemented with extraction of chlorides that are the main deteriorating chemicals in reinforced concrete structures. Finally, the paper shows a framework developed for the electrokinetic transport of ionic species in concrete applied to chloride extraction from concrete and how it can be modified also for transport of nanoparticles.

Smart electrically responsive hybrid ion-selective membranes for selective gated transport of ionic species

Gate-keeper ion exchange membranes with up to 6 fold increase in ionic diffusion are designed by controlling the pseudo-capacitance and resistance of hybrid semi-permeable membranes.

Effect of the pore size of cement based materials on ionic transport

The study of the electrochemical behavior of the cement-based materials/pore solution interface is an important topic in order to understand the transport of ionic species. It is also relevant for the purpose of interpreting the experimental results obtained in ionic transport tests (natural diffusion, or migration). The inherent issue in the interpretation of experimental results from ionic transport tests is the link between transport phenomena occurring at pore scale and the access to only macroscopic data and results. Indeed, the ionic concentrations of the pore solution are necessary data for the application of the Nernst-Planck equation.We demonstrate here that the pore size has impact on the results on the ionic concentrations distribution at macroscopic scale. Consequently the electrical conductivity is also modified. This works helps to understand why the results of migration tests may lead to wrong interpretations in terms of material conductivity and ionic diffusivity.

Efficacy of iontophoresis-assisted ablative fractional laser photodynamic therapy with short incubation time for the treatment of actinic keratosis: 12-month follow-up results of a prospective, randomised, comparative trial

BackgroundIontophoresis is a transdermal drug-delivery technique that enhances the transport of ionic species across membranes and may have significant benefit for the treatment of actinic keratosis (AK) by ablative fractional laser–primed photodynamic therapy (AFL-PDT). The aims of this study were to compare the efficacy, recurrence rate, cosmetic outcome and safety of iontophoresis-assisted AFL-PDT with 2h of incubation vs. those of conventional AFL-PDT with 2- and 3-h incubation in patients with facial and scalp AK. MethodsPatients were randomly assigned to iontophoresis-assisted AFL-PDT with a 2-h incubation time (group A) and conventional AFL-PDT with a 2-h (group B) and 3-h (group C) incubation time. All patients underwent AFL-PDT, and group A patients were assigned to treatment with iontophoresis after methyl-aminolevulinate (MAL) application. After 2 or 3h, MAL-applied lesions were irradiated using a red light. Patients were followed up at 1-week, 3 months and 12 months after treatment. Efficacy, cosmetic outcomes and adverse events were assessed. ResultsIn total, 41 patients (160 AK lesions) completed the study and were evaluated. Efficacy was significantly higher in Group A (88.7%) than in Group B (73.2%); the efficacy of groups A and C (92.2%) at 3 months follow-up was comparable. The recurrence rates were not significantly different between the groups at 12 months (P=0.841). The three groups did not differ in terms of cosmetic outcomes and safety. ConclusionsIontophoresis-assisted AFL-PDT showed higher efficacy than AFL-PDT with short incubation time. Iontophoresis may effectively reduce the incubation time in AFL-PDT.

Mass Spectrometry Analysis of the Real-Time Transport of Plasma-Generated Ionic Species Through an Agarose Tissue Model Target

With ambient mass spectrometry, we followed the transport of neutral gas species and ionic species through a 3.2 mm thick agarose tissue model target during He non-thermal atmospheric pressure plasma (NT-APP) jet treatment. We found that the neutral gas species are unable to efficiently penetrate the agarose target. But both positively and negatively charged ionic species readily penetrate through the agarose target, following an initial time-lag period of several minutes. Interestingly, we also found that the ionic species are easily hydrated. The trends in the He NT-APP jet transport of ionic species observed in this study correlate well with the He NT-APP jet transport of reactive oxygen and nitrogen species (RONS) through agarose tissue model targets that was investigated in previous studies. Therefore, mass spectrometry might prove to be a useful tool in the future for analyzing the dosages of NT-APP-generated RONS in real biological tissues.

Gated Molecular Transport in Highly Ordered Heterogeneous Nanochannel Array Electrode.

In biology, all protein channels share a common feature of containing narrow pore regions with hydrophobic functional groups and selectivity filter regions abundant with charged residues, which work together to account for fast and selective mass transport in and out of cells. In this work, an ultrathin layer of polydimethylsiloxane (PDMS) was evaporated on the top orifices of charged silica nanochannels (2-3 nm in diameter and 60 nm in length) vertically attached to the electrode surface, and the resulting structure is designated as heterogeneous silica nanochannels (HSNs). As evidenced by voltammetric studies, the transport of ionic species in these HSNs was controlled by both hydrophobic rejection and electrostatic force arising from the top PDMS layer and from the bottom silica nanochannels, respectively. Anionic species encountered both hydrophobic rejection and electrostatic repulsion forces, and thus, their transport was strongly prohibited, while the transport of cationic species was permitted once the electrostatic attraction exceeded the hydrophobic rejection. Moreover, the magnitude of hydrophobic force could be regulated by the PDMS layer thickness, and that of the electrostatic force can be modulated by the salt concentration, solution pH, or applied voltage. It was demonstrated that the HSNs could be activated from an OFF state (no ion can transport) to an ON state (only cation transport occurs) by decreasing the salt concentration, increasing the solution pH, or applying negative voltages.

Ionic Conductivity in Polyelectrolyte Hydrogels

Transport of ionic species in heterogeneous polymeric media is highly dependent on the charge distributions and interactions between mobile and immobile groups. Here we perform coarse-grained molecular dynamics simulations to study the ion dynamics in swollen polyelectrolyte gels under external electric fields. A nonlinear response of the ionic conductivity to an applied electric field, for field strengths that are comparable to the ionic coupling strength, is observed. This behavior correlates to a broadening of the ionic distribution around the polymer backbone under an increasing electric field. Also, we find that the weak-field ionic mobility in gels increases with density, which is opposite to the behavior of simple electrolytes. This relates to the mean coupling between charges that decreases in gels, but increases in simple electrolytes, with increasing density. These results provide more insights into the electric response of polyelectrolyte gels to support the development of applications that com...

Understanding Lithium Sulfur Cells, Modelling the Mechanisms behind Voltage- and Capacity-Drop during Discharge

The lithium-sulphur (Li-S) cell could provide the next step-change in battery technology with a promising practical energy density of 500-600 Wh/kg. However, a lack of understanding of the complex electrochemical, transport, and phase-change phenomena in Li-S cells is arguably holding back development. Acquiring this knowledge requires experimental characterizations in tandem with mechanistic modelling. In this presentation, we will give an overview of our work on understanding and modelling lithium sulfur cells, and include our latest work on models that capture the essential features of lithium sulfur cell performance. We will also discuss how these models are being used to increase the useable performance of lithium sulfur cells, inform cell design and materials selection, and to create reduced order models for control and system design. Existing Li-S models do not sufficiently capture the voltage- and capacity-drop mechanisms of Li-S cells during discharge. We first demonstrate that introducing a concentration dependence of the electrolyte conductivity is necessary to retrieve the experimentally documented trends in electrolyte resistance, which contributes to a major voltage-loss mechanism for high-energy density Li-S cells. We further illustrate the existence of an often overlooked potential drop mechanism – the ‘precipitation overpotential’ – which originates from the limited rate of lithium sulphide precipitation. In addition, we propose that the rate capability of high energy-density Li-S cells is mainly limited by the slow transport of ionic species, as is evident from the good agreement between experimental and model-predicted capacity loss at high discharge currents as well as a cell capacity recovery phenomenon that we report for the first time.

Modelling Li-S Cells: Mechanisms behind Voltage- and Capacity-Drop during Discharge

The lithium-sulphur (Li-S) cell could provide the next step-change in battery technology with a promising practical energy density of 500-600 Wh/kg. However, a lack of understanding of the complex electrochemical, transport, and phase-change phenomena in Li-S cells is arguably holding back development. Acquiring this knowledge requires experimental characterizations in tandem with mechanistic modelling. In this presentation, we point out that existing Li-S models do not sufficiently capture the voltage- and capacity-drop mechanisms of Li-S cells during discharge. We first demonstrate that introducing a concentration dependence of the electrolyte conductivity is necessary to retrieve the experimentally documented trends in electrolyte resistance, which contributes to a major voltage-loss mechanism for high-energy density Li-S cells. We further illustrate the existence of an often overlooked potential drop mechanism – the ‘precipitation overpotential’ – which originates from the limited rate of lithium sulphide precipitation. In addition, we propose that the rate capability of high energy-density Li-S cells is mainly limited by the slow transport of ionic species, as is evident from the good agreement between experimental and model-predicted capacity loss at high discharge currents as well as a cell capacity recovery phenomenon that we report for the first time.

Kinetic Approach to Model Reactive Transport and Mixed Salt Precipitation in a Coupled Free-Flow–Porous-Media System

Abstract Evaporative salinization of the agricultural soil is a chronic problem in arid, semiarid and coastal regions worldwide. As a shallow subsurface issue, it is strongly influenced by the free-flow (henceforth, FF) and porous-media (henceforth, PM) flow and transport processes. In specific, it is mainly affected by the mass, momentum and energy exchange between the FF and the PM regions. Furthermore, salt precipitation in such systems is strongly determined by the interaction between different dissolved ionic species. In the scope of this work, we extend the REV-scale coupled FF–PM model concept for salinization proposed by Jambhekar et al. (Transp Porous Media, 2015), to describe reactive transport of ionic species $$\text {Na}^+$$ Na + , $$\text {Cl}^-$$ Cl - and $$\text {I}^-$$ I - and mixed salt precipitation (here, NaCl and NaI). In the first part of our numerical analysis, we illustrate precipitation behavior of NaCl using equilibrium and kinetic approaches. Both approaches are found to be in good agreement with experimental observations. However, in the literature it is often discussed that for mixed salt systems found in the nature, the equilibrium precipitation–dissolution assumption is not easily justifiable. Therefore, in the second part of our numerical analysis, we extend the kinetic approach to describe mixed salt precipitation in an NaCl–NaI system and compare it with the equilibrium precipitation approach. Our numerical analysis indicate that the simulation results for these approaches are very similar and analogous with the phenomenological explanations.

The active modulation of drug release by an ionic field effect transistor for an ultra-low power implantable nanofluidic system.

We report an electro-nanofluidic membrane for tunable, ultra-low power drug delivery employing an ionic field effect transistor. Therapeutic release from a drug reservoir was successfully modulated, with high energy efficiency, by actively adjusting the surface charge of slit-nanochannels 50, 110, and 160 nm in size, by the polarization of a buried gate electrode and the consequent variation of the electrical double layer in the nanochannel. We demonstrated control over the transport of ionic species, including two relevant hypertension drugs, atenolol and perindopril, that could benefit from such modulation. By leveraging concentration-driven diffusion, we achieve a 2 to 3 order of magnitude reduction in power consumption as compared to other electrokinetic phenomena. The application of a small gate potential (±5 V) in close proximity (150 nm) of 50 nm nanochannels generated a sufficiently strong electric field, which doubled or blocked the ionic flux depending on the polarity of the voltage applied. These compelling findings can lead to next generation, more reliable, smaller, and longer lasting drug delivery implants with ultra-low power consumption.