Search Results (230)

The oxygen evolution reaction (OER) plays a central role as an anode in electrocatalytic processes such as energy conversion and storage and the generation of molecular oxygen from the electrolysis of water. Currently, precious metal oxides such as IrO₂ and RuO₂ are recognized as reference OER electrocatalysts with reasonably high activity; however, their widespread use in practical devices has been severely hindered by their high cost and scarcity. It is essential to design alternative OER electrocatalysts made of low-cost and abundant earth elements with significant activity and robustness. We report four new nanocellulose-derived Fe–zeolite nanocomposites, namely Fe/Zeolite@CCNC (1), Fe/Zeolite@CCNF (2), Fe/Zeolite/CNT@CCNC (3), and Fe/Zeolite/CNT@CCNF (4). Two different types of nanocellulose were investigated: nanocellulose nanofibrils and nanocellulose nanocrystals. Characterization with TEM, SEM-EDS, PXRD, and XPS is reported. The nanocomposites exhibited electrocatalytic activity for OER that varies based on the origin of biocarbon and the composition content. The effect of adding carbon nanotubes to the nanocomposites was studied, and an improvement in OER catalysis was observed. The electrochemical double-layer capacitance and electrochemical impedance spectroscopy of the nanocomposites are reported. The nanocomposite 3 exhibited the highest performance, with an onset potential value of 1.654 V and an overpotential of 551 mV, which exceeds the activity of RuO₂ for OER catalysis at 10 mA/cm² in the glassy carbon electrode. A 24 h chronoamperometry study revealed that the catalyst is active for ~2 h under continuous operating conditions. BET surface analysis showed that the crystalline nanocellulose-derived composite exhibited 301.47 m²/g, and the fibril nanocellulose-derived composite exhibited 120.39 m²/g, indicating that the increased nanoporosity of the former contributes to the increase in OER catalysis. Full article

This study investigates the development and sensing profile of synthetic melanin nanoparticle-coated electrodes for the electrochemical detection of heavy metals, including lead (Pb), cadmium (Cd), cobalt (Co), zinc (Zn), nickel (Ni), and iron (Fe). Synthetic melanin films were prepared in situ by the deacetylation of diacetoxy indole (DAI) to dihydroxy indole (DHI), followed by the deposition of DHI monomers onto indium tin oxide (ITO) and glassy carbon electrodes (GCE) using cyclic voltammetry (CV), forming a thin layer of synthetic melanin film. The deposition process was characterized by electrochemical quartz crystal microbalance (EQCM) in combination with linear sweep voltammetry (LSV) and amperometry to determine the mass and thickness of the deposited film. Surface morphology and elemental composition were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). In contrast, Fourier-transform infrared (FTIR) and UV–Vis spectroscopy confirmed the melanin’s chemical structure and its polyphenolic functional groups. Differential pulse voltammetry (DPV) and amperometry were employed to evaluate the melanin films’ electrochemical activity and sensitivity for detecting heavy metal ions. Reproducibility and repeatability were rigorously assessed, showing consistent electrochemical performance across multiple electrodes and trials. A comparative analysis of ITO, GCE, and graphite electrodes was conducted to identify the most suitable substrate for melanin film preparation, focusing on stability, electrochemical response, and metal ion sensing efficiency. Finally, the applicability of melanin-coated electrodes was tested on in-house heavy metal water samples, exploring their potential for practical environmental monitoring of toxic heavy metals. The findings highlight synthetic melanin-coated electrodes as a promising platform for sensitive and reliable detection of iron with a sensitivity of 106 nA/ppm and a limit of quantification as low as 1 ppm. Full article

This paper proposes an environmentally friendly sensor for determining trace amounts of diclofenac (DCF)—an activated glassy carbon electrode (aGCE). Such a sensor was achieved by simple surface activation of a glassy carbon electrode to perform five cyclic voltammetric scans from −1.5 to 2.5 V at a scan rate (υ) of 100 mV/s in 0.1 M NaOH. This type of activation results in the formation of surface functional groups, which provide several advantages such as the creation of new active sites, the improvement of electron transfer dynamics, and sensor electrocatalytic activity. The electrode prepared in this way was used to develop a new differential pulse adsorptive stripping voltammetric procedure (DPAdSV) for rapid, simple, and sensitive DCF analysis. Thanks to this procedure, the following calibration curve range was obtained: 1–100 nM with low detection and quantification limits of 0.25 and 0.83 nM, respectively. To show the practical application of the method, DCF was successfully determined in commercially available pharmaceutical preparations with the standard addition method. Full article

Herein, a novel, highly efficient electrochemical adsorption method is introduced for detection of the potent anti-inflammatory synthetic corticosteroid, dexamethasone (DEX). Unlike conventional electrochemical techniques that rely on high reduction potentials, the proposed sensor offers an alternative adsorption-based mechanism with a gold nanostar-modified glassy carbon electrode (AuNS|GCE). This enables DEX detection at a less negative or moderate reduction potential of +200 mV, circumventing potential window limitations of a GCE and providing a suitable microenvironment for detection in biological media. DEX is known to effectively prevent or suppress symptoms of inflammation due to its small applied dosage; however, an overdose thereof in the human body could lead to adverse drug effects such as gastrointestinal perforation, seizures, and heart attacks. Therefore, a sensitive method is essential to monitor DEX concentration in biofluids such as urine. NMGA-capped AuNSs were leveraged to enhance the active surface area of the sensing platform and allow adsorption of DEX onto the gold surfaces through its highly electronegative fluorine atom. Under optimized experimental conditions, the developed AuNS|GCE sensor showed excellent analytical performance with a remarkably low limit of detection (LOD) of 1.11 nM, a good sensitivity of 0.187 µA.nM⁻¹, and a high percentage recovery of 92.5% over the dynamic linear range of 20–120 nM (linear regression of 0.995). The favourable electrochemical performance of this sensor allowed for successful application in the sensitive determination of DEX in synthetic urine (20% v/v in PBS, pH 7). Full article

Nanocomposite hydroxypropyl-beta-cyclodextrin functionalized reduced graphene oxide sheets (HpβCD@rGOs) with zinc oxide flaky structures (ZnOFs) were synthesized. The ZnOFs/HpβCD@rGOs were first characterized to examine their physicochemical characteristics. The ZnOFs exhibited a highly crystalline structure intertwined with HpβCD@rGO sheets. The electrocatalyst experienced excellent electrochemical oxidation current responses toward melatonin (MTN). The interaction between the catalyst and MTN improves electrochemical activity through a synergistic action, which can be measured by a glassy carbon electrode (GCE) modified with ZnOFs/HpβCD@rGOs. This modified electrode with the increased reactive sites and a large electrochemically active surface area allows the rapid oxidation reaction of MTN. The oxidation of MTN was detected and measured with a linearity range around 0.014–0.149 and 1.149–643.341 (µM), with a low detection limit (LOD) of around 0.0105 µM or 10.5 nM. The sensitivity was around 6.19 μA μM⁻¹ cm⁻². The constructed electrode demonstrated a notable level of selectivity to MTN when the interfering (biological) chemicals with a similar structure to MTN were introduced. The real samples were tested in order to examine whether the ZnOFs/HpβCD@rGOs/GCE can be developed for the biomedical monitoring of compounds. The results suggest that ZnOFs/HpβCD@rGOs/GCE can detect MTN in in vitro human samples. Furthermore, the cost-effectiveness, enhanced electrochemical capabilities, and easy fabrication of the electrode make the ZnOFs/HpβCD@rGOs composite a feasible solution for the future industrial development of monitoring tools as sensors. Full article

The cobalt crystalline islands (Co_cryst) were electrochemically deposited onto a glassy carbon (GC) support and then modified by a facile spontaneous deposition of platinum. The electrocatalytic activity of the resulting Co_cryst-Pt core-shell catalyst was evaluated for the oxygen reduction reaction (ORR) in an alkaline medium. The XRD characterization of the Co_cryst-Pt islands revealed that the cobalt core had a hexagonal close-packed (hcp) crystalline structure, and that the platinum shell exhibited a crystalline structure with a preferential (111) orientation. SEM images showed that the average lateral size of the Co_cryst islands was 1.17 μm, which increased to 1.32 μm after adding platinum. The XPS analysis indicated that the outer layer of the bulk metallic Co_cryst islands was fully oxidized. During the spontaneous deposition of platinum, the outer Co(OH)₂ layer was dissolved, leaving the cobalt core in a metallic state, while the platinum shell remained only partially oxidized. The high electrochemically active surface area of the Co_cryst-Pt/GC electrode, along with a suitable crystalline structure of the Co_cryst-Pt islands, contributes to enhancing its ORR activity by providing a greater number of surface active sites for oxygen adsorption and subsequent reduction. The ORR on the Co_cryst-Pt catalyst occurs via a four-electron reaction pathway, with onset and half-wave potentials of 1.07 V and 0.87 V, respectively, which exceed those of polycrystalline platinum and a commercial benchmark Pt/C. Full article

This work focuses on developing a Zn₂SnO₄-based electrochemical sensor for detecting parathion-ethyl (EP), a toxic organophosphorus pesticide. Monitoring such hazardous compounds is essential to ensure environmental and food safety. Zn₂SnO₄, known for its excellent electrical conductivity, catalytic activity, simple synthesis process, and eco-friendly nature, was utilized as an electrode material to enhance the detection of EP. Zn₂SnO₄ was synthesized via a hydrothermal method and characterized using XRD to confirm its crystalline structure. Zn₂SnO₄ was subsequently modified onto a glassy carbon electrode (GCE), enabling the study of its electrochemical properties and interaction with EP. River water and carrot samples were collected, pretreated, and analyzed for EP detection to evaluate real-world applicability. Electrochemical detection of EP using differential pulse voltammetry (DPV) showed a linear response in the concentration range of 0.01–78.4 μM, with a detection limit of 0.0059 µM. The sensor demonstrated excellent repeatability and selectivity in the presence of potential interferents. Real sample analysis confirmed the sensor’s effectiveness, achieving satisfactory recovery rates in river water and carrot samples. The high surface area and conductivity of Zn₂SnO₄ significantly enhanced the electrochemical response, validating its potential for reliable EP detection in environmental and agricultural samples. Full article

The current environmental pollution and energy crises are global concerns that must be addressed. Considering this background, three perovskites (YMnO₃, Co-doped YMnO₃, and Sn-doped YMnO₃) were synthesized via a sol–gel method and characterized by XRD, SEM, and EDX. Their water-splitting electrocatalytic activity was evaluated in a strongly alkaline medium. The highest activity was observed during hydrogen evolution reaction (HER) experiments on a glassy carbon electrode coated with a catalyst ink containing the Co-doped material. Initially, the HER overpotential value at −10 mA/cm² was 0.59 V, and the Tafel slope was 115 mV/dec. Following a chronoamperometric stability test, the overpotential became 0.46 V and the Tafel slope 119 mV/dec. The higher HER activity of the modified electrode is ascribed to a higher number of catalytic sites exposed to the electrolyte solution and the presence of Carbon Black. The photocatalytic activity of the perovskites was investigated as well, using different experimental conditions and simulated solar irradiation. The results show that the photocatalytic activity can be improved by doping, and the highest removal efficiency is achieved in the presence of the Co-doped YMnO₃ when ~60% of 17α-ethynylestradiol is degraded. Furthermore, the initial pH has no favorable effect on the degradation efficiency. The reusability of Co-doped YMnO₃ was also tested and minimal activity loss was found after three photocatalytic cycles. Full article

This paper shows the fabrication of a new environmentally friendly sensor, an activated glassy carbon electrode with an in situ deposited bismuth film (aGCE/BiF), to determine Cd(II) and Pb(II) at the nanotrace level. The electrochemical activation of the GCE surface was achieved in a solution of 0.1 M phosphate-buffered saline (PBS) of pH = 7 by performing five cyclic voltammetric scans in the range of −1.5–2.5 V at ν of 100 mV/s. The newly developed electrode provides several advantages, such as an increased electron active surface (compared to the glassy carbon electrode) and improved electron transfer kinetics. As a result, the new voltammetric procedure (square-wave anodic stripping voltammetry, SWASV) was established and optimized. With the SWASV method, the following calibration curves and low detection limits (LODs) were obtained for Cd(II) and Pb(II), respectively: 5–100 nM, 0.62 nM, 2–200 nM, and 0.18 nM. The newly prepared method was used to determine the amounts of Pb(II) and Cd(II) in the certified reference material, and the results agreed with the certified values. Moreover, the procedure was successfully applied to determine the Cd(II) and Pb(II) in river samples. The official and standard addition methods validated the measurement results. Full article

Vanillin (VAN) is an organic compound which not only functions as a flavoring and fragrance enhancer in some foods but also has antioxidant, anti-inflammatory, anti-cancer, and anti-depressant effects. However, the excessive use of VAN can be associated with negative side effects on human health. As a result, it is crucial to find a reliable method for the rapid determination of VAN to enhance food safety. Herein, we developed a sensor using Ni and Co bimetallic hydroxide and reduced graphene oxide nanostructure (NiCo(OH)₂.rGO). Our prepared material was characterized using various physico-chemical techniques. The electrocatalytic efficiency of the NiCo(OH)₂.rGO-modified glassy carbon electrode was investigated using cyclic and square wave voltammetry. The developed sensor showed a limit of detection of 6.1 nM and a linear range of 5–140 nM. The synergistic effect of NiCo(OH)₂ and rGO improved the active sites and enhanced its catalytic efficiency. The practical applicability of the prepared sensor was investigated for the determination of VAN in food samples such as biscuits and chocolates, showing promise in practical applications. Full article

Tetracycline antibiotics, which are recognized as emerging environmental pollutants, are overused and retained in large quantities in terminal water bodies, seriously endangering the ecological environment and human health. Therefore, establishing a straightforward, rapid, and sensitive method for quantitatively detecting and evaluating the toxicity of tetracyclines is highly important. Compared with traditional detection methods, emerging electrochemical methods have many advantages, such as simplicity and rapidity. In this work, an electrochemical sensor—a graphene ionic liquid composite glass carbon electrode (Gr/IL/GCE) with excellent catalytic properties for both tetracycline and cellular purine bases—was prepared by modifying a glassy carbon electrode with graphene and an ionic liquid for the quantitative detection of tetracycline and evaluation of its toxicity to cells. Graphene and the ionic liquid were uniformly distributed on the surface of the electrode and increased the electrically active surface area. The linear range of detection of tetracycline by a Gr/IL/GCE was 10–500 μM, with a detection limit of up to 2.06 μM. The Gr/IL/GCE demonstrated remarkable electrocatalytic efficacy against purine bases within human hepatocellular carcinomas (HepG2) cells. To evaluate the cytotoxicity of tetracycline, the median inhibition concentration (IC₅₀) was determined, which was 243.82 μM. Full article

Elevated dopamine (DA) levels in urine denote neuroblastoma, a pediatric cancer. Saccharide-derived carbon dots (CDs) were applied to assay DA detection in simulated urine (SU) while delineating the effects of graphene defect density on electrocatalytic activity. CDs were hydrothermally synthesized to vary graphene defect densities using sucrose, raffinose, and palatinose, depositing them onto glassy carbon electrodes (GCEs). Co₃O₄ nanoparticles (NPs) were encapsulated by the CDs. Cyclic (CV) and linear sweep (LSV) voltammetry measurements were obtained, drop-casting the CDs onto GCEs and measuring DA in a phosphate-buffer solution (pH = 7). DA had an oxidation peak at +0.2 V with SucCDs, with the highest current correlating with the highest defect density. PalCD-Co₃O₄ exhibited the largest signal for DA detection in simulated urine (SU) using the oxidation peak at +0.5 V; the composite had a lower defect density compared to SucCD-Co₃O₄. The Co₃O₄-PalCDs had a DA detection range of 1 to 90 µM with an LOD of 0.88 μM in SU. SEM-EDX analysis of the electrode surface revealed semi-spherical structures with an average particle diameter of 80 ± 19 nm (n = 347) with PalCDs decorating the Co₃O₄ NPs. XRD characterization showed the incorporation of PalCD and Co₃O₄ within the composite. XPS showed electron density donation from the PalCD to Co₃O₄. Full article

The use of nanozymes for electrochemical detection in the food industry is an intriguing area of research. In this study, we synthesized a laccase mimicking the MnO₂@CeO₂ nanozyme using a simple hydrothermal method, which was characterized by modern analytical methods, such as transmission electron microscope (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDX), etc. We found that the addition of MnO₂ significantly increased the laccase-like activity by 300% compared to CeO₂ nanorods. Due to the excellent laccase-like activity of the MnO₂@CeO₂ nanozyme, we developed an electrochemical sensor for the detection of hazardous phenolic compounds such as bisphenol A and catechol in red wines by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). We used the MnO₂@CeO₂ nanozyme to develop an electrochemical sensor for detecting harmful phenolic compounds like bisphenol A and catechol in red wine due to its excellent laccase-like activity. The MnO₂@CeO₂ nanorods could be dispersion-modified glassy carbon electrodes (GCEs) by polyethyleneimine (PEI) to achieve a rapid detection of bisphenol A and catechol, with limits of detection as low as 1.2 × 10⁻⁸ M and 7.3 × 10⁻⁸ M, respectively. This approach provides a new way to accurately determine phenolic compounds with high sensitivity, low cost, and stability. Full article

Dihydromyricetin (DMY), as the main active ingredient in Ampelopsis grossedentata, is a naturally occurring flavonoid that has attracted extensive attention for its multiple biological activities. For the quick and accurate measurement of DMY, a novel electrochemical sensor based on a glassy carbon electrode (GCE) modified with a cobalt metal-organic framework (Co-MOF) was proposed in this work. The Co-MOF was synthesized via a single-step hydrothermal process using Co(NO₃)₂·6H₂O. Fourier infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy were used to study the morphology and structure of the synthesized Co-MOF. Utilizing differential pulse voltammetry and cyclic voltammetry methods, the effectiveness of DMY electro-oxidation on the Co-MOF/GCE was examined. The results showed that, in comparison to the bare GCE, the electro-oxidation peak current of DMY was considerably increased by the Co-MOF/GCE. The detection limit was 0.07 μM, and the peak current demonstrated two linear relationships in the ranges of 0.2−20 μM and 20−100 μM, with the linear equations of Ip (μA) = 0.4729c (μM) + 1.0822 (R² = 0.9913) and Ip (μA) = 0.0939c (μM) + 8.4178 (R² = 0.9971), respectively. The average DMY content in Ampelopsis grossedentata samples was measured to be 3.275 μM, with a good recovery of 108.27% and a relative standard deviation value of 3.46%. The proposed method is simple, rapid and sensitive and can be used for the determination of DMY in Ampelopsis grossedentata. Full article

Toxic heavy metal ions, such as lead ions, significantly threaten human health and the environment. This work introduces a novel method for the simple and sensitive detection of lead ions based on biochar-loaded titanium dioxide nanoparticles (BC@TiO₂NPs) nanocomposites. Eco-friendly biochar samples were prepared from spent coffee grounds (500 °C, 1 h) that were chemically activated with TiO₂ nanoparticles (150 °C, 24 h) to improve their conductivity. Structural characterizations showed that BC@TiO₂NPs have a porous structure. The BC@TiO₂NPs material was evaluated for lead ion determination by assembling glassy carbon electrodes. Under optimal conditions, the sensor was immersed in a solution containing the analyte (0.1 M NaAc-HAc buffer, pH = 4.5) for the detection of lead ions via differential pulse voltammetry. A linear dynamic range from 1 pM to 10 μMwas achieved, with a detection limit of 0.6268 pM. Additionally, the analyte was determined in tap water samples, and a satisfactory recovery rate was achieved. Full article