Electrochemical sensor for Cd2+ and Pb2+ detection based on nano-porous pseudo carbon paste electrode

An electrochemical sensor based on self-made nano-porous pseudo carbon paste electrode (nano-PPCPE) has been successfully developed, and used to detect Cd²⁺ and Pb²⁺. The experimental results showed that the electrochemical performance of nanoPPCPE is evidently better than both glassy carbon electrode (GCE) and pure carbon paste electrode (CPE). Then the prepared nano-PPCPE was applied to detect Cd²⁺ and Pb²⁺ in standard solution, the results showed that the electrodes can quantitatively detect trace Cd²⁺ and Pb²⁺, which has great significance in electrochemical analysis and detection. The linear ranges between the target ions concentration and the DPASV current were from 0.1–3.0 μmol/L, 0.05–4.0 μmol/L for Cd²⁺ and Pb²⁺, respectively. And the detection limits were 0.0780 μmol/L and 0.0292 μmol/L, respectively. Moreover, the preparation of the nano-PPCPE is cheap, simple and has important practical value.     

Carbon Nanotubes/Ionophore Modified Electrode for Anodic Stripping Determination of Lead

Bifunctional combination of carbon nanotubes and ionophore is introduced for anodic stripping analysis of lead (Pb²⁺). Carbon nanotubes are employed to improve the detection sensitivity due to their excellent electrical conductivity and strong adsorption ability. An ionophore is utilized for its excellent selectivity toward Pb²⁺. The proposed carbon nanotubes/ionophore modified electrode shows improved sensitivity and selectivity for Pb²⁺. Low detection limit (1 nM), wide linear range (5 nM–8 µM) and excellent selectivity over other metal ions (Cd²⁺, Cu²⁺, and Hg²⁺) was obtained. The practical application has been carried out for determination of Pb²⁺ in real water samples.     

Ordered Mesoporous Carbon and Thiolated Polyaniline Modified Electrode for Simultaneous Determination of Cadmium(II) and Lead(II) by Anodic Stripping Voltammetry

The fabrication and evaluation of a glassy carbon electrode (GCE) modified with ordered mesoporous carbon (OMC), 2‐mercaptoethanesulfonate (MES)‐tethered polyaniline (PANI) and bismuth for simultaneous determination of trace Cd²⁺ and Pb²⁺ by differential pulse anodic stripping voltammetry (DPASV) are presented here. The morphology and electrochemical properties of the fabricated electrode were respectively characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Experimental parameters such as PANI disposition, preconcentration potential, preconcentration time and bismuth concentration were optimized. Under optimum conditions, the fabricated electrode exhibited linear calibration curves ranged from 1 to 120 nM for Cd²⁺ and Pb²⁺. The limits of detection (LOD) were 0.26 nM for Cd²⁺ and 0.16 nM for Pb²⁺ (S/N=3), respectively. Additionally, repeatability, reproducibility, interference and application were also investigated, and the proposed electrode exhibited excellent performance. The proposed method could be extended for the development of other new sensors for heavy metal determination.     

Anodic Stripping Voltammetry of Heavy Metals on a Metal Catalyst Free Carbon Nanotube Electrode

Anodic stripping voltammetry (ASV) determination of Pb²⁺, Cd²⁺, and Zn²⁺ was done using metal catalyst free carbon nanotube (MCFCN) electrodes. Osteryoung square wave stripping voltammetry (OSWSV) was selected for detection. The MCFCNTs are synthesized via Carbo Thermal Carbide Conversion method which leads to residual transition metal free in the CNT structure. The new material shows very good results in detecting heavy metal ions, such as Pb²⁺, Cd²⁺, and Zn²⁺. The calculated limits of detection were 13 nM, 32 nM and 50 nM for Pb²⁺, Cd²⁺ and Zn²⁺, respectively with a deposition time of 150 s.     

ABTS‐Multiwalled Carbon Nanotubes Nanocomposite/Bi Film Electrode for Sensitive Determination of Cd and Pb by Differential Pulse Stripping Voltammetry

A 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulfonate) diammonium salt (ABTS)‐multiwalled carbon nanotubes (MWCNTs) nanocomposite/Bi film modified glassy carbon (GC) electrode was constructed for the differential pulse stripping voltammetric determination of trace Pb²⁺ and Cd²⁺. This electrode was more sensitive than ABTS‐free Bi/GC and Bi/MWCNTs/GC electrodes. Linear responses were obtained in the range from 0.5 to 35 μg L^?1 for Cd²⁺ and 0.2 to 50 μg L^?1 Pb(II), with detection limits of 0.2 μg L^?1 for Cd²⁺ and 0.1 μg L^?1 for Pb²⁺, respectively. This sensor was applied to the simultaneous detection of Cd²⁺ and Pb²⁺ in water samples with satisfactory recovery.     

Bifunctional polydopamine@Fe3O4 core–shell nanoparticles for electrochemical determination of lead(II) and cadmium(II)

The present paper has focused on the potential application of the bifunctional polydopamine@Fe₃O₄ core–shell nanoparticles for development of a simple, stable and highly selective electrochemical method for metal ions monitoring in real samples. The electrochemical method is based on electrochemical preconcentration/reduction of metal ions onto a polydopamine@Fe₃O₄ modified magnetic glassy carbon electrode at −1.1 V (versus SCE) in 0.1 M pH 5.0 acetate solution containing Pb²⁺ and Cd²⁺ during 160 s, followed by subsequent anodic stripping. The proposed method has been demonstrated highly selective and sensitive detection of Pb²⁺ and Cd²⁺, with the calculated detection limits of 1.4 × 10⁻¹¹ M and 9.2 × 10⁻¹¹ M. Under the optimized conditions, the square wave anodic stripping voltammetry response of the modified electrode to Pb²⁺ (or Cd²⁺) shows a linear concentration range of 5.0–600 nM (or 20–590 nM) with a correlation coefficient of 0.997 (or 0.994). Further, the proposed method has been performed to successfully detect Pb²⁺ and Cd²⁺ in aqueous effluent.     

Detection of Trace Heavy Metal Ions Using Carbon Nanotube‐ Modified Electrodes

A sensitive voltammetric method for detection of trace heavy metal ions using chemically modified carbon nanotubes (CNTs) electrode surfaces is described. The CNTs were covalently modified with cysteine prior to casting on electrode surfaces. Cysteine is an amino acid with high affinities towards some heavy metals. In this assay, heavy metals ions accumulated on the cysteine‐modified CNT electrode surfaces prior to being subjected to differential pulse anodic stripping voltammetry analysis. The resulting peak currents were linearly related to the concentrations of the metal ions. The method was optimized with respect to accumulation time, reduction time and reduction potential. The detection limits were found to be 1 ppb and 15 ppb for Pb²⁺ and Cu²⁺ respectively. The technique was used for the detection of Pb²⁺ and Cu²⁺ in spiked lake water. The average recoveries of Pb²⁺ and Cu²⁺ were 96.2% and 94.5% with relative standard deviations of 8.43% and 7.53% respectively. The potential for simultaneous detection of heavy metal ions by the modified CNTs was also demonstrated.     

Non-conductive nanomaterial enhanced electrochemical response in stripping voltammetry: The use of nanostructured magnesium silicate hollow spheres for heavy metal ions detection

Nanostructured magnesium silicate hollow spheres, one kind of non-conductive nanomaterials, were used in heavy metal ions (HMIs) detection with enhanced performance for the first time. The detailed study of the enhancing electrochemical response in stripping voltammetry for simultaneous detection of ultratrace Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺ was described. Electrochemical properties of modified electrodes were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The operational parameters which have influence on the deposition and stripping of metal ions, such as supporting electrolytes, pH value, and deposition time were carefully studied. The anodic stripping voltammetric performance toward HMIs was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The detection limits achieved (0.186 nM, 0.247 nM, 0.169 nM and 0.375 nM for Cd²⁺, Pb²⁺, Cu²⁺ and Hg²⁺) are much lower than the guideline values in drinking water given by the World Health Organization (WHO). In addition, the interference and stability of the modified electrode were also investigated under the optimized conditions. An interesting phenomenon of mutual interference between different metal ions was observed. Most importantly, the sensitivity of Pb²⁺ increased in the presence of certain concentrations of other metal ions, such as Cd²⁺, Cu²⁺ and Hg²⁺ both individually and simultaneously. The proposed electrochemical sensing method is thus expected to open new opportunities to broaden the use of SWASV in analysis for detecting HMIs in the environment.     

Voltammetric Simultaneous Determination of Cu2+, Cd2+ and Pb2+ in Full Aqueous Medium Using Organic Nanoparticles of Disulfide Based Receptor

Disulfide based receptor was prepared using single step condensation reaction and suspended into organic nanoparticles to extend its practical application in aqueous samples. The prepared nanoparticles were used for the simultaneous recognition of three different metallic species (Cu²⁺, Cd²⁺, and Pb²⁺) in aqueous media through voltammetric studies. These metals can be determined simultaneously and without interferences from any of the other potential interferent metal ions, as different signals are displayed in cyclic as well as differential pulse voltammograms, with a detection limit of 193.0 nM for Cu²⁺, 52.0 nM for Cd²⁺ and 32.0 nM for Pb²⁺. The study was extended to real sample analysis by preparing the artificial mixtures of said metal ions.     

Synthesis of Bismuth‐Nanoparticle‐Enriched Nanoporous Carbon on Graphene for Efficient Electrochemical Analysis of Heavy‐Metal Ions

A BiNPs@NPCGS nanocomposite was designed for highly efficient detection of multiple heavy‐metal ions by in situ synthesis of bismuth‐nanoparticle (BiNP)‐enriched nanoporous carbon (NPS) on graphene sheet (GS). The NPCGS was prepared by pyrolysis of zeolitic imidazolate framework‐8 (ZIF‐8) nanocrystals deposited on graphene oxide and displayed a high surface area of 1251 m² g^?1 and a pore size of 3.4 nm. BiNPs were deposited on NPCGS in situ by chemical reduction of Bi³⁺ with NaBH₄. Due to the restrictive effect of the pore/surface structure of NPCGS, the BiNPs were uniform and well dispersed on the NPCGS. The BiNPs@NPCGS showed good conductivity and high effective area, and the presence of BiNPs allowed it to act as an efficient material for anodic‐stripping voltammetric detection of heavy‐metal ions. Under optimized conditions, the BiNPs@NPCGS‐based sensor could simultaneously determine Pb²⁺ and Cd²⁺ with detection limits of 3.2 and 4.1 nM , respectively. Moreover, the proposed sensor could also differentiate Tl⁺ from Pb²⁺ and Cd²⁺. Owing to its advantages of simple preparation, environmental friendliness, high surface area, and fast electron‐transfer ability, BiNPs@NPCGS showed promise for practical application in sensing heavy‐metal ions.     

Sensitive Determination of Trace Pb2+ in Seawater Using Columnar Glassy Carbon Electrode

We herein report a mercury‐free approach for the sensitive determination of trace Pb²⁺ in seawater using differential pulse stripping voltammetric (DPSV) method with a novel columnar glassy carbon electrode (CGCE). Compared with the conventional disk glassy carbon electrode with the same diameter, it has much larger electrochemical area (0.627 ± 0.003 cm²). The CGCE shows good accumulation ability and consequently acceptable behavior which makes it suitable as a working electrode in the DPSV determination of Pb2+ with the great advantage of the avoidance of harmful mercury. Using acidified artificial seawater as supporting electrolyte, there was a good linear relationship between the peak currents and the concentration of Pb²⁺ in the range of 0.6～140.0 μg L^‐1 with a detection limit of 0.3 μg/L (S/N = 3) when the accumulation time was 300 s. The method was employed to determine trace levels of Pb²⁺ in real seawater samples successfully.     

An inorganic-organic hybrid material from the co-intercalation of a cationic surfactant and thiourea within montmorillonite layers: application to the sensitive stripping voltammetric detection of Pb2+ and Cd2+ ions

A smectite-based inorganic-organic hybrid material was prepared by a one-step intercalation of cetyltrimethylammonium ions and thiourea within the interlayer space of montmorillonite (MT). The surface and textural properties of the resulting material were examined using several techniques (X-ray diffraction, elementary analysis and N₂ adsorption-desorption experiments (BET method)) that demonstrated the presence of both modifiers in the clay mineral structure. The presence of thiourea molecules in the modified MT greatly improved its ability towards the fixation of Pb²⁺ and Cd²⁺ ions when the organoclay material was used for sensing purposes as a glassy carbon electrode modifier. The electro-analytical procedure was based on the chemical accumulation of both analytes under open-circuit conditions, followed by the detection of the preconcentrated species using square wave voltammetry. Upon optimization of different parameters likely to influence the electrode response, linear calibration graphs were obtained in the concentration ranges from 0.1 to 1 μM and 0.01 to 0.1 μM for Cd²⁺ and Pb²⁺, respectively, leading to low limits of detection (4.2 × 10⁻¹⁰ M for Pb²⁺and 1.2 × 10⁻⁹ M for Cd²⁺).     

Hydroxyapatite Wrapped Multiwalled Carbon Nanotubes/Ionic Liquid Composite Electrode: A High Performance Sensor for Trace Determination of Lead Ions

A nanocomposite consisting of multiwalled carbon nanotubes wrapped with hydroxyapatite (HA/MWCNTs) was used in the construction of a new composite paste electrode using an ionic liquid as the binder. The stable surface in aqueous solutions as well as the high sorptive behaviors towards heavy metal ions and the favorable charge transfer make the electrode highly efficient especially for stripping or adsorptive analysis. The analysis of Pb²⁺ as a model of heavy metal ions has been performed. Good sensitivity, detection limit, selectivity and reproducibility were obtained for the suggested sensor. The linear range of the electrode response covered four orders of magnitude (1 nM–10 µM), in two linear ranges. The obtained detection limit for Pb²⁺ was 2×10^?11 M.     

Highly selective in situ metal ion determination by hybrid electrochemical "adsorption-desorption" and colorimetric methods

A novel and facile hybrid analytical method coupling electrochemical “adsorption–desorption” and colorimetric analyses was developed to detect heavy metal ions in turbid water samples. The target metal ions were deposited onto an electrode inserted into the original sample, which was referred to as the “adsorption” process. After changing the medium, the concentrated target metal ions were dissolved in a new, clean buffer (blank buffer), which was referred to as the “desorption” process. The concentrations of the target metal ions were measured by colorimetric analyses after the addition of specific indicator amounts. We demonstrated the applicability of this method by detecting Cd²⁺, Pb²⁺ and Cu²⁺ with co-depositing Bi³⁺ on portable screen-printed electrodes (SPEs). A good correlation (correlation coefficient of R = 0.997) was observed between concentrations ranging from 1 to 200 μM and absorbance values. After the multiple “desorption” process, the even better detection limits as low as 10, 10 and 100 nM were achieved for Cd²⁺, Pb²⁺ and Cu²⁺, respectively. The practicality of this hybrid method was confirmed by the detection of Cd²⁺, Pb²⁺ and Cu²⁺ in wastewater samples, and these results were in agreement with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Overall, this hybrid method provides a simple, selective and effective technique for environmental pollutant analyses.     

A Simple and Highly Sensitive Electrochemically Reduced p‐Nitrobenzoic Acid Film Modified Sensor for Determination of Mercury

Herein, a simple electrochemical sensor was fabricated for sensing Hg²⁺ ions by using electrochemically reduced p‐nitrobenzoic acid molecules modified (ERpNBA) glassy carbon electrode (GCE). The modified electrode was applied for the determination of Hg²⁺ ions by using differential pulse anodic stripping voltammetry (DPASV). Experimental parameters such as concentration of p‐nitrobenzoic acid used for electrode modification, pH, accumulation time and deposition potential used for the determination of Hg²⁺ ions were optimized. The strong interaction between the Hg²⁺ ions and the lone pair of electrons on the nitrogen atoms of ERpNBA molecules leads to highly selective adsorption of Hg²⁺ ions on the modified electrode. Under the optimum experimental conditions, the sensor showed higher sensitivity and very low detection limit for Hg²⁺ ions than other metal ions such as Cd²⁺, Pb²⁺ and Zn²⁺ ions. The LOD for Hg²⁺ ions was 240 pM which is below the guideline value given by the World Health Organization and the earlier reports.     

Anodic Stripping Voltammetric Determination of Lead in Tap Water at an Ordered Mesoporous Carbon/Nafion Composite film Electrode

A sensitive mercury‐free lead (Pb²⁺) sensor has been proposed based on an ordered mesoporous carbon and Nafion composite film (OMC/Nafion) coated glassy carbon electrode. The analysis of Pb²⁺ using anodic stripping voltammetry (ASV) includes two steps. Pb²⁺ ions are firstly reduced and deposited on the electrode surface in a Pb²⁺ solution (10 mL) during a preconcentration step biased at ?1.0 V, followed by a measurement step by differential pulse voltammetry (DPV) within the potential range of ?0.8 to ?0.3 V (scan rate: 20 mV/s, frequency: 20 Hz, amplitude: 50 mV, pulse width: 50 ms). Linear calibration curve was found to be from 20 nM to 2 μM for Pb²⁺ with a sensitivity of 17.4±1.38 μA/μM after a 5‐min of preconcentration. The detection limit was estimated to be around 4.60±0.12 nM at the signal to noise ratio of 3. Reproducibility (RSD%) was found to be 3.0% for a single sensor with eight measurements and 4.3% for five sensors prepared with identical procedures. The practical application of the proposed lead sensor was verified by determination of trace level of Pb²⁺ in tap water sample.     

Selective Determination of Copper (II) Based on Aluminum Silicon Carbide Nanoparticles Modified Glassy Carbon Electrode by Square Wave Stripping Voltammetry

The morphology and structure of as‐prepared aluminum silicon carbide (Al₄SiC₄) were characterized using X‐ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscopy (TEM) and UV‐vis spectra. The Al₄SiC₄ nanoparticles modified glassy carbon electrode (GCE) was further investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Based on this, this kind of new electrode was used for the detection of trace Cu²⁺ by square wave anodic stripping voltammetry (SWASV) for the first time. The electrochemical parameters influencing on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential and deposition time, were also optimized. The results showed that the Al₄SiC₄ modified GCE exhibited excellent stripping response of Cu²⁺ and the stripping peaks response increased linearly with increasing concentration of Cu²⁺ in the ranges of 400 to 2200 nM. Under the optimized conditions the favorable sensitivity of the Al₄SiC₄ modified GCE toward trace Cu²⁺ was 1.49 μA μM⁻¹ and the limit of detection (S/N=3) was estimated to be 2.76 nM. More importantly, Al₄SiC₄ modified GCE had an excellent stability and negligible interference from other coexisting metal ions in the electrochemical determination of Cu²⁺.     

Biomass valorization of walnut shell into biochar as a resource for electrochemical simultaneous detection of heavy metal ions in water and soil samples: Preparation,characterization, and applications

Lately, due to its accessibility and eco-friendliness, walnut shell biochar (WS-BC) is gaining attention as an electrode material component in the electrochemical detection of water pollutants. The overall performance of WS-BC is reliant on the nature of raw biomass and the production methods as well. In our concept, biochar, prepared from raw walnut shell (WS) by pyrolysis, was added to a carbon paste electrode (CPE), and poly-tyrosine (p-Tyr) was electrodeposited on the surface of the BC-doped electrode. The conditions of the elaboration of the electrode, such as pH, potential, and the number of deposition cycles, pH were optimized. The obtained p-Tyr-BC-CPE platform was tested for the determination of cadmium, lead, copper, and mercury ions in water and soil samples, using square wave voltammetry (SWV). The raw WS biomass and its BC were examined by thermal analysis (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) techniques. The synergistic effects of the coexistence of the WS-BC and the thin film of p-Tyr, for the detection of traces of heavy metal ions were investigated by electrochemical tests. The electrochemical characterization of the unmodified and modified electrodes was performed using the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods, while the Cd²⁺, Pb²⁺, Cu^2+, and Hg²⁺ detection experiments were studied using the CV and SWV techniques. The optimized experimental conditions for the p-Tyr-BC-CPE platform were evaluated. The obtained electrochemical results showed that the p-Tyr-BC-CPE platform produced excellent sensitivity toward the heavy metal ions: LOD of 0.086, 0.175, 0.246, and 0.383 nM for Cd(II), Pb(II), Cu(II) and Hg(II), respectively. The modified electrode platform displayed high selectivity, stability, and good reproducibility.     

Electrochemical determination of cadmium and lead based on the joint enhancement effects of SBA-16 and iodide

Mesoporous SBA-16 was synthesized using tetraethoxysilane as silicon source and a ternary system consisting of surfactant F127, water and butanol. Owing to the excellent properties of SBA-16 such as lager surface area and strong accumulation ability, the stripping peak current of Cd²⁺ and Pb²⁺ remarkably increases at the SBA-16 modified carbon paste electrode. Moreover, the peak current of Cd²⁺ and Pb²⁺ further enhances after the addition of I^?. Under the joint enhancement effects of SBA-16 and I^?, the detection sensitivity of Cd²⁺ and Pb²⁺ is greatly improved. The influences of concentration of I^?, amount of SBA-16, accumulation potential and time were investigated. As a result, a new electrochemical method with high sensitivity was developed for the simultaneous determination of Cd²⁺ and Pb²⁺. The limit of detection is 0.6 nM for Cd²⁺ and 1 nM for Pb²⁺. It was used to determine Cd²⁺ and Pb²⁺ in waste water sample, and the results consisted with the values that obtained by atomic absorption spectrometry.     

Study on Cd2+ Determination Using Bud-like Poly-L-Tyrosine/Bi Composite Film Modified Glassy Carbon Electrode Combined with Eliminating of Cu2+ Interference by Electrodeposition

A bud-like poly-L-tyrosine/Bi modified glassy carbon electrode (p-Tyr/Bi/GC) was prepared by CV and in situ Bi plating, whose conductivity and membrane morphology were characterized by CV, EIS and SEM, respectively. The p-Tyr membrane can effectively promote the enrichment of Cd²⁺. The optimal Tyr concentration and scanning number for p-Tyr/GC preparation were 2.0 mmol ⋅ L⁻¹ and 35, while the optimal Bi³⁺ concentration, pH and Cd²⁺ accumulation potential in test medium were 3.0 μmol ⋅ L⁻¹, 6.5 and −1.3 V, respectively. The linear equation of p-Tyr/Bi/GC's response to Cd²⁺ (1.0 nmol ⋅ L⁻¹ to 2.0 μmol ⋅ L⁻¹) was i_p (μA) = −0.6809 + 100.2c (μmol ⋅ L⁻¹) (R² = 0.9985) with a detection limit of 0.11 nmol ⋅ L⁻¹ (3S/N). The elimination of interference caused by Cu²⁺ in sample was studied by electrodeposition. The p-Tyr/Bi/GC electrode was successfully used for detecting Cd in rice samples with good reliability and accuracy. The developed Cd²⁺ sensor exhibits high sensitivity, wide linear range and low detection limit, especially the designed method of eliminating Cu²⁺ interference has the characteristics of high selectivity, simple operation and wide application range.