Ion-track Membranes Research Articles

Effect of external electric fields on the ionic conductivity of the PET ion-track membrane

Polymeric ion track-etched membranes with asymmetric pores have been the subject of increased interest in both the academia and industry in recent decades. This interest is related to the rectification behavior of the membranes and their possible applications. In this work, the polyethylene terephthalate (PET) membranes with conical ion tracks were investigated for different etching conditions. Thin PET membranes were prepared using irradiated foils etched in a NaOH bath with the help of external electric fields (AC/DC) of a specific polarity. After etching, the I-V characteristics of the membranes were examined in the KCl solutions with different molarities. The obtained results showed that the I-V relations are strongly non-linear, thus confirming the rectification behavior of the membranes. It turned out that the external AC and DC fields applied during etching play an important role. They make it possible to influence the pore etching process, and so the properties of the membranes, which is important for the intended applications. Keywords: polymeric membranes, asymmetric pores, polyethylene terephthalate, I-V characteristics, transport phenomena

Fabrication of Hydrophobic PET Track-Etched Membranes using 2,2,3,3,4,4,4-Heptafluorobutyl Methacrylate for Water Desalination by Membrane Distillation

The world is currently facing a drinking water problem. Human activity, climate change and pollution of existing water bodies are exacerbating the problem. The scientists around the world are currently trying to purify water using effective and inexpensive methods. One such method is membrane distillation. Membrane distillation is a versatile thermally driven membrane separation process. This method of water purification has the potential to remove salts and other non-volatile components. The work is concerned with the desalination of salt solutions by membrane distillation using ion-track membranes based on polyethylene terephthalate (PET). PET ion-track membranes (PET TMs) were modified by photoinitiated graft polymerization of 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (HFBMA) to make them hydrophobic. Optimal polymerization conditions (monomer concentration, reaction time) were determined, which led to an increase of water CA from 51 to 105°. The obtained membranes were used to purify the solution from NaCl. The effect of salt concentration as well as membrane properties on performance and degree of purification was studied. The results show that large pore size PET TMs modified with HFBMA has the potential to desalinate water in an efficient manner.

Sensor label with polyaniline-metal composites for meat freshness monitoring

ABSTRACT In this study, ion-track membranes with pore diameters of 2 ± 0.1 μm and a fluence of 107 cm−2, with a thin layer of gold sputtered on one side, were used for the electrochemical synthesis of thin films from a polyaniline (PANI) composite with gold (Au) or silver (Ag) nanoparticles. PET (polyethylene terephthalate ion-track membranes) films with the thin film of TM+PANI/Au and TM+PANI/Ag composites, featuring a developed microstructured surface, were designed. Using ATR-FTIR (Attenuated Total Reflection – Fourier-transform infrared spectroscopy) and Raman spectroscopy, it was determined that PANI was synthesised predominantly in the form of an emeraldine salt, with a minor presence of the emeraldine base form. The TM+PANI/Au and TM+PANI/Ag films exhibited high sensitivity to ammonia, with detection thresholds of approximately 40 mg/L and 20 mg/L, respectively.

Modification of AgNP-Decorated PET: A Promising Strategy for Preparation of AgNP-Filled Nuclear Pores in Polymer Membranes.

Polymer-based membranes represent an irreplaceable group of materials that can be applied in a wide range of key industrial areas, from packaging to high-end technologies. Increased selectivity to transport properties or the possibility of controlling membrane permeability by external stimuli represents a key issue in current material research. In this work, we present an unconventional approach with the introduction of silver nanoparticles (AgNPs) into membrane pores, by immobilising them onto the surface of polyethyleneterephthalate (PET) foil with subsequent physical modification by means of laser and plasma radiation prior to membrane preparation. Our results showed that the surface characteristics of AgNP-decorated PET (surface morphology, AgNP content, and depth profile) affected the distribution and concentration of AgNPs in subsequent ion-track membranes. We believe that the presented approach affecting the redistribution of AgNPs in the polymer volume may open up new possibilities for the preparation of metal nanoparticle-filled polymeric membranes. The presence of AgNPs on the pore walls can facilitate the grafting of stimuli-responsive molecules onto these active sites and may contribute to the development of intelligent membranes with controllable transport properties.

Influence of High Surfactant Concentrations on the Morphology and Crystallinity of Electrodeposited Antimony and Bismuth Nanowires

Antimony and bismuth nanowires are excellent model systems to investigate the interplay of various size-dependent transport phenomena relevant for applications in thermoelectrics, spintronics, or catalysis. The properties of these nanowires can be significant influenced by size effects due to the large mean free path and Fermi wavelength of charge carriers and phonons. Since antimony and bismuth possess highly anisotropic Fermi surfaces, the transport is also strongly dependent on the crystallographic orientation. Therefore, it is very important to develop and control suitable electrodeposition processes that allow us to understand the nanowire growth and to accordingly adjust preferred orientation and morphology of the synthesized nanowires.The so called template route employed in the presented work allows to control number density, alignment, geometry, length and diameter of the nanowires. The electrolytes and plating processes influence crystallinity, crystal orientation, and morphology of the electrodeposited materials. Here, antimony and bismuth nanowires are grown by potentiostatic electrodeposition in polycarbonate etched ion-track membranes using SbCl3 and BiCl3 in aqueous electrolytes.In this talk, we will show the influence of the presence of nonionic and anionic surfactants in high concentrations in the electrolyte during the electrodeposition of Bi and Sb nanowires. The recorded current-time curves of the plating process will be presented. Systematic characterization of the nanowires by scanning- and transmission electron microscopy, and X-ray diffraction reveal a strong change in crystallinity as a function of surfactant concentration, which will be discussed in detail.

Ion Track Formation and Nanopore Etching in Polyimide: Possibilities in the MeV Ion Energy Regime

AbstractPolyimide films of thickness 7.5 µm are irradiated by a wide range of ions (1H to 197Au) with energies between 1.05 and 48 MeV. Irradiated samples are then chemically etched in sodium hypochlorite solution to investigate nanopore formation due to ion track etching. A threshold in terms of electronic stopping power, Set, needs to be surpassed to preferentially etch the ion tracks. Close to Set, intermittent tracks are formed where only part of the track is etchable. The fraction of these etchable parts increases as we move away from Set, toward higher stopping powers, eventually yielding continuous etchable tracks. Both intermittent and continuous track formation thresholds are observed to be velocity‐dependent, yielding a decrease of the thresholds in the present work compared to previously reported thresholds for swift heavy ions. This finding leads the authors to suggest that electrostatic ion accelerators with terminal voltages of several MV are applicable for the production of ion track membranes up to ≈10–20 µm in thickness. Suitable ions for nanopores in 7.5 µm polyimide films include 42 MeV 59Co and 48 MeV 197Au. The growth mechanism for the pores during etching is discussed, relating it to the properties of the original ion track.

Features of the Process of Galvanic Deposition of Metals into the Pores of Ion Track Membranes

Features of the Process of Galvanic Deposition of Metals into the Pores of Ion Track Membranes

Features of the Process of Galvanic Deposition of Metals into the Ion Track Membranes’ Pores

The paper considers some aspects of obtaining metal nanowires by matrix synthesis based on track membranes. In the first part of the paper, the main ideas of the method are considered and a review of the literature on the synthesis of nanowires of various types of single component (from one metal) and multicomponent—from two or more metals is given. In the second part of the review, variants of obtaining homogeneous structures of so-called alloyed nanowires and heterogeneous structures of so-called layered nanowires are considered. Several specific features of the electrodeposition method during the process in a limited volume of membrane pores are considered. In the second part of the work, the experimental results obtained by the authors in the study of electrodeposition of nanowires made of an iron–nickel alloy are considered. The so-called abnormal electrodeposition of iron was detected. The dependence of the integral element composition of the obtained nanowires on the pore diameter and on the growth voltage is discussed. Data on the nature of the distribution of elements along the length of nanowires are obtained. The unevenness of the composition is determined by the conditions of production (in particular, the different diffusion mobility of ions in narrow pore channels) and also depends on the voltage and diameter of the pore channels. Based on the X-ray diffraction data, the type of lattice (hcc) is determined and the nature of the change in the lattice parameter is shown, presumably associated with the difference in the ionic radii of metals.

Electrochemical Conversion of Cu Nanowire Arrays into Metal-Organic Frameworks HKUST-1

We explore the conversion of free-standing Cu nanowire arrays produced by electrodeposition in polymer etched ion-track membranes into metal-organic frameworks KHUST-1 by electrochemical oxidation. HKUST-1 particles are built up when the as-formed Cu2+ ions bind to the benzene tricarboxylic acid ligands (BTC3−) in the electrolyte solution. The morphology and crystallinity of the samples at different transformation stages are investigated by scanning and transmission electron microscopy. X-ray diffraction data taken at different conversion times confirm the formation of HKUST-1 particles. The conversion process resulted in octahedral structures of several μm in size. Comparison of the Raman spectra with the band positions derived from density functional theory (DFT) calculations, suggests that vibrations involving Cu atoms appear only below 490 cm−1 wavenumbers and involve the entire HKUST-1 lattice rather than vibrations of single bonds.

A wound dressing based on a track-etched membrane modified by a biopolymer nanoframe: physicochemical and biological characteristics

Ion track membranes (TMs) are obtained by irradiating thin polymer films, which are usually composed of polycarbonate and polyethylene terephthalate (PET). In medicine and biology, TMs are used for the filtration and separation of molecules and cells in addition to studies of cell migration, intercellular interactions, cell proliferation, and differentiation processes. However, the possibilities and prospects of using TMs as components of wound dressings have not been sufficiently explored. In our study, TMs composed of PET were tested since this material is biocompatible and used in prosthetics and reconstructive surgery. The method of combining TM and electroforming nanofibers, which we used in this study, is relatively new and still requires additional research.Thus, it was found that the main structural elements of the TM surface covered with a biolayer of a mixture of collagen and chitosan are fibers. Coating the TM with a bio-layer preserves its gas and water permeabilities. By varying the fixation method of the biopolymer layer, it is possible to regulate the physicochemical and biological functional properties of the wound dressing. The combination of the high biocompatibility of natural polymers and the stability of synthetic materials can be a successful strategy in manufacturing wound dressings of a new type with specified functional properties. Ion-track PET membranes with applied electrospun fibers from a mixture of chitosan and collagen can be used to produce the wound dressing.Abbreviated title: A wound dressing based on a track-etched membrane.

(Digital Presentation) Electrochemical Conversion of Cu Nanowires Synthesized By Electrodeposition in Track-Etched Templates to HKUST-1

Metal-organic frameworks (MOFs) are a novel type of nanoporous materials that have attracted widespread attention over the past two decades [1]. Cu-based metal-organic frameworks such as Cu3(BTC)2 (also known as HKUST-1) are one of the most famous MOF representatives, which exhibit a huge open porosity and thus a remarkably capacity to store and uptake different gases [2, 3]. Recently, increasing efforts are devoted toward finding synthetic routes that enable downsizing MOF crystals to the nanoscale. Achieving control over the size and shape of nanoMOFs and finding ways to assemble them is essential for their exploitation in integrated devices such as sensors, gas separation membranes or photoelectrodes.In this study we explore the conversion of free-standing arrays Cu nanowires with controlled diameter and length synthesized by electrodeposition in etched ion-track membranes into HKUST-1. In a first process step, free-standing Cu wires are produced by dissolving the ion-track polymer template. In a second step, the wires are converted into HKUST-1 structures by electrochemical oxidation. Applying 2.5 V versus a Cu counter electrode, the Cu nanowires are oxidatively dissolved and the MOF is built up as the as-formed Cu2+ ions bind to the BTC3− ligands in the electrolyte solution. The morphology and crystallinity of the samples at different transformation stages is investigated by scanning electron microscopy (Fig. 1) and transmission electron microscopy, respectively. X-ray diffraction spectra measured at different conversion times reveal the appearance of the characteristic reflections of HKUST-1. These results will be compared with previous studies of the transformation of Cu nanowires to HKUST-1 nanowires inside the polymer membrane [4].Figure 1: SEM images of cylindrical Cu nanowires (a) before and (b) during the electrochemical conversion process, and (c) of a representative octahedral particle after complete conversion to HKUST-1.

Electrodeposition of Three-Dimensional Au Nanowire Networks and Their Application As Catalysts for Methanol Electro-Oxidation

In this talk we will first present the synthesis of free-standing, stable gold nanowire network with controlled morphology and geometry by ion-track technology and electrodeposition. Etched ion-track membranes with interconnected nanochannels are produced by sequential GeV heavy ion irradiation of polymer foils from four directions, and subsequent etching and enlargment of the created ion-tracks. Au nanowire networks with three different nanowire diameters are synthesized by potentiostatic electrodeposition in the templates. Nanowire growth rate and homogeneity are tuned by varying the deposition potential. The electrochemical surface area was determined for each sample by CV analysis of surface oxide reduction reaction charge transfer. We will also discuss the catalytic performance of these Au nanowire networks towards methanol electro-oxidation, acting as an electrode in a half-cell setup. High current density and high catalytic activity were recorded. The Au nanowire networks provided up to 200 times higher peak current density than a flat Au electrode, along with excellent long term cyclability, which the current density drops only 5% over 200 CV cycles. SEM studies of the morphology and crystallinity of the nanowires before and after the methanol oxidation reaction will also be presented in the talk.Figure 1. (a) SEM image of Au nanowire network, (b) Cyclic Voltammograms recorded for a of Au nanowire network in 0.1 M KOH with (solid line) and without (dash line) 1 M MeOH. Figure 1

Detection of Polynitro Compounds at Low Concentrations by SERS Using Ni@Au Nanotubes

The identification of high-energy compounds in trace concentrations not only in the laboratory, but also in field conditions is of particular interest. The process should be clear, easy, and well-recognizable. We formed SERS-active substrates by using elongated nickel nanotubes synthesized by electrochemical deposition in the pores of ion-track membranes and coated them with gold for further application in the detection of low concentrations of analytes. The substrates were characterized using various techniques to determine the morphology of the nanotubes and modifying gold layer. The possibility of obtaining two types of gold-layer morphology was shown: in the form of a smooth film up to 20–50 nm thick and a coating with nanoneedles up to 250 nm long. The electric fields around the nanotubes were simulated at a laser wavelength of 532 nm to demonstrate the influence of the gold-layer morphology on the field distribution. The “needle” morphology was chosen to form the most effective SERS-active substrates for detection of low concentrations of aromatic polynitro compounds. The spectral peaks were identified by comparing the model and experimental Raman spectra at concentrations down to 10−5 M. Within this limit, all peaks (“fingerprints” of the substance) were clearly distinguishable.

Photo-induced graft (co)polymerization of glycidyl methacrylate and acrylonitrile on PET ion-track membranes for electrochemical detection of uranyl ions

Uranium and their compounds are harmful to human health and with rapid development of nuclear industry, development of fast and reliable method of detection of uranium in the environment has become relevant task. In this article, we present the results of preparation of electrochemical sensor based on poly(ethylene terephthalate) ion-track membranes (PET TMs) for sensing of uranium in water. Graft (co)polymerization of glycidyl methacrylate (GMA) and acrylonitrile (AN) and subsequent polymer analogous reactions of grafted chains with formation of amino and amidoxime groups allow us to obtain sensors with LOD of up to 5.45 μg/L (R2 = 0.9981, linear relationship in in concentration range from 1 to 100 μg/L) for PET TMs-g-PAN/PGMA using square wave anodic stripping voltammetry (SW-ASV). The influence of the type of grafted polymer on the sensitivity of sensors was also studied. Optimal parameters that led to functionalization of the surface by photo-induced grafting with preservation of the pore structure were found. Morphology and pore size of the membranes were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), gas permeability test. Chemical changes on the membrane were proven by infrared spectroscopy (FTIR).

Increasing the structural and compositional diversity of ion-track templated 1D nanostructures through multistep etching, plastic deformation, and deposition

Ion-track etching represents a highly versatile way of introducing artificial pores with diameters down into the nm-regime into polymers, which offers considerable synthetic flexibility in template-assisted nanofabrication schemes. While the mechanistic foundations of ion-track technology are well understood, its potential for creating structurally and compositionally complex nano-architectures is far from being fully tapped. In this study, we showcase different strategies to expand the synthetic repertoire of ion-track membrane templating by creating several new 1D nanostructures, namely metal nanotubes of elliptical cross-section, funnel-shaped nanotubes optionally overcoated with titania or nickel nanospike layers, and concentrical as well as stacked metal nanotube-nanowire heterostructures. These nano-architectures are obtained solely by applying different wet-chemical deposition methods (electroless plating, electrodeposition, and chemical bath deposition) to ion-track etched polycarbonate templates, whose pore geometry is modified through plastic deformation, consecutive etching steps under differing conditions, and etching steps intermitted by spatially confined deposition, providing new motifs for nanoscale replication.

Catalytic Activity of Ni Nanotubes Covered with Nanostructured Gold

Ni nanotubes (NTs) were produced by the template method in the pores of ion-track membranes and then were successfully functionalized with gold nanoparticles (Ni@Au NTs) using electroless wet-chemical deposition with the aim to demonstrate their high catalytic activity. The fabricated NTs were characterized using a variety of techniques in order to determine their morphology and dimensions, crystalline structure, and magnetic properties. The morphology of Au coating depended on the concentration of gold chloride aqueous solution used for Au deposition. The catalytic activity was evaluated by a model reaction of the reduction of 4-nitrophenol by borohydride ions in the presence of Ni and Ni@Au NTs. The reaction was monitored spectrophotometrically in real time by detecting the decrease in the absorption peaks. It was found that gold coating with needle-like structure formed at a higher Au-ions concentration had the strongest catalytic effect, while bare Ni NTs had little effect. The presence of a magnetic core allowed the extraction of the catalyst with the help of a magnetic field for reusable applications.

Conical Nanotubes Synthesized by Atomic Layer Deposition of Al2O3, TiO2, and SiO2 in Etched Ion-Track Nanochannels.

Etched ion-track polycarbonate membranes with conical nanochannels of aspect ratios of ~3000 are coated with Al2O3, TiO2, and SiO2 thin films of thicknesses between 10 and 20 nm by atomic layer deposition (ALD). By combining ion-track technology and ALD, the fabrication of two kinds of functional structures with customized surfaces is presented: (i) arrays of free-standing conical nanotubes with controlled geometry and wall thickness, interesting for, e.g., drug delivery and surface wettability regulation, and (ii) single nanochannel membranes with inorganic surfaces and adjustable isoelectric points for nanofluidic applications.

Etched ion-track membranes as tailored separators in Li–S batteries

Lithium–sulfur (Li–S) batteries are considered a promising next generation alternative to lithium-ion batteries for energy storage systems due to its high energy density. However, several challenges, such as the polysulfide redox shuttle causing self-discharge of the battery, remain unresolved. In this paper, we explore the use of polymer etched ion-track membranes as separators in Li–S batteries to mitigate the redox shuttle effect. Compared to commercial separators, their unique advantages lie in their very narrow pore size distribution, and the possibility to tailor and optimize the density, geometry, and diameter of the nanopores in an independent manner. Various polyethylene terephthalate membranes with diameters between 22 and 198 nm and different porosities were successfully integrated into Li–S coin cells. The reported coulombic efficiency of up to 97% with minor reduction in capacity opens a pathway to potentially address the polysulfide redox shuttle in Li–S batteries using tailored membranes.

Hydrophilization of the polyethyleneterephthalate ion track membrane surfaces

Results of polyethylenterephtalate ion track membranes hydrophilization by (Chytozan/Dextran)4 multilayers with using Layer-by-Layer method and by Nafion monolayer with using Langmuir – Blodgett and spin-coating methods are presented in articles. The structure, contact angles and polar component of specific surface energy of modified membranes has been researched.

Ion transmission spectroscopy of pores filled with Au nanoparticles

Ion track membranes (ITM) are of long-term interest due to the high potential of applications in science and industry. However, the use of the membranes requires a detailed knowledge of (i) their structural parameters, i.e., the density and distribution of the ITM pores, the pore size (radius) and spatial shape, or (ii) the pore filling with other materials (demanding the knowledge of filling efficiency, filler confinement, or filler density). In this work, we studied the nuclear membranes prepared with pores of certain density and size and filled with Au nanoparticles. The analysis was carried out by Ion Transmission Spectroscopy (ITS). ITS is a nondestructive technique to determinate the spatial structure of (sub)micron inhomogeneities (pores, protrusions, etc.) in thin foils from the energy loss of even quasi-monoenergetic alpha particles (e.g., from a thin 241Am source) transmitted through the (empty or filled) pores. The reconstruction of the shape of the pores or pore fillings is performed by simulation of the transmission spectra using the MC code. The nuclear membranes were prepared by the irradiation of a thin polyethylene terephthalate with 157 MeV Xe+26 ions (with the fluence 106 cm−2) and the subsequent chemical etching in 9 M NaOH water solution at 50 °C for 40 min. The pores were filled with the Au nanoparticles (NPs) of a sub-micrometer size using the Pulse Laser Deposition (PLD), and studied by ITS. From the transmission spectra the shape of the pores filled (partially or fully) with Au NPs could be reconstructed. The ITM with pores filled with NPs were also analyzed by scanning electron microscopy (SEM). The results showed good agreement with the MC simulation of the ITS data.