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.     

In situ electrochemical spectroscopy for boron-doped diamond electrode reactions: recent progress and perspectives

Over the past years, great attention has been given to the developments of boron-doped diamond (BDD) materials in various fields because of the advantages of electrochemical features, such as large potential range and low background current. This minireview aims to present the recent progress of in situ electrochemical spectroscopy for BDD electrode reactions. After a concise state of the widely used in situ electrochemical spectroscopy techniques, including in situ electrochemical Raman, infrared, and electron paramagnetic resonance spectroscopy, the current progress of BDD electrode reactions using in situ electrochemical spectroscopy has been summarized. Finally, challenges and perspectives for the tendency of the BDD study via in situ electrochemistry are provided, of which several potential electrochemical combined technologies relating to the mechanism exploration of BDD are proposed.     

In situ DNA oxidative damage by electrochemically generated hydroxyl free radicals on a boron-doped diamond electrode

In situ DNA oxidative damage by electrochemically generated hydroxyl free radicals has been directly demonstrated on a boron-doped diamond electrode. The DNA-electrochemical biosensor incorporates immobilized double-stranded DNA (dsDNA) as molecular recognition element on the electrode surface, and measures in situ specific binding processes with dsDNA, as it is a complementary tool for the study of bimolecular interaction mechanisms of compounds binding to DNA and enabling the screening and evaluation of the effect caused to DNA by radicals and health hazardous compounds. Oxidants, particularly reactive oxygen species (ROS), play an important role in dsDNA oxidative damage which is strongly related to mutagenesis, carcinogenesis, autoimmune inflammatory, and neurodegenerative diseases. The hydroxyl radical is considered the main contributing ROS to endogenous oxidation of cellular dsDNA causing double-stranded and single-stranded breaks, free bases, and 8-oxoguanine occurrence. The dsDNA-electrochemical biosensor was used to study the interaction between dsDNA immobilized on a boron-doped diamond electrode surface and in situ electrochemically generate hydroxyl radicals. Non-denaturing agarose gel-electrophoresis of the dsDNA films on the electrode surface after interaction with the electrochemically generated hydroxyl radicals clearly showed the occurrence of in situ dsDNA oxidative damage. The importance of the dsDNA-electrochemical biosensor in the evaluation of the dsDNA-hydroxyl radical interactions is clearly demonstrated.     

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     

Hydroxyl radicals electrochemically generated in situ on a boron-doped diamond electrode

The hydroxyl radicals electrochemically generated in situ on a boron-doped diamond (BDD) electrode have been investigated for the first time in different electrolyte media, over the whole pH range between 1 and 11. A more extensive characterisation of BDD electrochemical properties is very important to understand the reactivity of organic compounds towards electrochemical oxidation on the BDD electrode, which is related to their interaction with adsorbed hydroxyl radicals due to water oxidation on the electrode surface. An oxidation peak corresponding to the transfer of one electron and one proton was observed in pH <9 electrolytes, associated with the water discharge process and electrochemical generation of hydroxyl radicals, which can interact and enhance the electro-oxidation of organic compounds. In pH >9 electrolytes the electrochemical generation of hydroxyl radicals was not observed; ammonia buffer electrolyte gave a pH-independent peak corresponding to the ammonia oxidation reaction. Additionally, for most pH values studied, a few small peaks associated with the electrochemical interaction between non-diamond carbon species on the doped diamond electrode surface and the electrolyte were also seen, which suggests that the doped diamond is relatively unreactive, but not completely inert, and the electrogenerated hydroxyl radicals play a role as mediator in the oxidation of organics.     

Direct electrochemical assay of glucose using boron-doped diamond electrodes

We report linear sweep and square wave voltammetric studies on glucose oxidation at boron-doped diamond (BDD) electrodes in an alkaline medium in efforts to evaluate the techniques for electrochemically assaying glucose. The bare BDD electrode showed good linear responses to glucose oxidation for a concentration range from 0.5 to 10 mM glucose, which well encompasses the physiological range of 3-8 mM. The BDD electrodes did not experience interferences from ascorbic acid or uric acid during glucose detection. This method, when applied to real blood samples, gave results similar to those obtained by a commercial glucose monitor.     

Non-enzymatic electrochemical detection of glycerol on boron-doped diamond electrode

A non-enzymatic direct electrochemical glycerol detection method at a commercial boron-doped diamond (BDD) electrode in 0.1 M NaOH supporting electrolyte was developed. All the used electrochemical techniques proved useful features for the oxidation and direct amperometric determination of glycerol at a BDD electrode in 0.1 M NaOH aqueous solution. It was found that the direct electrooxidation of glycerol on the BDD electrode requires both adsorbed glycerol and hydroxyls at the electrode surface. Also, the sp(2) carbon did not allow enhancement of the glycerol oxidation process. The electronalytical sensitivity for the determination of glycerol at the BDD electrode ranged from 0.040 to 0.226 μA mM(-1) as a function of the technique used. The highest electroanalytical sensitivity for the determination of glycerol at the BDD electrode was reached in batch system amperometric quantification under stirring conditions. Performed recovery studies indicated that it is possible to determine glycerol in real samples, and the proposed batch system analysis-based methodology can be a valuable tool for practical glycerol analysis.     

Direct and mediated electrochemical oxidation of ammonia on boron-doped diamond electrode

Direct (non-mediated) electrochemical oxidation of ammonia on boron-doped diamond (BDD) electrode proceeds mainly at high pH (> 8) via free ammonia (NH₃) oxidation. To enhance ammonia oxidation on BDD at low pH (< 8), where mainly ammonium (NH₄⁺) is present, oxidation of ammonia was mediated by active free chlorine. In this process, electro-generated in situ active chlorine rapidly reacts with ammonia instead of being further electro-oxidized to chlorate at the electrode surface. Thus, active chlorine effectively removes ammonia from an acidic solution, while the formation of by-products such as chlorate and possibly perchlorate is minimized.     

Recent advances of boron-doped diamond electrochemical sensors toward environmental applications

The electrocatalytic properties of boron-doped diamond (BDD) electrodes have been considered for a variety of sensing applications. The unusual electrochemical properties of BDD include a large potential window, a small background current, and better resistance to fouling than other carbon-based electrodes. The use of BDD for remediation and environmental sensing applications has recently attracted the interest of the sensor research community. This review focuses on recent developments that involve the use of BDD as an environmentally friendly sensing material for environmental analysis. The electrochemical properties of boron-doped diamond that has undergone surface modification (e.g., with metals or enzymes) will be considered. Recent achievements involving the use of BDD electrodes for detecting pesticides, mycotoxins, peroxides, and phenolic compounds are considered.     

Development and application of electrochemical sensor of boron-doped diamond (BDD) modified by drop casting with tin hexacyanoferrate

Journal of Solid State Electrochemistry - This work presents the development and characterization of an electrochemical sensor of tin hexacyanoferrate (SnHCF), produced from the modification by...     

Low-frequency electrochemical impedance of benzene oxidation on anode of boron-doped diamond

Kinetics of low-frequency adsorption of benzene oxidation products are studied in 0.5 M K₂SO₄ on an anode of boron-doped diamond. A combination of current polarograms and impedance with analysis of the impedance spectroscopy in the frequency range of 0.05–10 Hz allowed studying in detail the mechanism of adsorption oxidation of benzene under the conditions of competition between this process and the more anodic process of oxygen evolution that is also based on adsorption. A frequency-polarization diagram of dependences of characteristic frequencies (CFs) of adsorption and desorption stages on potential was obtained for the product of benzene oxidation and oxygen-containing intermediate of the oxygen evolution reaction. Controlled stages of coupled processes, potentials, and characteristic frequencies of the points of changes in the reaction mechanism are determined: 0.22 Hz at 2.0 V for benzene oxidation; 0.63 Hz at 2.22 V for oxygen evolution. The potential of maximum adsorption of the organic substance is 2.15 V. The obtained results can be useful in the studies of the mechanism of coupled reactions including organic and inorganic intermediate adsorbates.     

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.     

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.     

Microchip capillary electrophoresis with a boron-doped diamond electrochemical detector for analysis of aromatic amines

The attractive features of a boron-doped diamond (BDD) thin-film detector for microchip capillary electrophoretic (CE) separations of dye-related amino-substituted aromatic compounds are described. The diamond electrode was employed in the end-column amperometric detection of 4-aminophenol (4-AP), 1,2-phenylenediamine (1,2-PDA), 2-aminonaphthalene (2-AN), 2-chloroaniline (2-CA), and o-aminobenzoic acid (o-ABA), and its attractive behavior was compared to commonly used screen-printed carbon and glassy-carbon electrodes. These conventional electrode materials exhibit a significant degree of passivation and low sensitivity to the above-mentioned environmental pollutants. The diamond-based electrochemical detection system displayed a favorable analytical performance, including lower noise levels, higher peak resolution with enhanced sensitivity, and improved resistance against electrode passivation. Factors influencing the on-chip analysis were assessed and optimized. The diamond detector displayed detection limits of 2.0 and 1.3 microM for 4-AP and 2-AN, respectively, and a wide linear response for these compounds over the 2-50 microM range. The enhanced stability was demonstrated by relative standard deviation (RSD) values of 1.4% and 4.7% for 100 microM 1,2-PDA and 200 microM 2-CA, respectively, for repetitive detections (n = 7). Besides, the simultaneously observed current decrease was 2.4 and 9.1% for 1,2-PDA and 2-CA, respectively (compared to 21.8 and 41.0% at the screen-printed carbon electrode and 28.3 and 34.1% at the glassy carbon electrode, respectively). The favorable properties of the diamond electrode indicate great promise for environmental applications in CE and other microchip devices.     

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L^?1 KCl electrode in an acidic medium and 1 mol L^?1 H₂SO₄ was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L^?1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L^?1 and a low limit of detection (LD = 1.64 µmol L^?1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.     

Kinetics and mechanism of the deep electrochemical oxidation of sodium diclofenac on a boron-doped diamond electrode

The kinetics and mechanism of the deep oxidation of sodium diclofenac on a boron-doped diamond electrode are studied to develop a technique for purifying wastewater from pharmaceutical products. The products of sodium diclofenac electrolysis are analyzed using cyclic voltammetry and nuclear magnetic resonance techniques. It is shown that the toxicity of the drug and products of its electrolysis decreases upon its deep oxidation.     

Promising electrochemical performance of high-surface-area boron-doped diamond/carbon nanotube electroanalytical sensors

Porous boron-doped diamond (p-BDD) electrodes of high-surface-area have been prepared on vertically aligned carbon nanotube substrates, and their electrochemical performance has demonstrated promising results for application in electroanalysis. The electrochemical features of the p-BDD electrodes were investigated and compared with those of a conventional flat BDD electrode (f-BDD). From cyclic voltammetry studies performed for the electrochemical probes [Fe(CN)₆]^3? and N,N,N′,N′-tetramethyl-para-phenylenediamine (TMPD), a fast charge transfer was observed at the p-BDD/electrolyte interface. For the [Fe(CN)₆]^3? redox probe, the heterogeneous electron-transfer rate constant (k ⁰) value obtained for p-BDD was 10.9 times higher than that obtained using a f-BDD electrode. Moreover, the p-BDD electrodes also gave a smaller peak potential separation, ΔE _p, and larger analytical signal magnitude for different biomolecules, such as dopamine (DA), acetaminophen (AC), and epinephrine (EP). These set of results demonstrated that the p-BDD electrode is a suitable candidate for applications in electroanalytical chemistry.     

Indirect electrochemical oxidation of reverse osmosis membrane concentrates at boron-doped diamond electrodes

The treatment or disposal of concentrates generated from the filtrative treatment of water is rapidly becoming a factor of major environmental concern. This preliminary study discusses a novel approach in the abatement of reverse osmosis membrane retentate i.e. electrochemical oxidation. The recalcitrant organic constituents as well as the ammonia nitrogen in the retentate could be readily oxidised using boron-doped diamond electrodes. From the model fitted to these data, a constant removal rate and current efficiency was calculated. Analysis of the inorganic chlorinated species revealed that the oxidation mechanism was mainly due to the indirect oxidative action of electrogenerated hypochlorite.     

Study of the electrochemical degradation of diclofenac on a boron-doped diamond electrode by UV spectroscopy

Electrochemical degradation of diclofenac in aqueous solutions was studied using a thin-film boron-doped diamond electrode deposited onto a niobium plate. The process was monitored by means of UV spectroscopy and elemental analysis.