Carbon Disk Research Articles

Nonenzymatic amperometric sensor for ascorbic acid based on hollow gold/ruthenium nanoshells

We report a new nonenzymatic amperometric detection of ascorbic acid (AA) using a glassy carbon (GC) disk electrode modified with hollow gold/ruthenium (hAu–Ru) nanoshells, which exhibited decent sensing characteristics. The hAu–Ru nanoshells were prepared by the incorporation of Ru on hollow gold (hAu) nanoshells from Co nanoparticle templates, which enabled AA selectivity against glucose without aid of enzyme or membrane. The structure and electrocatalytic activities of the hAu–Ru catalysts were characterized by spectroscopic and electrochemical techniques. The hAu–Ru loaded on GC electrode (hAu–Ru/GC) showed sensitivity of 426μAmM−1cm−2 (normalized to the GC disk area) for the linear dynamic range of <5μM to 2mM AA at physiological pH. The response time and detection limit were 1.6s and 2.2μM, respectively. Furthermore, the hAu–Ru/GC electrode displayed remarkable selectivity for ascorbic acid over all potential biological interferents, including glucose, uric acid (UA), dopamine (DA), 4-acetamidophenol (AP), and nicotinamide adenine dinucleotide (NADH), which could be especially good for biological sensing.

Invited Commentary

This article reminds us of a disaster in cardiac surgery [1]. The first Björk-Shiley valve was implanted in 1969. In 1979 a convexo-concave disc was developed, and in 1980 the opening angle was increased to 70°. A free-floating pyrolite carbon disc was suspended in a stellite cage, constrained within the device by inlet and outlet struts. The outlet strut was welded to the prosthesis flange [2]. During the premarket trial, catastrophic failure occurred from outlet strut fractures. An increase in the strut clearance apparently eliminated the problems.

A Comparative Study Between Two Different Conventional Working Electrodes for Detection of Δ9-Tetrahydrocannabinol Using Square-Wave Voltammetry: a New Sensitive Method for Forensic Analysis

Marijuana is a widely consumed illicit drug. Therefore, drug dealers have sought new ways to mask its forensic (spot test) analysis. In this article we describe a methodology for delta-9-tetrahydrocannabinol (Δ9-THC) detection by square-wave voltammetric (SWV) analysis in organic medium (N,N-dimethylformamide) using tetrabutylammonium tetrafluoroborate (TBATFB) as supporting electrolyte, and glassy carbon and platinum disc as working electrode. Applying a potential of -0.5 ± 0.01 V vs. Ag/AgCl, KCl(sat), we detected a well-defined anodic peak current after the pre-concentration step; Δ9-THC detection presented linear dependence at concentrations ranging from 1.0 × 10-9 mol L-1 to 2.2 × 10-8 mol L-1, with a linear correlation coefficient 0.999 and a detection limit of 6.2 × 10-10 mol L-1, using the glassy carbon disc working electrode. These results confirm that optimized SWV technique using glassy carbon disc working electrode enables qualitative analysis of Δ9-THC at concentrations higher than 1.0 nmol L-1.

Block copolymer-templated nitrogen-enriched nanocarbons with morphology-dependent electrocatalytic activity for oxygen reduction

Binder-free films of nitrogen-enriched nanocarbons, prepared by the pyrolysis of polyacrylonitrile-block-poly(n-butyl acrylate) copolymer drop-casted on glassy carbon disk electrode, exhibited high electrocatalytic activity for the oxygen reduction reaction (ORR), matching that of Pt-based electrocatalyst. Dependence of the activity on pyrolysis temperature revealed that it is governed by the interplay of nitrogen content and electrical conductivity of the material. It was demonstrated that a nanocarbon formed by pyrolysis at 800 °C provided both large number of electrons transferred and high kinetic current density. ORR performance has been shown to critically depend on the presence of a nanoporous structure, suggesting that it facilitates high density and accessibility of catalytic sites, such as nitrogen-terminated edges of nanographitic domains.

Characterization and kinetic study of a nanostructured rhodium electrode for the hydrogen oxidation reaction

The hydrogen oxidation reaction was studied on a nanostructured rhodium electrode at different rotation rates. The electrode was prepared via sputtering on a glassy carbon disc support and it was characterized by X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and cyclic voltammetry, which allowed verifying the nanostructured morphology and the absence of any phase other than metallic rhodium. The real surface area was evaluated by CO stripping voltammetry. Experimental current density (j) – overpotential (η) curves of the hydrogen oxidation reaction were obtained in the range −0.015 V ≤ η ≤ 0.25 V at different rotation rates in sulphuric acid solution. They were correlated by kinetic expressions derived from the Tafel–Heyrovsky–Volmer mechanism and thus the kinetic parameters were evaluated. It was verified that over this overpotential region the reaction proceeds through the simultaneous occurrence of the Tafel–Volmer and the Heyrovsky–Volmer route.

Determination of Diphenylarsinic Acid, Phenylarsonic Acid and Inorganic Arsenic in Drinking Water by Graphite-furnace Atomic-absorption Spectrometry after Simultaneous Separation and Preconcentration with Solid-phase Extraction Disks

A simple method of graphite-furnace atomic-absorption spectrometry (GFAAS) after solid-phase extraction (SPE) was developed for the determination of diphenylarsinic acid (DPAA), phenylarsonic acid (PAA), and inorganic arsenic (iAs) in drinking water. This method involves the simultaneous collection of DPAA, PAA, and iAs using three stacked SPE disks, i.e., an Empore SDB-XD disk (the upper layer), an activated carbon disk (the middle layer), and a Cation-SR disk loaded with Zr and Ca (ZrCa-CED; the lower layer). A 200-mL aqueous sample was adjusted to pH 3 with nitric acid and passed through the SPE disks at a flow rate of 15 mL min(-1), to concentrate DPAA on the SDB-XD disk, PAA on the activated carbon disk, and iAs on the ZrCa-CED. The As compounds were eluted from the disks with 10 mL of ethanol containing 0.5 mol L(-1) ammonia solution for DPAA, 20 mL of 1 mol L(-1) ammonia solution for PAA, and 20 mL of 6 mol L(-1) hydrochloric acid for iAs. The eluates of DPAA, PAA, and iAs were diluted to 20, 25, and 25 mL, respectively, with deionized water, and then analyzed by GFAAS. The detection limits of As (three-times the standard deviation (n = 3) of the blank values) were 0.13 and 0.16 μg L(-1) at enrichment factors of 10 and 8, respectively, using a 200-mL water sample. Spike tests with 2 μg (10 μg L(-1)) of DPAA, PAA, and iAs in 200 mL of tap water and bottled drinking water showed good recoveries (96.1-103.8%).

The Electrode as Organolithium Reagent: Catalyst-Free Covalent Attachment of Electrochemically Active Species to an Azide-Terminated Glassy Carbon Electrode Surface

The reaction of a lithium acetylide-ethylenediamine complex with azide-terminated glassy carbon surfaces affords 1,2,3-triazolyllithium surface groups that are active toward covalent C-C coupling reactions, including salt metathesis with an aliphatic halide and nucleophilic addition at an aldehyde. Surface ferrocenyl groups were introduced by reaction with (6-iodohexyl)ferrocene; the voltammetry of electrode samples shows narrow, symmetric peaks indicating uniform attachment. X-ray photoelectron and reflectance infrared spectroscopic data provide further support for the surface-attached products. Formation of the 1,2,3-triazolyllithium linkage requires neither a catalyst nor a strained alkyne. Coverages obtained by this route are similar to those obtained by the more common Cu(I)-catalyzed alkyne-azide coupling (CuAAC) of ethynylferrocene with surface azides. Preconditioning of the glassy carbon disk electrodes at ambient temperature under nitrogen affords coverages comparable to those reported with preconditioning at 1000 °C under hydrogen/nitrogen.

Fourier‐Transformed Large‐Amplitude AC Voltammetric Study of Tetrathiafulvalene (TTF): Electrode Kinetics of the TTF0/TTF.+ and TTF.+/TTF2+ Processes

AbstractLarge‐amplitude Fourier‐transformed (FT) AC voltammetry was used at high frequency to study the electrode kinetics of tetrathiafulvalene (TTF), its radical cation TTF.+ and that of the dication TTF2+ in acetonitrile (0.1 M Bu4NPF6). The two oxidized forms were prepared by quantitative bulk electrolysis of TTF under dry‐box conditions. A high frequency of 233 Hz was used at glassy carbon (GC) and platinum (Pt) macro disk electrodes to enhance the kinetic sensitivity and hence upper limit of the measurable heterogeneous charge transfer rate constant (k0). Difficulties associated with the use of high frequencies at macro disk electrodes are discussed. Comparison of experimental data with simulations is used to extract k0 and other parameters for each of the TTF0/.+ and TTF.+/2+ processes from both reduction and oxidation perspectives. k0 values for TTF0/.+and TTF.+/0 processes are ≥1.0 cm s−1 and consequently regarded as reversible under the AC conditions used. However, the significantly slower quasi‐reversible behaviour observed for the TTF.+/2+ redox couple, with k0 being 0.3±0.05 cm s−1, can be precisely estimated.

Electrochemical control of the standard potential of solid-contact ion-selective electrodes having a conducting polymer as ion-to-electron transducer

This work addresses the well-known problem of variations in the standard potential (E°) of solid-contact ion-selective electrodes (SC-ISEs) that have a conducting polymer (CP) as ion-to-electron transducer covered by a polymeric ion-selective membrane. Poly(3,4-ethylene dioxythiophene) doped with poly(sodium 4-styrenesulfonate), i.e. PEDOT(PSS), was electrodeposited on glassy carbon (GC) disk electrodes and used as the solid contact for three different types of PVC-based membranes in order to elucidate the possibility to electrochemically control E° for this type of SC-ISE. The GC/PEDOT(PSS) electrode was thus coated with potassium-selective membranes with and without the lipophilic salt tetradocedylammonium tetrakis(4-clorophenyl)borate (ETH-500) and by a cation-sensitive membrane without ionophore. The results show that the standard potential of the studied types of SC-ISEs can be shifted by applying a potential that deviates from the open-circuit potential of the electrode in the chosen electrolyte solution or by applying current pulses in the nA range.

Mechanistic Studies of Zinc Electrodeposition from Deep Eutectic Electrolytes

Deep eutectic electrolytes have been suggested as alternatives to classical room temperature ionic liquids and been used for the electrodeposition of metals. We have investigated the electrodeposition of zinc from a Lewis-basic choline chloride/ethylene glycol deep eutectic solvent containing ZnCl2. Raman spectroscopy confirmed the presence of the [ZnCl4]2− ion in the electrolyte that was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes. The formation of a dissolved, intermediate reducible zinc species Z during the cathodic sweep is proposed to account for the unusual zinc electrodeposition behavior observed in the deep eutectic electrolyte in agreement with the effect of rotation rate, cathodic switching potential and potential sweep rate on the deposition current in RDE voltammetry. The zinc electrodeposition behavior with sodium ethoxide added to the deep eutectic solvent supports the suggestion that Z is a complex of Zn2+ and deprotonated components of the solvent. The absence of a current plateau in RDE experiments with ethoxide containing electrolyte is thought to be the result of a potential dependent blocking of the reduction of Z by a layer adsorbed on the electrode.

Characterization of nanostructured allophane clays and their use as support of iron species in a heterogeneous electro-Fenton system

Nanostructured allophane clays supported with iron oxide (AlSi2Fe6) were characterized by X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy showing the presence of both Fe3+ and Fe2+ species on the allophane surface. A glassy carbon disk (GC) modified with a film obtained by the deposition of drops of a dispersion formed by graphite and AlSi2Fe6 in water was used as working electrode in a heterogeneous electro-Fenton system (HE-Fenton) for the oxidation of atrazine. The effect of the initial pHs and the proportion of AlSi2Fe6/graphite in the mixture were studied and compared with the heterogeneous Fenton process. The HE-Fenton system using AlSi2Fe6-GC electrodes showed higher efficiency towards the oxidation of atrazine than the heterogeneous Fenton one; mainly due to the continuous and simultaneous electro-regeneration of iron species (Fe3+/Fe2+) and electro-generation of hydrogen peroxide by the oxygen reduction process. The degradation of atrazine in this HE-Fenton system reached almost 100% at pH3.0 after 8h, whereas at more neutral pH (~6) a 76% of degradation was obtained. Two reaction products were identified by HPLC: desethyl-atrazine (DEA) and desethyl-desisopropyl-atrazine (DEIA).

Use of micro‐Raman spectrometry coupled with scanning electron microscopy to determine the chemical form of uranium compounds in micrometer‐size particles

In the frame of nuclear safeguards, knowledge of the chemical form (stoichiometry) of the uranium compounds present in the micrometric particulate material sampled by wiping surfaces in an inspected nuclear facility may point out the industrial process implemented in the installation. Micro‐Raman spectroscopy (MRS) coupled with scanning electron microscopy (SEM) has been used for the first time to analyze micrometer‐size particles of various uranium oxides [UO2, U3O8, UO3, and UO4 · 4(H2O)] deposited on carbon disks. Uranium particles are detected by means of SEM, and Raman analysis is then directly carried out inside the SEM measurement chamber without moving the carbon disk from SEM to MRS. When particles are deposited on appropriate carbon disks (sticky carbon tapes), despite a loss of signal‐to‐noise ratio of about an order of magnitude with regard to the stand‐alone MRS, all uranium oxides are successfully identified in particles by in‐SEM Raman analysis, obtaining similar characteristic bands as the ones obtained with the stand‐alone MRS. Moreover, with the SEM–MRS coupling, particles as small as 1 µm can be analyzed, whereas, without the SEM–MRS coupling, only particles larger than ~5 µm are efficiently analyzed, after localization inside the SEM, transfer of the sample holder into the MRS, and relocation of the particles inside the MRS. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Antioxidant activities and radical scavenging activities of flavonoids studied by the electrochemical methods and ESR technique based on the novel paramagnetic properties of poly(aniline-co-5-aminosalicylic acid)

Four kinds of flavonoid, viz. flavanone naringenin, Flavone apigenin, flavonol kaempferol, and flavanol (+)-catechin, are used to investigate their antioxidant and radical scavenging activitis in the water-methanol solution of pH 6.3, using the electrochemical methods and electron spin resonance (ESR) technique. Poly(aniline-co-5-aminosalicylic acid) (PAASA) is first used as a radical source that was polymerized on a reduced graphene oxide (RGO)/glassy carbon (GC) disk or on the RGO/graphite fiber electrode. The assessment of the antioxidant activities is performed using both cyclic voltammetry and the open circuit potential measurement. On the basis of results from both electrochemical mathods, the order of the antioxidant actitvities of flavonoids is as follows: (+)-catechin>kaempferol>apigenin>naringeninHowever, the difference in the antioxidant activities between naringenin and apigenin is very small. On the basis of the ESR signal intensities of PAASA, the order of the radical scavenging activities of flavonoids is in good agreement with that of the above antioxdant activities.Three oxidation peaks on the cyclic voltammograms of (+)-catechin are first detected, which gives us a deep insight into the oxidation mechanism of (+)-catechin.

Development of a production target for FRIB: thermo-mechanical studies

One of the challenges for the Facility for Rare Isotope Beams (FRIB) is the development of a high power target capable of rare isotope production by projectile fragmentation and in-flight separation at primary beam powers of up to 400 kW and at beam energies of 200 MeV/u for uranium. A small beam spot is required to achieve a high resolution in fragment separation which implies high power densities in the target. For FRIB a multi-slice rotating solid carbon disk was selected as the technical baseline concept. This paper presents the results from a number of critical experimental studies on the thermo-mechanical behavior of such a target. These studies were accompanied by extensive simulations in support of the development of a single-slice target. As a final step, a multi-slice 50 kW target that is a prototype for the FRIB production target was designed, built, and mechanically tested prior to beam tests to be performed.

Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene) doped with sulfonated calixarenes and sulfonated calixarene–fullerene complexes

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically deposited on glassy carbon (GC) disk electrodes using aqueous solutions containing 3,4-ethylenedioxythiophene (EDOT) and sulfonated calixarenes or fullerene-sulfonated calixarene (C60–calixarene) complexes. The EDOT monomer was added to aqueous sulfonated calixarene solutions with and without C60 and from these solutions PEDOT(calixarene) and PEDOT(C60–calixarene) films were electrochemically deposited on GC disk electrodes. The electrochemical properties of GC/PEDOT(C60–calixarene) were compared with those of GC/PEDOT doped with other ions, both in aqueous and organic electrolyte solutions using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV measurements carried out on GC/PEDOT(C60–calixarene) in 0.1M aqueous KCl solution showed a reduction peak at ca. −0.55V vs. Ag/AgCl/3M KCl only during the first potential scan. This was attributed to the irreversible reduction of C60 to C60− inside the PEDOT film. This additional reduction peak was, however, not observed when recording the CVs in organic solution, indicating that C60 was dissolved from the PEDOT film into the organic electrolyte solution, that is a good solvent for C60. When performing CV measurements in an organic electrolyte solution containing C60, all GC/PEDOT electrodes with various doping ions and bare GC electrodes showed a reversible reduction peak characteristic for the C60/C60− redox couple. Interestingly, the peak potential and the shape of the reoxidation peak for the fulleride anion (C60−) on GC/PEDOT in the organic electrolyte solution were found to depend on the PEDOT film thickness. The electrochemical properties of GC/PEDOT(C60–calixarene) were compared further to those of GC/PEDOT(calixarene) by fitting EIS data to equivalent electrical circuits and the morphology was studied by scanning electron microscopy.

The Effect of PtRuIr Nanoparticle Crystallinity in Electrocatalytic Methanol Oxidation.

Two structural forms of a ternary alloy PtRuIr/C catalyst, one amorphous and one highly crystalline, were synthesized and compared to determine the effect of their respective structures on their activity and stability as anodic catalysts in methanol oxidation. Characterization techniques included TEM, XRD, and EDX. Electrochemical analysis using a glassy carbon disk electrode for cyclic voltammogram and chronoamperometry were tested in a solution of 0.5 mol L−1 CH3OH and 0.5 mol L−1 H2SO4. Amorphous PtRuIr/C catalyst was found to have a larger electrochemical surface area, while the crystalline PtRuIr/C catalyst had both a higher activity in methanol oxidation and increased CO poisoning rate. Crystallinity of the active alloy nanoparticles has a big impact on both methanol oxidation activity and in the CO poisoning rate.

Discrimination of Inner- and Outer-Sphere Electrode Reactions by Cyclic Voltammetry Experiments

A laboratory experiment for undergraduate students who are studying homogeneous and heterogeneous electron-transfer reactions is described. Heterogeneous or electrode reaction kinetics can be examined by using the electrochemical reduction of three FeIII/FeII redox couples at platinum and glassy carbon disk electrodes. Cyclic voltammetric measurement is suitable for determining the electrode-reaction rate constants. The dependence of the rate constant on the electrode materials enables the students to discriminate and discuss the mechanism of the electrode reaction. The experiment is completed in a 5-h laboratory period for pairs of students in analytical chemistry lab class. This material is also suitable for an inorganic chemistry lab class.

Sensitive capillary electrophoretic profiling of nicotine and nornicotine in mushrooms with amperometric detection

A highly sensitive capillary electrophoretic profiling of nicotine (NIC) and nornicotine (NNIC) was developed and applied to mushrooms with amperometric detection (AD). Effects of the experimental factors including detection potential, separation parameters, and sample pretreatment conditions were investigated. Under the optimal conditions, the electrophoretic analysis of NIC and NNIC was achieved within 8 min on a pencil carbon disc working electrode at 0.95 V, which was lower than those reported previously. Good calibration curves were obtained in 0.01-2.0 μg/mL and 0.02-3.0 μg/mL with the LOD of 2 ng/mL and 5 ng/mL for NIC and NNIC, respectively. The feasibility of the resultant method was verified. Average recoveries of different fortified levels ranged in 80.7-86.0% and 94.0-98.6% for NNIC and NIC were gained, respectively. Applied to a range of mushrooms (Boletus edulis and Lentinus edodes), the NIC contained naturally was successfully found in the level of 19.71-79.20 μg/kg. The results obtained with CE-AD method were acceptable and close to that of HPLC-MS.

Gold, Carbon, and Aluminum Low-Reflectivity Compact Discs as Microassaying Platforms

Compact disc (CD) surface modification with different reflective materials offers new working perspectives as bioanalytical platforms. The potential of gold, carbon, and aluminum low-reflectivity compact discs as a substrate for microassaying is presented. CD polycarbonate bases were coated with these reflecting materials, maintaining optical properties. Probes immobilization onto reflective layers was studied by both passive adsorption and covalent linking. Different chemical modifications were made on substrates to provide functional groups capable of anchoring probes with primary amines covalently. Thus, self-assembled monolayers were performed by chemisorption of 11-mercaptoundecanoic acid on gold surfaces, and silanization with N-(trimethoxysilylpropyl)ethylenediamine triacetic acid on aluminum to provide a carboxylic acid functional group. Carbon oxidation with oxygen plasma afforded similar functionalization on the discs coated with this material. Performance of the studied materials as reflective layers was evaluated, and as proof of concept, a microimmunoassay for a neurotoxic compound was studied on the three surfaces. The results show the possibility of doing assays on this new supports with good analytical performances while maintaining discs' optical and mechanical properties to be read by a CD player.

Mechanistic Studies of Zinc Electrodeposition from Deep Eutectic Electrolytes

Deep eutectic electrolytes have been suggested as alternatives to classical room temperature ionic liquids and been used for the electrodeposition of metals. We have investigated the electrodeposition of zinc from a Lewis-basic choline chloride/ethylene glycol deep eutectic solvent containing ZnCl2. The system was examined by cyclic voltammetry at static and rotating glassy carbon disc electrodes. The formation of a dissolved, intermediate species Z during the cathodic sweep is proposed to account for the observed deposition behaviour in the deep eutectic electrolyte in agreement with the effect of rotation rate on the deposition current in RDE voltammetry. The zinc electrodeposition behaviour with sodium ethoxide added to the deep eutectic solvent supports the suggestion that Z is a complex of Zn2+ and deprotonated components of the solvent. The absence of a plateau current in RDE experiments points to the potential dependent blocking of the reduction of Z by an adsorbed layer.