Basal Plane Pyrolytic Graphite Research Articles

Voltammetry at graphite electrodes: The oxidation of hexacyanoferrate (II) (ferrocyanide) does not exhibit pure outer-sphere electron transfer kinetics and is sensitive to pre-exposure of the electrode to organic solvents

Through theoretical modelling based upon a diffusion domain approach, we show that for a basal plane pyrolytic graphite electrode with a 10–20% surface coverage of edge plane sites, minimal differences in the voltammetric response should be expected from that of an edge plane pyrolytic graphite electrode. Further through the use of organic solvents, for the modification of the electrode surface, it is demonstrated that the voltammetry of the oxidation of ferrocyanide in aqueous solution is surface sensitive and we infer that it likely occurs through the formation of a bridging ion complex with the electrode surface. Accordingly it is suggested that the electron transfer mechanism for the oxidation of ferrocyanide at a graphite electrode should not be viewed as being outer-sphere in nature. These results have implications for voltammetric experimentation with both graphite and carbon nanotube modified electrodes.

Nanocrystalline graphite-like pyrolytic carbon film electrode for electrochemical sensing of hydrazine

Pyrolytic carbon film (PCF) electrode fabricated by a non-catalytic chemical vapor deposition (CVD) process was used as an electrochemical sensor for the detection of hydrazine. The electrode response was found to be electrocatalytic producing a reduction in the overpotential compared to other unmodified carbon-based electrodes such as glassy carbon (GC), basal-plane pyrolytic graphite (BPPG), and edge-plane pyrolytic graphite (EPPG) electrodes. The overall number of electrons involved in the electro-oxidation of hydrazine, the number of electrons involved in the rate-determining step, and diffusion coefficient of hydrazine at PCF electrode were estimated using cyclic voltammetry and chronoamperometry. The performance of PCF electrode was comparable to and in some cases even better than many chemically modified electrodes in terms of detection limit, linear dynamic range, and sensitivity. Moreover, the sensor exhibited fast response time (within 2 s), high response stability, and reproducibility. All the results indicated this sensor is suitable for hydrazine analysis.

On reproducibility of preparation of basal plane pyrolytic graphite electrode surface

The basal plane pyrolytic graphite (BPPG) electrode is widely used as a “standard” electrode for studies of electrochemical activity of graphite, graphene and carbon nanotubes. We compared here different methods for preparation of the surface of BPPG using statistical analysis of the data. We showed that including/omitting of polishing step or including/omitting of acetone washing step in the preparation procedure exhibits statistically significant difference. However, using acetone of different purities does not lead into statistically significant results. In addition, all methods with BPPG provided RSD < 10% and did not produce any outlying results.

Direct Electrooxidation of Ascorbic Acid at the Nanocrystaline Graphite‐like Pyrolytic Carbon Film Electrode

AbstractPyrolytic carbon films (PCFs) were prepared by chemical vapor deposition (CVD) at different deposition temperatures. As an example of using PCF electrode in electroanalysis, the direct electrooxidation of ascorbic acid (AA) at the PCF electrode was investigated and compared with common carbon‐based electrodes such as glassy carbon (GC), edge plane pyrolytic graphite (EPPG), and basal plane pyrolytic graphite (BPPG) electrodes. It was found that the PCF electrodes prepared under deposition temperatures higher than 1050 °C showed a higher sensitivity and lower overpotential compared to the other carbon electrodes. The electrode was successfully applied for determination of AA in real samples.

Anthraquinone functionalized carbon composite electrode: Application to ammonia sensing

A simple strategy has been used to covalently modify the glassy carbon spheres with anthraquinone moieties through the diazonium salt reduction. The derivatized glassy carbon spheres were used to modify the basal plane pyrolytic graphite electrode by immobilizing them on its surface and examining its electrochemical behaviour. The composite electrode has been used to detect trace level ammonia in the concentration range 5 × 10 −8 to 3 × 10 −5 M and it was successfully applied to detect low levels of ammonia present in natural samples like urine and soil.

Activity of carbon electrodes towards oxygen reduction in acid: A comparative study

The oxygen reduction reaction (ORR) has been investigated on a variety of carbon substrates, in acidic conditions, including glassy carbon (GC), edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and boron doped diamond (BDD). Along with these macro-sized substrates, a selection of carbon nanotube modified BPPG electrodes have also been examined. These include single walled (SWCNT), bamboo multi walled (B-MWCNT) and hollow multi walled (H-MWCNT) carbon nanotube modified BPPG. Low potential responses for ORR are found for substrates with large quantities of edge plane sites, namely EPPG and MWCNT modified BPPG. Along with being analytically significant in respect of gas sensing, these results have implications for proton exchange membrane (PEM) fuel cell catalyst supports.

Electrochemical feasibility study of methyl parathion determination on graphite-modified basal plane pyrolytic graphite electrode

A low-cost electrochemical method was developed for the determination of trace-level of methyl parathion (MP) based on the properties of graphite-modified basal plane pyrolytic graphite electrode (graphite-bppg). A combination of graphite-bppg with square-wave voltammetric (SWV) analysis resulted in an original, sensitive and selective electrochemical method for determination of MP pesticide in drinking water. The electrode was constructed and the electrochemical behavior of MP was studied. Immobilization is achieved via film modification from dispersing graphite powder in deionized water and through pipeting a small volume onto the electrode surface allowing the solvent to volatilize. The strong affinity of the graphite modifier for the phosphorous group of the MP allowed the deposition of a significant amount of MP in less than 60 seconds. The cyclic voltammetric results indicate that the graphite-bppg electrode can enhance sensitivity in current intensity towards the quasi-reversible redox peaks of the products of the cathodic reduction of the nitro group at negative potential (peak I = 0.077 V and peak II = -0.062 V) and that the cathodic irreversible peak (peak III = -0.586 V) in comparison with bare bppg electrode and is also adsorption controlled process. Under optimized conditions, the concentration range and detection limit for MP pesticide are respectively 79.0 to 263.3 μmol L-1 and 3.00 μmol L-1. The proposed method was successfully applied to MP determination in drinking water and the performance of this electrochemical sensor has been evaluated in terms of analytical figures of merit.

Triple Phase Boundary Photovoltammetry: Resolving Rhodamine B Reactivity in 4‐(3‐Phenylpropyl)‐Pyridine Microdroplets

Rhodamine B base is employed as a photoactive redox system in a liquid | liquid | electrode triple phase boundary electrochemical experiment. Microdroplets of the water-immiscible 3-(4-phenylpropyl)-pyridine (PPP) containing rhodamine B are deposited onto a basal plane pyrolytic graphite electrode surface which is then immersed into an aqueous solution containing 0.5 M phosphate buffer solution (pH 12). In cyclic voltammetry experiments, it is shown that dark reduction of rhodamine B to leuco-rhodamine B in PPP occurs in two steps--both one electron processes--and the re-oxidation occurs in a single two-electron process. Voltammetric signals are consistent with Na(+) transfer (for the first reduction step) and proton transfer (for the second reduction step) coupled to the electron transfer. A proton-driven disproportionation reaction (with k(dis)=3 mol(-1) dm(3) s(-1) at pH 12) is observed for the one-electron reduced intermediate. In the presence of light, a new photocatalysed oxidation process for the two-electron conversion of leuco-rhodamine B to rhodamine B is observed. Photoexcitation of rhodamine B is shown to trigger an effective photo-comproportionation mechanism. Quantitative insights into the dark and photomechanisms are obtained by comparison of rhodamine B and rhodamine B octadecylester and by applying an approximate numerical simulation procedure based on DigiSim.

A comparison of edge- and basal-plane pyrolytic graphite electrodes towards the sensitive determination of hydrocortisone

Electrochemical sensor employing edge-plane pyrolytic graphite electrode (EPPGE) for the sensitive detection of hydrocortisone (HC) is delineated for the first time. The electrochemical properties are investigated exercising the cyclic voltammetry and square-wave voltammetry (SWV). When equating with the bare basal-plane pyrolytic graphite electrode (BPPGE), the EPPGE gave better response towards the detection of HC both in terms of sensitivity and detection limit. The voltammetric results indicated that EPPGE remarkably enhances the reduction of HC which leads to considerable amelioration of peak current with shift of peak potential to less negative values. The difference in the surface morphology of two electrodes has been studied. Also, the EPPGE delivered an analytical performance for HC with a sensitivity of 45 nA nM −1 and limit of detection of 88 nM in the concentration range 100–2000 nM. The method has been utilized for the determination of HC in pharmaceuticals and real samples. The electroanalytical method using EPPGE is the most sensitive method for determination of HC with lowest limit of detection to date. The major metabolites present in blood plasma did not intervene with the present investigation as they did not exhibit reduction peak in the experimental range used. A comparison of results with high performance liquid chromatography (HPLC) signalizes a good agreement.

Determination of formal potential of NADH/NAD + redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes

The electrochemical regeneration of NADH/NAD + redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be − 0.365 ± 0.002 V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2 M NaClO 4/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670 mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2 M H 2SO 4 solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 10 3–10 4 M − 1 s − 1 depending on the preparation conditions of the PPS-modified electrodes.

Electrochemical Oxidation of Guanine: Electrode Reaction Mechanism and Tailoring Carbon Electrode Surfaces To Switch between Adsorptive and Diffusional Responses

The electrochemical oxidation of guanine is studied in aqueous media at various carbon electrodes. Specifically edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG), and highly ordered pyrolytic graphite (HOPG) were used, and the voltammetry was found to vary significantly. In all cases, signals characteristic of adsorbed guanine were seen and the total charge passed varied from surface to surface in the order roughened BPPG > EPPG > BPPG > HOPG. It is of note that the peak height for the EPPG electrode is less than that found for roughened BPPG; furthermore, across the series of electrodes, there is a significant decrease in peak potential with increasing density of edge plane sites present at the electrode surface. This leads us to conclude that there are two dominating and controlling factors present: (i) the density of basal plane sites on which guanine can adsorb and (ii) the density of edge plane sites necessary for the electro-oxidation of the analyte. This conclusion is corroborated through further experiments with multi- and single-walled carbon nanotubes. Adsorption was seen to be enhanced by modification of the EPPG surface with alumina particles, and as such, increased peak signals were observed in their presence. It is further reported that via the pre-adsorption of acetone onto the graphite surface that the adsorption of guanine may be blocked, resulting in a diffusional voltammetric signal. This diffusional response has been successfully modeled and gives insight into the complex -4e(-), -4H(+) oxidation mechanism; specifically, it enables explanation of the observed change in rate-determining step with scan rate. The oxidation of guanine first proceeds via a two-electron oxidation followed by a chemical step to form 8-oxoguanine, then 8-oxoguanine is then further oxidized to form nonelectroactive products. The change is mechanism is attributed to the variation in potential of the first and second electron transfer with scan rate.

Spectroscopic and thermal characterization of carbon nanotubes functionalized through diazonium salt reduction

Chemical reduction of anthraquinone diazonium chloride (Fast Red AL salt) in presence of hypophosphorous acid and carbon nanotubes results in anthraquinonyl functionalized carbon nanotubes. The surface functionalized moieties have been examined electrochemically by immobilizing them onto the surface of basal plane pyrolytic graphite electrode and studying its voltammetric behaviour. The effect of pH, and scan rate has revealed that the modified species are confined on the electrode surface. The spectroscopic characterization of the modified single walled carbon nanotubes using Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, thermogravimetric analysis and transmission electron microscopy have revealed that the modifier molecules are covalently bonded on the surface of carbon nanotubes.

Voltammetric studies of the redox mediator, cobalt phthalocyanine, with regard to its claimed electrocatalytic properties

It is widely reported in the literature that cobalt phthalocyanine (CoPC) facilitates a wide variety of redox processes. This conclusion is often made without any comparison of analytical parameters (such as sensitivity and detection limit) for the reaction at both CoPC modified and a bare unmodified electrodes. Another important issue is a lack of full and proper study of the electrochemical properties of dissolved and adsorbed CoPC before adding an analyte to the solution. It is also generally reported, without presenting convincing argument, that the nature of active form of CoPC at the surface of carbon electrodes is always a monolayer. We report a thorough electrochemical study on the solution phase and solid phase cobalt phthalocyanine with regard to its claimed electrocatalytic properties towards oxidation of nitrite. The cyclic voltammetry of cobalt phthalocyanine has been examined in dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF) at a glassy carbon (GC) electrode. In both solvents three redox couples are present: one ring based and two cobalt based processes. The aqueous voltammetry of CoPC adsorbed on basal plane pyrolytic graphite (BPPG) and edge plane pyrolytic graphite (EPPG) was also studied in phosphate buffer solution. Two couples are present: Co (II/I) and Co (III/II). Cyclic voltammetry experiments suggest that the number of electroactive adsorbed CoPC molecules on EPPG is approximately 3.5 times higher than on BPPG. The surface properties of both electrodes modified by immersing in 0.1 mM CoPC in dimethylformamide (DMF) solution were characterized by SEM and energy dispersive X-ray spectroscopy (EDS). It was observed that CoPC adsorbed on EPPG and BPPG electrodes exists as microcrystals, not as a monolayer reported in the literature for other carbon electrodes. The use of EPPG-CoPC modified electrode for sensing nitrite (NO 2 −) was also investigated. It was found that CoPC on EPPG has no influence on the oxidation of nitrite.

A Comparison of Electron Transfer Kinetics of Three Common Carbon Electrode Surfaces in Acetonitrile and in Room Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidiazonium Hexafluorophosphate: Correlation to Surface Structure and the Limit of the Diffusion Domain Approximation

AbstractWe report the comparison of electron transfer kinetic parameters of the ferrocene redox couple in both acetonitrile and in room temperature ionic liquid (RTIL) 1‐butyl‐3‐methylimidiazonium hexafluorophosphate ([C4mim] [PF6]), using edge plane pyrolytic graphite (EPPG), basal plane pyrolytic graphite (BPPG) and glassy carbon (GC) electrodes. Each electrode surface was characterized using SEM and AFM and the surface morphology was analyzed in terms of surface heterogeneity including the distribution of edge plane defects. The experimental data were modeled using both one and two dimensional simulations to correlate the electron transfer parameters obtained with the different surface structure of each electrode. Furthermore, we show that the diffusion domain approximation (commonly used to accurately simulate electron transfer kinetics at graphitic surfaces) breaks down when a BPPG electrode is used in RTIL and demonstrate the near impossibility of assigning rate constant to the basal plane surface.

Assembly of N-hexadecyl-pyridinium-4-boronic acid hexafluorophosphate monolayer films with catechol sensing selectivity

The highly water insoluble N-hexadecyl-pyridinium-4-boronic acid hexafluorophosphate is synthesised and investigated for sensor applications. This amphiphilic molecule is immobilised by evaporation of an acetonitrile solution at a basal plane pyrolytic graphite (HOPG) electrode surface and is shown to provide a monolayer film. By varying the amount of deposit partial or full coverage can be achieved. The N-hexadecyl-pyridinium-4-boronic acid hexafluorophosphate monolayer acts as an active receptor for 1,2-dihydroxy-benzene (catechol) derivatives in aqueous media. The ability to bind alizarin red S is investigated and the Langmuirian binding constant determined as a function of pH. It is shown that the immobilised boronic acid monolayer acts as sensor film for a wider range of catechols. A comparison of Langmuirian binding constants for alizarin red S (1.4 × 105 mol−1 dm3), catechol (8.4 × 104 mol−1 dm3), caffeic acid (7.5 × 104 mol−1 dm3), dopamine (1.0 × 104 mol−1 dm3), and L-dopa (8 × 103 mol−1 dm3) reveals that a combination of hydrophobicity and electrostatic interaction causes considerable selectivity effects.

Effects of thin-layer diffusion in the electrochemical detection of nicotine on basal plane pyrolytic graphite (BPPG) electrodes modified with layers of multi-walled carbon nanotubes (MWCNT-BPPG)

The oxidative electrochemistry of nicotine is measured in aqueous solution at a multi-walled carbon nanotube modified basal plane pyrolytic graphite (MWCNT-BPPG) electrode. Quantitative detection of nicotine is obtained with a limit of detection of 1.5 μM (based on 3 σ) and a linear range of at least up to 1 mM. Evidence is found for a mass transport regime that includes thin-layer (within the MWCNT layers) as well as semi-infinite (from bulk solution) diffusional signatures, adding to the growing picture that the fundamental source of the ‘electrocatalytic’ properties claimed of many porous and multi-walled carbon nanotube-based modified electrodes may, at least in some cases, be due to mass transport effects rather than electronic or structural peculiarities of the modifying layers.

Graphene modified basal and edge plane pyrolytic graphite electrodes for electrocatalytic oxidation of hydrogen peroxide and β-nicotinamide adenine dinucleotide

Graphene was cast on basal and edge plane pyrolytic graphite electrodes for electrochemical applications. The morphology of the resulting graphene modified electrode was investigated by atomic force microscopy. In cyclic voltammetric responses, both anodic and cathodic peak currents varied linearly with the square root of scan rates over the range of 25–600 mV in 0.1 M KCl containing 5 mM Fe ( CN ) 6 4 - at graphene modified basal and edge plane pyrolytic graphite electrodes, which suggests a diffusion-controlled process. The graphene modified basal and edge plane pyrolytic graphite electrodes exhibited the abilities to lower the electrooxidation potentials of β-nicotinamide adenine dinucleotide and hydrogen peroxide in comparison with bare basal and edge plane pyrolytic graphite electrodes. The electrocatalytic behavior obtained at the graphene modified basal and edge plane pyrolytic graphite electrodes may led to new applications in electroanalysis.

Hydrogen Peroxide Electroreduction at a Silver-Nanoparticle Array: Investigating Nanoparticle Size and Coverage Effects

The cathodic reduction of hydrogen peroxide displays altered electrochemical behavior between silver macro- and nanoscale electrodes. In acidic media, two parallel reduction mechanisms have been reported: “normal” and “autocatalytic”. The reduction potentials are reported in the literature versus mercury/mercurous sulfate reference electrode. The “normal” reduction of H2O2, in the presence of H+, forms water and the intermediate OH(ads), taking place at <−0.4 V. The presence of the OH(ads) allows the “autocatalytic” process to proceed at a higher rate, operating at a smaller potential of −0.1 V. We report that “autocatalysis” is absent at a silver nanoparticle (NP)-modified electrode. Moreover, experimentally obtained voltammetry at silver nanoparticle (AgNP)-modified basal plane pyrolytic graphite electrodes, for the “normal” H2O2 reduction, demonstrates a negative peak shift for decreasing NP size as well as a positive peak shift for increased surface coverage. Several factors are involved in this compl...

Effect of substrate and embedded metallic impurities of fullerene in the determination of nandrolone

A comparison of edge plane pyrolytic graphite substrate is made with other substrates like indium tin oxide, glassy carbon, gold and basal plane pyrolytic graphite as a substrate for fullerene modification for the determination of nandrolone by Osteryoung square wave voltammetry (OSWV) in phosphate buffer media. Comparative study of voltammetric response of nandrolone at untreated, purified and super-purified fullerene modified edge plane pyrolytic graphite electrode (EPPGE) is also carried out to determine the role of embedded metallic impurities of fullerene on determination of nandrolone. It is observed that EPPGE serves as best substrate among the studied for casting fullerene. The removal of embedded metals from fullerene shifts the peak potential of nandrolone to more positive potentials and peak current decreases. A linear calibration curve is obtained in the concentration range of 0.01–50 nM with a detection limit and sensitivity of 1.5 × 10 −11 M and 1.838 μA nM −1, respectively. The developed method was satisfactorily applied to the determination of nandrolone in several commercially available medicinal samples.

Improved Electrochemical Detection of Purine Nucleobases at Mechanically Roughened Edge‐Plane Pyrolytic Graphite Electrode

AbstractMechanically grinded edge‐plane pyrolytic graphite electrode (g‐PGEe) was applied in voltammetric analysis of purine nucleobases, acid‐hydrolyzed synthetic oligodeoxynucleotides and a nonhydrolyzed plasmid DNA. Properties of the mechanically grinded electrodes in these analytical applications were compared with some other carbon electrode types. We show that the electrode surface grinding with 15‐μm SiC particles resulted in a remarkable improvement of oxidation signals of purine bases with no addition of copper ions. Addition of the copper ions, causing a strong enhancement of the purine oxidation responses at fine‐polished carbon electrodes, had only small effect on the purine signals at the g‐PGEe. On the other hand, the g‐PGEe appeared less suitable for the ex situ AdTS voltammetric measurements of nonhydrolyzed plasmid DNA, compared to freshly peeled basal plane pyrolytic graphite electrode.