Unmodified Electrode Research Articles

Electrochemical determination of nitrate on Ag nanoparticles‐decorated poly (direct blue 15) electrodes

AbstractIn this study, for the first time, the electro‐polymerization of Direct blue15 (DB15), an azo dye, was carried out on the surface of ITO. Furthermore, the poly(DB15) surface was electrochemically decorated with Ag nanoparticles (AgNPs), and the fabricated AgNPs/PDB15 electrodes were examined as nitrate sensors. Compared to unmodified ITO electrode, the AgNPs/PDB15 electrode had greatly improved electrochemical response to nitrate reduction. The nitrate determination in a linear range from 1.0×10−5 mol L−1 to 2.27×10−3 mol L−1 was performed with a detection limit of 9.66 μM. The synthesized electrode is a promising sensor for the electrochemical detection of nitrate pollutants in water.

NiO and Co3O4 nanoparticles decorated La0.8Sr0.2MnO3-based electrodes for electrochemical NOx removal in solid electrolyte cells

Solid electrolyte cells (SECs) have great application prospect for nitrogen oxides (NOx) removal due to no required reductant addition in contrast to the conventional selective catalytic reduction (SCR) method. Perovskites are the potential electrode materials in SECs but their reaction activity is insufficient at the intermediate-low temperature. Herein, NiO and Co3O4 nanoparticles are decorated on the La0.8Sr0.2MnO3-based electrode to improve the electrode activity. A variety of characterizations were conducted to analyze the electrode properties, and the electrode performance was systematically evaluated. The results show that the decorated NiO and Co3O4 nanoparticles both improved the electrode performance significantly and the NiO-modified electrode had a better performance. Compared with the unmodified electrodes, the surface NiO nanoparticles decreased the area-specific polarization resistance by 63.1% to 81.7 Ω cm2 while the NO conversion was increased by 85.9% to 59.3% at 1.4 V in 1000 ppm NO, 700 ℃. The electrochemical impedance spectra revealed that the nanoparticles not only promoted the species adsorption, dissociation and diffusion processes but facilitated the charge transfer between electrode and electrolyte. The first-principle calculation confirmed that the decorated NiO nanoparticles decreased the energy gap of electrodes and promoted the electron transfer between electrode and NO molecule, in agreement well with the experimental results. This work presented a new way to increase the NOx removal performance of SECs and offered guidance for the future construction of high-performance electrodes.

Synthesis of Nanostructured Mixed-Valence Fe(II,III) Metal-Organic Framework and Its Application in Electrochemical Sensing of Amoxicillin

The study reports the development of a nanostructured mixed-valence Fe(II)Fe(III)BTC metal-organic framework (BTC = 1, 3, 5-benzenetricarboxylate) modified carbon paste electrode as a novel sensor for the amoxicillin detection in aqueous solutions using square wave voltammetry. The physicochemical properties of FeBTC were characterized using X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller analysis, electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. These techniques revealed that FeBTC has a surface area of 1211 m2 g−1, a total pore volume of 1.46 cm3 g−1, particle sizes ranging from 10 to 20 nm, and a mixed-valence structure. Furthermore, SEM, TEM, and energy-dispersive X-ray spectroscopy exhibited the homogeneous distribution of FeBTC throughout the modified electrode. The electrochemical study showed that the mixed-valence FeBTC improved the electron transfer capabilities of the electrode. Under optimal conditions, the modified electrode exhibited a significant increase in peak height compared to the unmodified electrode (4.6 times higher), with an acceptable reproducibility of 4.88% relative standard deviation. The linear range of the sensor was 1–100 μM with a good coefficient of determination of 0.9985, and a detection limit of 0.107 μM. Additionally, the sensor demonstrated excellent performance with the satisfactory recoveries and a good correlation with LC-MS/MS analysis.

Promising Electrode Surfaces, Modified with Nanoparticles, in the Sensitive and Selective Electroanalytical Determination of Antibiotics: A Review

This review highlights the importance of monitoring the levels of antibiotics in different matrices and the need for sensitive and selective detection methods of antibiotic residues in various samples. Additionally, this article discusses the use of modified electrodes, specifically those modified with nanoparticles, for the detection of antibiotics using electroanalytical techniques. These modified electrodes have been found to have advantages over unmodified electrodes, such as enhanced sensitivity, selectivity, and stability. Nanoparticles such as graphene, carbon nanotubes, metal nanoparticles, and metal oxides have been used to modify electrodes because of their excellent properties, such as their large electroactive surfaces. The review provides examples of nanoparticle-modified electrodes that have been used successfully for the determination of a broad range of antibiotics.

BaO-MWCNT composite material-based electrocatalytic amperometric sensor for the detection of environmentally hazardous Diuron

Population growth has prompted industrialization and intensive agricultural methods, which are linked to issues with flora and fauna and result in deteriorated water quality due to contamination by hazardous, persistent pesticides. In this paper, we have concentrated on the herbicide Diuron (DIU) determination as one such priority pollutant. This study was conducted keeping in mind key factors for a proficient electrochemical sensor development for DIU. The working electrode surface area was modified with the as-synthesized BaO-MWCNT composite material to reinforce the efficiency of the Faradaic reaction. A three-fold magnification in DIU anodic peak current was witnessed at the modified electrode in contrast to an unmodified electrode, demonstrating the enhanced electrochemical surface area of the BaO-MWCNT/MCPE. Additionally, the least charge transfer resistance and facile reaction catalysis for strong analyte interaction are the key factors in the fabrication of the sensor. The Nyquist plot and cyclic voltammograms provided evidence that the BaO-MWCNT/MCPE sensor has caused electrocatalytic oxidation of DIU. Thus, BaO-MWCNT composite material is a viable modifier in an electrochemical sensor. However, the study also evaluated the dearth of published studies on the electrochemical detection of other interfering species, such as amitrole, bentazone, and carbendazim, during real sample analysis. Furthermore, the sensor was efficiently utilized for the electrochemical DIU quantification in soil and water samples. These results emphasize the developed sensor to portray good selectivity, sensitivity, and reliability for DIU determinations.

Selective Aptamer Modification of Au Surfaces in a Microelectrode Sensor Array for Simultaneous Detection of Multiple Analytes

Aptamers have been employed as the biorecognition element in electrochemical aptamer-based (E-AB) biosensors, for the detection of a diverse range of analyte molecules, on electrodes with sizescales ranging from a few microns to several millimeters. Simultaneous detection of multiple different analytes requires the selective modification of multiple electrode surfaces with different aptamers. This process is typically achieved by incubating separate macroscale electrodes in a solution with the desired aptamer, which is unsuitable for microelectrode arrays in which the electrodes are closely spaced. In this work, we selectively modified electrode surfaces with thiolated aptamers of different single-stranded DNA sequences, by successive removal and addition of thiol monolayers. This was achieved by electrodesorption of thiol monolayers using controlled potential, to expose unmodified gold electrodes to be modified with a different thiolated aptamer, thus enabling multiple different aptamers to be used on the surfaces of closely spaced microelectrodes. All aptamers were methylene blue terminated, allowing redox currents to be measured and used to monitor aptamer probe packing density on the electrode surface and the selectivity of the sensors. Here, we demonstrate the microscale E-AB sensor multianalyte detection method using aptamers for target analytes, adenosine triphosphate, dopamine, and serotonin, which can ultimately be applied to perform localized simultaneous detection using electrode arrays.

Carbon based electrodes for the voltammetric determination of capsaicin in spicy samples

A voltammetric sensor based on the modification of a screen-printed carbon electrode with reduced graphene oxide (rGO-SPCE) is presented for the cyclic voltammetric determination of capsaicin in a wide range of concentrations. Special attention was given to factors affecting sensitivity and repeatability in order to overcome common reported issues related to the voltammetric determination of capsaicin. Fouling associated to the adsorption of capsaicin was minimized using a simple and effective washing step, allowing sensors to be reused for at least 10 measurements with a repeatable signal. The developed rGO-SPCE presented two well-defined linear ranges (from 1.1 to 25.0 and from 25.0 to 150.3 µmol L−1) and provided an increased sensitivity as compared to the unmodified electrode as well as to other modified electrodes based on carbon nanomaterials commercially available. Furthermore, a low limit of detection of 0.3 µmol L−1 was achieved and the accuracy of the method was demonstrated for the determination of capsaicin in chilli pepper, paprika samples and Tabasco sauce, obtaining comparable results to those achieved by liquid chromatography with UV–vis detection.

Surface modification of Ti3C2Tx using terminal groups and heteroatoms with excellent electrochemical performance in supercapacitors

Surface modification of Ti3C2Tx greatly enhances its charge storage mechanism as an electrode material. Herein, we demonstrate the role of surface terminals and heteroatoms in the electrochemical behavior of Ti3C2Tx electrodes. The abundance of –F and –OH surface terminals may be obtained with an acidic or base medium while etching of Ti3C2Tx. Further treatment with ammonia or glucose may help to get a thin layer of N or C at the surface of Ti3C2Tx. It is found that abundant reaction sites and larger interlayer spacing can help in improving the specific capacitance by nearly 2.5 times to unmodified Ti3C2Tx electrodes. This superior performance can be achieved without sacrificing the conductivity and accordion-like structure of Ti3C2Tx MXene two-dimensional material.

Anti-fouling TiO2-Coated Polymeric Membrane Ion-Selective Electrodes with Photocatalytic Self-Cleaning Properties

Nowadays, using a polymeric membrane ion-selective electrode (ISE) to achieve reliable ion sensing in complex samples remains challenging because of electrode fouling. To address this challenge, we describe a polymeric membrane ISE with excellent anti-fouling and self-cleaning properties based on surface covalent modification of an anatase TiO2 coating. Under ultraviolet illumination, the reactive oxygen species produced by photocatalytic TiO2 can not only kill microorganisms but also degrade organic foulants into carbon dioxide and water, and a formed superhydrophilic film can effectively prevent the adsorption of foulants, thus inhibiting the occurrence of biofouling and organic fouling of the sensors. More importantly, residual foulants could be fully self-cleaned through the flow of water droplets. By using Ca2+-ISE as a model, an anti-fouling polymeric membrane potentiometric sensor has been developed. Compared to the unmodified electrode, the TiO2-coated Ca2+-ISE exhibits remarkably improved anti-biofouling properties with a low bacterial adhesion rate of 4.74% and a high inhibition rate of 96.62%. In addition, the proposed electrode displays unique properties of anti-organic dye fouling and a superior self-cleaning ability even after soaking in a concentrated bacterial suspension of 109 CFU mL-1 for 60 days. The present approach can be extended to improve the fouling resistance of other electrochemical or optical membrane sensors and is promising for the construction of contamination-free sensors.

Polysulfide-derived anion heterogeneous interfaces engineering to facilitate high-efficiency sodium ion storage

Poor structural stability and inherent low conductivity of the transition metal polysulfides often trigger continuous capacity decay. Here, an anionic heterogeneous modification engineering of the VS4 system is achieved by employing one-step strategy. The prepared layered V1.11S2/V1.13Se2/C heterostructure (VSSe/C) exhibits expanded layer distance (5.926 Å) and improved metallicity properties. Furthermore, the constructed built-in electric field achieves lower free energy and effective adsorption of reaction products. Resultantly, when applied to the sodium-ion battery anode, a high specific capacity of 784.9 mA h g−1 is achieved with 500 cycles at a current density of 2 A g−1. Impressively, a high capacity retention of 553.2 mA h g−1 is performed after 1000 cycles at 10 A g−1, which is significantly better than the unmodified VS4 electrode. Additionally, the assembled sodium ion capacitor exhibits excellent energy densities of 89.1 W h kg−1 at 380 W kg−1 and an ultra-high capacity retention rate of 96.6% over 2000 cycles at a high power density of 3800 W kg−1. Ex-situ XRD and XPS results reveal a stable disulfide/selenide conversion process, and no intermediate polysulfide formation. The design of anionic heterostructures using polysulfide derivatives may provide a reference for improving the structural properties of anion-rich based anode materials.

Validated portable device for the qualitative and quantitative electrochemical detection of MDMA ready for on-site use

Identifying and quantifying 3,4-methyl​enedioxy​methamphetamine (MDMA) on-site in suspected illicit drug samples, whether it be at recreational settings or manufacturing sites, is a major challenge for law enforcement agencies (LEAs). Various analytical techniques exist to fulfil this goal, e.g. colourimetry and portable spectroscopic techniques, each having its specific limitations (e.g. low accuracy, fluorescence, no quantification) and strengths (e.g. fast, easy to use). In this work, for the first time, an electrochemical MDMA sensor is presented to become a detection tool that can realistically be used on-site. More specifically, the use of a single buffer solution and an unmodified screen-printed electrode, along with the integration of a data analysis algorithm and mobile application permits the straightforward on-site identification and quantification of MDMA in suspicious samples. Multiple studies investigating different parameters, including pH, concentration, reproducibility, temperature and binary mixture analyses, were executed. To fully understand all the occurring redox processes, liquid chromatography coupled with high-resolution mass spectrometry analysis of partially electrolyzed MDMA samples was performed unravelling oxidation of the methylenedioxy group. Validation of the methodology was executed on 15 MDMA street samples analysed by gas chromatography coupled with mass spectrometry and compared with the performance of a commercial portable Raman and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) device. The novel methodology outperformed the spectroscopic techniques, correctly identifying all 15 street samples. Additionally, the electrochemical sensor predicted the purity of the tablets with a mean absolute error of 2.3%. Overall, this new, electrochemical detection strategy provides LEAs the rapid, low-cost, on-site detection and quantification of MDMA in suspicious samples, without requiring specialized training.

Electrochemical oxidation of chloramphenicol by modified Sm-PEG-PbO2 anodes: Performance and mechanism

Chloramphenicol (CAP) is used extensively in industry and daily life, but its abuse has seriously affected the environment and public health. In this paper, a new composite PbO2 electrode was obtained through the modification Sm and polyethylene glycol (PEG), and an electrocatalytic oxidation technology of CAP degradation was investigated. The results showed that the catalytic degradation ability and industrial service life of the PEG-Sm-PbO2 composite electrode were significantly enhanced. Co-doping inhibited the growth of grains, resulting in the formation of refined pyramidal grains on the surface of the electrode, which increased the number of active spots. The industrial service life of the modified electrode was improved by 87.0%. In addition, the degradation effect under different conditions and mechanism of CAP were also explored. The optimal conditions for CAP degradation were explored, at which time the CAP degradation rate reached 99.1%. The degradation process was in accordance with the primary reaction kinetics, and the apparent rate constant of CAP at the PEG-Sm-PbO2 electrode was raised by 57.1% in comparison with the unmodified electrode, indicating that the modification facilitated the degradation of CAP in the electrode. Finally, two possible CAP degradation pathways were deduced. The results will provide technical support and a theoretical basis for the degradation of persistent organic pollutants.

Development of unmodified and CTAB-modified carbon paste electrodes (CPE) for direct electrochemical analysis of nitrites in aquarium water and rat blood

Development of unmodified and CTAB-modified carbon paste electrodes (CPE) for direct electrochemical analysis of nitrites in aquarium water and rat blood

Voltammetric determination of vitamin B6 in the presence of vitamin C based on zinc ferrite nano-particles modified screen-printed graphite electrode.

The zinc ferrite nano-particles (ZnFe2O4) modified screen-printed graphite electrode (ZnFe2O4/SPGE) was used for the voltammetric determination of vitamin B6 in real samples, using differential pulse voltammetry (DPV). It has been found that the oxidation of vitamin B6 at the surface of such an electrode occurs at a potential about 150 mV less positive compared to an unmodified screen-printed graphite electrode. After optimization, a vitamin B6 sensor with a linear range from 0.8 to 585.0 μM and a detection limit of 0.17 μM. The ZnFe2O4/SPGE sensor exhibits good resolution between the voltammetric peaks of vitamin B6 and vitamin C, making it suitable for detecting vitamin B6 in the presence of vitamin C in real samples.

Utilizing epicatechin voltammetric oxidation signal for the estimation of total phenolic content in the tea samples via the unmodified boron-doped diamond electrode surface

In this work, the boron-doped diamond (BDD) electrode surface was employed for the first time in conjunction with the epicatechin (EC) oxidation signal to estimate the total phenolic content of tea samples by voltammetry. During cyclic voltammetry analysis of the EC, an easily identifiable, irreversible, and adsorption-controlled oxidation peak was observed at around +1.05 V (vs. Ag/AgCl) in HNO3 solution. Our experimental setup was fine-tuned by investigating the effect of electrode pretreatment, pH of the supporting electrolyte, accumulation factors, and instrumental parameters on the oxidation peak response of EC. When measuring EC in a 0.1 mol L−1 HNO3 solution at +1.0 V, square-wave adsorptive stripping voltammetry provided a highly linear response (at open-circuit accumulation for 30 s). The dynamic range was determined to be between 1.0 and 50.0 μg mL−1 (3.4510−6–1.7210−4 mol L−1), while the detection limit was found to be 0.28 μg mL−1 (9.6510−7 mol L−1). Selectivity studies were performed with other phenolic compounds found in tea such as epigallocatechin gallate, catechin, tannic acid, and gallic acid. Finally, by assessing the total phenolic content in the black and green tea samples, the suggested approach's applicability was shown by providing an estimate of the EC equivalents present in the samples.

Bio-Electroanalysis Performance of Heme Redox-Center for π-π Interaction Bonding of a Methylene Blue-Graphene Modified Electrode.

Hemeprotein detection has motivated extensive research on the direct reaction of a heme molecule and a redox dye. The present study used methylene blue as both donor and acceptor for a redox reaction. First, the solid phases of methylene blue (MB) and graphene (GP) formed a π-π interaction bond at the aromatic rings. The conductivity of GP was better than that of carbon in a carbon electrode (CE). Then, the working CE was modified using strong adsorption of MB/GP on the electrode surface. The surface of the electrode was investigated using a modified and an unmodified electrode. The electrode's properties were studied using voltammograms of redox couple K3[Fe(CN)6]3-/4-. Its reaction was used to find the active area of the modified electrode, which was 1.76 times bigger than that of the unmodified electrode. The surface coverage values of the modified and unmodified electrodes were 8.17 × 10-6 and 1.53 × 10-5 mol/cm2, respectively. This research also studied the application of hemeprotein detection. Hemoglobin (Hb), myoglobin (Mb), and cytochrome c (Cyt. C) were studied by the reaction of Fe (III/II) at the heme-redox center. The electrocatalytic reaction between MB/GP and hemeproteins produced an anodic peak at 0.35 V for Hb, Mb, and Cyt. C. This nanohybrid film enhanced electron transfer between protein molecules and the modified carbon electrode. The amperometric measurements show that the limit of detection was 0.2 µM, 0.3 µM, and 0.1 µM for Hb, Mb, and Cyt. C, respectively. The measurement spanned a linear range of 0.2 µM to 5 µM, 0.3 µM to 5 µM, and 0.1 µM to 0.7 µM for Hb, Mb, and Cyt. C, respectively. Hb showed the lowest sensitivity compared with Mb and Cyt. C due to the role of steric hindrance in the hemeprotein specificity structure. This study offers a simple and efficient fabrication platform for electrochemical sensors for hemeproteins. When compared to other complex immobilization processes, the fabrication method for this sensor has many benefits, including no need for special chemicals and easy preparation and electrode modification-both of which are crucial for the development of electrochemical sensing devices.

Electrocatalytic Performance of Ethanol Oxidation on Ni and Ni/Pd Surface-Decorated Porous Structures Obtained by Molten Salts Deposition/Dissolution of Al-Ni Alloys.

Ni coatings with high catalytic efficiency were synthesised in this work, obtained by increasing the active surface and modifying Pd as a noble metal. Porous Ni foam electrodes were obtained by electrodeposition of Al on a nickel substrate. Deposition of Al was carried out with potential -1.9 V for a time of 60 min in NaCl-KCl-3.5 mol%AlF3 molten salt mixture at 900 °C, which is connected with the formation of the Al-Ni phase in the solid state. Dissolution of Al and Al-Ni phases was performed by application of the potential -0.5 V, which provided the porous layer formation. The obtained porous material was compared to flat Ni plates in terms of electrocatalytic properties for ethanol oxidation in alkaline solutions. Cyclic voltammetry measurements in the non-Faradaic region revealed the improvement in morphology development for Ni foams, with an active surface area 5.5-times more developed than flat Ni electrodes. The catalytic activity was improved by the galvanic displacement process of Pd(II) ions from dilute chloride solutions (1 mM) at different times. In cyclic voltammetry scans, the highest catalytic activity was registered for porous Ni/Pd decorated at 60 min, where the maximum oxidation peak for 1 M ethanol achieved +393 mA cm-2 compared to the porous unmodified Ni electrode at +152 mA cm-2 and flat Ni at +55 mA cm-2. Chronoamperometric measurements in ethanol oxidation showed that porous electrodes were characterised by higher catalytic activity than flat electrodes. In addition, applying a thin layer of precious metal on the surface of nickel increased the recorded anode current density associated with the electrochemical oxidation process. The highest activity was recorded for porous coatings after modification in a solution containing palladium ions, obtaining a current density value of about 55 mA cm-2, and for a flat unmodified electrode, only 5 mA cm-2 after 1800 s.

Simple and rapid determination of clonidine in pharmaceutical samples by voltammetry using a bare glassy carbon electrode

AbstractThis work presents, for the first time, the voltammetric behavior of clonidine (CLO) drug and its determination, using an unmodified glassy carbon electrode (GCE). CLO exhibited only an irreversible oxidation process on the GCE, with peak potential at +0.85 V in pH 12 (vs Ag/AgCl). CLO oxidation process is pH‐dependent and the electrochemical mechanisms on the GCE were proposed in acidic and basic medium. The determination of CLO was optimized in 0.1 mol L−1 phosphate buffer solution at pH 12.0 using differential pulse voltammetry (DPV), which provides a good linear range (0.65 to 106.00 μmol L−1) and low theoretical limit of detection (0.14 μmol L−1) for the quality control of this drug in pharmaceutical samples. In addition, stable responses of CLO at the GCE were obtained in the same day (RSD = 3.4 %; n = 5) and different days (RSD = 2.0 %; n = 3). Moreover, the determination of CLO in a pharmaceutical formulation using the proposed GCE‐DPV method presented good accuracy, since the recovery was close to 100 % and the dosing result was in agreement with an official method (HPLC‐UV). The proposed method demonstrates a good analytical performance for CLO determination in pharmaceutical samples, providing a faster, simpler and lower‐cost alternative for quality control of CLO than other reported methods.

New electrode material GCE/AgNPs‐D3 as an electrochemical sensor used for the detection of thallium ions

AbstractOptimal working parameters for the innovative electrode GCE/AgNPs‐D3 were determined and the selectivity was assessed. The stripping anodic peak current of thallium characterized in linearity over range from 4.9 ⋅ 10−8 to 4.9 ⋅ 10−7 mol ⋅ dm−3, with LOD = 7.16 ppb (3.5 ⋅ 10−8 mol ⋅ dm−3). Furthermore, the new electrode showed more than sevenfold improvement in the thallium current signal compared to the unmodified electrode GCE. High selectivity was achieved using EDTA disodium salt as a complexing agent for other metals.

Detection of Allura Red in Food Samples Using Carbon Paste Modified with Lanthanum and Titanium Oxides

AbstractThis report describes a new electroanalytical application for the detection of Allura Red (AR) using a carbon paste electrode (CPE) modified with lanthanide oxide and titanium oxide (LaOX‐TiOX/CPE). The standard potential (Eo) for oxidation of AR was obtained from the E (V) vs. pH relation with the regression equation Ep(V)=−0.038pH+0.922, where the intercept on the axis Ep(V) is equal to the standard potential. Moreover, the anodic peak current for AR was increased almost 160 % compared to the unmodified electrodes, and this current increase allowed us to obtain a detection limit of 0.09 μmol/L. The active surface area of the modified electrode La‐TiOX/CPE is reported for the first time in this report and was increased by almost 200 % compared to the unmodified electrodes. The usefulness of the new method was tested by analyzing real food samples with acceptable results. The real samples do not need pretreatment before analysis