The Polypyrrole/Multiwalled Carbon Nanotube Modified Au Microelectrode for Sensitive Electrochemical Detection of Trace Levels of Pb2+

Simultaneous Electrochemical Detection of Cu2+ and Zn2+ in Pig Farm Wastewater

In recent years, the rapid development of pig farming has led to a large quantity of heavy metal-polluted wastewater. Thus, it was desirable to develop a simple heavy metal detection method for fast monitoring of the wastewater from the pig farms. Therefore, there was an urgent need to develop a simple method for rapidly detecting heavy metal ions in pig farm wastewater. Herein, a simple electrochemical method for simultaneous detection of Cu2+ and Zn2+ was developed and applied to pig farm wastewater. With a glassy carbon electrode and anodic stripping voltammetry, simultaneous detection of Cu2+ and Zn2+ in water was achieved without the need for complicated electrode modification. Furthermore, it was found that the addition of Cd2+ can enhance the response current of the electrode to Zn2+, which increased the signal by eight times. After systematic optimization, the limit of detection (LOD) of 9.3 μg/L for Cu2+ and 45.3 μg/L for Zn2+ was obtained. Finally, it was successfully applied for the quantification of Cu2+ and Zn2+ with high accuracy in pig farm wastewater. This work provided a new and simple solution for fast monitoring of the wastewater from pig farms and demonstrated the potential of electrochemical measurement for application in modern animal husbandry.

A Planar Disk Electrode Chip Based on MWCNT/CS/Pb2+ Ionophore IV Nanomaterial Membrane for Trace Level Pb2+ Detection

Unlike conventional lead ion (Pb2+) detecting methods, electrochemical methods have the attractive advantages of rapid response, good portability and high sensitivity. In this paper, a planar disk electrode modified by multiwalled carbon nanotube (MWCNTs)/chitosan (CS)/lead (Pb2+) ionophore IV nanomaterial and its matched system are proposed. This system presented a good linear relationship between the concentration of Pb2+ ions and the peak current in differential pulse stripping voltammetry (DPSV), under optimized conditions of -0.8 V deposition potential, 5.5 pH value, 240 s deposition time, performed sensitive detection of Pb2+ within sensitivity of 1.811 μA · μg^-1 and detection limit of 0.08 μg · L^-1. Meanwhile, the results of the system in detecting lead ions in real seawater samples are highly similar to that of inductively coupled plasma emission spectrometer (ICP-MS), which proved a practicability for the system in detection of trace-level Pb2+.

Potentiometric extractive sensing of lead ions over a nickel oxide intercalated chitosan-grafted-polyaniline composite

The present research paper reports the extractive potentiometric sensing of lead ions over a chemically functionalized ternary nanocomposite of nickel oxide intercalated chitosan grafted polyaniline (NiO-in-CHIT-g-PANI) prepared by the in situ chemical polymerization and composite formation technique under optimized conditions. The structural, morphological, and physical properties of the composite material were investigated by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and other suitable ASTM methods. The obtained analytical result suggests the formation of a porous hybrid composite matrix with better electrical conductivity ∼ 5.25 × 10^-3 S cm^-1, free interactive carbonyl sites, and evolved aligned crystallinity. Furthermore, a film of the synthesized composite was cast on ITO coated glass by the spin coating technique for potentiometric sensing and the recovery of adsorbed Pb²⁺ ions from natural and artificial water solutions. Under optimum conditions of ∼pH = 7.0 and a temperature of 25 °C, the electrode exhibited potential responses for Pb²⁺ ions in concentrations ranging from 1.0 × 10^-6 M to 1 × 10^-3 M along with a sensitivity of 0.2379 mV μM^-1 cm^-2, response time of 40 s, recovery time of 10 s, and stability for 64 days. The adsorbed Pb²⁺ ions were recovered at a rate of 84% after applying an optimized reverse voltage on the above-used electrodes. The adsorption and desorption mechanism has been explained based on the induced potential due to the electrochemical surface interaction between Pb²⁺ and the NiO-in-CHIT-g-PANI based electrode. The analytical application of the fabricated electrode in the real sample was also explored for the sensing and recovery of the respective metal ions in wastewater samples along with the possibility of optimization of the required metal concentrations.

Epitaxial Graphene Sensors Combined with 3D-Printed Microfluidic Chip for Heavy Metals Detection

In this work, we investigated the sensing performance of epitaxial graphene on Si-face 4H-SiC (EG/SiC) for liquid-phase detection of heavy metals (e.g., Pb and Cd), showing fast and stable response and low detection limit. The sensing platform proposed includes 3D-printed microfluidic devices, which incorporate all features required to connect and execute lab-on-chip (LOC) functions. The obtained results indicate that EG exhibits excellent sensing activity towards Pb and Cd ions. Several concentrations of Pb²⁺ solutions, ranging from 125 nM to 500 µM, were analyzed showing Langmuir correlation between signal and Pb²⁺ concentrations, good stability, and reproducibility over time. Upon the simultaneous presence of both metals, sensor response is dominated by Pb²⁺ rather than Cd²⁺ ions. To explain the sensing mechanisms and difference in adsorption behavior of Pb²⁺ and Cd²⁺ ions on EG in water-based solutions, we performed van-der-Waals (vdW)-corrected density functional theory (DFT) calculations and non-covalent interaction (NCI) analysis, extended charge decomposition analysis (ECDA), and topological analysis. We demonstrated that Pb²⁺ and Cd²⁺ ions act as electron-acceptors, enhancing hole conductivity of EG, due to charge transfer from graphene to metal ions, and Pb²⁺ ions have preferential ability to binding with graphene over cadmium. Electrochemical measurements confirmed the conductometric results, which additionally indicate that EG is more sensitive to lead than to cadmium.

Comparison of backing materials of screen printed electrochemical sensors for direct determination of the sub-nanomolar concentration of lead in seawater

An anodic stripping voltammetric method is reported in this study for the determination of sub-nanomolar Pb concentration using disposable sensors, each consisting of three (counter, working and reference) screen-printed electrodes. Sensor performance was optimized for the determination of Pb through several surface modifications, by using single-walled carbon nanotubes, electro-reduced graphene oxide and gold nanoparticles. A scanning electron microscopy study of the deposition of electrogenerated gold nanoparticles of various sizes on the working electrode surface showed that spherical nanoparticles of around 100 nm provided the best results. The modification of working electrodes with graphene and gold nanoparticles permitted the determination of Pb²⁺ in seawater (Detection Limit: 3.21·10^-10 M) without modifying the pH of the sample. The electrode systems were printed on both rigid and textile backing materials, to observe the influence of those materials on the final performance of the sensor.