Oxidation Peak Research Articles

Enhancement of aluminum powder reaction behavior at high temperatures—Aluminum powders with “sea urchin structure” coated by AP

To solve the problem of high ignition temperature of aluminum powder and easy to burn into blocks at high temperatures, “sea-urchin-structured” aluminum powders (μAl@nAl) obtained by electro-explosion were coated by ammonium perchlorate (AP) on its surface. AP in a high-temperature environment has a rapid decomposition, then the gas production will promote the dispersion of aluminum powder into micro-clusters, thus preventing the aluminum powder agglomeration during the combustion process. The micro-nano composite aluminum powder (μAl@8 %nAl) and physical mixed aluminum powder (μAl + 8 %nAl) coated by AP were completed by solvent volatilization method. The coating surface was observed by scanning electron microscopy. The heat of combustion and pressure curves for different AP contents were tested using a chamber with a constant volume, and the ignition and combustion performance of the AP samples were investigated using a carbon dioxide (CO2) laser ignition device. The AP samples shortened the ignition delay time and improved the combustion performance in the fixed-volume combustion and laser ignition tests. Under atmospheric air, taking into account the theoretical calorific value, pressure curve, and combustion performance, the optimal AP content is 10 %. The thermal decomposition process of two samples was further analyzed using the thermogravimetric and differential scanning calorimetry (TG-DSC) method. The decomposition of AP advanced the first oxidation peak of aluminum powder; however, in the second step oxidation peak, the peak temperature of μAl@8 %nAl@10 %AP sample was delayed compared to μAl + 8 %nAl@10 %AP sample. High-voltage electrical explosions and high-energy laser-induced air shock waves were created to simulate the high-temperature environment of the detonation reaction zone, and pictures of the reaction process and pressure change curves of the “sea urchin structure” aluminum powder coated by AP at high temperatures were recorded. The results showed that the “sea urchin structure” aluminum powder coated by AP exhibited better combustion performance, and the reaction degree of the aluminum powder had been deepened.

A multi-layer membrane filter made of potassium catalyst and three-way catalyst for a passive after-treatment system

A multi-layer membrane has been fabricated to integrate a Three-Way Catalyst (TWC) and Gasoline Particulate Filter (GPF) into one device, called a four-way catalytic converter. The top layer, made of nano-scale potassium catalyst particles, traps Particulate Matter (PM) with almost 100% filtration efficiency at all times and oxidizes PM (mostly soot) with a significantly reduced temperature of 476°C at the oxidation peak. Moreover, the bottom layer catalyst is comprised of sub-micro TWC particles to combine NO reduction and CO oxidation capabilities. The effective temperature range for the simultaneous removal of all pollutants was between 420°C–500°C.

SIMULTANEOUS DETERMINATION OF ASCORBIC ACID, URIC ACID, AND DOPAMINE ON CARBON NANOTUBE PASTE ELECTRODE

Background: Ascorbic acid (AA), uric acid (UA), and dopamine (DA) play crucial roles in human metabolism. These substances coexist in biological fluids, and their levels are directly associated with various pathologies. A significant problem encountered in the direct and simultaneous electrochemical detection of AA, UA, and DA is that these species present very close oxidation potentials on most electrode materials, leading to an overlap in the voltammetric response. Aim: The main goal of this work was to determine the concentration of AA, UA, and DA in a natural water sample on a carbon nanotube paste electrode (CNTPE). Methods: All voltammetric measurements were performed on a µAutolab potentiostat/galvanostat (Metrohm) connected to an electrochemical cell of three electrodes: working, reference (Ag/AgCl, KCl3.0M), and auxiliary (platinum). The working electrode was handmade in our laboratory. The following proportions were used to prepare the paste: 50% CNT + 50% mineral oil and 65% CNT + 35% mineral oil. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the electroanalytical study. Results: The linear ranges for the simultaneous determination of AA, DA, and UA by DPV were: 0.45 – 1.0 mM, 50 – 200 ?M, and 10 – 90 ?M, respectively. The LODs of the proposed method for AA, DA, and UA were: 7.97 mM; 8.57 ?M, and 5.96 ?M, respectively. The relative standard deviations (RSD) were 4.6, 2.8, and 1.6% for 0.45 mM of AA, 50 ?M of DA, and 50 ?M of UA. Discussion: The oxidation mechanism of: AA, UA, and DA is a process that involves two electrons and 2 protons. Electrochemical detection of DA in the presence of high levels of AA on carbon-based electrodes becomes difficult due to the catalytic oxidation of AA by DA. For the three molecules, AA, UA, and DA, it is observed that the oxidation peak currents increased with increasing concentration. Conclusions: CNTPE allowed the separation of the oxidation peaks of the ternary mixture of AA, UA, and DA by cyclic voltammetry and, when associated with DPV allowed the simultaneous quantitative determination of AA, UA, and DA.

Real samples sensitive dopamine sensor based on poly 1,3-benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)acetonitrile on a glassy carbon electrode

Herein, a novel electrochemical sensor that was used for the first time for sensitive and selective detection of dopamine (DA) was fabricated. The new sensor is based on the decoration of the glassy carbon electrode surface (GC) with a polymer film of 1,3-Benzothiazol-2-yl((4-carboxlicphenyl)hydrazono)) acetonitrile (poly(BTCA). The prepared (poly(BTCA) was examined by using different techniques such as 1H NMR, 13C NMR, FTIR, and UV-visible spectroscopy. The electrochemical investigations of DA were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results obtained showed that the modifier increased the electrocatalytic efficiency with a noticeable increase in the oxidation peak current of DA in 0.1 M phosphate buffer solution (PBS) at an optimum pH of 7.0 and scan rate of 200 mV/s when compared to unmodified GC. The new sensor displays a good performance for detecting DA with a limit of detection (LOD 3σ), and limit of quantification (LOQ 10σ) are 0.28 nM and 94 nM respectively. The peak current of DA is linearly proportional to the concentration in the range from 0.1 to 10.0 µM. Additionally, the fabricated electrode showed sufficient reproducibility, stability, and selectivity for DA detection in the presence of different interferents. The proposed poly(BTCA)/GCE sensor was effectively applied to detect DA in the biological samples.

Conducting Nickel Hydroxide Thin Film on Molybdenum Disulfide – Reduced Graphene Oxide Composite Electrode for Simultaneous Detection of Uric Acid, Dopamine and Ascorbic Acid

AbstractHerein we report the fabrication of a simple electrochemical sensor based on an electrode containing reduced graphene oxide and molybdenum disulphide (RGO/MoS2) as a conducting film onto the glassy carbon electrode (GCE) via a drop dry method to form GCE‐RGO/MoS2. The surface (GCE‐RGO/MoS2) was further modified with nickel hydroxide thin film using electrodeposition method to form GCE‐RGO/MoS2/Ni(OH)2. The materials and modification steps were thoroughly characterized using microscopy and spectroscopy methods. The composite electrode, GCE‐RGO/MoS2/Ni(OH)2, showed excellent electrocatalytic potential separation for the detection of dopamine, uric acid, and ascorbic acid. The electrocatalytic oxidation peak potentials were at 3 mV, 157 mV and 303 mV for AA, DA and UA, respectively. The composite electrode was also selective towards the determination of ascorbic acid (AA), dopamine (DA), uric acid (UA), and simultaneously in mixture of analytes. The low detection limits for AA, DA and UA were 1.17 μM, 0.15 μM and 1.15 μM, respectively. The composite electrode was applied for the detection of AA, DA and UA in spiked newborn calf serum samples with high percentage recoveries ranging from 96.6–100.8 % for AA, 92.8–104.2 % for DA and 99.4–102.3 % for UA.

Electrochemically deposited Au nano-island on laser-scribed graphene substrates as EC-SERS biochips for uremic toxins detection

BackgroundChronic kidney disease (CKD) leads to uremic toxin buildup, requiring early detection for better management. Existing methods lack sensitivity, speed, or affordability for point-of-care diagnosis. This work addresses this by creating a novel sensor for rapid, sensitive uremic toxin detection. MethodsThe sensor leverages the combined effects of surface-enhanced Raman scattering (SERS) and electrochemistry (EC) for superior detection. The LIG substrate provides a stable platform for AuNPs, facilitating interaction with target molecules. Additionally, electrochemical deposition optimizes the sensor's sensitivity by amplifying the local electromagnetic field around AuNPs and offering specific binding sites for uremic toxins. Significant findingsThe developed sensor demonstrates exceptional performance in detecting uremic toxins. It achieves remarkably low detection limits (10-3 M for creatinine/uric acid, 10-4 M for urea) and offers distinct, concentration-dependent responses for different toxins in cyclic voltammetry (CV) measurements. Furthermore, characteristic oxidation peaks at specific potentials allow for direct identification and quantification of the toxins. These findings highlight the immense potential of this cost-effective and scalable sensor for point-of-care diagnostics and remote monitoring of kidney function. This advancement can significantly improve patient care by facilitating early detection of kidney problems and enabling timely intervention.

Liquid Redox Probe-Free Plastic Antibody Development for Malaria Biomarker Recognition.

Malaria is a major public health challenge worldwide and requires accurate and efficient diagnostic methods. Traditional diagnostic approaches based on antigen-antibody interactions are associated with ethical and economic concerns. Molecularly imprinted polymers (MIPs) offer a promising alternative by providing a complementary polymer structure capable of selectively binding target molecules. In this study, we developed a liquid, redox-probe-free, MIP-based electrochemical biosensor to detect the Plasmodium falciparum malaria marker histidine-rich protein (HRP2) at the point-of-care (PoC). The imprinting phase consists of the electropolymerization of the monomer methylene blue (MB) in the presence of the target protein HRP2 at the working electrode (WE) of the modified carbon screen printed electrode (C-SPE). Subsequent removal of the protein with proteinase K and oxalic acid yielded the MIP material. The sensor assembly was monitored by cyclic voltammetry (CV), Raman spectroscopy and scanning electron microscopy (SEM). The analytical performance of the biosensor was evaluated by square-wave voltammetry (SWV) using calibration curves in buffer and serum with a detection limit of 0.43 ± 0.026 pg mL-1. Selectivity studies showed minimal interference, indicating a highly selective assay. Overall, our approach to detect the HRP2 infection marker offers simplicity, cost-effectiveness and reliability. In particular, the absence of a redox solution simplifies detection, as the polymer itself is electroactive and exhibits oxidation and reduction peaks.

Electro-generating Cu2+ ions based on electrochemically modified CPE for the determination of malathion pesticide using valid SW-ASV method

This work investigates the validation of the SW-ASV method for the determination of malathion organophosphorus pesticide based on an electrochemically modified (CPE) carbon paste electrode with copper metal. The surface of the modified CPE was constructed by electrodepositing the copper layer at the accumulation step in 1-mM CuSO4.5H2O, PBS at pH 6.6, E accumulation: − 0.8 V, and Taccumulation 240 s. The determining step was performed by adding different concentrations of malathion pesticide and applying the potential toward more positive potential at (− 0.8–+ 1.4 V) to enhance the oxidation of Cu0 metal. It was noticed that the malathion concentration gradient enhances the oxidation peak current of copper at + 0.03 V gradually. SW-ASV method validation was performed at a linearity range confined in (1–10 µM). An analytical curve was constructed and R2 was equal to 0.99995 with good fitted linear relationship. LOD and LOQ were calculated to be 0.0247 and 0.08236 µM, respectively. ANOVA for two sets of measurements using the standard gas chromatographic method and the suggested SW-ASV method was demonstrated via the calculations of F-value and t-value. F and t-values were calculated to be 1.698 and 0.289, respectively, which did not exceed the tabulated F and t-values resulting in the great similarity of results and ensuring the reliability of the suggested test method. This valid SW-ASV method was used to perform the routine analysis of the 95% technical grade and the pesticide formulation 57% emulsion concentrate of the malathion. Valid results were achieved with satisfactory limits of accuracy and precision.Graphical abstract

Optimizing Ni–Cr patterned boron-doped diamond band electrodes: Doping effects on electrochemical efficiency and posaconazole sensing performance

There is growing interest in developing diamond electrodes with defined geometries such as, for example, micrometer-sized electrode arrays to acquire signals for electroanalysis. For electroanalytical sensing applications, it is essential to achieve precise conductive patterns on the insulating surface. This work provides a novel approach to boron-doped diamond patterning using nichrome masking for selective seeding on an oxidized silicon substrate. The optimized process involves nichrome deposition, sonication, chemical etching, seeding, and tailored chemical vapor deposition of boron-doped diamond with an intrinsic layer to suppress boron diffusion. Through a systematic investigation, it was determined that isolated boron-doped diamond band electrodes can be efficiently produced on non-conductive silica. Additionally, the influence of boron doping on electrochemical performance was studied, with higher doping enhancing the electrochemical response of band electrodes. To demonstrate sensing capabilities, boron-doped diamond bands were used to detect posaconazole, an antifungal drug, exploiting its electroactive behaviour. A linear correlation between posaconazole concentration and oxidation peak current was observed over 1.43 × 10−8 – 5.71 × 10−6 M with a 1.4 × 10−8 M detection limit. The developed boron-doped diamond microbands could significantly impact the field of electroanalysis, facilitating detection of diverse biologically relevant molecules. Overall, this diamond patterning approach overcomes major challenges towards all-diamond electrochemical sensor chips.

Electrochemical determination of wine polyphenols using carbon electrodes: A review

AbstractWine′s phenolic compounds present a group of hundreds of chemical compounds, contributing to the wine taste, color, and stability during the ageing. These compounds include phenolic acids, flavonols, anthocyanins, catechins, proanthocyanidins etc. They are very important because they offer numerous good benefits for human body. Electrochemical methods show a valuable technique for the determination of redox compounds in wine. In this review, a lot of attention is paid to carbon‐based electrodes and to the voltammetric signals obtained in red and white wines using different modifiers for the electrode surface with nanoparticles and natural compounds used in the construction of biosensors. These electrodes are widely used due to their non‐toxic properties, wide potential ranges, high conductivity and the possibility of use in aqueous and non‐aqueous solutions. Different carbon electrodes are considered and briefly discussed. This review explores the current advancements in the electrochemical determination of most important polyphenolic compounds in wine using carbon electrodes. Also, this review gives a clear view about the oxidation peaks of various phenolic compounds in wine. It encompasses ‐the in‐depth analysis of the different types of carbon electrodes used, such as glassy carbon, carbon paste, carbon nanotubes, screen‐printed,graphene‐based electrodes, biosensors and their respective benefits in polyphenolic compounds analysis. In conclusion, the electrochemical determination of polyphenolic compounds in wine using carbon electrodes offers a promising route for accurate and reliable analysis, with important implications for the wine industry and research. This review provides comprehensive information for researchers, winemakers and analytical chemists seeking to understand and apply these techniques for improving wine quality and advancing knowledge.

Glycosylated flavonoid kaempferitrin: Electroanalytical detection and the proposal of an oxidation mechanism supported by quantum chemical calculations

In this work, the electrochemical behavior of the glycosylated flavonoid kaempferitrin was studied, and an electroanalytical methodology was developed for its determination in infusions of Bauhinia forficata using a boron-doped diamond electrode (BDD). The electrochemical behavior of the flavonoid was studied by cyclic voltammetry, and two irreversible oxidation peaks at 0.80 and 1.0 V vs Ag/AgCl were observed. The influence of the pH on the voltammograms was examined, and higher sensitivity was found at pH 7.0. The electrochemical process corresponding to peak 1 at 0.80 V is predominantly diffusion-controlled, as the study shows at varying scan rates. An analytical plot was obtained by square wave voltammetry at optimized experimental conditions (frequency = 100 s−1, amplitude = 90 mV, and step potential = 8 mV) in the concentration range from 3.4 μmol L−1 to 58 μmol L−1, with a linearity of 0.99. The limit of detection and limit of quantification values were 1.0 μmol L−1 and 3.4 μmol L−1, respectively. Three samples of Bauhinia forficata infusions (2 g of sample in 100 mL of water) were analyzed, and the KF values found were 5.0 × 10−4 mol L−1, 3.0 × 10−4 mol L−1, and 7.0 × 10−4 mol L−1, with recovery percentages of 98 %, 106 % and 94 %, respectively. Finally, experiments were performed with two other flavonoids (chrysin and apeginin) to compare and propose an electrochemical oxidation mechanism for kaempferitrin, which was supported by quantum chemical calculations.

Development of a molecularly imprinted polymer-based electrochemical sensor with metal-organic frameworks for monitoring the antineoplastic drug vismodegib

A novel and robust electrochemical sensing tool for the determination of vismodegib (VIS), an anticancer drug, has been developed by integrating the selective recognition capabilities of molecularly imprinted polymer (MIP) and the sensitivity enhancement capability of metal-organic framework (MOF). Prior to this step, the electrochemical behavior of VIS was investigated using a bare glassy carbon electrode (GCE). It was observed that in 0.5 M H2SO4 solution as electrolyte, VIS has an oxidation peak around 1.3 V and the oxidation mechanism is diffusion controlled. The determination of VIS in a standard solution using a bare GCE showed a linear response in the concentration range from 2.5 μM to 100 μM, with a limit of detection (LOD) of 0.75 μM. Since sufficient sensitivity and selectivity could not be achieved with bare GCE, a MIP sensor was developed in the next step of the study. For this purpose, the GCE surface was first modified by drop casting with as-synthesized Co-MOF. Subsequently, a MIP network was synthesized via a thermal polymerization approach using 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as monomer and VIS as template. MOFs are ideal electrode materials due to their controllable and diverse morphologies and modifiable surface properties. These characteristics enable the development of MIPs with more homogeneous binding sites and high affinity for target molecules. Integrating MOFs could help the performance of sensors with the desired stability and reproducibility. Electrochemical analysis revealed an observable enhancement of the output signal by the incorporation of MOF molecules, which is consistent with the sensitivity-enhancing role of MOF by providing more anchoring sites for the attachment of the polymer texture to the electrode surface. This MOF-MIP sensor exhibited impressive linear dynamic ranges ranging from 0.1 to 1.0 pM for VIS, with detection limits in the low picomolar range. In addition, the MOF-MIP sensor offers high accuracy, selectivity and precision for the determination of VIS, with no interference observed from complex media of serum samples. Additionally, in this study, Analytical GREEnness metric (AGREE), Analytical GREEnness preparation (AGREEprep) and Blue Applicability Grade Index (BAGI) were used to calculate the green profile score.

Mechanisms Associated with Superoxide Radical Scavenging Reactions Involving Phenolic Compounds Deduced Based on the Correlation between Oxidation Peak Potentials and Second-Order Rate Constants Determined Using Flow-Injection Spin-Trapping EPR Methods.

Flow-injection spin-trapping electron paramagnetic resonance (FI-EPR) methods that involve the use of 5,5-dimethyl-pyrroline-N-oxide (DMPO) as a spin-trapping reagent have been developed for the kinetic study of the O2•- radical scavenging reactions occurring in the presence of various plant-derived and synthetic phenolic antioxidants (Aox), such as flavonoid, pyrogallol, catechol, hydroquinone, resorcinol, and phenol derivatives in aqueous media (pH 7.4 at 25 °C). The systematically estimated second-order rate constants (ks) of these phenolic compounds span a wide range (from 4.5 × 10 to 1.0 × 106 M-1 s-1). The semilogarithm plots presenting the relationship between ks values and oxidation peak potential (Ep) values of phenolic Aox are divided into three groups (A1, A2, and B). The ks-Ep plots of phenolic Aox bearing two or three OH moieties, such as pyrogallol, catechol, and hydroquinone derivatives, belonged to Groups A1 and A2. These molecules are potent O2•- radical scavengers with ks values above 3.8 × 104 (M-1 s-1). The ks-Ep plots of all phenol and resorcinol derivatives, and a few catechol and hydroquinone derivatives containing carboxyl groups adjacent to the OH groups, were categorized into the group poor scavengers (ks < 1.6 × 103 M-1 s-1). The ks values of each group correlated negatively with Ep values, supporting the hypothesis that the O2•- radical scavenging reaction proceeds via one-electron and two-proton processes. The processes were accompanied by the production of hydrogen peroxide at pH 7.4. Furthermore, the correlation between the plots of ks and the OH proton dissociation constant (pKa•) of the intermediate aroxyl radicals (ks-pKa• plots) revealed that the second proton transfer process could potentially be the rate-determining step of the O2•- radical scavenging reaction of phenolic compounds. The ks-Ep plots provide practical information to predict the O2•- radical scavenging activity of plant-derived phenolic compounds based on those molecular structures.

Preparation of CoFe@C composite modified electrode for neohesperidin dihydrochalcone sensing and its application in Chinese medicine.

CoFe@C was first prepared by calcining the precursor of CoFe-metal-organic framework-74 (CoFe-MOF-74), then an electrochemical sensor for the determination of neohesperidin dihydrochalcone (NHDC) was constructed, which was stemmed from the novel CoFe@C/Nafion composite film modified glassy carbon electrode (GCE). The CoFe@C/Nafion composite was verified by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) was used to evaluate its electrical properties as a modified material for anelectrochemical sensor. Compared with CoFe-MOF-74 precursor modified electrode, CoFe@C/Nafion electrode exhibited a great synergic catalytic effect and extremely increased the oxidation peak signal of NHDC. The effects of various experimental conditions on the oxidation of NHDC were investigated and the calibration plot was tested. The results bespoken that CoFe@C/Nafion GCE has good reproducibility and anti-interference under the optimal experimental conditions. In addition, the differential pulse current response of NHDC was linear with its concentration within the range0.08 ~ 20µmol/L, and the linear regressioncoefficient was 0.9957. The detection limit was as low as 14.2nmol/L (S/N = 3). In order to further verify the feasibility of the method, it was successfully used to determine the content of NHDC in Chinese medicine, with a satisfactory result, good in accordance with that of high performance liquid chromatography (HPLC).

Electroanalysis of Catechol and Hydroquinone by Glassy Carbon Electrode Modified with Multi-Walled Carbon Nanotubes, β-cyclodextrin Decorated with Reduced Graphene Oxide - Gold Nanoparticle Nanocomposite

In this work, the glassy carbon electrode was modified by multi-walled carbon nanotubes, β-cyclodextrin, reduced graphene oxide, and gold nanoparticle nanocomposites GC/MWCNTs/β-CD-rGO@Au). The GC/MWCNTs/β-CD-rGO@Au electrode was utilized for simultaneous monitoring of catechol (CC) and hydroquinone (HQ). The modified electrode has a clear pair of voltammetric peaks for CC and HQ, which makes it an appropriate tool for the simultaneous determination of the two isomers. Under optimized conditions, the oxidation peak currents of CC and HQ at GC/MWCNTs/β-CD-rGO@Au were increased linearly in the 1–173 μM and 2–80 μM concentration range with the limit of detection (LOD) (based on S/N = 3) of 0.17 μM and 0.26 μM. The GC/MWCNTs/β-CD-rGO@Au exhibits adequate stability, repeatability, and recovery in analyzing two dihydroxybenzenes isomers.

Simultaneous electrochemical detection of hydroquinone and catechol using flexible laser-induced metal-polymer composite electrodes

The conversion of waste polymers into functional materials presents a promising approach for PET upcycling. In this study, we exploit PET transformed into a Laser-Induced Graphene/Al NPs/PET nanocomposite (LIMPc − Laser-Induced Metal-Polymer composite) modified with electrodeposited gold nanoparticles (AuNPs). The morphology and structure of the material were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The nanocomposite was employed as a flexible electrochemical sensor for the simultaneous electrochemical detection of hydroquinone (HQ) and catechol (CT). The LIMPc-plasma-NaOH-Au composite displayed well-defined oxidation peaks for HQ and CT during electrochemical analysis, with limits of detection (LOD) as low as 47 nM for CT and 56 nM for HQ, within a linear range of 0.1–300 μM for both compounds. The long-term stability of LIMPc-plasma-NaOH-Au and its performance in real sample analysis demonstrate its potential for environmental monitoring applications.

Simultaneous detection of pesticides, carbendazim, and isoproturon using a novel nanocomposite based on graphene oxide/multi-wall carbon nanotube as an electrochemical sensor

This study demonstrates the fabrication of an electrochemical probe and superior performance in the simultaneous determination of two pesticides, carbendazim (CBZ) and isoproturon (ISO), using a modified glassy carbon (GC) electrode with a novel graphene oxide/multi-walled carbon nanotube (GO-MWCNT) nanocomposite for the first time. The existing hydrophilic properties of GO can facilitate the development of a stable dispersion of GO-CNT nanocomposite material through π-π stacking interactions for their intriguing electrochemical detection. This novel nanocomposite was completely characterized by XRD, FT-IR, SEM, and TEM techniques. The MWCNT were dispersed/spread over the crumpled GO nano-sheets, as confirmed by the TEM images. Their oxidation potentials and current are significantly varied with various modified electrodes, such as bare GCE, MWCNT, GO, and GO-MWCNT in 0.1 M PBS (pH 2) at 50 mVs−1. The oxidation of ISO and CBZ on the GO-MWCNT-modified electrode has shown 3 and 5.2 times of current enhancement respectively, compared to the bare GCE. The feasibility of the proposed nanocomposite for the analysis has been shown by the observed maximum oxidation peak current recorded at pH 2. The cyclic voltammogram containing 0.1 mM of ISO and CBZ on the modified GO-MWCNT/GCE have yielded linear plots with the logarithm of scan rate vs peak potential with R2 values of 0.99 and 0.987 respectively, implying the occurred surface adsorption-controlled reaction process. Its reproducibility with 100 μM of ISO and 10 μM of CBZ has shown the related standard deviation for five experiments as 2.8 % and 1.58 % respectively. Moreover, the real sample analysis was optimized with GO-MWCNT/GCE by differential pulse voltammetry technique towards CBZ and ISO in the river and paddy water samples, and the recovery percentages were found to be 99–103 and 99.7–101.3 % respectively.

Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite–epoxy composite electrode: Hydrogen adsorption capacity of graphite–epoxy composite is one–third of that of platinum

A new possibility of indirect determination of free chlorine using a graphite–epoxy composite(GEC) electrode instead of Pt disk electrode was suggested by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of the free chlorine. The linear response range of concentration was 0.06–0.2 mg∙L−1 with correlation coefficient of 0.9951 (n = 5) and the sensitivity of 1225 μA cm−2 mg−1 L. The limit of detection (LOD) calculated from the 3σ IUPAC criteria was 1.2 × 10−2 mg L−1. The relative standard deviation (RSD) to 0.06 mg L−1 was 4.65%(n = 10). The results show that the amount of free chlorine in the disinfected seawater can be indirectly determined by using a GEC electrode without influence of interferences unlike a Pt disk electrode. On the other hand, in this paper, a new method is proposed to evaluate the relative hydrogen adsorption capacity by the sensitivity of GEC electrode compared with that of Pt disk electrode. During the investigation of the hydrogen adsorption on the surface of the working electrode, we obtained the result that the hydrogen adsorption capacity of GEC is one-third of that of platinum.

Voltammetric determination of the antifungal drug posaconazole in the presence of an anionic surfactant on a boron-doped diamond electrode

This study describes a new, fast and simple procedure of electrochemical assay of posaconazole (PCZ), which is currently regarded as one of the most important antifungal agents, recommended in the treatment of systemic infections, effective even against rare and atypical kinds of fungi. PCZ is very effective and safe, displaying much lower toxicity than other traditional antifungal drugs. A new, attractive procedure of assaying the compound on boron-doped diamond (BDD) electrode after cathodic pretreatment in the presence of sodium dodecyl sulfate (SDS) is presented in the work. The anionic surfactant SDS was selected after the comparative analysis of various cationic surfactants. PCZ gave a single irreversible oxidation peak at the potential of 0.59 V. The addition of SDS resulted in an almost 5-fold growth in the value of recorded currents as compared to those observed in the absence of the surfactant. The highest peak was obtained in Britton-Robinson buffer at pH 3.78. The calibration curve of PCZ plotted using the SWV technique was linear in the concentration range from 1.34·10−8 mol/L to 1.44·10−6 mol/L. The limit of detection and limit of quantification were 3.78·10−9 mol/L and 1.14·10−8 mol/L, respectively. The value of relative standard deviation of the measurements did not exceed 4.42 %, which proves good precision of the proposed method. The proposed procedure was successfully used in assaying PCZ in simulated gastric juice.

Reaction characteristics of Al–Mg alloy fuels with heterogeneous oxidation shell structures

Al–Mg alloy fuels are the most widely used Al-based alloy fuel in energetic material systems owing to their low ignition temperature and fast reaction. However, their surface oxide layer structure and oxidation, ignition, and combustion mechanisms differ from those of single-metal fuels. Furthermore, insufficient information has been reported on Al–Mg alloy fuels. In this study, Al–Mg alloy fuels were formed by introducing Mg into Al via centrifugal atomization. The microstructure and thermal reaction characteristics of the Al–Mg alloy fuel were evaluated. The ignition and combustion characteristics of the Al–Mg alloy fuels were monitored via single-particle ignition. When the Mg content was increased from 5 % to 40 %, a typical core–shell structure formed, the oxide shell thickness increased from 4.50 to 6.41 nm, and the content of the internal alloy compounds gradually increased. The surfaces of the Al–Mg alloy fuel particles with different Mg contents exhibited heterogeneous oxidation shells. Compared to Al powder, the Al–Mg alloy fuel exhibited better melting and oxidation peak temperatures and higher oxidation weight gain. As the Mg content was increased, the combustion of the Al–Mg alloy fuel intensified with more severe microexplosions and a shorter combustion time. The microexplosion of the Al–Mg alloy fuel was elucidated by theoretical calculations, and its combustion mechanism was proposed. The detailed description of the oxide layer structure, oxidation, and combustion of the Al–Mg alloy fuel provides a reliable explanation of its energy release mechanism in energetic material systems.