Reticulated Vitreous Carbon Electrode Research Articles

Superporous agarose—Reticulated vitreous carbon electrodes for electrochemical sandwich bioassays

We report on the use of flow-through electrodes fabricated from a composite of superporous agarose (SPA) and reticulated vitreous carbon (RVC) for carrying out sandwich bioassays via a model sandwich assay scheme. The flow-through design of the SPA–RVC electrodes allows for ease in solution handling with the use of micropipettors while allowing sandwich assays to be performed on the SPA matrix inside the RVC. A sandwich bioassay was devised for detecting biotinylated bovine serum albumin (b-BSA) as a proof-of-concept scheme to demonstrate applicability of SPA–RVC electrodes to carry out sandwich assays. In this bioassay scheme, SPA–RVC electrodes with avidin molecules immobilized on the SPA matrix were incubated with low quantities of b-BSA followed by incubation with avidinylated alkaline phosphatase (av-ALP). This construct creates a sandwich bioassay whereby b-BSA is sandwiched between the two avidin complexes. Av-ALP labels captured on the bound b-BSA catalytically hydrolyze conversion of 4-aminophenylphosphate (PAPP) to electrochemically active 4-aminophenol (PAP) which is then voltammetrically detected inside the RVC. The lower concentration detection limit for b-BSA was 0.32 ± 0.1 ng mL −1 and the absolute detection limit was 32 ± 10 pg. Non-specific binding of av-ALP enzyme labels onto the avidin-activated SPA–RVC electrodes was low. Catalytic generation of PAP by non-specifically bound av-ALP occurs at a rate less than 2% of that for PAP generation by av-ALP in [(SPA-av) − (b-BSA-b) − (av-ALP)] sandwich constructs.

Preparation and characterization of superporous agarose–reticulated vitreous carbon electrodes as platforms for electrochemical bioassays

Three-dimensional flow-through electrodes were fabricated using superporous agarose (SPA) and reticulated vitreous carbon (RVC) composite materials that were suitable as a platform for sandwich assays. These SPA–RVC composite electrodes were fabricated by fitting a SPA–RVC composite cylinder inside a graphite tube and subsequently fixing the graphite tube onto a polypropylene micropipette tip. The electrode design allows for ease in reagent/washing steps involved in sandwich assay protocols and could easily be made portable. The electrode materials were characterized with respect to pore-size distribution, total free volume, ligament and bulk densities of the RVC, and physical structural characteristics. Coulometric detection of redox molecules such as K 3Fe(CN) 6 and 4-aminophenol was possible using SPA–RVC electrodes by the trapping of these redox molecules inside the SPA–RVC electrodes. Avidin affinity molecules were covalently immobilized onto the SPA matrix inside the RVC electrodes by periodate-activation followed by reductive amination. The amount of avidin immobilized inside the SPA–RVC electrodes was (5 ± 0.06) × 10 −11 mol, which was determined by saturating the avidin sites with biotinylated fluorescein (b-fluo) and subsequently determining the amount of immobilized b-fluo via a standard addition method using fluorescence spectroscopy. Non-specific binding of labeled enzymes such as biotinylated alkaline phosphatase (b-ALP) onto the SPA–RVC electrodes without avidin capture sites was determined to be less than 1% compared to the specific binding of b-ALP on avidinylated SPA–RVC electrodes.

Strategies for the determination of the convective-diffusion limiting current from steady state linear sweep voltammetry

The limiting current is an important parameter for the characterization of mass transport in electrochemical systems operating under convective-diffusion control. Four methods to determine the limiting current from current (I) vs. potential (E) plots are considered. Strategies to determine the limiting current values include: (1) direct measurement from I vs. E curves, (2) estimation from the current value at EL = ΔE/2 where ΔE is the length of the limiting current plateau, (3) evaluation of the first derivative dI/dE in the I vs. E curve and (4) from plots of E/I vs. I−1. The electrode reactions chosen to demonstrate the different strategies are: Cu(II) → Cu(I) and Cu(I) → Cu(0) in 1.5 mol dm−3 NaCl (pH 2) at a platinum rotating disc electrode and \( {\text{Fe}}({\text{CN}})^{{3 - }}_{6} \to {\text{Fe}}({\text{CN}})^{{4 - }}_{6} \) in 1 mol dm−3 NaOH at a 60 ppi reticulated vitreous carbon electrode (RVC).

Characterization of Oxidized Reticulated Vitreous Carbon for Generation of H2O2 from Flowing Acid Solutions

The oxidation of reticulated vitreous carbon (RVC) and its impact on the oxygen reduction reaction (ORR) in H2SO4 solutions has been studied and compared with that of a planar glassy carbon (GC) electrode. The oxidation process was characterized using different electrode configurations; GC (planar) and RVC electrodes both with flooded and flow-through assembly. Voltammetric techniques were used for the characterization of the ORR. Anodically oxidized GC and flooded RVC are similar in that the ORR on both electrodes gave a more defined limiting current plateau. For the flow- through porous electrode, the oxidation process caused a distribution of the oxidation extent within the bed thickness, as evident from the SEM images and X-ray photoelectron spectroscopy measurements, and only about half of the porous electrode was utilized in the oxidation process. Oxidation of RVC led to an enhancement of its electrocatalytic properties towards ORR. H2O2 production was tested at the oxidized RVC from flowing acid solutions. The oxidation of RVC resulted in higher current efficiencies and higher outlet concentrations of the H2O2 acid solutions.

Oxygen reduction on rotating porous cylinder of modified reticulated vitreous carbon

A rotating cylinder porous electrode (RCPE) of reticulated vitreous carbon (RVC) matrix was used for oxygen reduction reaction (ORR) in H2SO4 solutions. Cyclic voltammetry and hydrodynamic voltammetric techniques were used for electrochemical characterization of the ORR. Cyclic voltammograms in stationary solutions showed better performance of the anodically oxidized RVC (for periods of 1 and 5 min) for the ORR than the untreated RVC in which the first scan (ORR) after the surface treatment was of no utility, and the second scan was presented here. The hydrodynamic voltammograms obtained at the treated RCPE gave well-defined limiting current plateau with positively shifted onset potential as compared with the untreated (plain) RVC electrode. The analysis of the limiting current data on RCPE and the determination of a limiting current enhancement factor α enabled us to quantify the enhancement extent exerted by the anodic oxidation treatment. An enhancement factor of up to ∼3 was obtained at the RCPE electrode anodically oxidized for 5 min. It was found that the α slightly decreased with the rotation speed depending on the extent of anodic oxidation of RVC. This was attributed to the different mode of mass transfer (diffusion) to the interior of the micropores with different microstructure resulting from different extent of anodic oxidation. X-ray photoelectron spectroscopic and scanning electron microscopic measurements helped us to characterize the anodically oxidized RVC surface.

Characterization of oxidized reticulated vitreous carbon electrode for oxygen reduction reaction in acid solutions

The oxidation of reticulated vitreous carbon (RVC) and its impact on the oxygen reduction reaction (ORR) in H 2SO 4 solutions has been studied. The results are compared with that of a planar glassy carbon (GC) electrode. The oxidation process was characterized by using different electrode configurations, GC (planar) and RVC electrodes both with flooded (batch process) and flow-through assembly. Cyclic voltammetry, potentiodynamic and rotating ring-disk electrode voltammetry were used for the characterization of the ORR. Anodically oxidized GC and flooded RVC are similar in that the ORR on both electrodes gave a more defined limiting current plateau. For the flow-through porous electrode, the oxidation process caused a distribution of the oxidation extent within the bed thickness, as evident from the SEM images, and only about half of the porous electrode was utilized in the oxidation process. X-ray photoelectron spectroscopy (XPS) measurements confirmed the above distribution and a gradient of the oxygen-to-carbon ratio was obtained within the porous bed. Oxidation of RVC led to an enhancement of its electrocatalytic properties towards ORR. H 2O 2 production was tested at the oxidized RVC from flowing acid solutions. The oxidation of RVC resulted in higher current efficiencies and higher outlet concentrations of the H 2O 2 acid solutions.

Ozone Electrogeneration on Pt-Loaded Reticulated Vitreous Carbon Using Flooded and Flow-Through Assembly

Electrogeneration of ozone was investigated at platinum-loaded reticulated vitreous carbon (RVC). Stationary and flowing solutions, i.e., flooded and flow-through porous electrodes, respectively, were used at room temperature . The study evaluates the flow-through porous electrode for a continuous production of -aqueous solutions. was generated potentiostatically by applying a constant potential for . The flooded electrode showed a negligible current efficiency at the bare RVC compared to a value of 2.2% at the Pt-loaded RVC electrode (RVC/Pt). At the flow-through porous electrode, the effects of acid concentration and electrolyte flow rate on the concentration of generated and on the current efficiency of electrogeneration at RVC/Pt were explored. The concentration increased in the outlet stream with concentration. The current efficiency did not change significantly with the electrolyte flow rate, but the higher concentration of in the outlet stream was obtained at lower flow rates. The current efficiency remained nearly unchanged but the specific electrical energy consumption ( of ) decreased significantly with the acid concentration. The stability of the RVC/Pt electrodes was examined by measuring the time-course of the electrolysis current at a given applied potential and the scanning electron microscopy images of the electrode surfaces before and after the electrolysis.

Deposition of polyaniline on RVC electrodes: effect of substrate thickness

Polyaniline films, obtained by either chemical or electrochemical deposition on reticulated vitreous carbon (RVC), were investigated as a function of the substrate thickness. The electrochemical properties of these RVC/Pani electrodes were assessed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS), whereas the morphology of the Pani films on RVC was analyzed by scanning electron microscopy (SEM). The cyclic voltammetric results revealed that the oxidation/reduction charges for electrodeposited polyaniline decrease as the RVC thickness is increased. Conversely, the charge densities for the chemically deposited films do not present a significant dependence on the substrate thickness. Two time constants, appearing in all the EIS spectra, indicate that an ohmic drop effect within the RVC substrate affects the polymer electrodeposition and the electrochemical behavior of the obtained electrodes. Therefore, an electric equivalent circuit considering the different electrochemical environments at the outer and inner RVC surfaces was proposed to analyze the EIS data.

Electrochemical reversibility of reticulated vitreous carbon electrodes heat treated at different carbonization temperatures

Electrochemical response of ferri/ferrocyanide redox couple is discussed for a system that uses reticulated vitreous carbon (RVC) three dimensional electrodes prepared at five different Heat Treatment Temperatures (HTT) in the range of 700 °C to 1100 °C. Electrical resistivity, scanning electron microscopy and X ray Diffraction analyses were performed for all prepared samples. It was observed that the HTT increasing promotes an electrical conductivity increasing while the Bragg distance d002 decreases. The correlation between reversibility behavior of ferri/ferrocyanide redox couple and both surface morphology and chemical properties of the RVC electrodes demonstrated a strong dependence on the HTT used to prepare the RVC.

Influence of pH on Reduction of Cr(VI) at Reticulated Vitreous Carbon (RVC) and Polyaniline-modified RVC Electrode

not Available.

Development of an E-H2O2/TiO2 Photoelectrocatalytic Oxidation System for Water and Wastewater Treatment

In this study, an innovative E-H2O2/TiO2 (E-H2O2 = electrogenerated hydrogen peroxide) photoelectrocatalytic (PEC) oxidation system was successfully developed for water and wastewater treatment. A TiO2/Ti mesh electrode was applied in this photoreactor as the anode to conduct PEC oxidation, and a reticulated vitreous carbon (RVC) electrode was used as the cathode to electrogenerate hydrogen peroxide simultaneously. The TiO2/Ti mesh electrode was prepared with a modified anodic oxidation process in a quadrielectrolyte (H2SO4-H3PO4-H2O2-HF) solution. The crystal structure, surface morphology, and film thickness of the TiO2/Ti mesh electrode were characterized by X-ray diffraction and scanning electron microscopy. The analytical results showed that a honeycomb-type anatase film with a thickness of 5 microm was formed. Photocatalytic oxidation (PC) and PEC oxidation of 2,4,6-trichlorophenol (TCP) in an aqueous solution were performed under various experimental conditions. Experimental results showed that the TiO2/Ti electrode, anodized in the H2SO4-H3PO4-H2O2-HF solution, had higher photocatalytic activity than the TiO2/Ti electrode anodized in the H2SO4 solution. It was found that the maximum applied potential would be around 2.5 V, corresponding to an optimum applied current density of 50 microA cm(-2) under UV-A illumination. The experiments confirmed that the E-H2O2 on the RVC electrode can significantly enhance the PEC oxidation of TCP in aqueous solution. The rate of TCP degradation in such an E-H2O2-assisted TiO2 PEC reaction was 5.0 times that of the TiO2 PC reaction and 2.3 times that of the TiO2 PEC reaction. The variation of pH during the E-H2O2-assisted TiO2 PEC reaction, affected by individual reactions, was also investigated. It was found that pH was well maintained during the TCP degradation in such an E-H2O2/TiO2 reaction system. This is beneficial to TCP degradation in an aqueous solution.

Electrocatalytic production of hydrogen on reticulated vitreous carbon

Reticulated vitreous carbon (RVC) was used as a porous cathode for the production of hydrogen gas from flowing alkaline solution. Polarization curves were measured to evaluate the overall performance of the RVC electrode. By an aid of a mathematical model, the kinetic parameters for HER at different conditions were estimated by fitting the experimental data with the model predictions. Black nickel coatings onto the RVC porous matrix reduced the potential and consequently the electric power needed for water electrolysis. The results showed also that operating the cell at high electrolyte concentrations and/or temperatures decreases the potential required to obtain a certain rate of hydrogen production. Stable current-transient and SEM micrographs were obtained after operation of the coated electrodes for a relatively long time at high rates of hydrogen evolution. This indicated that black Ni coatings did not flack off the surface after this period.

A Comparative Study on Chemical and Electrochemical Degradation of Reactive Blue 4 Dye

The degradation of a reactive blue 4 dye in acidic solution has been compared using electrochemical reduction and oxidation at reticulated vitreous carbon electrode (RVC) and Ti/SnO2/SbOx (3%mol)/RuO2 (30%mol) electrodes and photo–Fenton method under UV irradiation. The reduction of RB4 dye at –0.6 V on RVC electrode results in 50% of color removal and up to 64% of TOC removal. The direct oxidation of RB4 dye at +1 V on RVC promotes only the oxidation of amine group and there is no color removal. On SnO2 electrode, 58% TOC was removed and the decolorization is around 100 % after 1 hour of electrolysis at 2.4 V indicating good efficiency. Best performance was obtained by photo-Fenton method that indicates 80% elimination of TOC and 100% of color removal but the method requires oxidant addition and time of rest to remove the generated residues.

Electrochemical recovery of silver from cyanide leaching solutions

In the hydrometallurgy industry cyanide solutions are the most common leaching baths used during the extraction of metals such as silver and gold. After extraction, the solution containing various cyanide species, and usually copper cyanide, has a higher concentration than the gold and silver complexes. Higher concentration of copper species may interfere during the selective recovery of precious metals. This work presents a study of the selective recovery of silver from leaching solutions mimicking those used in industry. Chemical speciation and cyclic voltammetry studies showed that copper reduction occurs at more negative potentials than silver in the cyanide leaching solutions. The cyclic voltammetry of cyanide solutions on a vitreous carbon electrode showed that copper cyanide ions modify the interface properties, lowering the overpotential required for silver reduction. A macroelectrolysis study of a simulated leaching solution (10−4 M Ag(I), 0.1 M Cu(I) in 0.5 M CN− at pH 10), was carried out in a filter press electrochemical reactor (ElectroCell AB) with a reticulated vitreous carbon electrode (RVC), nominally having 45 pores per inch and a flow rate of 5 cm3 s−1 at 25 °C. The study showed that the high copper concentration does not interfere in the selective deposition of silver.

Removal of Cd+2 from aqueous solutions onto polypyrrole coated reticulated vitreous carbon eletrodes

The development of simple methods for removal of heavy metals from aqueous samples is a relevant field of research. In this connection, the electrodeposition of the Cd+2 ion, one of the most toxic species for animals and human beings, was investigated in aerated pH 4.8 sulfuric-sulfate solutions. In potentiostatic conditions, the maximum rate of cadmium deposition at a neutral polypyrrole (PPy0) coated reticulated vitreous carbon (RVC) working electrode occurs at -3.0 V vs. the saturated calomel reference electrode (SCE). Moreover, the conversion rate depends both on the applied potential and on the mass transport regime, and, for solutions containing 10 mg L-1 of Cd2+, the highest removal efficiency achieved is 84% after 90 min of electrolysis. The concentration decay of the Cd+2 ion in the solution was monitored by anodic stripping voltammetry (ASV) at a hanging mercury drop electrode. Besides, metallic cadmium deposited onto the polypyrrole modified RVC electrode was evidenced by Scanning Electron Microscopy (SEM) analysis using the backscattered electron image (BEI) technique and by Energy Dispersive Spectrometry (EDS).

Diesel engine exhaust treatment with a pulsed streamer corona reactor equipped with reticulated vitreous carbon electrodes

Reticulated vitreous carbon (RVC) has been shown to be useful for high-voltage and ground electrodes in gas-phase pulsed streamer corona reactors. RVC disks with large macroscopic porosity are placed perpendicular to the gas flow and the main axis of a cylindrical corona reactor. This electrode geometry produces streamers that propagate in the direction of the gas flow and are uniformly distributed in the cross section of the reactor. This highly electrically conductive material has large macroscopic porosity, thus allowing for gas flow through the electrodes with low pressure drop. Previous work has considered the effects of RVC electrodes on NO/NO/sub x/ removal from various test gases containing air, water vapor, and ethylene. The present studies show removal of NO/NO/sub x/ from the exhaust of a 5 kW diesel engine. Under cold reactor operating conditions (12/spl deg/C) 81% NO and 53% NO/sub x/ could be removed at an energy yield of 4.8 g/kWh (based on NO). Furthermore, experiments with the combination of TiO/sub 2/ or /spl gamma/-Al/sub 2/O/sub 3/ catalyst particles placed in the region between the high-voltage and ground electrode disks gave NO removal at energy yields of 29 g/kWh and 9 g/kWh, respectively, at about 100/spl deg/C, and significant fractions of the nitrogen were recovered as NO/sub 3//sup -/ deposited on the catalyst surface. The RVC electrode system without catalysts was found to lead to efficient ozone production (55-70 g/kWh) in dry air at room temperature.

On the determination of limiting current density from uncertain data

The technique for determining the limiting current from I/E curves is normally simple. However, in the absence of a clearly de®ned plateau it is not straightforward. In a recent study of the concentration of nitric acid by electro-electrodialysis (membrane electrolysis), Robbins [2] plotted the normalized resistance E=I†= E=I†max against the reciprocal current density (1/I) corrected for catholyte acid concentration, in order to elucidate the cathodic reactions. He based his plot upon the work of Kuppinger et al. [3] but was unable to ®nd a theoretical basis for the apparent relationship between the minimum point in the curves and the mass transfer coecient. The purpose of this paper is twofold. First, it is to reintroduce the E=I against 1/I plot as a basis for the determination of the limiting current. Second, it is to show that the previously presented method using this approach [4] is mathematically incorrect. In fact, the authors never justi®ed their mathematical methodology but stated that the point at which the negative slope cuts the positive slope in the curve E=I against 1/I , is designated as a `limiting current density' because of its apparent relation (our emphasis) to di€usion. The point of intersection used by them will be clearly de®ned later and contrasted with other methodologies. Our proposed approach was tested for the reduction of oxygen and Fe(CN)3y 6 . The reduction of ferric cyanide ions was carried out in a commercially available laboratory electrolyser, the FM01-LC cell supplied by ICI, and oxygen reduction was carried out in a conventional ow cell constructed in our laboratory, both on a reticulated vitreous carbon electrode (RVC).

Reticulated vitreous carbon electrodes for gas phase pulsed corona reactors

A new design for gas phase pulsed corona reactors incorporating reticulated vitreous carbon (RVC) electrodes is demonstrated to be effective for the removal of nitrogen oxides from various gas mixtures containing O/sub 2/, N/sub 2/, water vapor and ethylene. The reactor consists of either a Plexiglass or glass cylindrical tube with macro-porous RVC electrodes placed perpendicularly to the cylinder axis. Streamers propagate between the RVC disks providing a uniform exposure of the flowing gas stream to the electrical discharge. This mode of operation provides for convenient reactor scale-up while maintaining the interelectrode spacing in a moderate range, thus allowing scale-up without the need for higher voltage power supplies. It is further envisioned that the reactor can be operated with multiple sets of electrodes placed in series down the length of the reactor in order to facilitate high efficiency removal of air pollutants.

Anion influence in lead removal from aqueous solution by deposition onto a vitreous carbon electrode

We investigated the electrolytic removal of Pb(II) from aqueous solutions containing different electrolytes (nitrate, chloride or sulfate), by electrolysis onto reticulated vitreous carbon electrode (RVC). The efficiency of the electrolytic process of lead removal was found to be a function of electrolyte composition. The chloride containing electrolyte, provided the highest efficiency of lead removal, while removing Pb(II) from the sulfate electrolytes turned out to be a very difficult and high energy consuming process. Cyclic voltammetry and the atomic force microscopy (AFM) were used to characterize lead deposits on RVC and fractured vitreous carbon (FVC) electrodes surface. Our study showed that in the chloride solution, a significantly larger amount of lead deposit was formed than in the sulfate electrolyte. Since the same phenomenon was observed with both electrode types, the FVC electrode is established as an appropriate laboratory model for studying the RVC, which is often used in industrial applications. AFM analysis revealed that lead deposits formed from different electrolyte solutions possess different surface morphologies, indicating different mechanism of formation or different kinds of interactions between the metal adlayer and the adsorbed anions. A highly dense lead deposit, spread all over the electrode surface, in the form of a 2-D film, was found when using the chloride-containing electrolyte. This was attributed to the surface annealing effect and the increased number of nucleation sites due to chloride coadsorption at the electrode surface. Deposits formed from the sulfate electrolyte consisted of numerous, isolated and rather small lead clusters, indicating that deposition from sulfate solutions was inhibited by the formation of the passivated salt adlayer over the lead clusters.

Polyethyleneimine-coated reticulated vitreous carbon electrode with immobilized enzymes as a substrate detector

Polyethyleneimine (PEI) was covalently coupled to carbodiimide-activated reticulated vitreous carbon (RVC). The PEI-coated RVC was activated with glutaraldehyde, and glycerol dehydrogenase and diaphorase were then immobilized. The PEI-coated RVC with immobilized enzymes functioned both as an enzyme reactor and a working electrode in an amperometric detection system where NAD +/NADH was recycled by the immobilized enzymes. The coated RVC electrode showed good properties compared to uncoated RVC, such as a long lifetime and a constant response to a series of injections in a flow-injection system, resulting in a relative standard deviation of 1.4%. The calibration graph was linear from the detection limit 0.1 μM to 2 mM NADH in the absence of recycling.