Polysterene Sulfonate Research Articles

(Keynote) Electrode-Assisted Electroless Metal Deposition – Palladium Nanocatalysts for Organic Fuel Oxidation

Electroless metal deposition can be completed by using a reactive surface consisting of a redox active material that acts as electron donating medium and drives the metal ions reduction reaction. The important peculiarity of the electroless process driven by surface-immobilized redox active species is that the reductant capacity is limited by the available surface-confined redox sites. Moreover, re-reducing the oxidized reactive surface provides the opportunity to repeat the electroless metal reduction without dissolving the once deposited metal phase. The necessary condition for driving this type of process is to keep the initial oxidation state of the reactive electrode surface at potentials negative enough with respect to the equilibrium potential of the depositing metal ions.Conducting polymer (CP) materials are characterized by several intrinsic interconvertible oxidation states and may easily take the role of reducing agent for electroless metal deposition both as immobilized surface layer on a carrying substrate or as solute species in bulk solution. If deposited as a thin layer on an electrode surface they present the opportunity to perform repeatedly redox-active surface- driven electroless metal deposition.Electroless deposition of Pd in the absence of solute reducing species is studied on pre-reduced poly(3,4-ethylenedioxythiophene) (PEDOT)-coated graphite electrodes. PEDOT coatings doped with either dodecyl sulfate (SDS) or polysterene sulfonate (PSS) ions are used in the studies. PEDOT-supported Pd catalysts with high-density homogeneous distribution of Pd nanoparticles (NPs) with sizes ranging between 4 and 12 nm are obtained. The amount of deposited metal depends significantly on the pre-reduction potential of PEDOT whereas the observed surface density of the metal NPs is largely influenced by the doping ions used to obtain the PEDOT material. Densely packed overlapping NPs are observed on PEDOT/SDS whereas individual, non-overlapping NPs with much smaller surface density are found on PEDOT/PSS [1-2].Once high negative potentials are used for PEDOT reduction large amounts of Pd become deposited that significantly exceed the quantity expected to be reduced at the expense of PEDOT re-oxidation alone [3]. Pd particles are observed to deposit also at bare pre-reduced graphite electrode. It is suggested that molecular hydrogen entrapped during the reductive treatment plays the role of additional reductant for the electroless Pd deposition.Furthermore, based on SEM, UV-vis and Raman investigations it is found that irreversible structural changes occur in the course of strong reductive treatment of PEDOT [3]. Especially in the case of SDS doping this results in a compact and ordered structure that allows for metal deposition preferentially at the polymer/solution interface. On the other hand Pd NPs seem to be present also inside the PEDOT/PSS layers.Oxidation of glycerol [4] and formic acid is studied in alkaline solutions under voltammetric and chronoamperometric conditions by varying the type of doping ions (PSS or SDS) used in the PEDOT synthesis. It is found that at constant Pd loading PEDOT/PSS-supported catalysts have three times higher peak currents for both glycerol and formic acid oxidation. This effect is ascribed to the lack of overlap of the individual Pd NPs in the case of PEDOT/PSS in contrast to the strong clustering of the Pd observed on the PEDOT/SDS surface. The mass activity of Pd/PEDOT/PSS for both investigated reactions competes with the best performing single metal Pd catalysts. Acknowledgments: Financial support of CEST Kompetenzzentrum für elektrochemische Oberflächentechnologie GmbH, Wiener Neustadt, Austria (PhD grant for A.N.) is gratefully acknowledged.[1] A. Nakova, M. Ilieva, Tz. Boiadjieva-Scherzer, V. Tsakova, Electrochim. Acta, 253 (2017) 128-133.[2] A. Nakova, M. Ilieva, Tz. Boiadjieva-Scherzer, V. Tsakova, J. Solid State Electrochem., 22 (2018) 1901–1908.[3] A. Nakova, E.M. Anghel, C. Lete, S. Lupu, Tz. Boijadjieva-Scherzer, V. Tsakova, Synth. Met., 247 (2019) 18-25.[4] A. Nakova, M. Ilieva, Tz. Boiadjieva-Scherzer, V. Tsakova, Electrochim. Acta, 306 (2019) 643-650.

Graphite electrode-assisted electroless deposition of palladium in the absence and presence of poly(3,4-ethylenedioxythiophene) coatings

Electroless deposition of Pd in the absence of solute reducing species is studied on pre-reduced non-coated and poly(3,4-ethylenedioxythiophene)(PEDOT)-coated graphite electrodes. PEDOT coatings doped with either dodecyl sulfate (SDS) or polysterene sulfonate (PSS) ions are used in the studies. Electrochemical reductive pre-treatment occurs at negative enough potential to initiate hydrogen reduction at the modified electrodes. Large amounts of deposited Pd significantly exceeding the quantity that is expected to be reduced at the expense of PEDOT re-oxidation alone are found to deposit irrespective of the polymer coating’s thickness. Pd particles are observed to deposit also at bare pre-reduced graphite electrode. It is suggested that molecular hydrogen entrapped during the reductive treatment plays the role of additional reductant for the electroless Pd deposition. SEM, UV–vis and Raman investigations are used to study possible structural changes of PEDOT provoked by the strong reductive treatment. The data give evidence for irreversible structural change in the PEDOT/SDS case resulting in a dense morphology that inhibits ionic transport and supports Pd electroless deposition.

Electroanalytical determination of caffeic acid – Factors controlling the oxidation reaction in the case of PEDOT-modified electrodes

The present studies focus on the intrinsic role of poly(3,4-ethylenedioxythiophene) (PEDOT) in electrooxidation of caffeic acid (CA) in view of the application of this electrode material in electroanalytical sensing. Electrosynthesized PEDOT layers with different thickness and different doping counterions are investigated. Based on the scan rate dependence of the voltammetric peak currents it is found that depending on the thickness of the polymer layer different factors, i.e. adsorption for thin layers and diffusion for thick layers, are rate determining. In terms of electroanalytical characteristics it is established that adsorption control provides the opportunity to obtain higher electroanalytical sensitivity in a narrow concentration range of linear response. Diffusion control results in markedly lower sensitivity values but extended range of linearity in the concentration dependence. In the case of adsorption control a hyperbolic equation of the Langmuir/Michaelis–Menten type is suggested to model the experimentally obtained non-linear concentration dependence of the peak currents. The use of a non-linear calibration curve provides an extended concentration range for electroanalytical work under the established adsorption controlled conditions. Doping counterions (polysterene sulfonate and dodecyl sulfate) are found to have no effect on the electroanalytical performance of PEDOT for CA oxidation.

High-density Pd nanoparticles distribution on PEDOT obtained through electroless metal deposition on pre-reduced polymer layers

Pd electroless deposition is carried out at the expense of oxidation of pre-reduced poly(3,4-ethylene dioxythiophene) (PEDOT)-coated electrodes. Two largely differing potentials for deep and mild pre-reduction of PEDOT are chosen and correspond to initial low (deep pre-reduction) and, correspondingly, high (mild pre-reduction) conductive states of the polymer material. The role of organic doping ions (polysterene sulfonate, PSS or dodecyl sulfate, SDS) used in the course of PEDOT synthesis for the electroless deposition of Pd is also investigated. PEDOT-supported Pd catalysts with high-density homogeneous distribution of Pd nanoparticles (NPs) with sizes ranging between 4 and 12nm are obtained. The amount of deposited metal depends significantly on the pre-reduction potential of PEDOT whereas the surface density of the metal NPs is largely influenced by the doping ions used to obtain the PEDOT material. Evidence for irreversible structural transformation obtained upon deep pre-reduction of PEDOT:SDS is obtained.

Characterization of Screen-Printed Organic Electrochemical Transistors to Detect Cations of Different Sizes.

A novel screen-printing fabrication method was used to prepare organic electrochemical transistors (OECTs) based on poly(3,4-ethylenedioxythiophene) doped with polysterene sulfonate (PEDOT:PSS). Initially, three types of these screen-printed OECTs with a different channel and gate areas ratio were compared in terms of output characteristics, transfer characteristics, and current modulation in a phosphate buffered saline (PBS) solution. Results confirm that transistors with a gate electrode larger than the channel exhibit higher modulation. OECTs with this geometry were therefore chosen to investigate their ion-sensitive properties in aqueous solutions of cations of different sizes (sodium and rhodamine B). The effect of the gate electrode was additionally studied by comparing these all-PEDOT:PSS transistors with OECTs with the same geometry but with a non-polarizable metal gate (Ag). The operation of the all-PEDOT:PSS OECTs yields a response that is not dependent on a Na+ or rhodamine concentration. The weak modulation of these transistors can be explained assuming that PEDOT:PSS behaves like a supercapacitor. In contrast, the operation of Ag-Gate OECTs yields a response that is dependent on ion concentration due to the redox reaction taking place at the gate electrode with Cl− counter-ions. This indicates that, for cation detection, the response is maximized in OECTs with non-polarizable gate electrodes.

An acoustic impedance study of PEDOT layers obtained in aqueous solution

The present investigation addresses the correlation between chemical and mechanical properties of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) used as an interface layer in bio-electronic devices. This correlation is important for the functional characteristics of PEDOT-based biosensors including neural electrodes. Electrochemical polymerization of PEDOT is studied in aqueous solutions of lithium perchlorate, sodium polysterenesulfonate(PSS) or sodium dodecylsulfate(SDS). Simultaneous electrochemical and acoustic impedance measurements are carried out in the course of polymerization and voltammetric cycling in acidic (0.4M HClO4) and neutral (0.1M sodium phosphate buffer) solutions. The acoustic impedance results are used to obtain data for the complex mechanical shear modulus, G, of the three types of PEDOT and to follow the ionic and solvent transport in the course of their electrochemical oxidation/reduction. It is established that the doping anion significantly affects the mechanical properties of PEDOT with PEDOT/dodecylsulfate displaying significant stiffness. PEDOT/perchlorate takes an intermediate position whereas PEDOT/PSS has the lowest G values. This trend in mechanical properties is preserved upon voltammetric cycling in both neutral and acidic media with marked increase in the stiffness observed in 0.4M HClO4 for the PEDOT/dodecylsulfate case. It is demonstrated that the type of ionic transport (anionic or cationic) and the amount of solvent molecules involved in the redox process depend on both the availability of immobilized negative charges (PSS or dodecylsulfate) and on the hydrophilicity of the PEDOT layers. The presented results point to versatile possibilities for controlling the mechanical properties of PEDOT in a way to match them to device-specific requirements.

Role of the anionic dopant of poly(3,4-ethylenedioxythiophene) for the electroanalytical performance: electrooxidation of acetaminophen

Poly(3,4-ethylenedioxythiophene) (PEDOT) films are synthesized in the presence of various anions and surfactants (perchlorate, dodecylsulfate (DDS), polysterenesulfonate (PSS) and poly(2-acrylamido-2-methyl-1-propanesulfonate (PAMPS), and polyoxyethylene-10-laurylether (PLE)) on glassy carbon electrodes. The electrocatalytical activity for acetaminophen electrooxidation is studied depending on the type of dopant and the polymerization charge of the PEDOT films. It is established that all PEDOT-coated electrodes show a marked electrocatalytical effect for this reaction. After exposure to acetaminophen, a new redox pair is observed to appear in the voltammetric curves measured in supporting electrolyte for all PEDOT-coated electrodes. The dopant used in the course of the PEDOT synthesis is found to play an important role for these redox currents with PEDOT/PSS-coated electrodes showing the smallest ones. The investigation of the role of the polymerization charge (i.e. the thickness of the polymer films) reveals that electrodes coated with thin PEDOT films perform better than those coated with thicker polymer films.Electroanalytical detection of acetaminophen is found to be effective by means of thin film PEDOT/PSS-coated electrodes. The concentration range of linear response is established to be 50μMdm−3 to 1mMdm−3 in linear sweep voltammetry experiments and 5μMdm−3 to 65μMdm−3 in DPV experiments. The corresponding LODs are 10μMdm−3 and 0.3μMdm−3, respectively. PEDOT/PSS-coated electrodes are used to determine acetaminophen in four medications containing various additional components.

Electrochemical polymerization of 3,4-ethylenedioxythiophene in the presence of dodecylsulfate and polysulfonic anions—An acoustic impedance study

PEDOT layers are synthesized in aqueous solutions in the presence of one of the three different anionic species – polysterenesulfonate (PSS), poly(2-acrylamido-2-methyl-1-propane-sulfonate) (PAMPS) and dodecylsulfate without any addition of further inorganic anions. Simultaneous electrochemical and acoustic admittance measurements are carried out in the course of polymerization. The data from the admittance spectra are used to extract information on the mechanical shear storage and loss moduli of the three types of PEDOT layers. The anionic species are found to affect the polymerization kinetics, the surface morphology and most markedly the viscoelastic properties of the three types of layers. The latter depend primarily on the innate structure arising in the course of polymerization whereas the solution specifics play a secondary role. Dodecylsulfate imparts significant stiffness to the PEDOT layers with high rigidity preserved for relatively large polymerization charges. The G moduli in this case exceed 109dyn/cm2. Both polyanion-doped PEDOT layers are found to be softer but there is nevertheless a clear difference between them with PEDOT/PAMPS having a strong predisposition for swelling.

Formation and electroanalytical performance of polyaniline–palladium nanocomposites obtained via Layer-by-Layer adsorption and electroless metal deposition

The Layer-by-Layer (LbL) adsorption technique is used to produce thin composite layers consisting of polyaniline (PANI) and Pd particles in two different ways: (i) multistep adsorption of PANI and pre-synthesized Pd nanoparticles (NPs) and (ii) multistep adsorption of PANI and polysterene sulfonate (PSS) followed by electroless deposition of palladium particles (Pdeless). The formation of both types of composite layers is characterized by electrochemical and microgravimetric measurements.Electrochemical measurements for hydrogen peroxide reduction are carried out at neutral pH under voltammetric and amperometric conditions. It is established that the PANI–Pd NPs composites show a sensitive voltammetric response for H2O2 reduction in the 40–300μM concentration range whereas the (PANI–PSS)Pdeless composites have high intrinsic electroactivity that masks the H2O2 reductive response. The amperometric data show high sensitivity for both types of composites: PANI–Pd NPs and (PANI–PSS)Pdeless (with Pd incorporated in several electroless deposition steps). For the PANI–Pd NPs material the concentration range of linear response is 10–700μM and the limit of detection 2.6μM. The obtained non-enzymatic electrocatalytic materials are suitable for monitoring the levels of H2O2 in drinking and waste waters.

Asking the question again: are cation exchange resins effective for the treatment of hyperkalemia?

Sodium polysterene sulfonate (Kayexalate ® ) is a crosslinked polymer to which reactive sulfonic groups are attached and preloaded with sodium (Na + ). When placed in a solution, its reactive sulfonate groups exchange their bound Na + for another cation in the solution. Sodium polysterene sulfonate (SPS) [Although ‘SPS’ is often used as an abbreviation for sodium polystyrene sulfonate, SPS ® is actually a brand name for sodium polystyrene sulfonate in sorbitol.] has long been used for the treatment of hyperkalemia, assuming that its reactive sulfonate groups exchange bound Na + for potassium (K + ) in the lumen of the gastrointestinal (GI) tract, causing loss of K +

Formation of hybrid polyanion/metal cation/anionic surfactant films via interface complexation and Langmuir–Blodgett technique

Abstract We demonstrate that highly-ordered supramolecular polyanion/polyvalent metal cation/anionic amphiphile complex ultrathin multilayer superlattice films with separating acidic amphiphile bilayers by highly rare-earth-doped hydrophilic polymeric interlayers can be fabricated using Langmuir–Blodgett technique along with interface ligand exchange and coordination reactions. The properties of stearic acid (SA) Langmuir monolayer on the aqueous subphase containing Gd acetate and polysterene sulfonate (PSS)-Na were studied and PSS-Gd-SA multilayer films were deposited successfully onto the solid substrates by conventional vertical dipping method. Built-up films were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction and atomic force microscopy (AFM). FTIR spectroscopy analysis of multilayer films showed high degree of amphiphile and polyanion acidic groups ionization under complexation with rare-earth cations. AFM study of surface morphology of the built-up films revealed unique structure of PSS-Gd-SA film different from polymeric Gd-PSS polymeric complex film and gadolinium stearate Langmuir–Blodgett film. The data obtained give evidence for the formation of high-quality superlattice structures PSS-Gd-SA hybrid films with stearate bilayers separated by Gd-PSS complex interlayers of ∼0.5 nm thickness.

Assembly of Alternated Multivalent Ion/Polyelectrolyte Layers on Colloidal Particles. Stability of the Multilayers and Encapsulation of Macromolecules into Polyelectrolyte Capsules

Alternating adsorption of multivalent ions and oppositely charged polyelectrolytes on colloid particles has been investigated. Multilayer films composed of Tb3+/polysterene sulfonate (PSS) and 4-pyrene sulfate/polyallylamine (PAH) were successfully assembled on polysterene sulfonate (PS) and melamine formaldehyde (MF) latex particles. The amount of assembled material was estimated by fluorescence and the linear growth of the film versus the number of layers was demonstrated. These multilayers are not stable and can be decomposed by salt and temperature. Dissolution of MF particles leads to formation of hollow capsules consisting of multivalent ion/polyelectrolyte multilayers. Comparative analysis of the capsules was done by confocal and scanning force microscopy. Complex hollow spheres consisting of Tb3+/PSS or 4-PS/PAH as an inner shell and stable PSS/PAH as an outer shell were produced. Due to selective permeability of the outer shell after degradation of the inner shell the multivalent ions are released out of the capsule while the polyelectrolytes fill the capsule interior. This is indicative of swelling of the capsule by osmotic pressure. The filled capsules were studied by confocal and scanning electron microscopy. Possibilities of encapsulating macromolecules in defined amounts per capsule are discussed.