Polished Glassy Carbon Research Articles

Influence of Nafion® Ionomer on the Electrocatalytic Behavior of Carbon-supported Pt Catalysts in Acidic Solutions

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Characterization of DNA Layers Adsorbed on Glassy Carbon Electrodes

AbstractA DNA layer adsorbed at glassy carbon electrodes (GCE) was characterized by ellipsometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The presence of the adsorbed DNA layer on polished glassy carbon electrodes was assessed indirectly by ellipsometric measurements. Ellipsometry was also useful to evaluate the influence of the oxide layer formed on glassy carbon electrodes, either spontaneously or after electrochemical pretreatments, on the DNA adsorption and further electrooxidation process. SEM and AFM images of the electrode surface covered by a thick layer of DNA reveal a nonuniform distribution, leaving channels and islands of the biological material.

Photochemical Grafting and Activation of Organic Layers on Glassy Carbon and Pyrolyzed Photoresist Films

Organic films have been grafted to polished glassy carbon (GC) and as-prepared pyrolyzed photoresist film (PPF) by photolysis of alkenes and an alkyne. The alkene or alkyne is spin-coated onto the carbon surface and photolyzed in air at 254 nm. Characterization by water contact angle measurements, depth profiling and surface roughness measurements using atomic force microscopy (AFM), and electrochemistry reveal that for most modifiers a loosely packed monolayer is grafted to the surface. Grafted layers of 1-decene were further reacted by drop-coating with oxalyl chloride and photolyzing at 254 nm in air. The procedure adds acid chloride groups to the film. Amines were attached to these films via amide bond formation, and were characterized by electrochemistry and assembly of citrate-capped gold nanoparticles. Amines were also coupled to photografted 1-undecylenic acid layers and to carboxyphenyl layers prepared by electroreduction of the corresponding diazonium salt. Quantitative analysis using electrochemistry established that the highest concentration of amines was attached to the oxalyl chloride treated film, and that a higher concentration of amines was attached via reaction with the photografted 1-undecylenic acid layer than the electrografted carboxyphenyl layer. Thus photografting and photoreaction with oxalyl chloride are simple methods for generating amine-reactive tethers on GC and PPF surfaces.

Electrochemical oxidation of catecholamines and catechols at carbon nanotube electrodes

The differences in the electrochemical oxidation of two commonly known catecholamines, dopamine and norepinephrine, and one catechol, dihydroxyphenylacetic acid (DOPAC), at three different types of carbon based electrodes comprising conventionally polished glassy carbon (GC), nitrogen-doped carbon nanotubes (N-CNTs), and non-doped CNTs were assessed. Raman microscopy and X-ray photoelectron spectroscopy (XPS) were employed to evaluate structural and compositional properties. Raman measurements indicate that N-CNT electrodes have ca. 2.4 times more edge plane sites over non-doped CNTs. XPS data show no evidence of oxygen functionalities at the surface of either CNT type. N-CNTs possess 4.0 at. % nitrogen as pyridinic, pyrrolic, and quaternary nitrogen functionalities that result in positively charged carbon surfaces in neutral and acidic solutions. The electrochemical behavior of the various carbon electrodes were investigated by cyclic voltammetry conducted in pH 5.8 acetate buffer. Semiintegral analysis of the voltammograms reveals a significant adsorptive character of dopamine and norepinephrine oxidation at N-CNT electrodes. Larger peak splittings, DeltaE(p), for the cyclic voltammograms of both catecholamines and a smaller DeltaE(p) for the cyclic voltammogram for DOPAC at N-CNT electrodes suggest that electrostatic interactions hinder oxidation of cationic dopamine and norepinephrine, but facilitate anionic DOPAC oxidation. These observations were supported by titrimetry of solid suspensions to determine the pH of point of zero charge (pH(pzc)) and estimate the number of basic sites for both CNT varieties. This study demonstrates that carbon purity, the presence of exposed edge plane sites, surface charge, and basicity of CNTs are important factors for influencing adsorption and enhancing the electrochemical oxidation of catecholamines and catechols.

Immobilization of DNA at Glassy Ccarbon Electrodes: A Critical Study of Adsorbed Layer

In this work we present a critical study of the nucleic acid layer immobilized atglassy carbon electrodes. Different studies were performed in order to assess the nature of theinteraction between DNA and the electrode surface. The adsorption and electrooxidation of DNAdemonstrated to be highly dependent on the surface and nature of the glassy carbon electrode. TheDNA layer immobilized at a freshly polished glassy carbon electrode was very stable even afterapplying highly negative potentials. The electron transfer of potassium ferricyanide, catechol anddopamine at glassy carbon surfaces modified with thin (obtained by adsorption under controlledpotential conditions) and thick (obtained by casting the glassy carbon surface with highly concentratedDNA solutions) DNA layers was slower than that at the bare glassy carbon electrode, although thiseffect was dependent on the thickness of the layer and was not charge selective. Raman experimentsshowed an important decrease of the vibrational modes assigned to the nucleobases residues,suggesting a strong interaction of these residues with the electrode surface. The hybridization ofoligo(dG)21 and oligo(dC)21 was evaluated from the guanine oxidation signal and the reduction of theredox indicator Co(phen)33+ . In both cases the chronopotentiometric response indicated that thecompromise of the bases in the interaction of DNA with the electrode surface is too strong, preventingfurther hybridization. In summary, glassy carbon is a useful electrode material to detect DNA in adirect and very sensitive way, but not to be used for the preparation of biorecognition layers by directadsorption of the probe sequence on the electrode surface for detecting the hybridization event.

Fundamental Electrochemical Properties of Carbon Nanotube Electrodes

We report on the fundamental electrochemical properties of inherently hydrophobic Multiwalled Carbon Nanotubes MWNT electrodes and acid treated MWNTs. The electrochemical response of the electrodes was investigated by cyclic voltammetry and ac impedance spectroscopy using the redox probe of (Fe(CN)6 3−/Fe(CN)6 4−, which has well‐known kinetic behaviour on carbon surfaces. Comparisons were made between the electrochemical behaviour observed at MWNT electrodes and electrochemically polished glassy carbon, GCE. Confirmation of carbon oxygen functionalities on the surface of acid treated nanotubes was accomplished by X‐ray photoelectron spectroscopy. Slow electron transfer kinetics with a peak separation larger than 200 eV, and an electron transfer resistance of approximately 370 Ω were observed on pristine MWNTs. However acid treatment was found to significantly improve the electron transfer kinetics of Fe(CN)6 −3/−4 redox couple, approaching almost reversible ET kinetics. Acid treatment modifies the charge carrier density at the surface by introducing surface states and serves to facilitate electron transfer. The better wetting properties of functionalised carbon nanotubes and the higher local density of states as compared to untreated MWNT could be responsible for favouring faster ET kinetics.

Fundamental Electrochemical Properties of Carbon Nanotube Electrodes

We report on the fundamental electrochemical properties of inherently hydrophobic Multi‐walled Carbon Nanotubes (MWNT) electrodes and acid‐treated MWNTs. The electrochemical response of the electrodes was investigated by cyclic voltammetry and AC impedance spectroscopy using the redox probe of (Fe(CN)6 3−/Fe(CN)6 4−, which has well‐known kinetic behaviour on carbon surfaces. Comparisons were made between the electrochemical behaviour observed at MWNT electrodes and electrochemically polished glassy carbon, GCE. Confirmation of carbon oxygen functionalities on the surface of acid‐treated nanotubes was accomplished by x‐ray photoelectron spectroscopy. Slow electron transfer kinetics with a peak separation larger than 200 eV, and an electron transfer resistance of approximately 370 Ω were observed on pristine MWNTs. However, acid treatment was found to significantly improve the electron transfer kinetics of Fe(CN)6 −3/−4 redox couple, approaching almost reversible ET kinetics. Acid treatment modifies the charge carrier density at the surface by introducing surface states and serves to facilitate electron transfer. The better wetting properties of functionalised carbon nanotubes and the higher local density of states as compared to untreated MWNT could be responsible for favouring faster ET kinetics.

An investigation of the capacitance dispersion on the fractal carbon electrode with edge and basal orientations

Capacitance dispersion on the fractal carbon electrode with edge and basal orientations was investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and a.c.-impedance spectroscopy. For this purpose, four types of as-received pyrolytic graphite electrode, as-received, mechanically polished, and as-activated glassy carbon electrodes were prepared with different surface irregularities and amounts of edge orientations. The apparent self-similar fractal dimensions of the carbon electrodes were determined from the analyses of AFM images based upon triangulation method. The amounts of edge orientations on the surface of the carbon electrodes were qualitatively estimated from the XPS analysis of surface acidic functional groups that were preferably formed on the edge planes by the heat treatment of the carbon electrodes. The values of the constant phase element exponent α determined from the apparent self-similar fractal dimensions did not accord with those α determined from the measured impedance spectra. Instead, they were closely related to the amounts of the edge orientations. From the results, it is indicated that the contribution of surface inhomogeneity is much higher than the contribution of the surface irregularity to the capacitance dispersion on the carbon electrode.

Electrochemical Characterization of Carbon Films with Porous Microstructures

This paper describes the structural and electrochemical characterization of porous carbon thin film electrodes formed via a recently developed film fabrication technique called glancing angle deposition (GLAD). The technique involves physical vapor deposition of thin films onto unheated substrates oriented at highly oblique angles to the vapor flux. The fabricated GLAD carbon thin film (GTF) electrodes have controllable porosity and microstructure on the 10 nanometer scale. The GTF surface structure was characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical response of the GTF electrodes was investigated by cyclic voltammetry using several redox probes with known kinetic behavior on carbon surfaces. GTF electrodes were compared to the commonly used glassy carbon (GC) electrodes in order to evaluate their electrochemical performance. Overall, the GTF electrodes exhibited well-defined, peak shape voltammograms for all the redox systems investigated. The results presented demonstrate that GTF surfaces show higher faradaic and background currents than polished GC. This is attributed to the large exposed surface area (63 cm2/cm2) of the porous film. © 2003 The Electrochemical Society. All rights reserved.

Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron‐Doped Diamond Electrodes: Effect of Solvent and Electrolyte

AbstractCyclic voltammetric measurements were made using well‐characterized microcrystalline boron‐doped diamond thin‐film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002 cm/s were observed in 0.1 M NaClO4/CH3CN, 0.1 M TBAClO4/CH3CN, and 0.1M TBAClO4/CH2Cl2, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron‐doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes.

Preparation of reproducible glassy carbon electrodes by removal of polishing impurities

This paper describes a simple and rapid electrochemical oxidative procedure that removes polishing contaminants from glassy carbon (GC) surfaces. The method involves oxidation of polished GC electrodes in basic media for short periods of time (∼10 s). Tapping mode scanning force microscopy (TM SFM), X-ray photoelectron spectroscopy (XPS) and nanoindentation surface characterization techniques were utilized to track the removal of the polishing layer. Several electrochemical characterizations of the modified GC surface were carried out to assess changes in electrode reactivity following removal of the microparticle polishing layer. Electrochemical measurements obtained on the anodized GC electrodes show a more reproducible surface relative to polished GC.

Preparation of extremely thin solid supported films of lipids by the method of electrostriction

Preparation of stable ultra thin lipid layers onto polished glassy carbon (GC) surface is reported in this work. The method of formation relies on additional thinning of wetting films by electrostriction. The possible final structure of the films, as well as, their relevance for sensor development are discussed.

Electrochemical analysis of acetaminophen using a boron-doped diamond thin film electrode applied to flow injection system

The electrochemistry of acetaminophen in phosphate buffer solution (pH 8) was studied at a boron-doped diamond (BDD) thin film electrode using cyclic voltammetry, hydrodynamic voltammetry, and flow injection with amperometric detection. Cyclic voltammetry was used to study the reaction as a function of concentration of analyte. Comparison experiments were performed using a polished glassy carbon (GC) electrode. Acetaminophen undergoes quasi-reversible reaction at both of these two electrodes. The BDD and GC electrodes provided well-resolved cyclic voltammograms but the voltammetric signal-to-background ratios obtained from the diamond electrode were higher than those obtained from the GC electrode. The diamond electrode provided a linear dynamic range from 0.1 to 8 mM and a detection of 10 μM ( S/ B≈3) for voltammetric measurement. The flow injection analysis results at the diamond electrode indicated a linear dynamic range from 0.5 to 50 μM and a detection limit of 10 nM ( S/ N≈4). Acetaminophen in syrup samples has also been investigated. The results obtained in the recovery study (24.68±0.26 mg/ml) were comparable to those labeled (24 mg/ml).

Electro-deposition as a sample preparation technique for total-reflection X-ray fluorescence analysis

A one-step sample preparation by electro-deposition for total-reflection X-ray fluorescence (TXRF) analysis has been developed using a common three-electrode arrangement with a rotating disc as the working electrode. Several elements such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Pb, As and U have been determined simultaneously in saline matrix. A special electrode tip has been constructed as a holder for the TXRF sample carrier, which consists of polished glassy carbon. The influence of parameters such as time, pH value, and trace element concentration on the deposition yield has been examined for 14 elements. From repeatability studies, the uncertainty in deposition yields at the 95% confidence level has been found to be less than 20% for most of these elements. Typical detection limits range from 5 to 20 ng/l under the experimental conditions applied here. By an appropriate choice of the reference element and by calculation of yield factors, reliable quantification can be achieved directly by internal standardization. First results obtained for the standard reference material CRM 505 are presented.

Glassy carbon electrodes: I. Characterization and electrochemical activation

Electrochemical properties of glassy carbon electrodes of two types were examined, one thermally treated at 1000°C (sample K) and another thermally treated at 2500° (sample G). Mechanically polished or electrochemically polarized electrodes were characterized in NaOH, HClO 4 and H 2SO 4 solutions by cyclic voltammetry (cv) at different sweep rates in the potential range between the hydrogen and oxygen evolution. The activity of the electrodes depended on the properties of the glassy carbon examined, as determined by both the temperature of thermal treatment and the mechanical or electrochemical pretreatment of the sample. It was noticed that both types of electrodes, when polished exhibited an increase in the double layer charge upon increasing the pH value of the solution. The cv charges, for both types of samples, increase upon anodic polarization. The higher the potential of oxidation, the more pronounced is the increase in charge, particularly in acidic solution. The increase in charge amounts from below 1 mC cm −2 for polished glassy carbon up to few hundreds of mC cm −2 for surfaces anodically polarized in acidic solution. Analysis of the dependence of voltammetric charge, as well as morphological changes of the electrode surface, on the time of oxidation suggests the existence of three stages in the electrochemical activation process. The first one occurs only once at the beginning of the activation, while the other two repeat themselves, reflecting a periodical activation and deactivation process. These stages were discussed and ascribed to a surface layer oxidation, graphite oxide layer growth and mechanical destruction of the surface. Independent surface analysis by AES, XPS and STM confirms the results obtained by electrochemical methods.

Determination of Pb and Cu by Anodic Stripping Voltammetry Using Glassy Carbon Electrodes Modified with Mercury or Mercury-Nafion Films

Two different approaches for the modification of glassy carbon electrodes using a mercury film and mercury-nafion are compared. The mixture of mercury(II) chloride solution with a nafion solution diluted in ethanol is used to coat the polished glassy carbon surface. The modified working electrodes are compared when measuring Pb and Cu in real seawater samples. An optimisation of the parameters during the formation of the films was done to obtain well-defined stripping peaks. The type of inert supporting electrolyte and the pH play an important role on the sensitivity of the measurement. Results for Pb and Cu determinations show the advantages of Hg-nafion modification as an alternative method. These advantages include a shorter modification time, the avoidance of Hg solutions during the formation of the Hg film and an improved sensitivity for Pb determination.

Electroanalytical study of sulfa drugs at diamond electrodes and their determination by HPLC with amperometric detection

Conductive boron-doped diamond thin film electrodes were examined for the electroanalysis of three sulfa drugs, sulfadiazine, sulfamerazine and sulfamethazine. Cyclic voltammetry, flow injection analysis and liquid chromatography with electrochemical detection were used to study the oxidation reactions. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for all three drugs with a signal to background (S/B) ratio of a factor of ten greater than that obtained at two types of freshly polished glassy carbon (GC) electrodes. Diamond exhibited a highly reproducible amperometric response, with a peak variation of ∼5%, even at a concentration of 100 nM. A detection limit of 50 nM and a linear dynamic range of three orders of magnitude were obtained. No fouling of the electrode was observed within the experimental period of several hours. A rapid stabilization of the background current is achieved, within 10 min after the application of the operating potential under flow conditions, unlike the case of GC electrodes, which requires more than 30 min for reasonable stabilization. We have demonstrated the application of the diamond electrode for the simple and sensitive amperometric detection of the sulfa drugs in a standard mixture after their separation with reverse-phase HPLC to produce chromatograms with a flat baseline and high reproducibility, even at concentrations as low as 100 nM.

Characterization of n-alkanethiolate monolayers adsorbed to electrochemically deposited gold nanocrystals on glassy carbon electrodes

In this work we combine electrochemical metal deposition with the self-assembly of thiolate monolayers in an effort to develop a novel method for attaching predefined functional groups to glassy carbon (GC) electrodes. Gold nanocrystals were electrochemically deposited on polished GC substrates by a potential step and subsequently modified by exposure to ethanolic solutions of n-alkanethiols. The structure of the resultant monolayers was then studied using electrochemical blocking analysis and infrared reflection absorption spectroscopy. Our analyses indicate that monolayers adsorbed to gold nanocrystals on GC adopt a more disordered structure relative to similar monolayers adsorbed to planar Au substrates. This is likely due to a high density of step sites on electrochemically deposited Au particles. Finally, we demonstrate our ability to employ a sequence of deposition and modification steps to introduce multiple functional groups on a single GC electrode.

Electrochemical oxidation of histamine and serotonin at highly boron-doped diamond electrodes.

The electrochemistry of histamine and serotonin in neutral aqueous media (pH 7.2) was investigated using polycrystalline, boron-doped diamond thin-film electrodes. Cyclic voltammetry, hydrodynamic voltammetry, and flow injection analysis (FIA) with amperometric detection were used to study the oxidation reactions. Comparison experiments were carried out using polished glassy carbon (GC) electrodes. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for histamine with a peak potential at 1.40 V vs SCE. The voltammetric signal-to-background ratios obtained at diamond were 1 order of magnitude higher than those obtained for GC electrodes at and above 100 microM analyte concentrations. A linear dynamic range of 3-4 orders of magnitude and a detection limit of 1 microM were observed in the voltammetric measurements. Well-defined sweep rate-dependent voltammograms were also obtained for 5-hydroxytryptamine (5-HT). The characteristics of the voltammogram indicated lack of adsorption of its oxidation products on the surface. No fouling or deactivation of the electrode was observed within the experimental time of several hours. A detection limit of 0.5 microM (signal-to-noise ratio 13.8) for histamine was obtained by use of the FIA technique with a diamond electrode. A remarkably low detection limit (10 nM) was obtained for 5-HT on diamond by the same method. Diamond electrodes exhibited a linear dynamic range from 10 nM to 100 microM for 5-HT determination and a range of 0.5-100 microM for histamine determination. The FIA response was very reproducible from film to film, and the response variability was below 7% at the actual detection limits.

Polycrystalline diamond electrodes: basic properties and applications as amperometric detectors in flow injection analysis and liquid chromatography

Diamond films, fabricated by chemical vapor deposition, provide electrochemists with an entirely new type of carbon electrode that meets the requirements of activity, conductivity, and stability for a wide range of applications. In this manuscript, the basic electrochemical properties of high quality diamond thin-films (3-6 μm thick) are highlighted. The films are polycrystalline, hydrogen terminated and doped with boron (ca. 10 19–10 20 cm −3). Some preliminary results using diamond in amperometric detection schemes, coupled with flow injection analysis and liquid chromatography, are presented for azide and nitrite, chlorpromazine, ascorbic acid and catecholamines. The use of diamond for the voltammetric detection of trace metal ions is also illustrated. The detector figures of merit (e.g., dynamic range, sensitivity, detection limit, response variability and response stability) for diamond are compared with freshly polished glassy carbon. Diamond exhibits as good or superior detector performance for each of these analytes. For example, the detection limit ( S/ N = 3) for chlorpromazine at diamond is 4 nM or 26 pg, and the response variability is 0.3%, while for glassy carbon the detection limit ( S/ N = 3) is 40 nM or 260 pg, and the response variability is 1%. The properties of diamond electrochemical interfaces are far from being fully understood, but the results reported herein portend the favorable possibilities for applications of diamond in electroanalysis.