Pencil Graphite Electrocatalytic Sensors Modified by Pyrene Coated Reduced Graphene Oxide Decorated with Molybdenum Disulfide Nanoroses for Hydrazine and 4-Nitrophenol Detection in Real Water Samples.

Novel nanostructured platforms based on Pencil Graphite Electrodes (PGEs), modified with pyrene carboxylic acid (PCA) functionalized Reduced Graphene Oxide (rGO), and then decorated by chronoamperometry electrodeposition of MoS2 nanoroses (NRs) (MoS2NRs/PCA-rGO/PGEs) were manufactured for the electrocatalytic detection of hydrazine (N2H4) and 4-nitrophenol, pollutants highly hazardous for environment and human health. The surface morphology and chemistry of the MoS2NRs/PCA-rGO/PGEs were characterized by scanning electron microscopy (SEM), Raman, and X-ray photoelectron spectroscopy (XPS), assessing the coating of the PCA-rGO/PGEs by dense multilayers of NRs. N2H4 and 4-nitrophenol have been monitored by Differential Pulse Voltammetry (DPV), and the MoS2NRs/PCA-rGO/PGEs electroanalytical properties have been compared to the PGEs, as neat and modified by PCA-rGO. The MoS2NRs/PCA-rGO/PGEs demonstrated a higher electrochemical and electrocatalytic activity, due to their high surface area and conductivity, and very fast heterogeneous electron transfer kinetics at the interphase with the electrolyte. LODs lower than the U.S. EPA recommended concentration values in drinking water, namely 9.3 nM and 13.3 nM, were estimated for N2H4 and 4-nitrophenol, respectively and the MoS2NRs/PCA-rGO/PGEs showed good repeatability, reproducibility, storage stability, and selectivity. The effectiveness of the nanoplatforms for monitoring N2H4 and 4-nitrophenol in tap, river, and wastewater was addressed.

Electrochemical Sensors Based on Au Nanoparticles Decorated Pyrene-Reduced Graphene Oxide for Hydrazine, 4-Nitrophenol and Hg2+ Detection in Water.

Monitoring hazardous chemical compounds such as hydrazine (N2H4), 4-nitrophenol (4-NP) and Hg2+ in natural water resources is a crucial issue due to their toxic effects on human health and catastrophic impact on the environment. Electrochemical nanostructured platforms integrating hybrid nanocomposites based on graphene derivatives and inorganic nanoparticles (NPs) are of great interest for such a purpose. In this work, disposable screen-printed carbon electrodes (SPCEs) have been modified with a hybrid nanocomposite formed by reduced graphene oxide (RGO), functionalized by 1-pyrene carboxylic acid (PCA), and decorated by colloidal Au NPs. These hybrid platforms have been tested for the electrocatalytic detection of N2H4 and 4-NP by differential pulse voltammetry and have been modified with an electropolymerized film of Hg2+ ions imprinted polycurcumin for the electroanalytical detection of Hg2+ by DPV. LODs, lower and in line with the lowest ones reported for state-of-the-art electrochemical sensors, integrating similar Au-graphene < nanocomposites, have been estimated. Additionally, good repeatability, reproducibility, and storage stability have been assessed, as well as a high selectivity in the presence of a 100-fold higher concentration of interfering species. The applicability of the proposed platforms for the detection of the compounds in real complex matrices, such as tap and river water samples, has been effectively demonstrated.

Molecularly imprinted curcumin nanoparticles decorated paper for electrochemical and fluorescence dual-mode sensing of bisphenol A.

A molecularly imprinted paper-based analytical device (MIP-µPAD) was developed for the sensing of bisphenol A (BPA). The platform was screen-printed onto a filter paper support, where the electrodes and the fluorescence µPADs were designed. Owing to its dual electrochemical and fluorescence responses, molecularly imprinted curcumin nanoparticles were used to sense BPA. The µPAD design was characterized by transmission electron microscopy, scanning electron microscopy, fluorescence spectroscopy, and electrochemical techniques. The sensor design comprised a wide linear range from 1 to 200 µg L-1 with limits of detection of 0.47 ± 0.2 and 0.62 ± 0.3 µg L-1 (LOD, S/N = 3) for electrochemical and fluorescence sensing, respectively. Furthermore, the system showed good analytical performance such as selectivity, stability, and reproducibility. The feasibility of the MIP-µPAD was demonstrated for the sensing of BPA in seawater, foods, and polycarbonate plastic packaged water with recovery values of 97.2 and 101.8%.

Curcumin graphite pencil electrode modified with molybdenum disulfide nanosheets decorated gold foams for simultaneous quantification of nitrite and hydrazine in water samples.

A non-enzymatic sensor based on a curcumin modified pencil graphite electrode, loaded with molybdenum disulfide nanosheets decorated gold foam, was constructed. Herein, the electrochemical deposition strategy was adopted throughout the sensing platform design stepwise. The electroactivity of the pencil electrode platform enables sensitive simultaneous quantification of hydrazine and nitrite where the respective working potentials typically are at + 0.2 V for hydrazine and + 0.75 V for nitrite (both vs. Ag/AgCl, saturated KCl). It is shown that the resulting sensor demonstrates excellent analytical performances in terms of limits of detection (18.3, 21.7 nM), sensitivities (0.051, 0.061 µA µM-1), and reproducibility standard deviations (RSD) of 3.1 and 2.7% for hydrazine and nitrite, respectively. Furthermore, long term stability studies showed that the electrodes exhibited an effectively unchanged response after some 30 days. The sensor was used to analyze spiked samples of river water and industrial wastewater.

Reduced graphene oxide nanosheets modified with nickel disulfide and curcumin nanoparticles for non-enzymatic electrochemical sensing of methyl parathion and 4-nitrophenol.

A method was designed for simultaneous voltammetric determination of methyl parathion pesticide (MP) and 4-nitrophenol (4-NP). Curcumin nanoparticles were deposited on reduced graphene oxide nanosheets that were modified with nickel disulfide. The material was placed on a screen-printed carbon electrode and then displayed high electrocatalytic activities toward MP and 4-NP, with a peak potential near -0.9 and - 0.7 V (vs. pseudo Ag/AgCl), respectively. Figures of merit include (a) good electrochemical sensitivities (7.165 and 6.252 µA·µM-1·cm-2), (b) wide linear ranges (from 0.25 to 80 µM), (c) low limits of detection (8.7 and 6.9 nM at S/N = 3) for MP and 4-NP, respectively, and (d) good selectivity, repeatability, reproducibility, and storage stability. The method was applied in the determination of MP and 4-NP in tomato and apple juices and spiked river water. Graphical abstract A novel electrocatalysis platform based on reduced graphene oxide-nickel disulfide nanosheets decorated with curcumin nanoparticles for simultaneous quantification of methyl parathion and 4-nitrophenol in various vegetarian juices and water samples.

Voltammetric simultaneous quantification of p-nitrophenol and hydrazine by using magnetic spinel FeCo2O4 nanosheets on reduced graphene oxide layers modified with curcumin-stabilized silver nanoparticles.

A sensor based on a screen-printed carbon electrode loaded with curcumin-stabilized silver nanoparticle-coated reduced graphene oxide magnetic spinel (FeCo2O4) nanosheets was constructed. The electrocatalytic activity of the electrode enables sensitive simultaneous quantification of hydrazine and p-nitrophenol. The respective working potentials typically are at +0.15 V for hydrazine and at -0.75 V for p-nitrophenol (both vs. pseudo Ag/AgCl), and the detection limits are 23 nM and 18 nM (at S/N = 3). Good selectivity, repeatability, reproducibility and storage stability are shown. The sensor was used to analyze spiked samples of river water and industrial wastewater. Graphical abstract Schematic of an electrochemical sensor for simultaneous quantification of hydrazine and 4-nitrophenol in various natural and wastewater samples. The electrocatalyst in this sensor is composed of graphene oxide nanosheets modified with a magnetic spinel of type FeCo2O4 and os curcumin-stabilized silver nanoparticles.

Graphene nanosheets modified with curcumin-decorated manganese dioxide for ultrasensitive potentiometric sensing of mercury(II), fluoride and cyanide.

A glassy carbon electrode (GCE) was modified by electropolymerization of curcumin on MnO2-Gr nanosheets to obtain a detection method for Hg(II) and for the anions fluoride and cyanide. The complexation by curcumin can be monitored by potentiometry. The results revealed a cathodic shift for the simultaneous detection of fluoride and cyanide and an anodic shift for the mercury(II) sensing, with peak potentials of -0.24, 0.12 and 0.82 V, respectively (vs. Ag/AgCl). The modified GCE is fairly selective, reproducible and repeatable. The detection limits are 19.2 nM for Hg(II), 17.2 nM for fluoride, and 28.3 nM for cyanide (LOD, S/N = 3). The method was successfully applied to the analysis of spiked samples of tap water, river water and petrochemical refinery wastewater. Graphical abstract Schematic of an electrochemical curcumin-MnO2-graphene nanosheet platform for the simultaneous assay of fluoride, cyanide and mercury(II) in the ppb concentration range in various natural and wastewater samples.