Electrochemical properties of undoped CVD diamond films

The electrochemical properties of undoped diamond polycrystalline films grown on tungsten wire substrates using methanol as a precursor are described. The diamond film quality was changed by introducing sp²-bonded non-diamond carbon impurity through adjustment of the methanol-to-hydrogen (C/H) source gas ratio used for diamond growth.The electrodes were characterized by Raman spectroscopy, scanning electronic microscopy (SEM) and cyclic voltammetry (CV).Diamond coated tungsten wires were then used as a working electrode to ascertain their electrochemical behavior in electrolytic medium. Electrochemical windows of these films were found to be suitable in the potential range of [−2.5 V, +2.2 V] vs. Ag/AgCl in acid medium (0.1 M KCl).The electrochemical behavior was evaluated also using the Fe(CN)₆^3−/4−redox couple.The results demonstrate that the grain boundaries and sp²-hybridized carbon impurity can have a significant influence on electrochemical window of undoped diamond electrodes. It was observed that with increasing sp² carbon impurity concentration the electrochemical window decreases.     

Electrochemical response of nitrogen-doped multi-walled carbon nanotubes decorated with gold and iridium nanoparticles toward ferrocyanide/ferricyanide redox system

Novel composite films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold (AuNP) and iridium (IrNP) nanoparticles possessing diameters of 12.5 and 2.7 nm, respectively. The electrochemical responses of fabricated composite films, further denoted as N-MWCNTs/MNPs (M: Au and Ir), toward ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple was probed by means of cyclic voltammetry and electrochemical impedance spectroscopy techniques. The findings demonstrate that both N-MWCNT/MNP composite films exhibit greater electrochemical response and sensitivity toward [Fe(CN)₆]^3−/4− compared to unmodified N-MWCNTs. The results verify that the N-MWCNT/MNP composite films are extremely promising for application in electrochemical sensing.

     

Electrochemical properties of compacts of nano-and microdisperse diamond powders in aqueous electrolytes

The electrochemical behavior of compacts of micro-and nanodisperse diamond powders were studied by using model redox K₃[Fe(CN)₆]-K₄[Fe(CN)₆] and Ce(SO₄)₂-Ce₂(SO₄)₃ systems in aqueous electrolytes. The current-voltage curves for compacts of microdisperse diamonds and the kinetics of reactions on these compacts in a solution of the [Fe(CN)₆]^3-/4- system are similar to those obtained by using a metal electrode. For nanodisperse diamonds, the same reactions are essentially irreversible.     

Synthesis and characterization of conducting polypyrrole-containing iron complexes

Electrochemical or chemical oxidation of pyrrole-containing complex anions of iron cyanide or iron chloride results in the formation of films or powders of conducting polypyrroles. Freshly prepared films exhibit an additional IR band at ca 1630–1640 cm⁻¹, slowly disappearing in air and not observed in previously studies polypyrrole-based systems. It is possible that this new band is associated with the existence of a CN bond in dehydrogenated pyrrole rings which are transformed into regular pyrrole rings, probably due to the protonation reaction occurring in air and simultaneous bond rearrangement. The polypyrrole structure favours the presence of Fe(CN)₆⁴⁻ over Fe(CN)₆³⁻ since the former is the only iron species detected by Mössbauer spectroscopy in electrochemically prepared samples. It is also the dominant iron species in the samples oxidized chemically. The polypyrrole-containing Fe(CN)₆⁴⁻ is more ordered than those containing monovalent anions, as evidence by X-ray diffraction studies. High-spin eron complexes can be inserted into polypyrrole during electrochemical oxidation of pyrrole in non-aqueous solutions containing LiCl/FeCl₃. The inserted species exhibit Mössbauer parameters characteristic of slightly distorted FeCl₄⁻.     

The electrochemical behavior of Dy(III) in eutectic LiF-DyF<Subscript>3</Subscript> at W electrode

The electrochemical reduction process of Dy ion on tungsten electrode at 1103 K in Dy₂O₃-LiF-DyF₃ molten system was studied by cyclic voltammetry, chronoamperometry, and chronopotentiometry methods with a three-electrode system on the electrochemical workstation AUTOLAB. The results showed that Dy³⁺ could be deposited at around ?0.75 V on inert W electrode compared with platinum electrode. The reduction process of Dy ion on W electrode occurred in a single step with the exchange of three electrons because one reduction peak was observed, and the calculated transfer electron number was three. Chronoamperograms indicated that the nucleation process of dysprosium ions was instantaneous three-dimensional nucleation on a tungsten electrode. The cathode electrochemical process on the tungsten electrode was controlled by the diffusion of ions, and the diffusion coefficient was 1.159 × 10^?4 cm²/s, which was calculated from a chronopotentiogram.     

Magnetic and Mössbauer studies of cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)6]·3H2O

Cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)₆]·3H₂O (cyclam=1,4,8,11-tetraazacyclotetradecane) was synthesized from the reaction of trans-[MnCl₂(cyclam)]Cl with K₃Fe(CN)₆. A linear chain structure consisting of alternating [Mn(cyclam)]³⁺ and [Fe(CN)₆]³⁻ units was indicated by the IR and Mössbauer spectra. The variable-temperature magnetization and Mössbauer measurements revealed that this complex exhibited a long-range ordering below 6.8 K. The magnetic behavior of the complex was based on intrachain ferromagnetic and interchain antiferromagnetic interactions.     

Electrochemical and surface characterisation of carbon-film-coated piezoelectric quartz crystals

The electrochemical properties of carbon films, of thickness between 200 and 500 nm, sputter-coated on gold- and platinum-coated 6 MHz piezoelectric quartz crystal oscillators, as new electrode materials have been investigated. Comparative studies under the same experimental conditions were performed on bulk electrodes. Cyclic voltammetry was carried out in 0.1 M KCl electrolyte solution, and kinetic parameters of the model redox systems Fe(CN)₆^3−/4− and [Ru(NH₃)₆]^3+/2+ as well as the electroactive area of the electrodes were obtained. Atomic force microscopy was used in order to examine the surface morphology of the films, and the properties of the carbon films and the electrode-solution interface were studied by electrochemical impedance spectroscopy. The results obtained demonstrate the feasibility of the preparation and development of nanometer thick carbon film modified quartz crystals. Such modified crystals should open up new opportunities for the investigation of electrode processes at carbon electrodes and for the application of electrochemical sensing associated with the EQCM.     

Porous carbon-coated graphite electrodes for energy production from salinity gradient using reverse electrodialysis

Performance of graphite foil electrodes coated by porous carbon black (i.e., Vulcan) was investigated in comparison with metal electrodes for reverse electrodialysis (RED) application. The electrode slurry that was used for fabrication of the porous carbon-coated graphite foil is composed of 7.2 wt% of carbon black (Vulcan X-72), 0.8 wt% of a polymer binder (polyvinylidene fluoride, PVdF), and 92.0 wt% of a mixing solvent (dimethylacetamide, DMAc). Cyclic voltammograms of both the porous carbon (i.e., Vulcan)-coated graphite foil electrode and the graphite foil electrode without Vulcan showed good reversibility in the hexacyanoferrate(III) (i.e., Fe(CN)₆³⁻) and hexacyanoferrate(II) (i.e., Fe(CN)₆⁴⁻) redox couple and 1 M Na₂SO₄ at room temperature. However, anodic and cathodic current of the Vulcan-coated graphite foil electrode was much higher than those of the graphite foil electrode. Using a bench-scale RED stack, the current–voltage polarization curve of the Vulcan-coated graphite electrode was compared to that of metal electrodes such as iridium (Ir) and platinum (Pt). From the results, it was confirmed that resistance of four different electrodes increased with the following order: the Vulcan-coated graphite foil<the Ir-coated titanium (Ti) mesh<the Pt-coated Ti plate<the graphite foil. Moreover, the Vulcan-coated graphite foil showed 5–10% higher power density than the metal mesh electrodes. From the polarization curve of the Vulcan-coated graphite foil electrode, it was found that total resistance decreased as thickness and geometric surface area of the electrode increased.     

Electrochemical immune bioassay for the antigen–antibody interaction based on [Fe(CN)<Subscript>6</Subscript>]<Superscript>4-/3-</Superscript> and [AuCl<Subscript>4</Subscript>]<Superscript>-</Superscript> ions-derivated biomimetic interface

A simple and sensitive electrochemical immune bioassay for the detection of hepatitis B surface antigen (HBsAg), as a model, was developed based on [Fe(CN)₆]^4-/3- and [AuCl₄]^- ions-derivated biomimetic interface in this study. A layer of [Fe(CN)₆]^4-/3- film (i.e., Prussian blue, PB) was initially electrodeposited onto a glassy carbon electrode, and then [AuCl₄]^- ions were reduced under the potentiostat to form gold nanoparticles on the PB film. Finally, hepatitis B surface antibody (HBsAb) was adsorbed onto the nanogold surface. The performance and factors influencing the immunosensor were assessed and optimized. The proposed immunosensor exhibits a specific response to HBsAg in the range of 2.13–314.3 ng∙ml^-1 with a detection limit of 0.42 ng∙ml^-1. In addition, the developed immunosensor shows high sensitivity, good reproducibility, and long-term stability. Importantly, the ions-derivated biomimetic interface could be further extended for the immobilization of other proteins and biocompound.     

On the electrochemical reactivity of the redox couple Fe(CN)63−/Fe(CN)64− at the single crystal zinc oxide electrode

The system zinc oxide/hexacyanoferrate was used to test the applicability of the theoretical model for electrochemical reactions at semiconductor electrodes based upon direct electron transfer between levels of equal energy. This model appears to be valid for electron transfer involving the conduction band. From the pH-dependence of the cathodic reactivity, a value of 0.75 eV is found for the rearrangement energy of Fe(CN)₆^3?/Fe(CN)₆^4?. This result, combined with capacity and potential data, allows the construction of a general energy scheme for the system under consideration. It is shown that direct electron transfer from filled redox levels to empty levels in the valence band is highly improbable, so that the observed hole capture by Fe(CN)₆^4? from the UV-illuminated ZnO anode presumably occurs by a more complicated mechanism, e.g. involving surface states.     

Anionic polymerization in Co and Fe doped ZnO: Nanorods,magnetism and photoactivity

The growth mechanism of Zn_1−xCo_xO (ZC) and Zn_1−xFe_xO (ZF) nanorods, and resulting magnetic and optical properties have been studied. The ZC and ZF nanorods were prepared by sol–gel synthesis route. X-ray diffraction results in polycrystalline phase with wurtzite structure of ZC and ZF nanorods. The transmission electron microscopy images show the formation of nanorods. The growth mechanism of nanorods is explained on the basis of agglomeration of Zn²⁺ with OH⁻ ions which is react with poly vinyl alcohol involve anionic polymerization of oriented growth. Magnetic measurement of ZC and ZF nanorods exhibit superferromagnetic behavior and the large value of saturation magnetization observed at room temperature. The magnetization below room temperature measurement confirms the origin of observed magnetism. Raman and photoluminescence spectra show good photoactivity. The observed Raman active modes show wurtzite structure belongs to C_6v symmetry group. Photoluminescence measurements of ZC and ZF nanorods exhibit ultraviolet peaks at 413.90 nm (∼3 eV) due to free exciton emission and at 546.31 nm (∼2.27 eV) due to transition from deep donor states which arises from oxygen vacancy.     

Optical and electrochemical properties of ordered macroporous gold array on the ITO surface

The electrochemical and optical properties of transparent, two-dimensional macroporous gold film were investigated. Colloidal crystal templates were assembled onto indium-doped tin oxide (ITO) glass surface through vertical depositing method. Following gold electrodeposition, they were removed by dissolution with tetrahydrofuran (THF). The highly ordered macroporous gold array was achieved. It was characterized by scanning electron microscope (SEM) and ultraviolet visible (UV-vis) spectrophotometry. The optical transparency of the gold film was near 25% and fairly constant between 300 and 900 nm. The macroporous gold film electrode was mounted into a thin-layer transmission cell. The electrochemical response was evaluated by thin-layer cyclic voltammograms (CV) of the Fe (CN)₆³⁻/Fe (CN)₆⁴⁻ couple. Thin-layer cell exhibits good shape of waves and nearly symmetric cathodic and anodic waves. E⁰′ value and n of TMPD⁺/TMPD (TMPD is acronyms for N,N,N′,N′-tetramethyl-p-phenylenediamine, and TMPD⁺ is its mono-cation radical) couple were determined. Furthermore, results demonstrated electrolytic equilibrium was faster reached in macroporous gold film than ITO electrode.     

Electrochemical Studies on Substituted Iron-Hexacyanoiron(III) Bi-Layered Thin Films at Glassy Carbon Electrode/Electrolyte Interface

Thin films (30–50 nm) of bilayered HCM (hexacyanometalates) were prepared using direct electrodeposition or electrochemically driven insertion-substitution of PB (Prussian Blue) or InHCF (Indium Hexacyanoferrate) or K..In _x [Fe{CN}₆] _y , as starting material. The redox behavior of the immobilized counter/central ions at GCE/electrolyte interface have been investigated in aqueous KCl (pH 1) electrolytes using dynamic voltammetric techniques. Studies show that when the counter Fe or In ion is replaced by expandable partially filled d orbits elements such as Ru³⁺ a redox wave of the inserted counter ion is observed. Furthermore, the substitution of Fe as a counter ion with other poly-valent cations was found to be reversible if PB was the starting material. Studies were extended to include the EC (electrochemical) behavior of related HCM compounds such as K...Al _x [Fe{CN}₆] _y K, Ni _x [Fe{CN}₆] _y Cu _x [Fe{CN}₆] _y , K..Zn _x [Fe{CN}₆] _y and, K..Ru[Fe{CN}₆]₃. Unlike studied 3d cations, GCE modified with thin films of copper-hexacyanoiron (III) KCu _x [Fe{CN}₆] _y or CHF showed two redox waves with E^o _f 0.6, 0.9 V vs Ag/AgCl. Studies showed that even immobilized Cu ions were capable of catalyzing the oxidation of hydrazine and sulfite. The mechanism for electro-oxidation is also included.     

Green synthesis of silver and gold nanoparticles using Rosa damascena and its primary application in electrochemistry

Biosynthesis and characterizations of nanoparticles have become an important branch of nanotechnology. In this paper, green synthesis of gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) using the flower extract of Rosa damascena as a reducing and stabilizing agent, has been discussed. This approach is simple, cost-effective and stable for a long time, reproducible at room temperature and in an eco-friendly manner to obtain a self-assembly of AuNPs and AgNPs. The resulting nanoparticles are characterized using UV–vis, TEM, XRD and FT-IR spectroscopic techniques. A modified glassy carbon electrode using AuNPs (AuNPs/GCE) was investigated by means of cyclic voltammetry in a solution of 0.1 M KCl and 5.0×10⁻³ M [Fe(CN)₆]^3−/4−. The results show that electronic transmission rate between the modified electrode and [Fe(CN)₆]^3−/4− increased.     

Electrochemical responses of carbon nanotubes-based films printed on polymer substances

The electrochemical responses of novel thin films, which consist of multiwalled carbon nanotubes (MWCNTs) printed on polymer substrates, were investigated towards ferrocyanide/ferricyanide, [Fe(CN)₆]^3?/4? redox couple in aqueous potassium chloride solutions. With this respect, MWCNT-based films were fabricated through transfer of water-dispersed MWCNTs onto the polymer substances polyethylene terephthalate (MWCNT-PET) and polycarbonate (MWCNT-PC) by means of mass flexographic printing process. For the electrochemical studies, the techniques of cyclic voltammetry and electrochemical impedance spectroscopy were employed. The findings reveal that the MWCNT-PC films exhibit better stability in solution, less oxidation overpotential, greater oxidation current density, and larger capacitance compared to MWCNT-PET films. In addition, the MWCNT-PC films provide fewer barriers for electron transfer process and faster electrode kinetics compared to MWCNT-PET films. The results are very promising and open the possibility of using mass-printing techniques for the construction of printed MWCNT-polymer films for electrochemical applications.     

Mössbauer studies of photochemical reaction products of Ru(bpy)3 2+ iron cyanide double complexes

The reductive and the oxidative electron-transfer photochemical reaction system of light-irradiated the mix solutions of Ru(bpy)₃ ²⁺ with [Fe(CN)₆]^4–, [Fe(CN)₆]^3–, [Fe(CN)₅NO]^2– and PB (Prussian Blue) have been studied. The double complexes which isolated from the precipitates of the photochemical reaction have been identified by means of Mössbauer spectroscopy. In order to clarify the chemical states of these isolated double complexes, we have (prepared and) studied Mössbauer spectra of the double complexes such as [Ru(bpy)₃]₃[Fe(CN)₆]₂.14H₂O, [Ru(bpy)₃]₂[Fe(CN)₆].10H₂O, [Ru(bpy)₃][Fe(CN)₅NO].4H₂O, and [Ru(bpy)₃][PB]₂.xH₂O.     

Poly(3-methylthiophene)-based porous silicon substrates as a urea-sensitive electrode

Poly(3-methylthiophene) (P3MT)-based porous silicon (PS) substrates were fabricated and characterized by cyclic voltammetry, scanning electron microscopy, and auger electron spectroscopy. After doping urease (Urs) into the polymeric matrix, sensitivity and physicochemical properties of the P3MT-based PS substrate was investigated compared to planar silicon (PLS) and bulk Pt substrates. PS substrate was formed by electrochemical anodization in an etching solution composed of HF, H₂O, and ethanol. Subsequently, Ti and Pt thin-films were sputtered on the PS substrate. Effective working electrode area (A_eff) of the Pt-deposited PS substrate was determined from a redox reaction of Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox couple in which nearly reversible cyclic voltammograms were obtained. The i_p versus v^1/2 plots showed that A_eff of the PS-based Pt thin-film electrode was 1.62 times larger than that of the PLS-based electrode.Electropolymerization of P3MT on both types of electrodes were carried out by the anodic potential scanning under the given potential range. And then, urease molecules were doped to the P3MT film by the chronoamperometry. Direct electrochemistry of a Urs/P3MT/Pt/Ti/PS electrode in an acetonitrile solution containing 0.1 mol/L NaClO₄ was introduced compared to a P3MT/Pt/Ti/PS electrode at scan rates of 10 mV s⁻¹, 50 mV s⁻¹, and 100 mV s⁻¹.Amperometric sensitivity of the Urs/P3MT/Pt/Ti/PS electrode was ca. 1.67 μA mM⁻¹ per projected unit square centimeter, and that of the Urs/P3MT/Pt/Ti/PLS electrode was ca. 1.02 μA mM⁻¹ per projected unit square centimeter in a linear range of 1-100 mM urea concentrations. 1.6 times of sensitivity increase was coincident with the results from cyclic voltammetrc analysis.Surface morphology from scanning electron microscopy (SEM) images of Pt-deposited PS electrodes before and after the coating of Urs-doped P3MT films showed that pore diameter and depth were 2 μm and 10 μm, respectively. Multilayered-film structures composed of metals and organics for both electrodes were also confirmed by auger electron spectroscopy (AES) depth profiles.     

Relation between 2p X-ray photoelectron and Kα X-ray emission spectra of manganese and iron oxides

The high resolution Mn and Fe Kα X-ray emission spectra (XES), and Mn and Fe 2p X-ray photoelectron spectra (XPS) for manganese and iron oxides were measured. The spectra were compared with those of [MnO₄]⁻, [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ ions. As the electronic structure of the latter compounds do not change with electron hole creation in the core levels, satellite peaks due to charge transfer are not observed in the 2p XPS spectra, and the peak profiles of metal 2p XPS and Kα XES are governed by the exchange splitting between 2p and valence electrons. The metal 2p XPS spectra of the oxides had satellite peaks, but the XES spectra had no satellites. FWHMs of the metal 2p_3/2 main peaks of the compounds being low spin states are smaller than those of metal Kα₁ XES spectra. However, FWHMs of Mn 2p_3/2 of the manganese oxide were nearly equal to those of Mn Kα₁ XES spectra, and those of Fe 2p_3/2 XPS spectra of the iron oxides are greater than those of Fe Kα₁ XES spectra.     

Ultrasonically assisted synthesis of barium stannate incorporated graphitic carbon nitride nanocomposite and its analytical performance in electrochemical sensing of 4-nitrophenol

We describe the ultrasonic assisted preparation of barium stannate-graphitic carbon nitride nanocomposite (BSO-gCN) by a simple method and its application in electrochemical detection of 4-nitrophenol via electro-oxidation. A bath type ultrasonic cleaner with ultrasonic power and ultrasonic frequency of 100 W and 50 Hz, respectively, was used for the synthesis of BSO-gCN nanocomposite material. The prepared BSO-gCN nanocomposite was characterized by employing several spectroscopic and microscopic techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infra-red, field emission scanning electron microscopy, and high resolution transmission electron microscopy, to unravel the structural and electronic features of the prepared nanocomposite. The BSO-gCN was drop-casted on a pre-treated glassy carbon electrode (GCE), and their sensor electrode was utilized for electrochemical sensing of 4-nitrophenol (4-NP). The BSO-gCN modified GCE exhibited better electrochemical sensing behavior than the bare GCE and other investigated electrodes. The electroanalytical parameters such as charge transfer coefficient (α = 0.5), the rate constant for electron transfer (k_s = 1.16 s⁻¹) and number of electron transferred were calculated. Linear sweep voltammetry (LSV) exhibited increase in peak current linearly with 4-NP concentration in the range between 1.6 and 50 μM. The lowest detection limit (LoD) was calculated to be 1 μM and sensitivity of 0.81 μA μM⁻¹ cm⁻²_. A 100-fold excess of various ions, such as Ca²⁺, Na⁺, K⁺, Cl⁻, I⁻, CO₃²⁻, NO₃, NH₄⁺ and SO₄²⁻ did not able to interfere with the determination of 4-NP and high sensitivity for detecting 4-NP in real samples was achieved. This newly developed BSO-gCN could be a potential candidate for electrochemical sensor applications.     

Surface‐enhanced Raman spectroscopy of 4‐tert‐butylpyridine on a silver electrode

We report the observation of large surface‐enhanced Raman scattering (SERS) (10⁶) for 4‐tert‐butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a₁, a₂, and b₂ modes at laser excitation of 488 nm. Enhancement of the non‐totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.