On the changing electrochemical behaviour of boron-doped diamond surfaces with time after cathodic pre-treatments

Synthesis, Surface Chemistry, and Applications of Non-Zero-Dimensional Diamond Nanostructures

Diamond nanomaterials are renowned for their exceptional properties, which include the inherent attributes of bulk diamond. Additionally, they exhibit unique characteristics at the nanoscale, including high specific surface areas, tunable surface structure, and excellent biocompatibility. These multifaceted attributes have piqued the interest of researchers globally, leading to an extensive exploration of various diamond nanostructures in a myriad of applications. This review focuses on non-zero-dimensional (non-0D) diamond nanostructures including diamond films and extended diamond nanostructures, such as diamond nanowires, nanoplatelets, and diamond foams. It delves into the fabrication, modification, and diverse applications of non-0D diamond nanostructures. This review begins with a concise review of the preparation methods for different types of diamond films and extended nanostructures, followed by an exploration of the intricacies of surface termination and the process of immobilizing target moieties of interest. It then transitions into an exploration of the applications of diamond films and extended nanostructures in the fields of biomedicine and electrochemistry. In the concluding section, this article provides a forward-looking perspective on the current state and future directions of diamond films and extended nanostructures research, offering insights into the opportunities and challenges that lie ahead in this exciting field.

Cloud point method applied to the extraction and preconcentration of thiabendazole pesticide from whole grape juice samples and amperometric detection by HPLC

A cloud point method was developed and applied for the first time to extract and preconcentrate thiabendazole (TBZ) from commercial whole grape juice samples, with determination by high performance liquid chromatography coupled to electrochemical detection (HPLC/EC), using a cathodically pretreated boron-doped diamond electrode (BDD). The best conditions for extraction and preconcentration of TBZ by cloud point extraction (CPE) were performed at pH 6.0, by adding 1 mL of the surfactant Tergitol TMN-6 at 10% (mass-to-mass ratio), without heating (at 27 °C) and ultrasonic stirring time of (20 kHz) for 60 min. The HPLC/EC determination was duly validated in a C8 column, in mobile phase with a 69 : 31 ratio (V/V) of phosphate buffer (pH 7.0):ACN, at a flow rate of 1.2 mL min-1 and electrochemical detection with BDD electrode by applying 1.40 V × Ag/AgCl (3.0 mol L-1). Under these conditions, the procedure showed a preconcentration factor (FC) of 21.7, and limits of detection (LOD) and quantification (LOQ) of 6.64 × 10-9 mol L-1 (or 1.33 μg L-1) and 1.66 × 10-8 mol L-1 (or 3.34 μg L-1), respectively. The method provided a percent recovery of 81% to 98%, with a coefficient of variation between 3% and 15%.

Electrochemical platform produced by 3D printing for analysis of small volumes using different electrode materials

Fused deposition modeling (FDM) 3D printing is a promising additive manufacturing technique to produce low-cost disposable electrochemical devices. However, the print of devices like well-known screen-printed electrodes (all electrodes on the same device) is difficult using the available technology (few materials available for production of working electrodes). In this paper we present a procedure to produce disposable and robust electrochemical devices by FDM 3D printing that allows reproducible analysis of small volumes (50-2000 μL). The device consists of just two printed parts that allow easy coupling of different conductive materials for using as disposable or non-disposable working electrodes with reproducible geometric area. Printed counter and pseudo-reference electrodes can also be easily fitted into the microcell. Moreover, conventional counter (platinum wire) and mini reference electrodes can also be used. As a proof of concept, paracetamol, cocaine and uric acid were used as model analytes using different materials as working electrodes. Linear calibration curves (r > 0.99) with similar slopes (0.29 ± 0.01 μA μmol L-1; RSD = 3.4%) were obtained by square wave voltammetry (SWV) using a complete printed system and different volumes of standard solutions of paracetamol (50, 100, and 200 μL). For uric acid, a linear range of 10-125 μmol L-1 (r > 0.99), was obtained using differential pulse voltammetry as the electrochemical technique and a disposable laser-induced graphene base as the working electrode. With the coupling of boron-doped diamond working electrode, screening tests were successfully performed in seized cocaine samples with selective detection of cocaine in the presence of its most common adulterants. The production cost per unit of a complete electrochemical system is around US 5.00. In large-scale production, only the working electrode needs to be replaced while the microcell and counter/pseudo reference electrodes do not need to be discarded.

Inkjet Printing-Manufactured Boron-Doped Diamond Chip Electrodes for Electrochemical Sensing Purposes

Fabrication of patterned boron-doped diamond (BDD) in an inexpensive and straightforward way is required for a variety of practical applications, including the development of BDD-based electrochemical sensors. This work describes a simplified and novel bottom-up fabrication approach for BDD-based three-electrode sensor chips utilizing direct inkjet printing of diamond nanoparticles on silicon-based substrates. The whole seeding process, accomplished by a commercial research inkjet printer with piezo-driven drop-on-demand printheads, was systematically examined. Optimized and continuous inkjet-printed features were obtained with glycerol-based diamond ink (0.4% vol/wt), silicon substrates pretreated by exposure to oxygen plasma and subsequently to air, and applying a dot density of 750 drops (volume 9 pL) per inch. Next, the dried micropatterned substrate was subjected to a chemical vapor deposition step to grow uniform thin-film BDD, which satisfied the function of both working and counter electrodes. Silver was inkjet-printed to complete the sensor chip with a reference electrode. Scanning electron micrographs showed a closed BDD layer with a typical polycrystalline structure and sharp and well-defined edges. Very good homogeneity in diamond layer composition and a high boron content (∼2 × 1021 atoms cm-3) was confirmed by Raman spectroscopy. Important electrochemical characteristics, including the width of the potential window (2.5 V) and double-layer capacitance (27 μF cm-2), were evaluated by cyclic voltammetry. Fast electron transfer kinetics was recognized for the [Ru(NH3)6]3+/2+ redox marker due to the high doping level, while somewhat hindered kinetics was observed for the surface-sensitive [Fe(CN)6]3-/4- probe. Furthermore, the ability to electrochemically detect organic compounds of different structural motifs, such as glucose, ascorbic acid, uric acid, tyrosine, and dopamine, was successfully verified and compared with commercially available screen-printed BDD electrodes. The newly developed chip-based manufacture method enables the rapid prototyping of different small-scale electrode designs and BDD microstructures, which can lead to enhanced sensor performance with capability of repeated use.

Boron-Doped Diamond Electrodes: Fundamentals for Electrochemical Applications

Boron-doped diamond (BDD) electrodes have emerged as next-generation electrode materials for various applications in electrochemistry such as electrochemical sensors, electrochemical organic synthesis, CO₂ reduction, ozone water generation, electrochemiluminescence, etc. An optimal BDD electrode design is necessary to realize these applications. The electrochemical properties of BDD electrodes are determined by important parameters such as (1) surface termination, (2) surface orientation, and (3) boron doping level.In this Account, we discuss how these parameters contribute to the function of BDD electrodes. First, control of the surface termination (hydrogen/oxygen) is described. The electrochemical conditions such as the solution pH and the application potential were studied precisely. It was confirmed that an acidic solution and the application of negative potential accelerate hydrogenation, and the mechanism behind this is discussed. For oxygenation, we directly observed changes in surface functional groups by in situ attenuated total reflection infrared spectroscopy and electrochemical X-ray photoelectron spectroscopy measurements.Next, the difference in surface orientation was examined. We prepared homoepitaxial single-crystal diamond electrodes comprising (100) and (111) facets with similar boron concentrations and resistivities and evaluated their electrochemical properties. Experimental results and theoretical calculations revealed that (100)-oriented single-crystal BDD has a wider space charge layer than (111)-oriented BDD, resulting in a slower response. Furthermore, isolated single-crystal microparticles of BDD with exposed (100) and (111) crystal facets were grown, and we studied the electrochemical properties of the respective facets by combination with hopping-mode scanning electrochemical cell microscopy.We also systematically investigated how the boron concentration and sp² species affect the electrochemical properties. The results showed that the appropriate composition (boron and sp² species level) is dependent on the application. The transmission electron microscopy images and electron energy loss spectra of highly boron-doped BDD are shown, and the relationship between the composition and electrochemical properties is discussed. Finally, we investigated in detail the effect of the sp² component on low-doped BDD. Surprisingly, although the sp² component is usually expected to induce a narrowing of the potential window and an increase in the charging current, low-doped BDD showed the opposite trend depending on the degree of sp² carbon.The results and discussion presented in this Account will hopefully promote a better understanding of the fundamentals of BDD electrodes and be useful for the optimal development of electrodes for future applications.

Enhancing electroanalytical performance of porous boron-doped diamond electrodes by increasing thickness for dopamine detection

Novel porous boron-doped diamond (BDD_porous)-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD_porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO₂ nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10²¹ atoms cm^-3 and increased content of non-diamond (sp²) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm^-2 to 1060 μF cm^-2), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm² to 7.72 mm²), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol^-1 L was achieved on a BDD_porous electrode with five layers and dropped to 35.9 μA μmol^-1 L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L^-1 was obtained on a BDD_porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD_porous electrodes.

Kinetics of the Organic Compounds and Ammonium Nitrogen Electrochemical Oxidation in Landfill Leachates at Boron-Doped Diamond Anodes

Electrochemical oxidation (EO) of organic compounds and ammonium in the complex matrix of landfill leachates (LLs) was investigated using three different boron-doped diamond electrodes produced on silicon substrate (BDD/Si)(levels of boron doping [B]/[C] = 500, 10,000, and 15,000 ppm—0.5 k; 10 k, and 15 k, respectively) during 8-h tests. The LLs were collected from an old landfill in the Pomerania region (Northern Poland) and were characterized by a high concentration of N-NH₄⁺ (2069 ± 103 mg·L⁻¹), chemical oxygen demand (COD) (3608 ± 123 mg·L⁻¹), high salinity (2690 ± 70 mg Cl⁻·L⁻¹, 1353 ± 70 mg SO₄²⁻·L⁻¹), and poor biodegradability. The experiments revealed that electrochemical oxidation of LLs using BDD 0.5 k and current density (j) = 100 mA·cm⁻² was the most effective amongst those tested (C_8h/C₀: COD = 0.09 ± 0.14 mg·L⁻¹, N-NH₄⁺ = 0.39 ± 0.05 mg·L⁻¹). COD removal fits the model of pseudo-first-order reactions and N-NH₄⁺ removal in most cases follows second-order kinetics. The double increase in biodegradability index—to 0.22 ± 0.05 (BDD 0.5 k, j = 50 mA·cm⁻²) shows the potential application of EO prior biological treatment. Despite EO still being an energy consuming process, optimum conditions (COD removal > 70%) might be achieved after 4 h of treatment with an energy consumption of 200 kW·m⁻³ (BDD 0.5 k, j = 100 mA·cm⁻²).

A Review on Recent Advances in the Applications of Boron-Doped Diamond Electrochemical Sensors in Food Analysis

The usage of boron-doped diamond (BDD) material has found to be very attractive in modern electroanalytical methods and received massive consideration as perspective electrochemical sensor due to its outstanding (electro)chemical properties. These generally known facilities include large potential window, low background currents, ability to withstand extreme potentials and strong tendency to resist fouling compared to conventional carbon-based electrodes. As evidence of superiority of this material, couple of reviews describing the overview of various applications of BDD electrodes in the field of analytical and material chemistry has been reported in scientific literature during last decade. However, herein proposed review predominantly focuses on the most recent developments (from 2009 to 2020) dealing with the application of BDD as an advanced and environmental-friendly sensor platform in food analysis. The main method characteristics of analysis of various organic food components with different chemical properties, including additives, flavor and aroma components, phenolic compounds, flavonoids and pesticides in food matrices are described in more details. The importance of BDD surface termination, presence of sp² content and boron doping level on electrochemical sensing is discussed. Apart from this, a special attention is paid to the evaluation of main analytical characteristics of the BDD electrochemical sensor in single- and multi-analyte detection mode in food analysis. The recent achievements in the utilizing of BDD electrodes in amperometric detection coupled to flow injection analysis, batch injection analysis, and high-performance liquid chromatography are also commented. Moreover, actual trends in sample preparation techniques prior to electrochemical sensing in food analysis are referred.

In Vivo Real-Time Simultaneous Examination of Drug Kinetics at Two Separate Locations Using Boron-Doped Diamond Microelectrodes

Methylcobalamin, which is used for the clinical treatment of patients with neuropathy, can have an impact on the sensorineural components associated with the cochlea, and it is possible that the auditory threshold in a certain population of patients with deafness may be recovered. Nonetheless, it remains uncertain whether the action site of methylcobalamin is localized inside or outside the cochlea and which cellular or tissue element is targeted by the drug. In the present work, we developed a method to realize in vivo real-time simultaneous examination of the drug kinetics in two separate locations using boron-doped diamond microelectrodes. First, the analytical performance of methylcobalamin was studied and the measurement protocol was optimized in vitro. Then, the optimized protocol was applied to carry out real-time measurements inside the cochlea and the leg muscle in live guinea pigs while systemically administering methylcobalamin. The results showed that the methylcobalamin concentration in the cochlea was below the limit of detection for the microelectrodes or the drug did not reach the cochlea, whereas the compound clearly reached the leg muscle.

Effect of the Presence of Carbon in Ti4O7 Electrodes on Anodic Oxidation of Contaminants

Magnéli phase titanium suboxide, Ti₄O₇, has attracted increasing attention as a potential electrode material in anodic oxidation as a result of its high efficiency and (electro)chemical stability. Although carbon materials have been amended to Ti₄O₇ electrodes to enhance the electrochemical performance or are present as an unwanted residual during the electrode fabrication, there has been no comprehensive investigation of how these carbon materials affect the electrochemical performance of the resultant Ti₄O₇ electrodes. As such, we investigated the electrochemical properties of Ti₄O₇ electrodes impregnated with carbon materials at different contents (and chemical states). Results of this study showed that while pure Ti₄O₇ electrodes exhibited an extremely low rate of interfacial electron transfer, the introduction of minor amounts of carbon materials (at values as low as 0.1 wt %) significantly facilitated the electron transfer process and decreased the oxygen evolution reaction potential. The oxygen-containing functional groups have been shown to play an important role in interfacial electron transfer with moderate oxidation of the carbon groups aiding electron uptake at the electrode surface (and consequently organic oxidation) while the generation of carboxyl groups-a process that is likely to occur in long-term operation-increased the interfacial resistance and thus retarded the oxidation process. Results of this study provide a better understanding of the relationship between the nature of the electrode surface and anodic oxidation performance with these insights likely to facilitate improved electrode design and optimization of operation of anodic oxidation reactors.

Boron Doped Diamond Electrodes in Flow-Based Systems

Boron-doped diamond (BDD) electrodes present several notable properties, such as the largest potential window of all electrode materials (especially in anodic potentials), low background and capacitive currents, reduced fouling compared to other electrodes, mechanical robustness, and good stability over time. On the other hand, flow-based systems are known as well-established approaches to minimize reagent consumption and waste generation and with good compromise between sample throughput and analytical performance (mechanization of chemical assays). This review focuses on the use of BDD electrodes for electrochemical detection in flow systems, such as flow injection analysis (FIA), batch injection analysis (BIA), high performance liquid chromatography (HPLC), and capillary electrophoresis (CE). The discussion deals with the historical evolution of BDD, types of electrochemical pre-treatments (cathodically/H-terminated or anodically/O-terminated), cell configurations, and analytical performance. Articles are discussed in chronological order and subdivided according to the type of flow system: FIA, BIA, HPLC, and CE.

Conductive diamond: synthesis, properties, and electrochemical applications

This review summarizes systematically the growth, properties, and electrochemical applications of conductive diamond.

Electrochemical properties of fluorinated boron-doped diamond electrodes via fluorine-containing plasma treatment

It was systematically demonstrated that the electrochemical properties of fluorinated boron-doped diamond electrodes could be attributed to interfacial band bending.

Amperometric Determination of Hydrogen Peroxide in Whitening Gels Using Boron-doped Diamond Electrode

The aim of this work was to develop an electrochemical cell and a methodology based on an amperometric determination of hydrogen peroxide in whitening gel samples under a boron-doped diamond electrode using flow injection analysis. Different parameters were evaluated to obtain the best conditions of analysis: among them, the flow of electrolyte at 2.8 mL min^-1, the loop sampling 175 μL (28.5 cm), an analytical length of 159 μL (25 cm) and an applied potential of +0.60 V vs. Ag/AgCl_(sat). The proposed method was suitable in terms of precision of results (RSD <10%); the accuracy was confirmed in the analysis of the gels through addition and recovery studies with results between 74 and 107%. The method was then applied to the analysis of tooth-whitening gel samples, acquired in different cities of the region. Regarding the results, a medium concentration value of 2.39% (w/w) was observed.

Fluorination of Boron-Doped Diamond Film Electrodes for Minimization of Perchlorate Formation

This research investigated the effects of surface fluorination on both rates of organic compound oxidation (phenol and terephthalic acid (TA)) and ClO₄^- formation at boron-doped diamond (BDD) film anodes at 22 °C. Different fluorination methods (i.e., electrochemical oxidation with perfluorooctanoic acid (PFOA), radio frequency plasma, and silanization) were used to incorporate fluorinated moieties on the BDD surface, which was confirmed by X-ray photoelectron spectroscopy (XPS). The silanization method was found to be the most effective fluorination method using a 1H,1H,2H,2H-perfluorodecyltrichlorosilane precursor to form a self-assembled monolayer (SAM) on the oxygenated BDD surface. The ClO₄^- formation decreased from rates of 0.45 ± 0.03 mmol m^-2 min^-1 during 1 mM NaClO₃ oxidation and 0.28 ± 0.01 mmol m^-2 min^-1 during 10 mM NaCl oxidation on the BDD electrode to below detectable levels (<0.12 μmoles m^-2 min^-1) for the BDD electrode functionalized by a 1H,1H,2H,2H-perfluorodecyltrichlorosilane SAM. These decreases in rates corresponded to 99.94 and 99.85% decreases in selectivity for ClO₄^- formation during the electrolysis of 10 mM NaCl and 1 mM NaClO₃ electrolytes, respectively. By contrast, the oxidation rates of phenol were reduced by only 16.3% in the NaCl electrolyte and 61% in a nonreactive 0.1 M KH₂PO₄ electrolyte. Cyclic voltammetry with Fe(CN)₆^3-/4- and Fe^3+/2+ redox couples indicated that the long fluorinated chains created a blocking layer on the BDD surface that inhibited charge transfer via steric hindrance and hydrophobic effects. The surface coverages and thicknesses of the fluorinated films controlled the charge transfer rates, which was confirmed by estimates of film thicknesses using XPS and density functional theory simulations. The aliphatic silanized electrode also showed very high stability during OH^• production. Perchlorate formation rates were below the detection limit (<0.12 μmoles m^-2 min^-1) for up to 10 consecutive NaClO₃ oxidation experiments.

Enhanced H2O2 Production at Reductive Potentials from Oxidized Boron-Doped Ultrananocrystalline Diamond Electrodes

This work investigates the surface chemistry of H₂O₂ generation on a boron-doped ultrananocrystalline diamond (BD-UNCD) electrode. It is motivated by the need to efficiently disinfect liquid waste in resource constrained environments with limited electrical power. X-ray photoelectron spectroscopy was used to identify functional groups on the BD-UNCD electrode surfaces while the electrochemical potentials of generation for these functional groups were determined via cyclic voltammetry, chronocoulometry, and chronoamperometry. A colorimetric technique was employed to determine the concentration and current efficiency of H₂O₂ produced at different potentials. Results showed that preanodization of an as-grown BD-UNCD electrode can enhance the production of H₂O₂ in a strong acidic environment (pH 0.5) at reductive potentials. It is proposed that the electrogeneration of functional groups at oxidative potentials during preanodization allows for an increased current density during the successive electrolysis at reductive potentials that correlates to an enhanced production of H₂O₂. Through potential cycling methods, and by optimizing the applied potentials and duty cycle, the functional groups can be stabilized allowing continuous production of H₂O₂ more efficiently compared to static potential methods.

Parabens abatement from surface waters by electrochemical advanced oxidation with boron doped diamond anodes

The removal efficiency of four commonly-used parabens by electrochemical advanced oxidation with boron-doped diamond anodes in two different aqueous matrices, namely ultrapure water and surface water from the Guadiana River, has been analyzed. Response surface methodology and a factorial, composite, central, orthogonal, and rotatable (FCCOR) statistical design of experiments have been used to optimize the process. The experimental results clearly show that the initial concentration of pollutants is the factor that influences the removal efficiency in a more remarkable manner in both aqueous matrices. As a rule, as the initial concentration of parabens increases, the removal efficiency decreases. The current density also affects the removal efficiency in a statistically significant manner in both aqueous matrices. In the water river aqueous matrix, a noticeable synergistic effect on the removal efficiency has been observed, probably due to the presence of chloride ions that increase the conductivity of the solution and contribute to the generation of strong secondary oxidant species such as chlorine or HClO/ClO ^-. The use of a statistical design of experiments made it possible to determine the optimal conditions necessary to achieve total removal of the four parabens in ultrapure and river water aqueous matrices.

Continuous and selective measurement of oxytocin and vasopressin using boron-doped diamond electrodes

The electrochemical detection of oxytocin using boron-doped diamond (BDD) electrodes was studied. Cyclic voltammetry of oxytocin in a phosphate buffer solution exhibits an oxidation peak at +0.7 V (vs. Ag/AgCl), which is attributable to oxidation of the phenolic group in the tyrosyl moiety. Furthermore, the linearity of the current peaks obtained in flow injection analysis (FIA) using BDD microelectrodes over the oxytocin concentration range from 0.1 to 10.0 μM with a detection limit of 50 nM (S/N = 3) was high (R(2) = 0.995). Although the voltammograms of oxytocin and vasopressin observed with an as-deposited BDD electrode, as well as with a cathodically-reduced BDD electrode, were similar, a clear distinction was observed with anodically-oxidized BDD electrodes due to the attractive interaction between vasopressin and the oxidized BDD surface. By means of this distinction, selective measurements using chronoamperometry combined with flow injection analysis at an optimized potential were demonstrated, indicating the possibility of making selective in situ or in vivo measurements of oxytocin.