Polyaniline Langmuir-Blodgett film modified glassy carbon electrode as a voltammetric sensor for determination of Ag ions

A highly sensitive electrochemical sensor made of a glassy carbon electrode (GCE) coated with a Langmuir-Blodgett film (LB) containing polyaniline (PAn) doped with p-toluenesulfonic acid (PTSA) (LB/PAn-PTSA/GCE) has been used for the detection of trace concentrations of Ag⁺. UV-vis absorption spectra indicated that the PAn was doped by PTSA. The surface morphology of the PAn LB film was characterized by atomic force microscopy (AFM). The electrochemical properties of this LB/PAn-PTSA/GCE were studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The LB/PAn-PTSA/GCE was used as a voltammetric sensor for determination of trace Ag⁺ at pH 5.0 using linear scanning stripping voltammetry. Under the optimal experimental conditions, the stripping current was proportional to the Ag⁺ concentration over the range from 6.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹. The high sensitivity, selectivity, and stability of this LB/PAn-PTSA/GCE also demonstrated its practical utility for simple, rapid and economical determination of Ag⁺ in water samples.     

A-type zeolite containing Ag/Zn as inorganic antifungal for waterborne coating formulations

The biocide cations Ag⁺ and Zn²⁺ were hosted in the cavities of an ordered aluminosiliceous framework. Starting from sodium A-type zeolite (NaA), LTA containing Ag⁺ (AgA), Zn²⁺ (ZnA) and Ag⁺/Zn (AgZnA) at different cation exchanged levels was obtained and its antifungal properties were evaluated. To determine the minimum inhibitory concentration (MIC) of the exchanged zeolites against Aspergillus niger, [Ag⁺] and [Zn²⁺] values ranging from 50 < [Ag⁺] < 1000 mg L⁻¹ to 650 < [Zn²⁺] < 2000 mg L⁻¹, respectively, were used for NaA, and for AgZnA: 30 < Ag⁺ < 250 mg L⁻¹. The zeolite sample having [Ag⁺] = 100 mg L⁻¹, [Zn²⁺] = 90 mg L⁻¹ produces a growth inhibition comparable to that achieved with 230 mg L⁻¹ of Ag⁺¹ (MIC value obtained for the single cation). The antifungal activity of these products after incorporation in waterborne coating formulations was also determined. Results indicate that Ag⁺ and Zn²⁺ supported on A-type zeolite could be a beneficial tool for the development of waterborne coatings with a longer protection against microbiological attack when compared to traditional organic biocides.     

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes for the electrochemical detection of copper(II)

Poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes obtained by electropolymerization of 2-amino-4-thiazoleacetic acid, were used for the voltammetric determination of copper ions. The voltammetric response of copper ions at poly(2-amino-4-thiazoleacetic acid)/multiwalled carbon nanotubes modified glassy carbon electrodes was evaluated by differential pulse stripping voltammetry. The peak currents were linearly dependent on the concentrations of the copper ions in the range from 7.0 × 10⁻⁷ M to 5.0 × 10⁻⁵ M, with a coefficiency of 0.9987. The detection limit is 5.0 × 10⁻¹⁰ M calculated for a signal-to-noise ratio of 3 (S/N = 3). And it could be used for the simultaneous determination of copper and cadmium ions. The proposed method was successfully applied to the determination of copper ions in natural water. The concentration of Cu²⁺ was calculated to be 2.0 × 10⁻⁵ M by standard addition method. The recovery rate was 94%.     

Plastic membrane electrodes for the determination of flavoxate hydrochloride and cyclopentolate hydrochloride

Four novel ion-exchangers (Fx-Rt (I), Fx-TPB (II), Cp3-PMA (III) and Cp3-PTA (IV)) of antispasmodic and anticholinergic drugs, flavoxate hydrochloride (FxCl), 2-piperidinoethyl-3-methyl-4-oxo-2-phenyl-4h-1-benzopyran-8-carboxylate hydrochloride, cyclopentolate hydrochloride (CpCl) and (2-(dimethylamino)ethyl (RS)-(1-hydroxycyclopentyl)phenylacetate) hydrochloride were synthesized and incorporated into poly(vinyl chloride)-based membrane electrodes for the quantification of FxCl and CpCl in different pharmaceutical preparations. The influence of membrane composition on the potentiometric response of the membrane electrodes was found to substantially improve the performance characteristics. The best performance was reported with membranes having compositions (w/w) of Fx-Rt (2%):PVC (49%):DOP (49%), Fx-TPB (7%):PVC (46.5%):DOP (46.5%), Cp3-PMA (8%):PVC (46%):DOP (46%) and Cp3-PTA (9%):PVC (45.5%):DOP (45.5%). The proposed sensors exhibited Nernstian responses in the concentration ranges of 1.39 × 10⁻⁶-5.00 × 10⁻⁴, 9.90 × 10⁻⁷-3.75 × 10⁻⁵, 1.39 × 10⁻⁵-2.53 × 10⁻³ and 3.21 × 10⁻⁶-8.62 × 10⁻⁴ M, with detection limits of 5.50 × 10⁻⁷, 9.8 × 10⁻⁷, 9.8 × 10⁻⁶ and 2.95 × 10⁻⁶ M for the (I), (II), (III) and (IV) electrodes, respectively. The membrane electrodes performed satisfactorily over pH ranges of 2.0-5.5, 2.0-5.5, 2.0-5.0 and 2.0-7.5, with fast response times of 20, 30, 15 and 20 s for the (I), (II), (III) and (IV) electrodes, respectively. The practical utility of the sensors was demonstrated by the determination of FxCl and CpCl in pure solutions and pharmaceutical preparations using standard additions and potentiometric titration.     

Electron-transfer characteristics of ferrocene attached to single-walled carbon nanotubes (SWCNT) arrays directly anchored to silicon(1 0 0)

High-density, surface-mounted ferrocene has been prepared using covalent immobilisation of an alcohol substituted ferrocene derivative to a pre-assembled single-walled carbon nanotubes directly anchored to silicon(1 0 0) surface (SWCNTs-Si). The formation of these ferrocene-modified electrodes (Fc-SWCNTs-Si) has been followed using X-ray photoelectron spectroscopy and atomic force microscopy. Electrochemical results show the surface concentration of ferrocenemethanol molecules is 9.26 × 10⁻⁸ mol cm⁻², which is about 500-1000 times greater than the experimentally measured coverage of ferrocene directly attached to flat Si(1 0 0) surfaces. The reversible one-electron wave of the ferrocene/ferrocenium couple was observed at 490 mV versus Ag⁺/Ag and the apparent rate constant of electron transfer, k_app, was 21 s⁻¹. These results suggest these ferrocene-modified electrodes are excellent candidates for molecular memory devices.     

Rhodamine-based fluorescent sensor for mercury in buffer solution and living cells

A novel fluorescent sensor based on thiooxorhodamine B has been prepared to detect Hg²⁺ in aqueous buffer solution. It demonstrates high selectivity for sensing Hg²⁺ with about 383-fold enhancement in fluorescence emission intensity and micromolar sensitivity (K_d = 7.5 × 10⁻⁶ mol L⁻¹) in comparison with alkali and alkaline earth metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺) and other transition metal ions (Mn²⁺, Ni²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Ag⁺, Pb²⁺, Cr³⁺, Fe³⁺). Meanwhile the distinct color changes and rapid switch-on fluorescence also provide ‘naked eyes’ detection for Hg²⁺ over a broad pH range. Moreover, such sensor is cell-permeable and can visualize the changes of intracellular mercury ions in living cells using fluorescence microscopy.     

Linear sweep anodic stripping voltammetry of heavy metals from nitrogen doped tetrahedral amorphous carbon thin films

Nitrogen doped tetrahedral amorphous carbon (ta-C:N) thin films were deposited on p-Si (1 1 1) substrates (1 × 10⁻³ to 6 × 10⁻³ Ω cm) by a filtered cathodic vacuum arc technique with different nitrogen flow rates (3 and 20 sccm). The ta-C:N film coated samples were used as working electrodes to detect trace heavy metals such as zinc (Zn), lead (Pb), copper (Cu) and mercury (Hg) by using linear sweep anodic stripping voltammetry in 0.1 M KCl solutions (pH 1). The influence of nitrogen flow rate on the sensitivity of the films to the metal ions was investigated. The results showed that the current response of the ta-C:N film electrodes was significant to differentiate all the tested trace metal ions (Zn²⁺, Pb²⁺, Cu²⁺, and Hg²⁺) and the three ions (Pb²⁺ + Cu²⁺ + Hg²⁺) could be simultaneously identified with good stripping peak potential separations.     

Microfabrication, characterization and analytical application of a new thin-film silver microsensor

The present research demonstrates the microfabrication of a novel thin-film silver microelectrode based on an ion-selective PVC organic membrane. First, the gold substrate thin-film surface is treated by depositing a thin-layer of Ag electrochemically. This pretreatment step is followed by applying the organic-membrane-sensitive layer using a new nebulization technique, which gives a high stability to the organic-membrane-sensitive layer. The performance of the resulting thin-film silver microelectrode is investigated by potentiometric measurements. The microelectrode provides a linear Nernstian response of high sensitivity (58 ± 0.5 mV/decade) covering the range of 1 × 10⁻⁶-1 × 10⁻¹ mol L⁻¹ of Ag⁺ ions with a fast response time (<20 s) and a relatively long life span (>3 months). The suggested microelectrode is successfully used in the analytical evaluation of Cl⁻ ions in some real environmental samples as well as in the simultaneous determination of halides using potentiometric titration. The results obtained are compared with those obtained by the commercial silver billet electrode and the conventional bulk ion-selective electrode based on the same ionophore.     

Electroanalytical studies on cobalt(II) selective potentiometric sensor based on bridge modified calixarene in poly(vinyl chloride)

A bridge modified 4-tert-butylthiacalix[4]arene (I) has been employed as electroactive material in the preparation of cobalt selective sensor. Polyvinyl chloride (PVC)-based membranes of (I) using sodium tetraphenylborate (NaTPB) as anion discriminator and bis(2-ethylhexyl) sebacate (DOS), chloronaphthalene (CN), tri-n-butylphosphate (TBP), o-nitrophenyl octyl ether (NPOE), tris(2-ethylhexyl)phosphate (TEHP) as plasticizers were prepared and investigated as cobalt selective sensors. A number of membranes of different compositions were prepared and investigated. The best performance was observed with the membrane having composition of 2:66:1.5:127 (mg) = I:NaTPB:PVC:NPOE. The potential response of this membrane is linear to Co²⁺ ions in the concentration range 5.3 × 10⁻⁶ to 1.0 × 10⁻¹ M with near-Nernstian slope of 30.0 mV/decade of activity and a detection limit of ∼0.3 ppm. This membrane also showed lowest response time of 10 s and works satisfactorily in partially non-aqueous medium. The selectivity studies of this sensor, evaluated with fixed interference method and matched potential method, show that the sensor under consideration possesses excellent selectivity for Co²⁺ over a large number of mono-, bi- and trivalent cations such as Na⁺, K⁺, Ag⁺, Ca²⁺, Mg²⁺, Cu²⁺, Hg²⁺, Pb²⁺, Li⁺, Ba²⁺, Zn²⁺, Sr²⁺, Cr³⁺, Ni²⁺, etc. The sensor could be used as an indicator electrode in the quantification of Co²⁺ by potentiometric titration against EDTA as well as in determination of cobalt content in wastewater and beer samples.     

PVC membrane and coated graphite potentiometric sensors based on 1-phenyl-3-pyridin-2-yl-thiourea for selective determination of iron(III)

The construction and performance characteristics of PVC membrane (PME) and coated graphite (CGE) Fe³⁺ ion selective electrodes based on 1-phenyl-3-pyridin-2-yl-thiourea (PPT) are described. The electrodes exhibit a Nernstian slope of 20.2 ± 0.8 (CGE) and 19.9 ± 0.4 (PME) mV decade⁻¹ of activity in Fe³⁺ ion over a wide concentration range from 3.0 × 10⁻⁷ to 1.0 × 10⁻² M for CGE and 6.9 × 10⁻⁷ to 1.0 × 10⁻² M Fe³⁺ for PME. The lower detection limits by CGE and PME are 2.0 × 10⁻⁷ and 3.9 × 10⁻⁷ M, respectively, in the pH range of 1.8-5.6 for PME and 1.8-5.8 for CGE with a fast response time (<10 s). The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the PME. The PME showed the working temperature range of 22-55 °C with isothermal temperature coefficient of 1.33 × 10⁻³ V/°C and it was also used in non-aqueous solvents. The electrodes were successfully applied to determine iron(III) in water samples.     

Manganese oxide embedded polypyrrole nanocomposites for electrochemical supercapacitor

MnO₂ embedded PPy nanocomposite (MnO₂/PPy) thin film electrodes were electrochemically synthesized over polished graphite susbtrates. Growing PPy polymer chains provides large surface area template that enables MnO₂ to form as nanoparticles embeded within polymer matrix. Co-deposition of MnO₂ and PPy has a complimentary action in which porous PPy matrix provides high active surface area for the MnO₂ nanoparticles and, on the other hand, MnO₂ nanoparticles nucleated over polymer chains contribute to enhanced conductivity and stability of the nanocomposite material by interlinking the PPy polymer chains. The MnO₂/PPy nanocomposite thin film electrodes show significant improvement in the redox performance as cyclic voltammetric studies have shown. Specific capacitance of the nanocomposite is remarkably high (∼620 F g⁻¹) in comparision to its constituents MnO₂ (∼225 F g⁻¹) and PPy (∼250 F g⁻¹). Photoelectron spectroscopy studies show that hydrated manganese oxide in the nanocomposite exists in the mixed Mn(II) to Mn(IV) oxidation states. Accordingly, chemical structures of MnO₂ and PPy constituents in the nanocomposite are not influenced by the co-deposition process. The MnO₂/PPy nanocomposite electrode material however shows significantly improved high specific capacitity, charge-discharge stability and the redox performance properties suitable for application in the high energy density supercapcitors.     

The use of silver solid amalgam electrode for voltammetric and amperometric determination of nitroquinolines

Solid amalgam electrodes represent a suitable alternative to mercury electrodes due to their similar electrochemical properties and non-toxicity of the amalgam material. Nitro derivatives of quinoline have been proven to be genotoxic, thus their presence in environmental samples is a legitimate cause for concern.In this contribution, meniscus modified silver solid amalgam electrode (m-AgSAE) was employed for the batch voltammetric determination and amperometric determination in connection with flow injection analysis of 5-nitroquinoline and 6-nitroquinoline (5-NQ, 6-NQ). Their electrochemical behavior was characterized by cyclic voltammetry, for their determination direct current voltammetry and differential pulse voltammetry were used. Linear calibration curves in the concentration range of 2 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ were obtained. These results are comparable with results obtained for polarographic determination of the same substances using mercury electrodes. Further, the meniscus modified silver solid amalgam electrode was employed in amperometric detection cell in “wall jet” arrangement for determination of 5-NQ in flow injection analysis. Under optimized conditions (run buffer 0.05 mol L⁻¹ borate buffer, pH 9.0; flow rate 4 mL min⁻¹; detection potential −1.6 V; injection volume 0.1 mL), the limit of quantitation of ∼4 × 10⁻⁶ mol L⁻¹ was achieved. The repeatability of the detector response is satisfactory (relative standard deviation ∼2.15% for c(5-NQ) = 1 × 10⁻⁴ mol L⁻¹). Practical applicability of the method was verified for the determination of micromolar concentrations of 5-NQ in drinking and river water model samples.     

Electrochemistry of ionophore-coordinated Cs and Sr ions in the tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide ionic liquid

The selective extraction of Cs⁺ and Sr²⁺ from aqueous solutions by using the ionophores calix[4]arene-bis(tert-octylbenzo-crown-6) (BOBCalixC6) and dicyclohexano-18-crown-6 (DCH18C6), respectively, was demonstrated in the hydrophobic, room-temperature ionic liquid (RTIL), tri-1-butylmethylammonium bis((trifluoromethyl)sulfonyl)imide (Tf₂N⁻). The electrochemistry of Cs⁺ coordinated by BOBCalixC6 and Sr²⁺ coordinated by DCH18C6 was examined at a mercury film electrode (MFE) in this ionic liquid by using cyclic staircase voltammetry, sampled current voltammetry at a rotating electrode, and chronoamperometry. Both BOBCalixC6·2Cs⁺ and DCH18C6·Sr²⁺ exhibit well-defined reduction waves at approximately −2.4 and −2.9 V versus the ferrocene/ferrocenium (Fc/Fc⁺) couple, respectively, in which the coordinated ions are reduced to their respective amalgams, permitting the recycling of the ionophores. The diffusion coefficients of BOBCalixC6·2Cs⁺ and DCH18C6·Sr²⁺ are (2.7 ± 0.1) × 10⁻⁹ and (2.1 ± 0.1) × 10⁻⁹ cm² s⁻¹, respectively, at 30 °C. The coulometric efficiency for the reduction and stripping of Cs at mercury pool electrodes was about 90% and was independent of the deposition time, whereas the efficiency for Sr was slightly less than 90% at short times and decreased with the deposition time, probably due to the formation of a passive layer of Sr(Tf₂N)₂.     

Aluminum assisted electrodeposition of europium in LiCl-KCl molten salt

Cyclic voltammetry (CV), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were employed to investigate the electrodeposition of Eu and Al in an LiCl-KCl eutectic melt containing Eu²⁺ and Al³⁺ at 450 °C. In order to deposit a pure Eu and Al alloy, the stoichiometrically lower concentration of Al³⁺ than that of Eu²⁺ and Al wires as a counter electrode was introduced into the bath of LiCl-KCl melt for the electrodeposition. The electrodeposition takes place at a potential more negative than −1.95 V vs. Ag|Ag⁺ while the deposit is oxidized at more positive potential than −1.92 V. Two new reduction peaks and an anodic peak on a W working electrode were observed at −2.39 V, −2.42 V, and −2.1 V, vs. Ag|Ag⁺, respectively, suggesting that the potential window of the Al system in LiCl-KCl melt can be extended to −2.43 V vs. Ag|Ag⁺. The EDS analysis indicated that AlEu can be deposited at the potential more negative than −2.37 V.     

Electrochemical behavior of folic acid at calixarene based chemically modified electrodes and its determination by adsorptive stripping voltammetry

Voltammetric behavior of folic acid at plain carbon paste electrode and electrode modified with calixarenes has been studied. Two peaks for irreversible oxidation were observed. Out of the three calixarenes chosen for modification of the electrodes, p-tert-butyl-calix[6]arene modified electrode (CME-6) was found to have better sensitivity for folic acid. Chronocoulometric and differential pulse voltammetric studies reveal that folic acid can assemble at CME-6 to form a monolayer whose electron transfer rate is 0.00273 s⁻¹ with 2-electron/2-proton transfer for the peak at +0.71 V against SCE. An adsorption equilibrium constant of 5 × 10³ l/mol for maximum surface coverage of 2.89 × 10⁻¹⁰ mol/cm² was obtained. The current is found to be rectilinear with concentration by differential pulse voltammetry. However, linearity in the lower range of concentration 8.79 × 10⁻¹² M to 1.93 × 10⁻⁹ M with correlation coefficient of 0.9920 was achieved by adsorptive stripping voltammetry. The limit of detection obtained was found to be 1.24 × 10⁻¹² M. This method was used for the determination of folic acid in a variety of samples, viz. serum, asparagus, spinach, oranges and multivitamin preparations.     

Interaction between promethazine hydrochloride and DNA and its application in electrochemical detection of DNA hybridization

The interactions of promethazine hydrochloride (PZH) with thiolated single-stranded DNA (HS-ssDNA) and double-stranded DNA (HS-dsDNA) self-assembled on gold electrodes have been studied electrochemically. The binding of PZH with ssDNA shows a mechanism containing an electrostatic interaction, while the mode of PZH interaction with dsDNA contains both electrostatic and intercalative bindings. The redox system belongs to the category of diffusion control approved by cyclic voltammetry (CV). The diffusion coefficients of PZH at the bare, HS-dsDNA and HS-ssDNA modified gold electrodes decrease regularly as 1.34 × 10⁻³ cm² s⁻¹, 1.04 × 10⁻³ cm² s⁻¹, 7.47 × 10⁻⁴ cm² s⁻¹, respectively. The electron transfer standard rate constant k_s of PZH at bare gold, HS-ssDNA and HS-dsDNA modified electrodes are 0.419 s⁻¹, 0.131 s⁻¹, and 0.154 s⁻¹, respectively. The presence of adsorbed dsDNA results in a great increase in the peak currents of PZH in comparison with those obtained at a bare or ssDNA adsorbed gold electrode. The difference between interactions of PZH with HS-ssDNA and HS-dsDNA has been used for hybridization recognition of 14-mer DNA oligonucleotide. The peak current (i_pa) of PZH is linearly proportional to the logarithmic concentration of complementary target DNA in the range from 2.0 × 10⁻⁹ mol L⁻¹ to 5.0 × 10⁻⁷ mol L⁻¹ with the detection limit of 3.8 × 10⁻¹⁰ mol L⁻¹.     

Novel chemosensory materials based on polyfluorenes with 2-(2′-pyridyl)-benzimidazole and 5-methyl-3-(pyridin-2-yl)-1,2,4-triazole groups in the side chain

Polyfluorenes with 2-(2′-pyridyl)-benzimidazole (P1, P2 and P4) and 5-methyl-3-(pyridin-2-yl)-1,2,4-triazole (P3) groups in the side chain were synthesized by Suzuki polycondensation. The responsive properties of polymers on metal ions and H⁺ were investigated by absorption and emission spectra. The fluorescences of polymers (P1-P4) were completely quenched upon the transition metal ions such as Co²⁺, Ni²⁺, Fe³⁺ and Ag⁺ due to the enhanced electronic communication properties of conjugated polymers. The obvious differences to Ni²⁺ ion responsive sensitivity were observed between P1 and P4 polymers. The fluorescences of P1 and P4 were quenched to 50 (I₀/I) and to 22 (I₀/I) upon the addition of a Ni²⁺ solution of 3.2 × 10⁻⁶ M, as well as 5.0 × 10⁻⁶ M, respectively, owing to the different conjugated backbone. The fluorescences of P2 and P3 were completely and hardly quenched upon the addition of a Al³⁺ solution of 1.0 × 10⁻⁴ M, respectively, owing to the different receptors in the side chain. P2 showed good selectivity to Ni²⁺ ion in the range of quencher concentration as low as 5 ppm, owing to the different chelating abilities of receptor with ions. Cu²⁺ and Mn²⁺ ions hardly quenched the fluorescences of polymers (P1-P4), which were different from the oligopyridyl-functionalized conjugated polymers. The results further opened the opportunities to develop the tailored sensory materials through the appropriate alteration of receptors in the side chain and the conjugated backbone.     

Impedance study of protecting film formation on lithium and lithiated graphite induced by bis(fluorosulfonyl) imide anion

The process of Li⁺ reduction from room temperature ionic liquids consisting of N-methyl-N-propylpyrrolidinium cation (MPPyr⁺) and bis(fluorosulfonyl) imide (FSI⁻) or bis(trifluoromethanesulfonyl) imide (TFSI⁻) anions was studied with the use of impedance spectroscopy. Reduction was carried out on both metallic lithium (Li) and graphite (G) electrodes. It has been found that the FSI anion in high amounts is able to form a protective film on both graphite and metallic lithium. The Li⁺/Li couple should rather be represented by a Li⁺/SEI/Li system. The SEI structure depends on the manner of its formation (chemical or electrochemical) and is not stable with time. The rate constant for the Li⁺ + e⁻ → Li process at the Li/SEI/Li⁺ (in MPPyrFSI) interface is k_o = 4.2 × 10⁻⁵ cm/s. In the case of carbon electrodes (G/SEI/Li⁺ interface), lithium diffusion in solid graphite is the rate determining step, reducing current by ca. two orders of magnitude, from ca. 10⁻⁴ A/cm², characteristic of the Li/SEI/Li⁺ electrode, to ca. 10⁻⁶ A/cm².     

Effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method

In this paper, the effect of hydroxyl ions on chloride penetration depth measurement using the colorimetric method was studied. Equivalent silver nitrate solution (i.e. Ag⁺ = Cl⁻) was added to the NaCl + NaOH solution with different concentrations, then the amount of precipitated silver chloride and silver oxide were determined by chemical methods, and the color of the precipitated products was examined. Results show that the amount of silver chloride formed decreases linearly as OH⁻ to Cl⁻ ratio (r) increases. Thus, the chloride concentration at color change boundary changes with the pH value of the concrete. AgCl has a white color, while Ag₂O has a dark brown color. When the value of r exceeds 4, the color of the mixture looks brown, and color change boundary cannot be easily distinguished.     

Polypyrrole/carbon composite electrode for high-power electrochemical capacitors

Nano-thin polypyrrole (PPy) layers with thickness from ∼5 nm to several 10s nm were deposited on vapor grown carbon fibers (VGCF) by an in situ chemical polymerization. Using different concentrations of the pyrrole could control the thicknesses of deposited PPy layers. Surface morphology and thickness of the deposited PPy layers were confirmed by means of scanning electron microscopy and scanning transmission emission microscopy. Pseudo-capacitive behavior of the deposited PPy layers on VGCF investigated by means of cyclic voltammetry. Then, the PPy/VGCF composites were mixed with activated carbons (AC) at various mixing ratios. For the PPy/VGCF/AC composite electrodes, characteristics of specific capacitance and power capability were examined by half-cell tests. As results of this study, it was investigated that nano-thin PPy layer below ∼10 nm deposited on VGCF had high pseudo-capacitance and fast reversibility. Its specific capacitance per averaged weight of active material (PPy) was obtained as ∼588 F g⁻¹ at 30 mV s⁻¹ and maintained as ∼550 F g⁻¹ at 200 mV s⁻¹ of scan rate. Also, from the mixing 60 wt.% of the PPy/VGCF with 25 wt.% of AC, the PPy/VGCF/AC composite electrode exhibited higher power capability maintaining the specific capacitance per active materials of PPy and AC as ∼300 F g⁻¹ at 200 mV s⁻¹ in 6 M KOH.