Stripping Peak Research Articles

AuNPs enhanced electrochemical and optical dual-mode fiber optic sensor for trace Hg2+ detection

Efficient and low-concentration detection of heavy metal ions is crucial for healthcare and environmental monitoring. Traditional fiber optic surface plasmon resonance (SPR) sensors face challenges in detecting trace heavy metal ions due to limited sensitivity and the need for complex specific modifications. To overcome these challenges, an innovative electrochemical and optical dual-mode fiber optic sensor for in situ, real-time detection of trace mercury ions is proposed in this paper. The sensor utilizes a reflection-type fiber optic probe coated with thin gold (Au)/indium tin oxide (ITO) film and gold nanoparticles (AuNPs), enabling simultaneous electrochemical and optical interrogation. The coupling effect between the SPR of thin film and the localized surface plasmon resonance (LSPR) of AuNPs significantly improves optical sensitivity, with AuNPs also offering additional active sites for the redox reaction of Hg2+. The ITO film not only facilitates the stripping of Hg2+, leading to sharper stripping peaks but also enhances the ability of the sensor to rapidly respond to anomalous potential changes. Experimental results show that the sensor has a wide dynamic detection range from 10−10 M to 10−5 M, with a limit of detection reaching the pM level. The dual-mode functionality allows the simultaneous collection of voltage, current, and optical information, enabling cross-validation of the detection results and improving the accuracy and reliability of detection.

Determination of silver ions in distilled water by stripping voltammetry at a Nafion-coated gold electrode in combination with quartz crystal microbalance and electrochemical impedance spectroscopy

Here, we propose a stripping voltammetric method for Ag+ ion determination in distilled water utilizing screen-printed Au electrodes coated with Nafion (Nafion/Au screen-printed electrodes). The concentration of Ag+ in pure water was determined by linear sweep voltammetry (LSV) after silver deposition on the Nafion/Au electrode. The anodic stripping peak current increased linearly with the concentration of Ag+ ion in the range from 1 ppm to 22 ppm. The LSV oxidative peak current was increased by extending the silver deposition time from 300 s to 500 s. Repetitive LSV measurements revealed satisfactory reproducibility of the Nafion/Au screen-printed electrodes. The detection mechanism was elucidated by recording mass changes of the Nafion/Au electrode with a quartz crystal microbalance (QCM), and by determining changes in the low-frequency capacitance of the Nafion/Au electrode by electrochemical impedance spectroscopy (EIS). The observed changes in mass and capacitance confirmed Ag+ accumulation and release processes at the Nafion/Au electrodes, in good agreement with stripping voltammetry. The combination of stripping voltammetry, QCM and EIS allowed a detailed characterization of the ion transfer, deposition and stripping processes at the Nafion/Au electrodes in presence of Ag+ ions. The Nafion/Au screen-printed electrode enabled voltammetric determination of low Ag+ concentrations in distilled water, without any sample pretreatment nor addition of supporting electrolyte.

Interrogation of Anodic Stripping Voltammetry Peaks of Metals for the Determination of Electrochemical Reaction Parameters

The aim of this study was to develop a method for the analysis of peaks obtained during anodic stripping voltammetry (ASV) at silver-based mercury film electrodes (SBMFE) in the presence of transition and rare earth metals. Such stripping peaks may originate from reversible or irreversible electrochemical processes, with a plethora of unknown parameters, such as number of electrons involved, electrochemical rate constant, formal potential, charge transfer coefficient, and metal concentration (in the film and/or solution). In particular, we were interested in the concentration of transition metals and rare earth elements deposited simultaneously in the mercury film during ASV in order to quantify the electrochemical amalgamation of each species and their rates of deposition.Herein, we studied the concurrent ASV of multiple metals using a mercury film electrode as part of the development of the OREATE (Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction) process. Certain of these species generate electrochemically irreversible processes, while others produce reversible ones. In addition, the reduction of most rare earth metals into the mercury film occurs well below the onset of the hydrogen evolution reaction, preventing us from probing these reduction processes. For example, the reduction of cerium(III) (an electrochemically irreversible process) occurs at a formal potential of −1.64 V vs. Ag/AgCl (3 M KCl). Furthermore, the presence of multiple metals in solution can lead to overlapping stripping peaks and mask these oxidative processes. For instance, the irreversible oxidative stripping of cerium (−0.75 V vs. Ag/AgCl (3 M KCl)) from the mercury film can obscure the reversible stripping of zinc (−0.95 V vs. Ag/AgCl (3 M KCl)).In this talk, we describe the use of thin layer electrochemistry equations to extract electrochemical parameters from the ASV at a mercury film electrode. This electroanalytical method enables investigation of processes that are otherwise obscured by the hydrogen evolution reaction, as well as resolution of overlapping stripping processes. This permits the determination of the concentration of each metal deposited in the film during the electrochemical amalgamation. By summing the thin layer electrochemical equations for reversible and irreversible processes, we were able to extract the number of electrons involved, the electrochemical rate constants, and the charge transfer coefficients for simultaneous oxidative processes. Finally, we were able to obtain the concentrations of multiple species in the mercury film and their rates of deposition.In conclusion, we have established a protocol for the interrogation of electrochemical reaction parameters in anodic stripping voltammetry of mixed-metal systems. Moreover, we demonstrated an electrochemical method to quantitatively separate overlapping peaks for the determination of the species’ concentrations, all based on the principles of thin layer behavior.

Electrochemical and microscopic study of a rotating disk Gold-Film electrode for voltammetric determination of arsenic (III)

This article is dedicated to the fabrication and thorough examination of the properties of a gold-film electrode (AuFE) intended for arsenic (III) determination using square-wave anodic stripping voltammetry (SWASV). The gold-film electrode was prepared ex-situ by potentiostatic electrodeposition of a gold layer onto a rotating glassy carbon electrode (GCE). Various deposition parameters were investigated and optimized, including the concentration of HAuCl4 solution (0.25 – 4 mM), deposition potential (0 – −600 mV), deposition time (120 – 1200 s), and electrode rotation speed (600 – 1500 rpm). Gold films prepared under different conditions were characterized using cyclic voltammetry (CV), optical microscopy, and scanning electron microscopy (SEM). The influence of AuFE characteristics on the parameters of the As(III) stripping peak was studied. Using the optimized AuFE, sensitivity and detection limit for As(III) of 0.468 μA/μg·L−1 and 1 μg/L, respectively, were achieved. The effects of interfering ions (Fe(III), Mn(II), Pb(II), Cu(II), Sn(IV), Tl(I)) on the As(III) response were investigated. The analytical utility of the optimized AuFE was validated for the quantitative determination of arsenic in tap water and seafood. The proposed procedure provides optimal conditions for the electrochemical preparation of gold-film electrodes aimed at routine arsenic monitoring.

A home-made nanoporous gold microsensor for lead(II) detection in seawater with high sensitivity and anti-interference properties.

A nanoporous gold microelectrode (NPG-μE) was fabricated and used for Pb(II) detection in seawater samples via square wave anodic stripping voltammetry (SWASV). The Au microelectrode (Au-μE) was fabricated by embedding a gold microfiber into a Pasteur pipette, and its surface was further modified by an anodization-electrochemical reduction (A-ECR) method, yielding the NPG-μE. The fabricated electrodes were characterized by cyclic voltammetry (CV) and field emission scanning electron microscopy (FE-SEM) for electrochemical and structural morphological investigations. SWASV results show a Pb(II) stripping peak at around -0.05 V vs. Ag/AgCl, sat. KCl, which is unusual for common Pb(II) detection (typically occurring at around -0.40 V) in anodic stripping voltammetry (ASV) analysis. The Pb(II) detection at less negative stripping potential is more beneficial. Hence, it exhibited anti-interference properties with Cd(II), which is attributed to the preferential deposition and stripping of the target analyte on the low-indexed crystal planes of the NPG structure. The calibration plot obtained by SWASV was linear in the concentration range of 0.1-10 μM, and the detection limit was found to be 57 nM (correlation coefficient of 0.9974). The NPG microsensor presented a 15-fold enhanced current response compared to Au-μE, with excellent sensitivity (27.2 μA μM-1 cm-2). The application of the NPG microsensor was examined by detecting Pb(II) in seawater samples, and a satisfactory performance was obtained.

Sensitive electrochemical detection of As(III) in soil based on CoFe2O4/AuNPs/IL nanocomposite modified electrode: Insight into the sensing mechanism of a dual electrocatalysis system

In this study, a CoFe2O4/AuNPs/IL (ionic liquids) nanocomposite modified glassy carbon electrode (GCE) (CoFe2O4/AuNPs/IL/GCE) was developed as an electrochemical sensor for the sensitive detection of As(III) in soil using square wave anodic stripping voltammetry (SWASV). Taking advantages of the catalytic systems of AuNPs, Fe(II)/Fe(III), and Co(II)/Co(III), along with the excellent adsorption capability of CoFe2O4 and the good conductivity of the IL, the proposed sensor exhibited an enhanced detection performance toward As(III). Additionally, the relevant parameters affecting the stripping peak current of As(III) were optimized, resulting in a detection limit of 0.22 ppb (S/N = 3) and a sensitivity of 0.69 µA ppb-1. Furthermore, the interference of high concentrations of nontarget ions on the peak current of As(III) was evaluated, wherein the current change rate was less than 10 %. Moreover, the developed sensor exhibited good stability and reusability with a relative standard deviation (RSD) of 1.44 % after repeating the measurements five times. The probable mechanism of the enhanced stripping signal based on a dual electrocatalysis system was investigated by X-ray photoelectron spectroscopy (XPS). Finally, the proposed CoFe2O4/AuNPs/IL/GCE sensor was successfully applied to the detection of As(III) in real soil samples, which demonstrated its good practical utility for the accurate detection of As(III) in environmental monitoring.

Voltammetry determination of Cd(II) and Pb(II) at TiO2/reduced graphene oxide modified electrodes

AbstractIn this article, a TiO2/reduced graphene oxide (rGO) composite was synthesized from rGO and soluble titanium hydroxide‐peroxide complexes. The obtained materials were characterized by X‐ray diffraction, scanning electron microscopy, nitrogen adsorption/desorption, Raman spectroscopy and energy dispersive X‐ray spectroscopy‐elementary mapping. The TiO2/rGO composite was used as an electrode modifier for developing an electrochemical sensor to simultaneous analysis of Cd(II) and Pb(II) by using differential pulse anodic stripping voltammetry (DP‐ASV). Under optimal conditions, the linear correlation between the stripping peak current and the metal ion concentration is good in the range of 5–100 ppb for both metals (R2 ≥ 0.998), and a low detection limit (3.17 ppb for Cd(II) and 2.42 ppb for Pb(II)) was obtained. The interference study revealed that some metal cations had little influence on the DP‐ASV signals of Cd(II) and Pb(II). In addition, the developed electrode exhibited satisfied reproducibility and repeatability. The TiO2/rGO‐modified electrode was tested toward the detection of Cd(II) and Pb(II) in river waters and the obtained exceptional recoveries and results were further associated with AAS results. This study indicates that the TiO2/rGO composite might be an alternative for practical applications in the electrochemical determination of heavy metal ions in aquatic solutions.

Poly(vinylidene fluoride)-based composite membranes with continuous metal–organic framework layer for high-performance separators of lithium-ion batteries

Lithium-ion batteries (LIBs) play a critical role in modern portable electronic devices, electric vehicles, and wearable electronics. However, the formation of lithium dendrites during cycling results in serious capacity loss and safety risks owing to the heterogeneous transport and deposition of Li+. In this work, we present a poly(vinylidene fluoride) (PVDF)-based composite membrane with a continuous metal–organic framework (MOF) layer as high-performance separators in LIBs. The PVDF membranes with uniform pore structures are prepared by using superspreading strategy, facilitating the growth of continuous and controllable MOF layer inside the membranes via a simple interfacial synthesis. The as prepared PVDF-MOF composite membranes display uniform and continuous subnanochannels with connected opened metal sites (OMS), which can generate a homogeneous transport of Li+. Taking advantages of the low impedance (∼2 Ω), high ionic conductivity (0.61 mS cm−1), and high stripping peak current (0.89 mA cm−2), the PVDF-MOF composite separators efficiently prevent the uneven deposition and the generation of lithium dendrites. Moreover, the PVDF-MOF-based LIBs showed a high capacity retention rate of 81.0 % after 250 cycles. This strategy paves a new avenue for MOF-based composite separator in LIBs.

Simultaneous effect of pH, deposition time, deposition potential, and step potential on the stripping peak current of lead and cadmium by response surface methodology

In this paper, a simple voltammetric method has been reported for the lead, and cadmium determination using platinum nanoflowers modified glassy carbon electrode (PtNFs/GCE). The effects of pH, deposition time, deposition potential, step potential were investigated on the stripping peak current of lead, and cadmium based on response surface methodology (RSM). The results of RSM analysis and analysis of variance (ANOVA) have shown that the experimental data could be well described by quadratic regression equations with determination coefficients (R2) of 0.935, and 0.972 for the stripping peak current of lead, and cadmium, respectively. Results of the statistical analysis showed that the fit of the model was good in all cases. The maximum stripping peak current of the lead, and cadmium of 5.54µA, and 2.81µA, respectively were obtained at the optimum levels of process variables (pH (4.72), deposition potential (-1.14V), deposition time (120s), step potential (7mV)). Testing the model to analyze lead, and cadmium on the PtNFs/GC electrode using differential pulse anodic stripping voltammetry (DPASV) and obtained with the stripping peak current of the lead, and cadmium of 5.43µA, and 2.75 µA, respectively.

Terbium Vanadate Nanowires-Based Electrochemical Sensors for Mercury Ions.

Terbium vanadate nanowires were synthesized via a facile chemical approach using sodium vanadate and terbium chloride. Morphology, structure, composition, and electrochemical characteristics of the terbium vanadate nanowires were investigated by different techniques. Terbium vanadate nanowires with single crystalline tetragonal TbVO4 phase possess smooth surface and flat tips. The length of the nanowires is longer than 5μm, and diameter is 40-100nm. Terbium vanadate nanowires modified electrode was used for trace-level mercury ions (Hg2+) detection. One well-defined stripping peak exists at - 0.34V at the terbium vanadate nanowires modified electrode in 0.1mM Hg2+ solution. Buffer solution pH value, deposition time, deposition potential, and standing time are pH = 1, 150s, - 1.5V, and 60s, respectively. Detection limit for Hg2+ detection is 0.18nM, and linear range is 0.01-100μM. The proposed terbium vanadate nanowires modified electrode exhibits significant selectivity, stability, and reproducibility toward Hg2+. The usefulness of the developed sensor based on the terbium vanadate nanowires modified electrode was verified by Hg2+ detection in real samples.

Highly sensitive electrochemical assay based on strand displacement polymerization-assisted CRISPR/Cas12a collateral cleavage

In this work, a novel strand displacement polymerization strategy is designed with a single hairpin-structured DNA probe acting as both of primer and template. After target miRNA-induced structural transitions, extension and displacement reactions occur at the dimer with recycled target miRNA. The generated double-stranded products further activate CRISPR/Cas12a collateral cleavage of substrate DNA at the electrode surface, which can be reflected by the silver stripping peak variations. By analyzing the reduced peak intensity, the concentration of miRNA can be determined. This method combines the strand displacement amplification and CRISPR/Cas12a’s shearing capability. Thus a highly sensitive electrochemical biosensor is established with the limit of detection as low as 31 aM. It may also inspire new ideas of electrochemical platforms integrating CRISPR/Cas system for biological studies and clinical applications.

Ionic liquid-modified multi-walled carbon nanotube paste electrode for cadmium and lead ion determinations

The detection of trace heavy metal ions is important in monitoring water quality, a vital freshwater source. This study presents the preparation of a multi-walled carbon nanotube (MWCNTs) paste electrode using a pasting mixture of 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid ([Bmim][PF6] IL) and paraffin oil for the determination of Cd2+ and Pb2+. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy were applied to characterize the paste composites. The electrochemical behavior of the fabricated electrodes was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The [Bmim][PF6]-MWCNTs electrode showed enhanced sensitivity for Cd2+ and Pb2+ detections over linear sweep anodic stripping voltammetry (LSASV) performances. Experimental results showed that the MWCNTs-IL-1 electrode using a pasting mixture of 10 μL of [Bmim][PF6] and 190 μL of paraffin oil was the most suitable for Cd2+ and Pb2+ determinations. The LSASV conditions for Cd2+ and Pb2+ analysis at the MWCNTs-IL-1 electrode were optimized, including the deposition potential, deposition time, and pH of the working solution. The stripping peak currents were linearly correlated with the concentration ranges of Cd2+ (1–35 μg/L) and Pb2+ (1–90 μg/L) for both individual and simultaneous determinations. The MWCNTs-IL-1 electrode exhibited high repeatability, reproducibility, and stability over a 30-day storage period. The real applicability of the MWCNTs-IL-1 electrode was demonstrated by successful determinations of Cd2+ and Pb2+ concentrations in tap water and surface water samples, which agreed with the results obtained by inductively coupled plasma mass spectrometry.

Evaluation of thallium ion as an effective ion in human health using an electrochemical sensor

Exposure to thallium (Tl), a noxious heavy metal, poses significant health risks to both humans and animals upon ingestion. Therefore, monitoring Tl levels in the environment is crucial to prevent human exposure and reduce the risk of developing severe health problems. This paper presents the development of a highly sensitive Tl ions sensor through surface modification of a glassy carbon electrode with a nanocomposite comprising MnO2 magnetic sepiolite and multi-walled carbon nanotubes (MnO2@Fe3O4/Sep/MWCNT/GCE). Multiple methodologies were employed to assess the performance of the newly developed sensor. By employing square wave anodic stripping voltammetry (SWASV) to optimize the measurement conditions, notable enhancements were observed in the stripping peak currents of Tl (I) on the MnO2@Fe3O4/Sep/MWCNT/GCE surface. The effectiveness of the nanocomposite in facilitating electron transfer between the Tl (I) ions (guest) and the electrode (host) was demonstrated from the enhanced signals observed at the different modified electrode surfaces under optimal conditions. The developed sensor displayed a wide linear range of 0.1–1500 ppb for Tl (I) and a low detection limit of 0.03 ppb for Tl (I). It was found to be selective for Tl (I) ions while remaining unaffected by interfering non-target ions in the presence of the target ions. Despite its simple preparation procedure, the modified electrode exhibited high stability and excellent reproducibility for measuring Tl (I). The outstanding electroanalytical performances of the MnO2@Fe3O4/Sep/MWCNT/GCE electrode enabled its successful use as an ultrasensitive sensor for determining trace amounts of Tl in environmental samples.

Revealing the solid-solution interface interference behaviors between Cu2+ and As(III) via partial peak area analysis of simulations and experiments

The mutual interference in the sensing detection of heavy metal ions (HMIs) is considerably serious and complex. Besides, the co-existed ions may change the stripping peak intensity, shape and position of the target ion, which partly makes peak current analysis inaccurate. Herein, a promising approach of partial peak area analysis was proposed firstly to research the mutual interference. The interference between two species on their electrodeposition processes was investigated by simulating different kinetics parameters, including surface coverage, electro-adsorption, -desorption rate constant, etc. It was proved that the partial peak area is sensitive and regular to these interference kinetics parameters, which is favorable for distinctly identifying different interferences. Moreover, the applicability of the partial peak area analysis was verified on the experiments of Cu2+, As(III) interference at four sensing interfaces: glassy carbon electrode, gold electrode, Co3O4, and Fe2O3 nanoparticles modified electrodes. The interference behaviors between Cu2+ and As(III) relying on solid-solution interfaces were revealed and confirmed by physicochemical characterizations and kinetics simulations. This work proposes a new descriptor (partial peak area) to recognize the interference mechanism and provides a meaningful guidance for accurate detection of HMIs in actual water environment.

Accurate Detection of Cd2+ and Pb2+ Concentrations in Soils by Stripping Voltammetry Peak Areas under the Mutual Interference of Multiple Heavy Metals

The accurate detection of Cd2+ and Pb2+ in soils by square-wave anodic stripping voltammetry (SWASV) faces great challenges because the interaction between multiple heavy metal ions (HMIs) interferes seriously with their SWASV signals. To detect Cd2+ and Pb2+ by SWASV with high accuracy, an overlooked but informative signal, i.e., stripping current peak area, was employed and combined with chemometric methods to suppress the above mutual interference. An easy-to-prepare electrode, i.e., in-site electroplating bismuth film modified glassy carbon electrode, was used to sense the multiple HMIs. Two machine learning algorithms, including SVR and PLSR, were used to establish the detection models of Cd2+ and Pb2+. In addition, this study developed a homemade algorithm to automatically acquire the stripping peak heights and stripping peak areas of Zn2+, Cd2+, Pb2+, Bi3+, and Cu2+, which acted as the inputs of machine learning models. Then, the detection performance of various SVR and PLSR models were compared based on the R2 and RMSE values of the validation dataset. Results showed that the SVR detection models established by the algorithmically acquired peak areas presented the best stability and accuracy for detecting both Cd2+ and Pb2+ concentrations under the existence of Zn2+ and Cu2+. The R2 and RMSE values of the SVR models built using the peak heights of HMIs acquired by electrochemical workstation control software (Imanu-SVR) were 0.7650 and 5.3916 μg/L for Cd2+, and 0.8791 and 20.0015 μg/L for Pb2+, respectively; the R2 and RMSE values of the SVR models built using the peak area automatically acquired by the developed algorithm (Aalgo-SVR) were 0.9204 and 2.9906 μg/L for Cd2+, and 0.9756 and 13.1574 μg/L for Pb2+, respectively. More importantly, the detection results of the proposed method in real soil extracts for Cd2+ and Pb2+ concentrations were close to those of ICP-MS, verifying its practicability. This study provides a new solution for the accurate detection of targeted heavy metals under the co-existence of multiple HMIs by the SWASV method.

RGO/MWCNTs-COOH 3D hybrid network as a high-performance electrochemical sensing platform of screen-printed carbon electrodes with an ultra-wide detection range of Cd(II) and Pb(II)

• Developed a high-performance SPCE sensor based on rGO-MWCNTs-COOH 3D hybrid. • The detection of Cd 2+ and Pb 2+ with an ultra-wide linear range was performed. • The electrochemical behaviour of modified SPCE reveals the sensing mechanism. • Shows an application potential for directly detecting high-concentration samples. In this study, we develop a high-performance screen-printed carbon electrodes (SPCE) based on reduced graphene oxide (rGO) - carboxy-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) hybrids for simultaneous detection cadmium ions (Cd 2+ ) and lead ions (Pb 2+ ). The surface morphology and electrochemical behaviour of the modified SPCE was characterised by SEM, AFM, EIS and CV. The control steps of the redox reaction on the modified SPCE and the influence of the morphology of modified SPCE on the shape of stripping peak have also been studied. In addition, Nafion and in-situ bismuth film (BFE) methods were introduced in this detection system to enhance the stability and stripping performance. Under the optimal experimental conditions, the Nafion/rGO-MWCNTs-COOH/SPCE showed excellent catalytic activity towards Cd 2+ and Pb 2+ (pH = 4.5) with a significantly increased SWASV peak current compared to the unmodified SPCE. The developed sensor obtains an ultra-wide dynamic concentration range from 0.1 to 1350 μg·L −1 due to the introduction of 3D hybrid material and the optimisation of the detection parameters. The limit of detection (S/N = 3) for Cd 2+ and Pb 2+ was 0.04 μg·L −1 and 0.02 μg·L −1 , respectively. Furthermore, the applicability of the developed SPCE was demonstrated by detecting Cd 2+ and Pb 2+ in tap water and lake water.

(Digital Presentation) Selective Lead Recovery from a Mixture of Lead and Tin for Silicon Solar Module Recycling

During the recycling of solar modules, it is imperative to recover all the toxic lead used in solder. In this experiment, acetic acid is investigated for lead leaching and electrowinning from a mixture of lead and tin. 0.0636 g of tin powder (Alfa Aesar, 325 mesh, 99.8%) and 0.0372 g of lead powder (Alfa Aesar, 100 mesh, 99.95%, atomized) were combined with 30 mL of 0.01 M acetic acid (Sigma Aldrich) and 100 μL hydrogen peroxide (Alfa Aesar, ACS, 29-33% w/w). The solution was allowed to sit for 48 hours before electrowinning to allow the hydrogen peroxide to decompose. A copper working electrode, graphite counter electrode, and silver/silver chloride reference electrode were used in a three-electrode system.A cyclic voltammogram shows lead reduction around –0.4 V vs Ag/AgCl, and a large stripping peak around –0.05 V. There is only one set of redox peaks in the graph, indicating only lead is reduced and oxidized. EDX confirms the presence of metallic lead on the working electrode after electrowinning at –0.6 V vs Ag/AgCl for 90 minutes. Only lead is present on the working electrode surface, no tin. These results show acetic acid to be a promising leachate for the electrowinning of metallic lead from silicon solar module solder waste. Figure 1

An ultrasensitive and highly selective nanomolar electrochemical sensor based on an electrocatalytic peak shift analysis approach for copper trace detection in water

Copper (Cu) sensing in the nanomolar range is an important challenge for marine water monitoring, especially with eco-friendly materials and reagents. For this purpose, electrochemical Cu(II) sensors appear as fully suitable because of their relatively high sensitivity, selectivity and adaptability for in situ measurements. So far, one of the usual electrochemical methods for Cu(II) sensing is adsorptive anodic stripping voltammetry (AdASV), since it offers a good selectivity, accumulation at open circuit potential and a reliable analytical response for concentrations above 10 nmol.L−1. Surprisingly, no work has ever addressed an electrocatalytic procedure to enhance the electrochemical copper sensing and allowed detection below 10 nM. Thus, we have developed an original two-step strategy based on the surface modification of pencil graphite electrodes (PGE) with p-aminobenzyl-C-functionalized cyclam, a strong chelating ligand for Cu(II), as well as the use of a simple reaction which can be electrocatalyzed by Cu such as HER (Hydrogen Evolution Reaction) to finally determine the accumulated amount of copper catalyst on the PGE. We show here that (i) a well-defined diffusion-limited catalytic peak can be obtained from cyclic voltammetry (CV) experiments with Cu(II)-cyclam-modified PGE, (ii) this HER peak potential is correlated to copper surface concentration, which can be sensed at the same time by adsorptive anodic stripping voltammetry and (iii) peak shift analysis (SA) of the voltammetric curves is a more sensitive method than the commonly used stripping voltammetry to reveal copper accumulation at modified PGE. Indeed, the limit of detection (LOD) reached with this method is one order of magnitude lower compared to AdASV (LOD = 1.1 nM and 16 nM, respectively). These results illustrate the ability of electrocatalysis to be a relevant tool under certain conditions for metal trace detection through SA.

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%).

Ultrasensitive indirect electrochemical sensing of thiabendazole in fruit and water by the anodic stripping voltammetry of Cu2+ with hierarchical Ti3C2Tx-TiO2 for signal amplification

The development of effective electrochemical methods for the determination of pesticide residues is highly desirable for food safety requirements. Herein, a novel electrochemical sensing strategy for indirect detection of thiabendazole (TBZ) was achieved by monitoring the anodic stripping peak signal change of media Cu2+ induced by a significant activity difference between active Cu2+ and inactive Cu2+-TBZ complexes. In this sensing system, a heterostructured Ti3C2Tx-TiO2 composite synthesized via a simple in-situ-oxidization strategy is used as the electrode material to boost the anodic stripping peak signal. After optimizing various conditions, the developed sensor presents satisfactory analytical performance for TBZ assay with a linear range from 0.3 to 100.0 nM and a limit of detection as low as 0.1 nM (S/N = 3). Furthermore, the proposed sensing platform also exhibits outstanding anti-interference, repeatability, and stability, which is effective for the determination of TBZ in fruit and water samples.