Effect of morphology of α-MnO2 nanocrystals on electrochemical detection of toxic metal ions

In-situ growth of porous rod-like tungsten oxide for electrochemical determination of cupric ion

Preconcentration can effectively enhance the detection performance of electrodes in the electrochemical detection of heavy metal ions, but it also presents challenges for real-time monitoring. Several attempts have been made to optimize preconcentration by improving the adsorption capacity or detection mechanism of the electrode. The valence transfer of tungsten oxide between W5+/W6+ can participate in the reduction between the electrode material and heavy metal ions, playing a role in preconcentration to some extent. Therefore, we developed a WO3/SSM electrochemical sensor for the detection of Cu(II) that utilizes the valence variation property of WO3. The crystallinity and microstructure of the WO3/SSM electrode can be regulated by controlling the deposition parameters, and we prepared three types of WO3/SSM with different morphologies to identify the influence of the electrochemical effective surface area. The proposed electrode shows high performance as a Cu(II) sensor under short preconcentration time (60 s), with an excellent sensitivity of 14.113 μA μM-1 cm-2 for 0.1-10.0 μM and 4.7356 μA μM-1 cm-2 for 10.0-20.0 μM. Overall, the combined effect of morphology and valence transfers shortens the preconcentration time and optimizes preconcentration while ensuring excellent electrode performance. This WO3/SSM electrode is expected to drive great advances in the application of tungsten oxide in the electrochemical detection of heavy metal ions.

Application of Co3O4 nanocrystal/rGO for simultaneous electrochemical detection of cadmium and lead in environmental waters

Sensing of cadmium (Cd) and lead (Pb) in environmental samples is crucial for identifying potential health risks associated with exposure to these heavy metals as well as understanding the extent of heavy metal contamination in different environments and its impact on the ecosystem. The present study elucidates the development of a novel electrochemical sensor that can detect Cd (II) and Pb (II) ions simultaneously. This sensor is fabricated using reduced graphene oxide (rGO) and cobalt oxide nanocrystals (Co₃O₄ nanocrystals/rGO). The characterization of Co₃O₄ nanocrystals/rGO was done by using various analytical techniques. The incorporation of cobalt oxide nanocrystals with intense absorption properties results in an amplification of the electrochemical current generated on the surface of the sensor by heavy metals. This, when coupled with the unique properties of the GO layer, enables the identification of trace levels of Cd (II) and Pb (II) in the surrounding environment. The electrochemical testing parameters were meticulously optimized to obtain high sensitivity and selectivity. The Co₃O₄ nanocrystals/rGO sensor exhibited exceptional performance in detecting Cd (II) and Pb (II) within a concentration range of 0.1-450 ppb. Notably, the limits of detection (LOD) for Pb (II) and Cd (II) were found to be highly impressive at 0.034 ppb and 0.062 ppb, respectively. The Co₃O₄ nanocrystals/rGO sensor integrated with the SWASV method displayed notable resistance to interference and exhibited consistent reproducibility and stability. Therefore, the suggested sensor has the potential to serve as a technique for detecting both ions in aqueous samples using SWASV analysis.

Fabrication of Screen-Printed Electrodes Modified by Hydrothermal MnO2 Microflowers and Carbon for Electrochemical Sensors in Copper Ions Detection

Porous MnO2 microflowers with a hexagonal crystalline structure were facilely prepared at a low hydrothermal temperature of 90°C, without using any template or capping agent. The as-prepared MnO2 only presented an excellent detection ability for copper (II) by a square wave anodic stripping voltammetry in the presence of super P carbon black as conducting agent, and Nafion as binder. In the present work, to evaluate the detection ability of copper (II) in the MnO2 microflowers, chips of screen-printed electrodes (SPEs) having a polyurethane substrate, a silver working electrode, a carbon counter electrode, and a silver pseudoelectrode, were designed. Then, the SPEs chips were modified with MnO2 microflowers and/or super P carbon and used as electrochemical sensors for the detection of copper (II) present in water sources. From the measured results, the fabricated sensors with excellent copper detection in a linear range from 0.625 nM to 15 nM (R2 = 0.9737), and a low detection limit (0.5 nM), high sensitivity (214.05 μA/cm2 nM), and rapid response (180 s) demonstrated high application potential for electrochemical sensors in the detection of copper in water resources.

A Novel Aptamer-Imprinted Polymer-Based Electrochemical Biosensor for the Detection of Lead in Aquatic Products

Lead contamination in aquatic products is one of the main hazard factors. The aptasensor is a promising detection method for lead ion (Pb(II)) because of its selectivity, but it is easily affected by pH. The combination of ion-imprinted polymers(IIP) with aptamers may improve their stability in different pH conditions. This paper developed a novel electrochemical biosensor for Pb(II) detection by using aptamer-imprinted polymer as a recognition element. The glassy carbon electrode was modified with gold nanoparticles and aptamers. After the aptamer was induced by Pb(II) to form a G-quadruplex conformation, a chitosan-graphene oxide was electrodeposited and cross-linked with glutaraldehyde to form an imprint layer, improving the stability of the biosensor. Under the optimal experimental conditions, the current signal change (∆I) showed a linear correlation of the content of Pb(II) in the range of 0.1-2.0 μg/mL with a detection limit of 0.0796 μg/mL (S/N = 3). The biosensor also exhibited high selectivity for the determination of Pb(II) in the presence of other interfering metal ion. At the same time, the stability of the imprinted layer made the sensor applicable to the detection environment with a pH of 6.4-8.0. Moreover, the sensor was successfully applied to the detection of Pb(II) in mantis shrimp.

An Efficient Voltammetric Sensor Based on Graphene Oxide-Decorated Binary Transition Metal Oxides Bi2O3/MnO2 for Trace Determination of Lead Ions

Herein we present a facile synthesis of the graphene oxide-decorated binary transition metal oxides of Bi₂O₃ and MnO₂ nanocomposites (Bi₂O₃/MnO₂/GO) and their applications in the voltammetric detection of lead ions (Pb²⁺) in water samples. The surface morphologies, crystal structures, electroactive surface area, and charge transferred resistance of the Bi₂O₃/MnO₂/GO nanocomposites were investigated through the scanning electron microscopy (SEM), power X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques, respectively. The Bi₂O₃/MnO₂/GO nanocomposites were further decorated onto the surface of a glassy carbon electrode (GCE), and Pb²⁺ was quantitatively analyzed by using square-wave anodic stripping voltammetry (SWASV). We explored the effect of the analytical parameters, including deposition potential, deposition time, and solution pH, on the stripping peak current of Pb²⁺. The Bi₂O₃/MnO₂/GO nanocomposites enlarged the electroactive surface area and reduced the charge transferred resistance by significant amounts. Moreover, the synergistic enhancement effect of MnO₂, Bi₂O₃ and GO endowed Bi₂O₃/MnO₂/GO/GCE with extraordinary electrocatalytic activity toward Pb²⁺ stripping. Under optimal conditions, the Bi₂O₃/MnO₂/GO/GCE showed a broad linear detection range (0.01-10 μM) toward Pb²⁺ detection, with a low limit of detection (LOD, 2.0 nM). The proposed Bi₂O₃/MnO₂/GO/GCE electrode achieved an accurate detection of Pb²⁺ in water with good recoveries (95.5-105%).

A high performance Pb(II) electrochemical sensor based on spherical CuS nanoparticle anchored g-C3N4

A new electrochemical sensor has been constructed for ultra-sensitive detection of lead ions (Pb²⁺) by square wave anodic stripping voltammetry (SWASV), based on the copper sulfide/graphitic carbon nitride nanocomposite modified glassy carbon electrode (CuS/g-C₃N₄/GCE). First, spherical CuS nanoparticles with good electrical conductivity were anchored on layered g-C₃N₄ with high coordination activity, affording an excellent electrode modifier CuS/g-C₃N₄ nanocomposite. Then, the performance of the CuS/g-C₃N₄/GCE and its electrochemical response to Pb²⁺ were thoroughly studied, and the sensing mechanism was investigated. On the one hand, the CuS/g-C₃N₄ nanocomposite has greatly improved the electron transportation and electrode performance through functional complementarity - CuS endows g-C₃N₄ with a good electrical conductivity and a large active specific surface area, while g-C₃N₄ endows CuS with high dispersibility and strong adsorption. On the other hand, the CuS/g-C₃N₄ modifier has effectively promoted the deposition of trace Pb²⁺ from the solution onto the electrode surface by means of synergistic enrichment (crucial for amplification of detection signals) - g-C₃N₄ can coordinate with Pb²⁺ by its large number of conjugated triazine heterocyclic rings in its molecular framework, while CuS can adsorb Pb²⁺ due to its inherent size effect of nanomaterials. The proposed sensor can efficiently detect Pb²⁺ in the concentration range of 0.050-5.000 μM with a limit of detection (LOD) as low as 4.00 nM, and can be well applied for the detection of trace Pb²⁺ in actual tea samples.

Design and development of a portable resistive sensor based on α-MnO2 /GQD nanocomposites for trace quantification of Pb(II) in water

The occurrence of heavy metal ions in food chain is appearing to be a major problem for mankind. The traces of heavy metals, especially Pb(II) ions present in water bodies remains undetected, untreated, and it remains in the food cycle causing serious health hazards for human and livestock. The consumption of Pb(II) ions may lead to serious medical complications including multiple organ failure which can be fatal. The conventional methods of heavy metal detection are costly, time-consuming and require laboratory space. There is an immediate need to develop a cost-effective and portable sensing system which can easily be used by the common man without any technical knowhow. A portable resistive device with miniaturized electronics is developed with microfluidic well and α-MnO2 /GQD nanocomposites as a sensing material for the sensitive detection of Pb(II). α-MnO2 /GQD nanocomposites which can be easily integrated with the miniaturized electronics for real-time on-field applications. The proposed sensor exhibited a tremendous potential to be integrated with conventional water purification appliances (household and commercial) to give an indication of safety index for the drinking water. The developed portable sensor required low sample volume (200 µL) and was assessed within the Pb(II) concentration range of 0.001 nM to 1 uM. The Limit of Detection (LoD) and sensitivity was calculated to be 0.81 nM and 1.05 kΩ/nM/mm2 , and was validated with the commercial impedance analyser. The shelf-life of the portable sensor was found to be ∼45 days.

Facile synthesis of g-C3N4 with various morphologies for application in electrochemical detection

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). The results obtained using square wave anodic stripping voltammetry (SWASV) showed that when g-C₃N₄ was applied as an electrochemical sensor, it exhibited excellent sensitivity and selectivity for the detection of heavy metal ions including Pb(ii), Cu(ii) and Hg(ii). Compared to nanoporous graphitic carbon nitride (npg-C₃N₄) and g-C₃N₄ nanosheet-modified glass carbon electrode (GCE), g-C₃N₄ successfully realized the individual and simultaneous detection of four target heavy ions for the first time. In particular, g-C₃N₄ displayed significant electrocatalytic activity towards Hg(ii) with a good sensitivity of 18.180 μA μM⁻¹ and 35.923 μA μM⁻¹ under the individual and simultaneous determination conditions, respectively. The sensitivity for simultaneous determination was almost 2 times that of the individual determination. Moreover, the fabricated electrochemical sensor showed good anti-interference, stability and repeatability; this indicated significant potential of the proposed materials for application in high-performance electrochemical sensors for the individual and simultaneous detection of heavy metal ions.

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods.

Nanostructured MnO₂ as Electrode Materials for Energy Storage

Manganese dioxides, inorganic materials which have been used in industry for more than a century, now find great renewal of interest for storage and conversion of energy applications. In this review article, we report the properties of MnO₂ nanomaterials with different morphologies. Techniques used for the synthesis, structural, physical properties, and electrochemical performances of periodic and aperiodic frameworks are discussed. The effect of the morphology of nanosized MnO₂ particles on their fundamental features is evidenced. Applications as electrodes in lithium batteries and supercapacitors are examined.

Electrochemical detection of mercury using biosynthesized hydroxyapatite nanoparticles modified glassy carbon electrodes without preconcentration

An electrochemical method for the determination of trace levels of mercury(ii) ions using Aloe vera (Av) assisted hydroxyapatite (HA) nanoparticles modified glassy carbon electrode (GCE) by square wave voltammetry is described for the first time.