Use of a Schiff base-modified conducting polymer electrode for electrochemical assay of Cd(II) and Pb(II) ions by square wave voltammetry

Green triiron tetraoxide@Algae (Fe3O4@Algae) nanoparticles for highly efficient removal of lead (Pb2+), cadmium (Cd2+), and aluminum (Al3+) from contaminated water: an isothermal, kinetic, and thermodynamic study

Developing and producing a versatile adsorbent for effective wastewater treatment remains a significant obstacle to wastewater processing. As the objective is to eliminate various metal ions (lead, cadmium, and aluminum) from wastewater, we therefore strategically designed and synthesized new iron oxide nanoparticles (Fe3O4 NPs) based on the green algae called triiron tetraoxide@algae nanoparticles (Fe3O4@Algae NPs) that grow in the same contaminated water using a facile one-pot green synthetic method. Investigations were conducted into the adsorption circumstances, including pH, starting concentration, adsorbent dosage, and adsorption time. More importantly, great absorption of lead, cadmium, and aluminum was achieved, with 97.5%, 81.3%, and 75.13%, respectively. The best conditions were 60 min, 0.1 g of nanoparticles, at 25 °C, and 150 mL of water containing 30 mg/L of Pb, Cd, and Al, with pH 6 for Cd and Pb and pH 5 for Al. To analyze the kinetics and equilibrium adsorption data and to evaluate the interaction between the metal ions and the adsorbent, a variety of kinetic and isotherm models were employed. The Langmuir isotherm and a pseudo-second-order were the best ways to look at the adsorption isotherm and kinetics data for how the Fe3O4@algae removes metal ions. Furthermore, thermodynamic studies showed that the adsorption process was an exothermic, favorable, and spontaneous reaction. For the elimination of Al(III), Pb(II), and Cd(II), the Fe3O4@algae experimental adsorption capacity was 33.8 mg/g, 56.70 mg/g, and 36.58 mg/g, respectively. The composite of Fe3O4@algae nanoparticles was characterized using several analytical techniques including scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and UV-vis spectroscopy. In addition, the material exhibited notable durability and recyclability, with the metal removal effectiveness remaining at a high level even after undergoing five successive adsorption cycles. This study paves the way to the use of green nanotechnology for eco-friendly, cheap, and rapid techniques that can be used in the purification of wastewater.

Synthesis of a triazine based COF and its application for the establishment of an electrochemical sensor for the simultaneous determination of Cd2+ and Pb2+ in edible specimens using Box-Behnken design

The study presented here describes the characterization and synthesis of a triazine-based covalent organic framework using different analytical procedures such as scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, cyclic voltammetry, Brunauer-Emmett-Teller analysis, and electrochemical impedance spectroscopy. The synthesized COF was then utilized as an electrocatalytic modifier for the selective and sensitive determination of Pb2+ and Cd2+ at nanomolar levels via square wave anodic stripping voltammetry. A Plackett-Burman design was employed to screen operational parameters influencing the sensitivity of the electroanalytical method, followed by optimization of the significant variables using Box-Behnken design. A linear response over 1.0-110.0 nmol L-1 and 5.0-300.0 nmol L-1 range for Pb2+ and Cd2+, with detection limits of 1.1 and 1.8 nmol L-1, respectively. Furthermore, the selectivity of the presented electrode over different species was evaluated with no significant interference found. The sensor was applied effectively to determine of Pb2+ and Cd2+ ions in samples.

Polypyrrole functionalized MoS2 for sensitive and simultaneous determination of heavy metal ions in water

Assessing heavy metal ion (HMI) contamination to sustain drinking water hygiene is a challenge. Conventional approaches are appealing for the detection of HMIs but electrochemical approaches can resolve the limitations of these approaches, such as tedious sample preparation, high cost, time consuming and the need for trained professionals. Here, an electrochemical approach is developed using a nano-sphered polypyrrole (PPy) functionalized with MoS2 (PPy/MoS2) by square wave anodic stripping voltammetry for the detection of HMIs. The developed sensor can detect Pb2+ with a limit of detection of 0.03 nM and a sensitivity of 36.42 μA nM-1. Additionally, the PPy/MoS2 sensor was employed for the simultaneous detection of HMIs of Cd2+, Pb2+, Cu2+ and Hg2+. The reproducibility, stability and anti-interference studies confirm that the sensor can be used to monitor HMI contamination of water.

Simple and fast self-polymerization of benzidine using anodic exfloated graphene oxide nanosheet

Nowadays, researchers are looking for green synthesis methods of polymers that solve the disadvantages of polymerization with different initiators and traditional methods. In this work, the self-polymerization process of benzidine by anodic exfloated graphene oxide Nanosheet electrode (AEGO Nsh) is reported for the first time in the world. The self-polymerization of benzidine onto AEGO Nsh electrode was done by an easy and simple method by anodizing the graphite sheet followed by immersing the AEGO Nsh electrode inside the benzidine monomer dissolved in organic and inorganic acid media. The surface morphology of the self-polymerized benzidine (SPB) onto the AEGO Nsh (SPB/AEGO Nsh) electrode was investigated by phone camera and scanning electron microscope (FE-SEM) imaging. The chemical characterization of the SPB/AEGO Nsh electrode was verified through XPS and ATR-IR analysis. Additionally, the self-polymerization of benzidine onto AEGO Nsh electrodes was confirmed by electrochemical tests using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. The results from these investigations unequivocally confirm the self-polymerization of benzidine onto the AEGO Nsh electrode.

S-S bridged Schiff bases as versatile ionophores: Synthesis and application for electrochemical sensing of Copper(II) and Mercury(II)

Schiff base derivates (3, 4 and 5) comprising pseudo cavity with different heteroatoms (O, N and S) were designed, synthesized and explored for their detection behaviour towards diverse metal ions. In UV and fluorescence studies, all three receptors exhibited sensitive response towards Cu2+ while 5 showed sensitivity for Hg2+ also. To explore the synthesized receptors for electrochemical behaviour, voltammetric studies were conducted where 3, 4 and 5 exhibited sensitive response towards Cu2+ with detection limits of 9.8 × 10-7 M, 9.0 × 10-7 M and 1.41 × 10-7 M, respectively. The receptor 5 also showed response towards Hg2+ with detection limit of 5.61 × 10-8 M. The formation of complexes, 3/4+Cu2+ and 5+Cu2+/Hg2+ was supported by large values of binding constant and associated negative free energy change. The binding mechanism of 3, 4 and 5 towards respective metal ions was confirmed using 1H-NMR and HR-MS studies. Further, to utilize the proposed sensors for on-site monitoring of analyte metal ions, carbon paste electrodes (CPEs) were constructed by incorporating 3, 4 and 5. All CPEs showed Nernstian response with lower detection limits and excellent selectivity and successfully utilized for the determination of Cu2+ and Hg2+ in groundwater samples.

Simulation study of a practical approach to enhance cadmium removal via biological treatment by controlling the concentration of MLSS

The fate of cadmium at the Muharram Aisha wastewater treatment plant in Karbala governorate, Iraq was studied using the TOXCHEM model. Cadmium, a known carcinogen, and is considered one of the most dangerous heavy metals and high concentrations, greater than permissible limits, were found in the treated wastewater. The plant operates using an activated sludge system and this was modeled via TOXCHEM with a sensitivity analysis carried out on the extended aeration system. Prior to analysis, the model was calibrated and validated for cadmium, with the adjustments leading to a mean square error (RMSE) and correlation coefficient (R) of 0.0001 and 0.81, respectively. The mass balance of cadmium in the Muharram Aisha treatment plant was found to be 4832.44 g/day (37.1726%) in the treated wastewater and 8164.52 g/day (62.804%) in the sludge, which indicated that the mix liquor suspended solid (MLSS) was the most sensitive factor. The sensitivity to cadmium was analyzed via MLSS in the extended aeration system and the results o indicated that the higher the MLSS concentration (mg/L), the greater the removal of cadmium in the treated wastewater. It was found that increasing the MLSS through a biological treatment method reduced the concentration of cadmium without the need for additional of any (potentially harmful) chemical treatments. The plant was subsequently operated for a period of 5 months with the MLSS increased from 1500 to 4500 mg/L, and this reduced the concentration of cadmium in the wastewater from 0.36 to 0.01 mg/L as a consequence. This research demonstrates how the novel application of TOXCHEM can be a useful tool in the reduction of heavy metal contamination in the environment.

Nanomaterials-based aptasensors: An efficient detection tool for heavy-metal and metalloid ions in environmental and biological samples

In light of potential risks of heavy metal exposure, diverse aptasensors have been developed through the combination of aptamers with nanomaterials for the timely and efficient detection of metals in environmental and biological matrices. Aptamer-based sensors can benefit from multiple merits such as heightened sensitivity, facile production, uncomplicated operation, exceptional specificity, enhanced stability, low immunogenicity, and cost-effectiveness. This review highlights the detection capabilities of nanomaterial-based aptasensors for heavy-metal and metalloid ions based on their performance in terms of the basic quality assurance parameters (e.g., limit of detection, linear dynamic range, and response time). Out of covered studies, dendrimer/CdTe@CdS QDs-based ECL aptasensor was found as the most sensitive option with an LOD of 2.0 aM (atto-molar: 10-18 M) detection for Hg2+. The existing challenges in the nanomaterial-based aptasensors and their scientific solutions are also discussed.

An Electrochemical Sensor Based on a Porous Biochar/Cuprous Oxide (BC/Cu2O) Composite for the Determination of Hg(II)

Mercuric ion (Hg²⁺) in aqueous media is extremely toxic to the environment and organisms. Therefore, the ultra-trace electrochemical determination of Hg²⁺ in the environment is of critical importance. In this work, a new electrochemical Hg²⁺ sensing platform based on porous activated carbon (BC/Cu₂O) modified with cuprous oxide was developed using a simple impregnation pyrolysis method. Differential pulse anodic stripping voltammetry (DPASV) was used to investigate the sensing capability of the BC/Cu₂O electrode towards Hg²⁺. Due to the excellent conductivity and large specific surface area of BC, and the excellent catalytic activity of Cu₂O nanoparticles, the prepared BC/Cu₂O electrode exhibited excellent electrochemical activity. The high sensitivity of the proposed system resulted in a low detection limit of 0.3 ng·L^-1 and a wide linear response in the ranges from 1.0 ng·L^-1 to 1.0 mg·L^-1. In addition, this sensor was found to have good accuracy, acceptable precision, and reproducibility. All of these results show that the BC/Cu₂O composite is a promising material for Hg²⁺ electrochemical detection.

Simultaneous immobilization of heavy metals and nutrient elements in contaminated sediment using a novel composite agent product

In this research, an innovative type of sediment resource treatment agent (SRA) was synthesized successfully, which could immobilize ammonia nitrogen (NH₃-N), total phosphorus (TP), potassium (K), and simultaneously stabilize cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) in dredged sediment. The effects of SRA dosage on stabilizing the nutrient elements and heavy metals were investigated. The results demonstrated that the increase of SRA dosage significantly enhanced the stabilization of nutrients and heavy metals. The 14-day rainwater infiltration and rainwater scouring experiments were carried out. With the simulation test of rainwater infiltration, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH₃-N, TP, and K with 2% SRA addition reached 80.8%, 76.8%, 80.3%, 77.5%, 78.0%, 72.7%, 64.3%, 73.9%, and 73.9%, respectively. Under the action of rainwater scouring, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 6.4% SRA addition reached 84.6%, 84.0%, 77.6%, 87.3%, 80.0%, 61.5%, 76.2%, 77.8%, and 91.7%, respectively. Therefore, the results demonstrate that SRA is an excellent composite material in stabilizing heavy metals while reserving the nutrients in dredged sediment, thus showing great potential in the application for dredged sediment resource treatment.

Electrochemical Evaluation of Cd, Cu, and Fe in Different Brands of Craft Beers from Quito, Ecuador

The presence of heavy metals in craft beers can endanger human health if the total metal content exceeds the exposure limits recommended by sanitary standards; in addition, they can cause damage to the quality of the beer. In this work, the concentration of Cd(II), Cu(II), and Fe(III) was determined in 13 brands of craft beer with the highest consumption in Quito, Ecuador, by differential pulse anodic stripping voltammetry (DPASV), using as boron-doped diamond (BDD) working electrode. The BDD electrode used has favorable morphological and electrochemical properties for the detection of metals such as Cd(II), Cu(II), and Fe(III). A granular morphology with microcrystals with an average size between 300 and 2000 nm could be verified for the BDD electrode using a scanning electron microscope. Double layer capacitance of the BDD electrode was 0.01412 μF cm^-2, a relatively low value; Ip_ox/Ip_red ratios were 0.99 for the potassium ferro-ferricyanide system in BDD, demonstrating that the redox process is quasi-reversible. The figures of merit for Cd(II), Cu(II), and Fe(III) were; DL of 6.31, 1.76, and 1.72 μg L^-1; QL of 21.04, 5.87, and 5.72 μg L^-1, repeatability of 1.06, 2.43, and 1.34%, reproducibility of 1.61, 2.94, and 1.83% and percentage of recovery of 98.18, 91.68, and 91.68%, respectively. It is concluded that the DPASV method on BDD has acceptable precision and accuracy for the quantification of Cd(II), Cu(II), and Fe(III), and it was verified that some beers did not comply with the permissible limits of food standards.

Adsorptive Stripping Voltammetry for Determination of Vanadium: A Review

The main purpose of this review is to present methods of adsorptive stripping voltammetry that can be used to determine trace amounts of VO₂⁽⁺⁾ in various types of samples. The detection limits achieved using different working electrodes are presented. The factors influencing the obtained signal, including the selection of the complexing agent and the selection of the working electrode, are shown. For some methods, in order to increase the range of applied concentrations in which vanadium can be detected, a catalytic effect is introduced to adsorptive stripping voltammetry. The influence of the foreign ions and organic matter contained in natural samples on the vanadium signal is analyzed. This paper presents methods of elimination associated with the presence of surfactants in the samples. The methods of adsorptive stripping voltammetry for the simultaneous determination of vanadium with other metal ions are also characterized below. Finally, the practical use of the developed procedures, mainly for the analysis of food and environmental samples, is summarized in a tabular version.

Three-dimensional porous high boron-nitrogen-doped carbon for the ultrasensitive electrochemical detection of trace heavy metals in food samples

Exposure to even trace amounts of Cd(II) and Pb(II) in food can have serious effects on the human body. Therefore, the development of novel electrochemical sensors that can accurately detect the different toxicity levels of heavy metal ions in food is of great significance. Based on the principle of green chemistry, we propose a new type of boron and nitrogen co-doped carbon (BCN) material derived from a metal-organic framework material and study its synthesis, characterization, and heavy-metal ion detection ability. Under the optimum conditions, the BCN-modified glassy carbon electrode was studied using square-wave anodic stripping voltammetry, which showed good electrochemical responses to Cd(II) and Pb(II), with sensitivities as low as 0.459 and 0.509 μA/μM cm², respectively. The sensor was successfully used to detect Cd(II) and Pb(II) in Beta vulgaris var. cicla L samples, which is consistent with the results obtained using inductively coupled plasma-mass spectrometry. It also has a strong selectivity for complex samples. This study provides a novel approach for the detection of heavy metal ions in food and greatly expands the application of heteroatom-doped metal-free carbon materials in detection platforms.

Rapid Detection of Mercury Ions Using Sustainable Natural Gum-Based Silver Nanoparticles

Fabrication of metal nanostructures using natural products has attracted scientists and researchers due to its renewable and environmentally benign availability. This work has prepared an eco-friendly, low-cost, and rapid colorimetric sensor of silver nanoparticles using tree gum as a reducing and stabilizing agent. Several characterization techniques have been exploited to describe the synthesized nanosensor morphology and optical properties. Ultraviolet−Visible (UV−Vis) spectroscopy has been used for monitoring the localized plasmon surface area. High-resolution transmission electron microscopy (HR-TEM) illustrated the size and shape of silver nanoparticles. X-ray diffraction spectra showed the crystallography and purity of the product. Silver nanoparticles decorated with almond gum molecules (AgNPs@AG) demonstrated high sensitivity and colorimetric detection of mercury ions in water samples. The method is based on the aggregation of AgNPs and the disappearing yellow color of AgNPs via a spectrophotometer. The detection limit of this method was reported to be 0.5 mg/L. This work aimed to synthesize a rapid, easy-preparation, eco-friendly, and efficient naked-eye colorimetric sensor to detect toxic pollutants in aqueous samples.

A Highly Selective and Sensitive Nano-Silver sol Sensor for Hg2+ and Fe3+: Green Preparation and Mechanism

The development of highly selective and highly sensitive nanometer colorimetric chemical sensors is an urgent requirement in the immediate detection of heavy metal ions. In this work, silver-nanoparticle (Ag NPs)-based chemosensors were prepared by a simple and green method, in which the silver nitrate, carboxymethyl cellulose sodium (CMS) and Polyvinylpyrrolidone (PVP), and glucose are used as the silver source, double stabilizer and green reductant, respectively. The obtained colloidal CMS/PVP-Ag NPs showed a high dispersibility and stability, and creating a high selectivity and sensitivity to detect Hg2+ and Fe3+ with remarkable and rapid color variation. Low limits of detection (LOD) of 7.1 nM (0–20 μM) and 15.2 nM (20–100 μM) for Hg2+ and 3.6 nM for Fe3+ were achieved. More importantly, the CMS/PVP-Ag NPs has a high sensitivity even in a complex system with multiple heavy ions, the result of the practical ability to detect Hg2+ and Fe3+ in tap water and seawater reached a rational range of 98.33~104.2% (Hg2+) and 98.85~104.80% (Fe3+), indicating the great potential of the as-prepared nanocomposites colorimetric chemosensor for practical applications.

Voltammetric Determination of Hg2+, Zn2+, and Pb2+ Ions Using a PEDOT/NTA-Modified Electrode

A novel electrochemical sensor for determining trace levels of Hg²⁺, Pb²⁺, and Zn²⁺ ions in water using square wave voltammetry (SWV) is reported. The sensor is based on a platinum electrode (Pt) modified by poly(3,4-ethylenedioxythiophene) and N _α,N _α-bis-(carboxymethyl)-l-lysine hydrate (NTA lysine) PEDOT/NTA. The modified electrode surface (PEDOT/NTA) was prepared via the introduction of the lysine-NTA group to a PEDOT/N-hydroxyphthalimide NHP electrode. The (PEDOT/NTA) was characterized via cyclic voltammetry (CV), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The effects of scan rates on the electrochemical properties of the polymer electrode were also investigated. The electrochemical results were used to estimate the coverage of the electrode polymer surface and its electrostability in background electrolyte solutions. Several analytical parameters, such as polymer film thickness, metal deposition time, and pH of the electrolyte, were examined. Linear responses to Hg²⁺, Pb²⁺, and Zn²⁺ ions in the concentration range of 5-100 μg L^-1 were obtained. The limits of detection (LODs) for the determination of Hg²⁺, Pb²⁺, and Zn²⁺ ions were 1.73, 2.33, and 1.99 μg L^-1, respectively. These promising results revealed that modified PEDOT/NTA films might well represent an important addition to existing electrochemical sensor technologies.

On the Electroanalytical Detection of Zn Ions by a Novel Schiff Base Ligand-SPCE Sensor

A novel bidentate Schiff base (L) is here proposed for the detection of Zn ions in water. The structure of the synthesized Schiff base L was characterized by FT-IR, ¹H NMR and ¹³C NMR. Optical characteristics were addressed by UV-Visible spectroscopy and Photoluminescence (PL) measurements. PL demonstrated that L displays a "turn-off" type fluorescence quenching in the presence of Zn²⁺ ion in aqueous solution, indicating its ability to preferentially coordinate this ion. Based on these findings, an L-M (where M is a suitable membrane) modified screen-printed carbon electrode (SPCE) was developed to evaluate the electrochemical behavior of the Schiff base (L) with the final objective of undertaking the electroanalytical determination of Zn ions in water. Using various electrochemical techniques, the modified L-M/SPCE sensor demonstrates high sensitivity and selectivity to Zn ions over some common interferents ions, such as Ca²⁺, Mg²⁺, K⁺, Ni⁺⁺ and Cd⁺⁺. The potentiometric response of the L-M/SPCE sensor to Zn ions was found to be linear over a relatively wide concentration range from 1 μM to 100 mM.