Hg detection by measuring thiol groups with a highly sensitive screen-printed electrode modified with a nanostructured carbon black film

A sensor based on a screen-printed electrode (SPE) modified with a stable dispersion of commercially available carbon black (CB) N220 was optimised and challenged with several thiol-containing compounds. This probe showed a significantly enhanced electrochemical activity respect to a bare SPE when tested with thiocholine, cysteine, glutathione and cysteamine. When challenged in amperometric batch mode, the response was stable and showed a linear dependence up to 1 × 10⁻⁵ mol l⁻¹ for thiocholine and cysteine. The very high sensitivity towards these thiols (299 mA mol⁻¹ l cm⁻² for thiocholine and 441 mA mol⁻¹ l cm⁻² for cysteine) was then used as the basis for developing an analytical method for mercury ion detection since a non electroactive complex (thiol–Hg) is formed in the presence of the metal. By selecting an appropriate concentration of thiocholine, a concentration of mercury as low as 5 × 10⁻⁹ mol l⁻¹ (1 ppb) was detected. Satisfactory recovery was obtained when the system was tested on drinking water samples.     

Thin films of amorphous nitrogenated carbon a-CNx: Electron transfer and surface reactivity

The electrochemical behaviour of thin films of nitrogenated amorphous carbon a-CN_x is similar to that of boron-doped diamond, with a wide potential window in aqueous media. They are elaborated by cathodic sputtering of a graphite target in an Ar-N₂ active plasma for varying nitrogen contents, determined by XPS (0.06 ≤ x ≤ 0.39). Their electrochemical reactivity is sensitive to the surface state. The present study reports on the influence of electrochemical pre treatment on the electronic transfer rate of a fast redox system ferri-ferrocyanide, by focusing on the direction of the potential excursion. On the other hand, the role of both the pH and the potential on the interfacial capacitance in the presence of Na₂SO₄ without redox species is documented. The results show up the sensitivity of the film surface to the electrochemical conditions.     

A modified composite film electrode of polyoxometalate/carbon nanotubes and its electrocatalytic reduction

Keggin-type polyoxometalate (H₄SiMo₁₂O₄₀) and carbon nanotubes (CNTs) coated by poly(allylamine hydrochloride) (PAH) were alternately deposited on glassy carbon (GC) electrodes by an electrochemical growth method in acidic aqueous solution. The preparation of the film electrode was simple and convenient. Thus-prepared multilayer films and the electrochemical behavior of the composite film modified electrode were characterized by UV–vis spectroscopy and cyclic voltammetry. It was shown that the multilayer films are uniform and stable. The resulting multilayer film modified electrode behaves as an electrochemical sensor because of its low overpotential for the catalytic reduction of S₂O₈ ²⁻ and NO₂ ⁻ in acidic aqueous solution.     

Fibrinogen and lysozyme adsorption on amorphous carbon film surface detected by multilayer device from the back side of the film

To develop hydrogenated amorphous carbon (a-C:H) as a biocompatible coating, a-C:H was studied in terms of its protein adsorption during the initial process of cell adsorption. A multilayer surface plasmon resonance (SPR) device consisting of an a-C:H layer on Au was built in the Kretschmann configuration to detect protein adsorption on an a-C:H film surface. From the dependence of reflectivity on the laser incident angle, SPR angle was determined to the incident angle in which the light intensity was reduced drastically. The proteins considered were lysozyme (Lyz) and fibrinogen (Fib). The SPR angle increased from 58.09 to 58.69° upon the adsorption of Lyz when the nonadsorbed Lyz was removed after introduction of 20 μM Lyz-containing solution. Upon the adsorption of Fib, the SPR angle increased from 60.95 to 61.76° when the nonadsorbed Fib were removed after the introduction of 0.4 μM Fib-containing solution. The shift in the SPR angle was small for both cases. Obtained results suggested that the number of adsorbed Lyz was higher than that of adsorbed Fib.     

Electrochemical study on cobalt film modified glassy carbon electrode and its application

A novel electroactive material for ascorbic acid (AA) determination was successfully prepared by plating/potential cycling method. The cobalt film was first deposited on the surface of glassy carbon electrode (GCE) in CoSO₄ solution by potential cycling, and then a cobalt film on the surface of GCE was activated by potential cycling in 0.1 mol L⁻¹ NaOH. The electrochemical performance of the resulted film (Co/GCE) and factors affecting its electrochemical activity were investigated by cyclic voltammetry and amperometry. This film electrode exhibited good electrocatalytic activity to the oxidation of AA. This biosensor had a fast response of AA less than 3 s and excellent linear relationships were obtained in the concentration range of 3 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 2 × 10⁻⁷ mol L⁻¹ (S/N = 3) under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Evaluation of the pseudocapacitance in RuO2 with a RuO2/GC thin film electrode

The pseudocapacitance of nanocrystalline RuO₂ with BET surface area of 42 m² g⁻¹ was evaluated using a RuO₂ modified Glassy Carbon (RuO₂/GC) thin film electrode. The charge storage behavior of the RuO₂/GC thin film electrode was studied from fast to slow scan cyclic voltammetry between various potential windows. The utilization of the thin film electrode method for nanocrystalline RuO₂ with known specific surface area allowed a semi-quantitative understanding of the electric double-layer capacitance (C_dl), adsorption related charge (C_ad), and the irreversible redox related charge (C_irr) per unit mass and surface area of RuO₂. Comparison of the cyclic voltammograms between different voltage windows revealed that the contribution from C_irr is especially dominant below 0.4 V (versus RHE) at slow scan rates.     

Electrochemical behavior of multi-wall carbon nanotubes and electrocatalysis of toluene-filled nanotube film on gold electrode

The cyclic voltammetric behaviors of empty nanotubes and toluene-filled nanotubes were described. When the nanotube films exposed to air for one night, a pair of redox waves was observed that is probably ascribed to the presence of oxygen-containing groups bound to the surface of the nanotubes. Toluene-filled nanotube film is demonstrated to catalyze the electrochemical response of biomolecules such as dopamine and epinephrine, while empty multi-wall carbon nanotube film shows no or less electrocatalytic behavior to these biomolecules. This suggests that filled nanotubes have some particular properties compared to empty multi-wall carbon nanotubes and the development of filled nanotubes is necessary.     

Photoelectrochemical water oxidation using hematite modified with metal-incorporated graphitic carbon nitride film as a surface passivation and hole transfer overlayer

Hematite (α-Fe₂O₃) is renowned as a promising photoanode for water oxidation, even though it displays poor photoconversion efficiency. In this study, ∼5 nm-thick graphitic carbon nitride (g-C₃N₄; CN) and metal-incorporated CN (M-CN; M = Ag, Fe, Co) films are uniformly deposited on hematite via a facile one-step evaporation method. Herein, the Co-CN layer leads to the highest photoelectrochemical activity with hematite-based photoanode. The subsequent loading of Co-CN layer with oxygen evolution catalysts (FeNiOOH and CoOOH) further enhances photocurrent density to ∼3.5 mA cm⁻² and oxygen evolution at > 95 % of Faradaic efficiency over 24 h at E = 1.23 V. Detailed analysis based on spectroscopic and electrochemical measurements demonstrate that the primary role of CN layer is improving the charge separation efficiency by passivating the hematite surface. Then the incorporated metals contribute to reducing charge transfer resistance and thereby mediating hole transfer to interfacial water.     

Comparative investigation on electrochemical behavior of hydroquinone at carbon ionic liquid electrode, ionic liquid modified carbon paste electrode and carbon paste electrode

Ionic liquid, 1-heptyl-3-methylimidazolium hexafluorophosphate (HMIMPF₆), has been used to fabricate two new electrodes, carbon ionic liquid electrode (CILE) and ionic liquid modified carbon paste electrode (IL/CPE), using graphite powder mixed with HMIMPF₆ or the mixture of HMIMPF₆/paraffin liquid as the binder, respectively. The electrochemical behaviors of hydroquinone at the CILE, the IL/CPE and the CPE were investigated in phosphate buffer solution. At all these electrodes, hydroquinone showed a pair of redox peaks. The order of the current response and the standard rate constant of hydroquinone at these electrodes were as follows: CILE > IL/CPE > CPE, while the peak-to-peak potential separation was in an opposite sequence: CILE < IL/CPE < CPE. The results show the superiority of CILE to IL/CPE and CPE, and IL/CPE to CPE in terms of promoting electron transfer, improving reversibility and enhancing sensitivity. The CILE was chosen as working electrode to determine hydroquinone by differential pulse voltammetry, which can be used for sensitive, simple and rapid determination of hydroquinone in medicated skin cosmetic cream.     

Electrochemical behaviors of thymine on a new ionic liquid modified carbon electrode and its detection

A new electrochemical method was proposed for the determination of thymine, which relied on the oxidation of thymine at a carbon ionic liquid electrode (CILE) in a pH 5.0 Britton-Robinson buffer solution. CILE was fabricated by using ionic liquid 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole acetate as the binder, which showed strong electrocatalytic ability to promote the oxidation of thymine. A single well-defined irreversible oxidation peak appeared with adsorption-controlled process and enhanced electrochemical response on the CILE, which was due to the presence of high conductive ionic liquid on the electrode. The reaction parameters of thymine were calculated with the electron transfer coefficient (α) as 0.27, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (k_s) as 6.87 × 10⁻⁶ s⁻¹ and the surface coverage (Г_T) as 5.71 × 10⁻⁸ mol cm⁻². Under the selected conditions the oxidation peak current was proportional to thymine concentration in the range from 3.0 to 3000.0 μM with the detection limit as 0.54 μM (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the thymine detection without the interferences of coexisting substances.     

Electrocatalytic oxidation of deoxyguanosine on a glassy carbon electrode modified with a ruthenium oxide hexacyanoferrate film

The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a D_ct value of 2.7 × 10⁻¹¹ cm² s⁻¹ for a film with Γ = 4.47 × 10⁻⁹ mol cm⁻². The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 10⁶ mol⁻¹ L¹ s⁻¹. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.     

Electrochemical synthesis of lepidocrocite thin films on gold substrate—EQCM, IRRAS, SEM and XRD study

Lepidocrocite thin films have been electrochemically synthesised on polycrystalline Au substrates following two ways, direct synthesis and synthesis via green rust (GR). The direct synthesis consists in oxidising Fe(II) species in a 0.4 M NaCl/0.02 M Met-Imidazole/0.01 M FeCl₂ solution at pH 7.5. The synthesis via GR consists in converting a green rust thin film into lepidocrocite thin film by galvanostatic oxidation. The thin films have been characterised by means of electrochemical quartz crystal microbalance, scanning electron microscopy, X-ray diffraction and infrared reflection-absorption spectroscopy.     

Electrochemical behavior and voltammetric determination of 4-aminophenol based on graphene-chitosan composite film modified glassy carbon electrode

The graphene-chitosan composite film modified glassy carbon electrode (GCE) was fabricated and used to determine 4-aminophenol (4-AP). In 0.1 M pH 6.3 phosphate buffer solution, the redox peak currents of 4-AP increased significantly and the peak-to-peak separation decreased greatly at graphene-chitosan composite film modified GCE compared with bare GCE and chitosan modified GCE, indicating that graphene possessed electrocatalytic activity towards 4-AP. The experimental conditions were optimized and the kinetic parameters were investigated. The oxidation mechanism was discussed. Under the optimal experimental conditions, the oxidation peak current was proportional to 4-AP concentration in the range from 0.2 to 550 μM with the correlation coefficient of 0.9930. The detection limit was 0.057 μM (S/N = 3). Using the proposed method, 4-AP was successfully determined in water samples and paracetamol tablets with standard addition method, suggesting that this method can be applied to determine 4-AP in environments and pharmaceuticals.     

Development of electrochemical oxidase biosensors based on carbon nanotube-modified carbon film electrodes for glucose and ethanol

Functionalised multi-walled carbon nanotubes (MWCNTs) were cast on glassy carbon (GC) and carbon film electrodes (CFE), and were characterised electrochemically and applied in a glucose-oxidase-based biosensor. MWCNT-modified carbon film electrodes were then used to develop an alcohol oxidase (AlcOx) biosensor, in which AlcOx-BSA was cross-linked with glutaraldehyde and attached by drop-coating. The experimental conditions, applied potential and pH, for ethanol monitoring were optimised, and ethanol was determined amperometrically at −0.3 V vs. SCE at pH 7.5. Electrocatalytic effects of MWCNT were observed with respect to unmodified carbon film electrodes. The sensitivity obtained was 20 times higher at carbon film/MWCNT-based biosensors than without MWCNT.     

Insights into the simultaneous chronopotentiometric stripping measurement of indium(III), thallium(I) and zinc(II) in acidic medium at the in situ prepared antimony film carbon paste electrode

The simultaneous measurement of microgram per liter concentration levels of indium(III), thallium(I) and zinc(II) at the antimony film carbon paste electrode (SbF-CPE) is demonstrated. The antimony film was deposited in situ on a carbon paste substrate electrode and employed in chronopotentiometric stripping mode in deoxygenated solutions of 0.01 M hydrochloric acid (pH 2). The chronopotentiometric stripping performance of the SbF-CPE was studied and compared with constant current chronopotentiometric stripping and anodic stripping voltammetric operation. In comparison with its bismuth and mercury counterparts, the SbF-CPE exhibited advantageous electroanalytical performance; namely, at the bismuth film electrode, the measurement of zinc(II) was practically impossible due to hydrogen evolution, whereas the mercury film electrode exhibited a poorly developed signal for thallium(I). The SbF-CPE revealed favorable calculated LoDs (3σ) of 1.4 μg L⁻¹ for thallium(I) and 2.4 μg L⁻¹ for indium(III) along with good linear response in the examined concentration range from 10 to 100 μg L⁻¹ with correlations coefficients (R²) of 0.992 for thallium(I) and 0.994 for indium(III) associated with a 120 s deposition time. The chronopotentiometric stripping performance of the SbF-CPE was characterized also by satisfactory reproducibility of 1.62% for indium(III), 3.96% for thallium(I) and 2.11% for zinc(II) (c = 40 μg L⁻¹, n = 11).     

Electrochemical behavior of an indenedione derivative electrodeposited on a renewable sol-gel derived carbon ceramic electrode modified with multi-wall carbon nanotubes: Application for electrocatalytic determination of hydrazine

A novel modified carbon ceramic electrode (CCE) containing multi-wall carbon nanotubes (MWCNTs) was fabricated by a sol-gel technique. The prepared MWCNT-CCE was modified by the electrodeposition of an indenedione derivative. The indenedione modified MWCNT-CCE (IMWCNT-CCE) shows one pair of peaks with surface confined characteristics. According to the theoretical model of Laviron, estimations were made in different pHs of the surface charge transfer rate constant, k_s, and the charge transfer coefficient, α, for electron transfer between the indenedione derivative and MWCNT-CCE. The modified electrode shows a highly catalytic activity toward hydrazine electrooxidation at a wide pH range (5-9). The kinetic parameters such as the electron transfer coefficient, α, the heterogeneous rate constant, k′, and the exchange current of hydrazine at the IMWCNT-CCE were calculated as 0.29 ± 0.01, 2.7(±0.3) × 10⁻³ cm s⁻¹ and 0.17 ± 0.03 μA, respectively. Also, the modified electrode shows an excellent analytical performance for voltammetric determination of hydrazine. Differential pulse voltammetry (DPV) exhibits two linear dynamic ranges, 0.6-8.0 μM and 8.0-100.0 μM, and a lower detection limit of 0.29 μM for hydrazine. Finally, the practical analytical utility is illustrated by differential pulse voltammetric determination of hydrazine in auxiliary cooling water at IMWCNT-CCE and the accuracy of the results is verified in comparison with those obtained from the standard ASTM method.     

Electrochemical modification of glassy carbon electrode by poly-4-nitroaniline and its application for determination of copper(II)

Electrochemical modification of glassy carbon (GC) electrode by poly-4-nitroaniline (P4NA), electrochemical reduction of P4NA and applicability of electrode modified in this way for determination of copper(II) (Cu(II)) is reported in this study. Electrochemical surface modification was performed by cyclic voltammetry in the potential range between +0.9 V and +1.4 V vs. Ag/Ag⁺ (in 10 mM AgNO₃) at the scan rate of 100 mV/s by 100 cycles in non-aqueous media. In order to provide electrochemical reduction of nitro groups on the P4NA-modified GC electrode surface (P4NA/GC), the cyclic voltammograms inducing/evidencing the reduction of nitro groups were performed in the potential range between −0.1 V and −0.8 V vs. Ag/AgCl/(sat.KCl) at the scan rate of 100 mV/s. The reduced P4NA/GC surfaces (Reduced-P4NA/GC) were treated with aqueous solution of nitrilotriacetic acid. The sensitivity of GC electrode modified in described way towards Cu(II) was investigated in Britton-Robinson buffer solution, pH 5.0. The potentiometric generic pulse technique was applied as innovative electrochemical method for detection of analytical signal. It was shown that GC electrodes modified in here described way will be suitable for the determination of Cu(II) in technological waste water and/or some other solutions containing Cu(II) ions.     

BDD薄膜电极电催化氧化处理DDNP生产废水的实验研究

采用新型膜电极——BDD薄膜电极,运用电催化氧化方法处理DDNP生产废水,考察了槽电压、极板间距、废水初始COD、电解质(NaCl)投加量等因素对废水降解效果的影响.研究发现,槽电压和废水初始COD对COD去除率的影响最大,而电解质的加入对电催化氧化影响不显著.此外对影响废水降解的主要因素进行了动力学分析.     

Electrochemical and morphological study of the effect of polymerization conditions on poly(tetrathiophene) with emphasis on carbon fiber microelectrodes: A cyclic voltammetry and atomic force microscopy study

Electropolymerization of tetrathiophene was carried out in various solvents on carbon fiber microelectrodes and platinum electrodes. Acetonitrile, dichloroethane and propylene carbonate were investigated as solvent systems for film formation, and solvent effect as well as the effect of other experimental conditions (scan rate, supporting electrolyte) on the electropolymerization has been discussed on the basis of the electropolymerization mechanism. Surface morphology was investigated by atomic force microscopy (AFM). Carbon fiber electrodes were found to be an effective microelectrode system for the electropolymerization of tetrathiophene, which was compared with polyterthiophene growth on carbon fibers.     

Stainless steel coupled with carbon nanotube-modified epoxy and carbon fibre composites: Electrochemical and mechanical study

The aim of this work is the study of the electrochemical and mechanical behaviour of stainless steel (SS304) adhesively bonded with carbon nanotube (CNT)-reinforced epoxies to either SS304 or carbon-reinforced composites substrates. For metal to metal (MtM) joints, the shear strength of nano-reinforced adhesives was studied using single lap shear specimen geometries. The lap shear strength was improved by almost 50% and the highest shear strength appeared for 0.6% CNT weight content in the adhesive. The metal to composite joint performed altogether better compared to the MtM joint, although the CNT inclusion had an adverse effect on the lap shear strength attributed to the physical property change of the epoxy. Although the incorporation of CNTs was found to increase the galvanic effect, it also enhanced corrosion protection, as the modified adhesives exhibited increased resistance to uniform corrosion and localised corrosion and prevented the electrolyte from reaching the substrate.