Voltammetric determination of o-chlorophenol using β-cyclodextrin/graphene nanoribbon hybrids modified electrode

Application of a PLA/PBAT/Graphite sensor obtained by electrospinning on determination of 2,4,6-trichlorophenol

The widespread use of pesticides requires effective detection and quantification tools to improve monitoring of environmental quality. Electrochemical sensors offer a fast and sensitive response, and can also be optimized by combining several constituents and techniques, including biodegradable materials, being useful in the determination of chemical agents from environmental samples. Here, we produced a polymer-based sensor for 2,4,6-trichlorophenol determination, through electrospinning of poly(lactic acid)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blend with graphite. The graphite-containing fibres were thermally treated and wetted in mineral oil, thus forming a paste, used as an electrode in the electrochemical sensor. The thermal analysis indicated a disorganization of the polymeric chains between the aromatic carbon chain of the PBAT polymer, resulting in a material with low enthalpy, lower crystallinity and greater thermal degradability after insertion of graphite in polymeric fibres. NIR spectra revealed changes related to the carbonyls of the polymeric ester groups. Cyclic voltammetry and square wave voltammetry techniques were applied to study the electrochemical behaviour of developed sensor. The thermal treatment of graphite-containing fibres increased the adhesion surface in which occurs the adsorption of the analyte on the electrode, which improved the peak current in the electrochemical tests. The PLA/PBAT/Graphite sensor applied to determination of 2,4,6-TCP presented the detection and quantification limits of 7.84 × 10-8 mol L-1 (0.0155 mg L-1) and 2.36 × 10-7 mol L-1 (0.0466 mg L-1) with a linearity response of 1.00 × 10-7 mol L-1 and 2.00 × 10-6 mol L-1 with correlation coefficient of 0.993 (r2).

Quick and accurate determination of hazardous phenolic compounds using CaCu2O3 nanorods based electrochemical sensor

In the present work, we report the fabrication of a novel electrochemical sensor based on nanostructured CaCu₂O₃ as electrode material for the simultaneous determination of 2-Aminophenol (o-AP), 2-Chlorophenol (o-CP) and 2-Nitrophenol (o-NP). Nanorods-shaped CaCu₂O₃ have been synthesized by chemical precipitation method and characterized by powder X-ray diffraction (XRD), X-ray photo-electron microscopy (XPS), field emission electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Glassy carbon electrodes (3 mm diameter) have been modified using CaCu₂O₃ nanorods by drop-casting method. Cyclic voltammetry (CV) studies at CaCu₂O₃/GCE exhibited excellent electrochemical behaviours towards the oxidation of 2-AP, 2-CP and 2-NP at different potentials well separated from each other. The CaCu₂O₃/GCE displayed the lowest detection limits of 5.74 nM (0.626 ppb), 1.38 nM (0.177 ppb) and 1.03 nM (0.143 ppb) for 2-AP, 2-CP and 2-NP respectively over wide measurable linear ranges of 175 nM-68 μM (2-AP), 50 nM-90 μM (2-CP) and 25 nM-32 μM (2-NP). Cyclic stability studies showed a loss of 7%, 13% and 14% from initial current responses after conducting 100 cycles of CV for 2-AP, 2-CP and 2-NP in PBS (pH 7.0) which indicated the excellent stability of the fabricated electrode. Reproducibility studies of six different CaCu₂O₃/GCEs exhibited good recoveries in the order of 3.23% (2-AP), 3.54% (2-CP) and 2.46% (2-NP) respectively. The fabricated electrode with excellent sensitivity, stability and reproducibility has been successfully applied for the determination of 2-AP, 2-CP and 2-NP simultaneously in tap water and agricultural water samples. Selectivity studies carried out on CaCu₂O₃/GCE revealed its ability to detect 4-aminophenol and 4-nitorphenol at different oxidation potentials. High performance liquid chromatography (HPLC) studies have been carried out to validate the practical utility of the fabricated sensor.

CuO nanoleaf and β-cyclodextrin functionalized reduced graphene oxide: a highly selective and sensitive electrochemical sensor for the simultaneous detection of 2-chlorophenol and 2, 4-dichlorophenol

Chlorophenols are considered priority pollutants and are harmful to humans and the environment; consequently, sensitive, and selective detection of chlorophenols is very significant. In the present article, a glassy carbon electrode was modified by copper oxide nanoleaves, β-cyclodextrin, and reduced graphene oxide through an electrostatic self-assembly method (CuO NLs-β-CD-rGO-GCE) and successfully utilized for the selective and sensitive detection of 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP). The modified electrodes were characterized by using SEM, EDX, ATR-FTIR, CV, and EIS. The electrochemical behaviour of 2-CP and 2,4 DCP on different modified electrodes was investigated by cyclic voltammetry whereas differential pulse voltammetry was used for the quantitative determination of chlorophenols. Under the optimized conditions, the anodic peak current displayed a good linear relationship to concentration in the range of 5 to 50 μM for 2-CP and 5 to 30 μM for 2,4-DCP, with detection limits of 0.22 nM and 0.52 nM, respectively. Moreover the proposed sensor exhibited good reproducibility, high sensitivity, and long term stability. To further study the practical applicability of the newly developed sensor, the modified electrode was successfully used to determine 2-CP and 2,4-DCP in a water sample with good recovery.

Engineering of core−shell Au nanorods@ZIF−8 electrocatalyst for sensitive voltammetric determination of 2−chlorophenol in aquaculture

Herein, polyvinylpyrrolidone−stabilized Au nanorods were controllably implanted into ZIF−8 to form well−uniformed AuNRs@ZIF−8 electrocatalyst with multicore−shell structure. After characterizing the chemical and physical properties, a novel electrochemical sensing platform was fabricated for 2−chlorophenol (2−CP) monitoring based on the AuNRs@ZIF−8 modified glassy carbon electrode. Due to the unique electrochemical property of AuNRs cores and ultra−porous architecture of ZIF−8 shell, the electrocatalyst would effectively accelerate the electron transfer and greatly improve the electrochemical response of 2−CP. Under the optimized experimental conditions, the oxidation peak current of 2−CP enhanced linearly with the increase of its concentration between 0.010 and 40 μM, and the limit of detection was 3.6 nM based on S/N = 3. Meanwhile, the prepared AuNRs@ZIF−8 electrode showed favorable stability, reproducibility, and selectivity, which could be applied to the accurate analysis of 2−CP in aquaculture with standard addition recovery ranging from 96.67% to 104.0%.

Sensing Methods for Hazardous Phenolic Compounds Based on Graphene and Conducting Polymers-Based Materials

It has been known for years that the phenolic compounds are able to exert harmful effects toward living organisms including humans due to their high toxicity. Living organisms were exposed to these phenolic compounds as they were released into the environment as waste products from several fast-growing industries. In this regard, tremendous efforts have been made by researchers to develop sensing methods for the detection of these phenolic compounds. Graphene and conducting polymers-based materials have arisen as a high potential sensing layer to improve the performance of the developed sensors. Henceforth, this paper reviews the existing investigations on graphene and conducting polymer-based materials incorporated with various sensors that aimed to detect hazardous phenolic compounds, i.e., phenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4-dimethylphenol. The whole picture and up-to-date information on the graphene and conducting polymers-based sensors are arranged in systematic chronological order to provide a clearer insight in this research area. The future perspectives of this study are also included, and the development of sensing methods for hazardous phenolic compounds using graphene and conducting polymers-based materials is expected to grow more in the future.