Preparation of boron-doped diamond nanowires and their application for sensitive electrochemical detection of tryptophan

The paper reports on the fabrication and electrochemical investigation of boron-doped diamond nanowires (BDD NWs) electrodes. The nanowires were obtained directly from highly doped polycrystalline diamond substrates using reactive ion etching (RIE) with oxygen plasma. The technique does not require any complicated processing steps such as mask deposition or template removal. The influence of the surface state on the electrochemical characteristics is discussed. The interface with the most favourable electrochemical response is investigated for the detection of tryptophan using differential pulse voltammetry. A detection limit of 5 × 10^?7 M was obtained on oxidized BDD NWs, as compared to 1 × 10^?5 M recorded on planar oxidized boron-doped diamond interfaces.     

Synthetic boron-doped carbonado,a new electrode material: synthesis in C–metal–B growth systems aimed at the lowering of the synthesis temperature without loss of electrochemical activity

New electrode material—boron-doped synthetic carbonado (bulk polycrystalline diamond)—was synthesized at high pressures and high temperatures in the C–metal (Co, Ni, or Fe) –B growth systems. The metal borides were used as the growth medium-forming substances for graphite-to-diamond transformation at a temperature of ~?1300 °C and pressure of 8 GPa. For comparison, etalon carbonado-type electrode with nearly limiting concentration of boron in diamond was synthesized by subjecting the mixture of amorphous boron with graphite to much higher temperatures (2200–2500 °C) under the same pressure. Despite the lower content of boron in diamond synthesized in the presence of metal borides, these new boron-doped carbonado electrodes are not inferior to the etalon compact in their electrochemical activity, as judging by the onset potential of anodic chlorine evolution from KCl solution. The presence of metal-containing structural defects in boron-doped diamond matrix is supposed to be responsible for the somewhat enhanced catalytic activity of the electrodes. High-pressure synthesis of bulk metal-modified boron-doped diamond opens a new avenue in the development of superior functional electrode materials.     

Carbon nanotube and diamond as electrochemical detectors in microchip and conventional capillary electrophoresis

As two important polymorphs of carbon, carbon nanotube (CNT) and diamond have been widely employed as electrode materials for electrochemical sensing. This review focuses on recent advances and the key strategies in the fabrication and application of electrochemical detectors in microchip and conventional capillary electrophoresis (CE) using CNT and boron-doped diamond. The subjects covered include CNT-based electrochemical detectors in microchip CE, CNT-based electrochemical detectors in conventional CE, boron-doped diamond electrochemical detectors in microchip CE, and boron-doped diamond electrochemical detectors in conventional CE. The attractive properties of CNT and boron-doped diamond make them very promising materials for the electrochemical detection in microchip and conventional CE systems and other microfluidic analysis systems.     

Sonoelectrochemistry at highly boron-doped diamond electrodes: silver oxide deposition and electrocatalysis in the presence of ultrasound

The use of boron-doped diamond has a considerable impact in electrochemistry owing to the wide potential range accessible, low background currents, extreme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that, although the electrodeposition of silver metal is known to yield very poorly adhering films with a poor electrical contact, a silver oxysalt deposit formed on anodically pre-treated diamond surfaces adheres strongly with good electrical contact. The deposit is stable even in the presence of ultrasound. Voltammetric and XPS studies reveal that the silver oxide deposit, in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative potential. The silver oxysalt Ag₇O₈NO₃, deposited onto two types of boron-doped diamond electrodes, a 50 μm thick polycrystalline thin film deposited on a tungsten substrate and a polished free standing diamond plate, is shown to act as an electrocatalyst for oxygen evolution and for the oxidation of toluene. This development opens up the possibility of boron-doped diamond being applied as an inert and conducting substrate material for a wide range of oxidic materials, which can then be utilised as active electrocatalysts at high applied potentials. Received: 17 March 2000 / Accepted: 10 April 2000     

Fabrication and electrochemical behaviour of vertically aligned boron-doped diamond nanorod forest electrodes

Vertically aligned boron-doped diamond nanorod forests (BDDNF) were successfully fabricated by depositing a diamond film onto silicon nanowires (SiNWs) using hot filament chemical vapor deposition (HFCVD). The boron-doped diamond nanorods were characterized by Raman spectroscopy and scanning electron microscopy (SEM). The BDDNF obtained from the SiNWs on the silicon wafer could be directly used as an electrode and its electrochemical behaviour is discussed here. Compared to a flat boron-doped diamond (BDD) electrode, the BDDNF electrode showed high sensitivity in the amperometric detection of adenine.     

Electrochemical evaluation and determination of antiretroviral drug fosamprenavir using boron-doped diamond and glassy carbon electrodes

Fosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H₂SO₄ and phosphate buffer at pH 2.0 which allow quantitation over a 4 × 10⁻⁶ to 8 × 10⁻⁵ M range using boron-doped diamond and a 1 × 10⁻⁵ to 1 × 10⁻⁴ M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods.     

Amperometric determination of chemical oxygen demand using boron-doped diamond (BDD) sensor

A new application of boron-doped diamond (BDD) electrode was developed for detecting chemical oxygen demand (COD) by amperometric method. The effects of some basic experimental parameters including pH and applied potential on the response of the BDD electrode were investigated and the optimal operating conditions were obtained. In the COD tests of standard samples, a wide linear range of 20–9000 mg l⁻¹ COD and a low detection limit of 7.5 mg l⁻¹ COD were well established with the present approach. Additionally, the BDD sensor was successfully employed to determine the COD of real samples from various chemical or pharmaceutical wastewaters and the performance still kept stable after over 400 measurements. The results obtained indicated that, as compared with the conventional COD determination techniques, the proposed sensor was an environmentally friendly method with the advantages of short analysis period, simplicity, and no requirement of complicated sample pretreatment even for a sample containing relatively high concentration of organic pollutants.     

Electroanalysis of tetracycline using nickel-implanted boron-doped diamond thin film electrode applied to flow injection system.

The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 microM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.     

Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction

Electrochemical oxidation of ammonia (NH₃ and NH₄ ⁺ ) on boron-doped diamond (BDD) electrode was studied using differential electrochemical mass-spectrometry (DEMS) and chronoamperometry. Electro-oxidation of ammonia induces inhibition of the oxygen evolution reaction (OER) due to adsorption of the ammonia oxidation products on the BDD surface. The inhibition of the OER enhances ammonia electro-oxidation, which becomes the main reaction. The amino radicals, formed during ammonia oxidation, trigger a reaction chain in which molecular oxygen dissolved in solution is involved in the ammonia electro-oxidation. Nitrogen, nitrous oxide, and nitrogen dioxide were detected as the ammonia oxidation products, with nitrogen being the main gaseous product of the oxidation.     

Electrochemically induced mineralization of organics by molecular oxygen on boron-doped diamond electrode

The complete mineralization of organic pollutants present in wastewater is usually achieved via thermally activated oxygen/air. This process occurs at high temperatures and pressures (300 °C, 200 atm) and often gives small amount of acetic acid as a final product. In this work, we demonstrate using acetic acid as a model compound that organic molecules can be activated electrochemically such that they react at room temperature with oxygen, resulting in mineralization of even acetic acid present in 1 M HClO₄ supporting electrolyte. This electrochemically induced activation occurs during anodic polarization of boron-doped diamond electrodes (BDD) in air/oxygen-saturated solutions. The direct evidence for this process was found during electro-oxidation of acetic acid saturated with isotopically labelled ¹⁸O₂ resulting in evolution of C¹⁸O₂ and C¹⁶O¹⁸O. We suggest that the mechanism of activation on BDD is initiated by hydroxyl radicals formed on the electrode surface.     

Fast electrochemical triple-interface processes at boron-doped diamond electrodes

Two important mechanisms for electron transfer processes at boron-doped diamond electrodes involving the oxidation of tetramethylphenylenediamine (TMPD) dissolved in aqueous solution and the oxidation of tetrahexylphenylenediamine (THPD) deposited in the form of microdroplets and immersed into aqueous eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows the equation: Remarkably slow heterogeneous kinetics at a H-plasma-treated boron-doped diamond electrode are observed, consistent with a process following a pathway more complex than outer-sphere electron transfer. At the same boron-doped diamond electrode surface a deposit of THPD undergoes facile oxidation following the equation: This oxidation and re-reduction of the deposited liquid material occurs at the triple interface organic droplet|diamond|aqueous electrolyte and is therefore an example of a facile high-current-density process at boron-doped diamond electrodes due to good electrical contact between the deposit and the diamond surface. Received: 3 February 2000 / Accepted: 18 February 2000     

Electroanalytical investigation and determination of pefloxacin in pharmaceuticals and serum at boron-doped diamond and glassy carbon electrodes

The anodic behavior and determination of pefloxacin on boron-doped diamond and glassy carbon electrodes were investigated using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. In cyclic voltammetry, pefloxacin shows one main irreversible oxidation peak and additional one irreversible ill-defined wave depending on pH values for both electrodes. The results indicate that the process of pefloxacin is irreversible and diffusion controlled on boron-doped diamond electrode and irreversible but adsorption controlled on glassy carbon electrode. The peak current is found to be linear over the range of concentration 2 × 10⁻⁶ to 2 × 10⁻⁴ M in 0.5 M H₂SO₄ at about +1.20 V (versus Ag/AgCl) for differential pulse and square wave voltammetric technique using boron-doped diamond electrode. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. Selectivity, precision and accuracy of the developed methods were also checked by recovery studies. The procedures were successfully applied to the determination of the drug in pharmaceutical dosage forms and humans serum samples with good recovery results. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and biological samples, respectively.     

Electrodes of synthetic diamond: The effects of Ti substrate pretreatment on the electrode properties

The electrode properties of boron-doped diamond thin films grown on Ti substrates by a hot-filament chemical vapor deposition technique are evaluated. The Ti substrate surface modifying conditions are devised, involving the surface roughening, annealing, and etching, which effectively improve the diamond electrode properties. The preetching of the Ti substrate produces the titanium hydride layer that can affect the boron-doped diamond film growth significantly. The substrate roughened surface obviously improved the diamond film adhesion and reduced the inner stress. The electrodes reveal minimal background current and better stability. A wider potential window, up to 3 V, is observed for the boron-doped diamond on the etched/annealed samples. The electrochemical activity of the electrodes in the Fe(CN) ₆ ^3-/4- redox system somewhat increases with increasing surface roughness. The apparent increase in the reversibility of the reaction may be explained by the decrease in the true current density. Suitability of the Ti-based boron-doped diamond electrodes for electroanalytical applications is exemplified by sensing the trace metal ions, such as Hg²⁺ and Pb²⁺.__________From Elektrokhimiya, Vol. 41, No. 4, 2005, pp. 387–396.Original English Text Copyright © 2005 by Pleskov, Evstefeeva, Krotova, Lim, Chu, Ralchenko, Vlasov, Kononenko, Varnin, Teremetskaya, Shi.This article was submitted by the authors in English.     

Reduction of Tetrachloroaurate(III) at Boron-Doped Diamond Electrodes: Gold Deposition Versus Gold Colloid Formation

Tetrachloroaurate(III) dissolved in dilute aqueous aqua regia is electrochemically reduced at boron-doped diamond electrodes to form gold metal. The reduction process is studied by voltammetric, SEM, and XPS techniques. Both the deposition of gold and the anodic stripping process are detected. The ratio of cathodic to anodic charge or stripping efficiency, Q_anodic/Q_cathodic, is shown to depend on the concentration of AuCl and on the pretreatment of the boron-doped diamond electrode surface. Cathodic pretreatment of the boron-doped diamond electrode considerably increases the rate for both deposition and stripping. In the presence of power ultrasound emitted from a glass horn system (24 kHz, 8 Wcm⁻²) the current associated with the reduction of AuCl is considerably enhanced and two components in the mass transport controlled limiting current are identified as (i) the deposition of gold onto the boron-doped diamond and (ii) the formation of colloidal gold.     

Application of boron-doped diamond electrodes for electrochemical oxidation of real wastewaters

Recently, the synthesis of boron-doped diamond electrodes on different substrates and shapes have reached a promising development stage. Now, these electrodes can also be effectively used to destroy toxic or biorefractory organics in real effluents, such as municipal wastewaters effluents, hospital wastewaters, groundwater, petrochemical effluent, wastewaters from agri–food activities, and so on. The results of this mini-review show that BDD is effectively even for such real effluents, allowing the removal of pollutants under several different conditions. Nevertheless, further efforts are necessary to reach a wider market; in particular, the next stages must face the optimization of cell design and the integration of the electrochemical system with other water treatment and renewable energy sources.     

Microwave activation of electrochemical processes: enhanced PbO2 electrodeposition, stripping and electrocatalysis

Microwave activation of electrochemical processes has recently been introduced as a new technique for the enhancement and control of processes at electrode|solution (electrolyte) interfaces. This methodology is extended to processes at glassy carbon and boron-doped diamond electrodes. Deposition of both Pb metal and PbO₂ from an aqueous solution of Pb²⁺ (0.1 M HNO₃) are affected by microwave radiation. The formation of PbO₂ on anodically pre-treated boron-doped diamond is demonstrated to change from kinetically sluggish and poorly defined at room temperature to nearly diffusion controlled and well defined in the presence of microwave activation. Calibration of the temperature at the electrode|solution (electrolyte) interface with the Fe^3+/2+ (0.1 M HNO₃) redox system allows the experimentally observed effects to be identified as predominantly thermal in nature and therefore consistent with a localized heating effect at the electrode|solution interface. The microwave-activated deposition of PbO₂ on boron-doped diamond remains facile in the presence of excess oxidizable organic compounds such as ethylene glycol. An increase of the current for the electrocatalytic oxidation of ethylene glycol at PbO₂/boron-doped diamond electrodes in the presence of microwave radiation is observed. Preliminary results suggest that the electrodissolution of solid microparticles of PbO₂ abrasively attached to the surface of a glassy carbon electrode is also enhanced in the presence of microwave radiation. Electronic Publication     

Direct electrochemical oxidation of polyacrylates

A promising elimination treatment of non-biodegradable organic pollutants is the direct electro-oxidation. In this work has been proposed the electrochemical elimination of polyacrylates by using boron-doped diamond (BDD) as anodic material. The complete elimination of organic contaminants has been obtained and this is the first case of successful electrochemical treatment of polymeric and bio-refractory species. The tests of the electrochemical oxidation have been conducted at constant current conditions and a complete elimination of organic species has been reached. The decrease of the COD value with time follows the behaviour of an ideal anode as in the case of low molecular organic compounds.     

Electrocatalytic Oxidation of Organic Pollutants on Boron-Doped Diamond and Ti–Ru Oxide Anodes in Sulfate Medium

Electrochemical oxidation for degradation of industrial dye Methyl Orange in aqueous sulfate solutions with various electrocatalytic materials: boron-doped diamond electrode and electrode based on titanium and ruthenium oxides. The influence exerted by the main working parameters of electrolysis (current density, concentration of Methyl Orange, pH) on the discoloration efficiency and on the chemical oxygen demand (COD) was examined. It was shown that an increase in the current density and a decrease in the pollutant concentration improve the process efficiency. However, this leads to an increase in the specific electric energy consumption per unit mass of COD. It was found that the boron-doped diamond electrode is a more efficient electrocatalytic material, compared with electrode based on titanium and ruthenium oxides. At low concentrations of Methyl Orange (<50 mg L^–1), there exists the possibility in principle of using the electrode based on titanium and ruthenium oxides not only for discoloration, but also for making lower the COD level.     

Structural and electrochemical heterogeneities of boron-doped diamond surfaces

This brief review is focussed on the recent progress in studies of the heterogeneous electrochemical behaviour of various boron-doped materials extending from zero-dimensional particles through polycrystalline or nanostructured three-dimensional surfaces. A boron-doped diamond reveals large heterogeneities induced by numerous factors, inter alia multi-faceted crystallinity, inhomogeneous boron concentration, sp²/sp³-carbon ratio, surface terminations and grain size distribution. We also present single nanodiamond particles and a nanostructured diamond, which are fabricated by either a top-down or a bottom-up procedure. Nanoarchitectured surfaces allow high areas and large aspect ratios to be achieved, exhibiting highly heterogeneous charge-transfer performance for catalytic, sensing and energy applications. We have anticipated multi-factor-originated heterogeneities of various boron-doped diamond surfaces displaying the essential fabrication and diagnostic methodologies and critically reviewing their benefits and drawbacks.