4-Cyanophenol herbicide sensor using multi-walled carbon nanotube embedded dual-microporous polypyrrole nanoparticles as metal-free and environmentally friendly hybrid electrode.

A highly sensitive 4-cyanophenol (4-CP) sensor was fabricated using multi-walled carbon nanotube (MWCNT)-embedded dual-microporous polypyrrole nanoparticle-modified screen-printed carbon electrodes (SPCE/DMPPy/MWCNT). The well-defined dual pores of DMPPy and MWCNT (~ 0.53 and ~ 0.65 nm) acted as good analyte absorption agents (shortening the ion diffusion path) and conducting agents (reducing the internal electron-transfer resistance). This enhanced electrical conductivity resulted in the improved electro-oxidation of 4-CP. A higher sensitivity (19.0 µA µM-1 cm-2) and lower limit of detection (0.8 nM) were achieved with a wide detection range of 0.001-400 µM (R2 = 0.9988). The proposed sensor exhibited excellent recovery of 4-CP in real-world samples. Therefore, the SPCE/DMPPy/MWCNT sensor is regarded highly suitable for rapidly detecting 4-CP.

Constructing Z-scheme g-C3N4/TiO2 heterostructure for promoting degradation of the hazardous dye pollutants.

The use of dyes and segments has increased widely in recent years, but it poses a serious health risk to ecosystems. In this work, TiO2 and two-dimensional g-C3N4 nanosheets (g-CN) were fabricated through co-precipitation and thermal polymerization technique, respectively. The g-CN-TiO2 photocatalyst (1: 3, 2: 2, 3: 1) in various weight percentages was prepared using a simple impregnation process. The photocatalytic behaviour of the g-CN, TiO2 NPs, and different weight percentages of g-CN-TiO2 photocatalyst was evaluated against methylene blue (MB) dye under UV-visible light illumination. Compared to pristine and other weight percentages of the g-CN-TiO2 nanocomposite, the optimized g-CN-TiO2 nanocomposite (3:1) showed promoted performance against MB dye. The enriched catalytic efficiency can be accredited to the low amount of TiO2 nanoparticles deposited on gCN nanosheets, possibly due to the boosted transport properties of the electron-hole pairs. The enriched photocatalytic behaviour can be attributed to the development of the Z-scheme system between TiO2 and g-CN. The current study is an outstanding demonstration of the development of maximum catalytic efficiency for destroying hazardous chemical dyes.

Hybrid nanostructures of Pd-WO3 grown on graphitic carbon nitride for trace level electrochemical detection of paraoxon-ethyl.

Well-defined crystal structures of Pd-doped WO3 nanorods were assembled on graphitic carbon sheets (Pd-WO3/g-C3N4) for ultrasensitive detection of paraoxon-ethyl (PEL) using an electrochemical method. The electrochemical behavior of PEL on the Pd-WO3/g-C3N4 hybrid composite was investigated using cyclic voltammetry (CV) and amperometric techniques. The Pd-WO3 crystallite was seen to modify the kinetics of g-C3N4, which improved the reduction/redox peak currents of PEL at the Pd-WO3/g-C3N4 composite compared to those of the g-C3N4 and WO3/g-C3N4-modified electrode. Moreover, the π-π interaction and hydrogen bond between the PEL and Pd-WO3/g-C3N4 composite improved the charge-transfer properties. The Pd-WO3/g-C3N4 hybrid composite was therefore able to obtain an enhanced sensitivity (3.70 ± 0.05 µA µM-1 cm-2) and low detection limit (0.03 nM; S/N = 3) with a wide range of linear concentrations (0.01-60 and 80-900.0 ± 5 µM) at applied potential of - 0.63 V (vs. Ag/AgCl). The detection of PEL in agricultural water and soil samples was successfully demonstrated with satisfactory RSD of 2.5 to 3.1% and recovery results of 97 to 102%, respectively.

Mixture of carbon aerogel with Pd-WO3 nanorods for amperometric determination of mesalazine.

We prepared, for the first time, carbon aerogels support on Pd-WO3 nanorods (CAs/Pd-WO3) hybrid nanocomposite via sol-gel and microwave-assisted methods. The as-prepared CAs/Pd-WO3-modified electrode was used as effective electrocatalyst for nanomolar level detection of mesalazine (MSA). The typical porous nature of carbon aerogels effectively prevented the aggregation of Pd-doped WO3 nanorods and increased the electrochemically active surface area. In addition, the Pd-WO3 nanointerface provides intrinsic improvement of the electrocatalytic activity and stability for the electrochemical oxidation process, and the interconnected conducting network of the porous surfaces of CAs accelerated rapid electron transport at the working electrode. The synergistic effect of the CAs/Pd-WO3 architecture has excellent electrocatalytic activity for the detection of MSA with high sensitivity of 2.403 ± 0.004 µA µM-1 cm-2, low detection limit of 0.8 ± 0.3 nM and wide linear response from 0.003-350 µM at a low applied potential of 0.30 V vs. Ag|AgCl. Satisfactory results were observed for its analytical performance in detecting MSA in human blood serum and urine samples, and recoveries ranged from 98.8 to 100.4%. We believe that the architecture of the modified CAs/Pd-WO3 electrocatalysts can be effectively used in clinical applications for the detection of MSA.

A chitosan grafted mesoporous carbon aerogel for ultra-sensitive voltammetric determination of isoniazid.

A screen-printed carbon electrode (SPCE) was modified with chitosan (Chit) supported on carbon aerogel (CA) to obtain an electrochemical sensor for the tuberculosis drug isoniazid (INZ). The interconnected mesoporous structure of Chit/CA provides a large surface area (SBET = 461 m2 g-1) and good porosity (VTot = 0.69 cm3 g-1). Besides, the modified SPCE displayed enhanced electrocatalytic activity due to the presence of numerous active sites (such as >C=O, -NH-, -NH2, -OH). Figures of merit include (a) a typical working voltage of 0.28 V (vs. Ag/AgCl), (b) high sensitivity (8.09 µA µM-1 cm-2), (c) a wide linear response to INZ (0.01-115 µM) and (d) a low detection limit (8 nM). The modified electrode has successfully been applied to the determination of INZ in spiked serum and urine, and recoveries ranged from 97.8 to 99.8%. Graphical abstract Schematic illustration of preparation and applications of a nanocomposite consisting of chitosan (Chit; CS) supported on carbon aerogel (CA) for electrochemical detection of isoniazid.

Voltammetric determination of vitamin B2 by using a highly porous carbon electrode modified with palladium-copper nanoparticles.

Palladium-copper nanoparticles were placed on activated carbon to give a nanocomposite for electrochemical sensing of riboflavin (vitamin B2). The activated carbon was produced by pyrolysis of natural waste of pistachio nutshells after KOH activation and under a nitrogen atmosphere. The carbons possess a large surface area and micro/meso-porosity. The nanocomposite was characterized by a variety of techniques to confirm structures and morphology. A screen-printed electrode modified with the composite was examined by EIS, CV, DPV, and amperometry. The effects of pH value, scan rate, and stability of the modified electrode were studied. Under optimized conditions, vitamin B2 displays a well-expressed oxidation peak at -0.15 V (vs. Ag/AgCl) in solutions with a pH value of 7.0. The voltammetric signal increases linearly in the 0.02 to 9 µM concentrations range and a lower detection limit of 7.6 pM. The sensor was successfully applied to the determination of vitamin B2 even in the presence of other common vitamins and in (spiked) raw milk samples. Graphical abstract A highly porous carbon was modified with palladium-copper alloy nanoparticles and used to coat an electrode for sensing of riboflavin (vitamin B2) by voltammetry.

Voltammetric determination of catechol and hydroquinone using nitrogen-doped multiwalled carbon nanotubes modified with nickel nanoparticles.

Nitrogen-doped multiwalled carbon nanotubes modified with nickel nanoparticles (Ni/N-MWCNT) were prepared by a thermal reduction process starting from urea and Ni(II) salt in an inert atmosphere. The nanocomposite was deposited on a screen printed electrode and characterized by X-ray diffraction, scanning and transmission electron microscopy, nitrogen adsorption, X-ray photoelectron spectroscopy, and thermogravimetric analyses. The performance of the composite was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The numerous active metal sites with fast electron transfer properties result in enhanced electrocatalytic activity towards the individual and simultaneous detection of catechol (CC) and hydroquinone (HQ), best at 0.21 V for CC and 0.11 V for HQ (vs. Ag/AgCl). For both targets the detection limit (S/N of 3) was 9 nM (CC) and 11 nM (HQ), and the Ni/N-MWCNT-electrode showed linear response from 0.1-300 µM CC, and 0.3-300 µM HQ. The electrode is selective over many potentially interfering ions. It was applied to the analysis of spiked water samples and gave satisfactory recoveries. It also is sensitive for CC (5.396 µA·µM-1 cm-2) and HQ (5.1577 µA·µM-1 cm-2), highly active, durable, acceptably repeatable and highly reproducible. Graphical abstract Voltammetric determination of catechol and hydroquinone using nitrogen-doped multiwalled carbon nanotubes modified with nickel nanoparticles.

Ruthenium Nanoparticles Decorated Tungsten Oxide as a Bifunctional Catalyst for Electrocatalytic and Catalytic Applications.

The syntheses of highly stable ruthenium nanoparticles supported on tungsten oxides (Ru-WO3) bifunctional nanocomposites by means of a facial microwave-assisted route are reported. The physicochemical properties of these Ru-WO3 catalysts with varied Ru contents were characterized by a variety of analytical and spectroscopic methods such as XRD, SEM/TEM, EDX, XPS, N2 physisorption, TGA, UV-vis, and FT-IR. The Ru-WO3 nanocomposite catalysts so prepared were utilized for electrocatalytic of hydrazine (N2H4) and catalytic oxidation of diphenyl sulfide (DPS). The Ru-WO3-modified electrodes were found to show extraordinary electrochemical performances for sensitive and selective detection of N2H4 with a desirable wide linear range of 0.7-709.2 µM and a detection limit and sensitivity of 0.3625 µM and 4.357 µA µM-1 cm-2, respectively, surpassing other modified electrodes. The modified GCEs were also found to have desirable selectivity, stability, and reproducibility as N2H4 sensors, even for analyses of real samples. This is ascribed to the well-dispersed metallic Ru NPs on the WO3 support, as revealed by UV-vis and photoluminescence studies. Moreover, these Ru-WO3 bifunctional catalysts were also found to exhibit excellent catalytic activities for oxidation of DPS in the presence of H2O2 oxidant with desirable sulfoxide yields.

Facile and novel synthesis of palladium nanoparticles supported on a carbon aerogel for ultrasensitive electrochemical sensing of biomolecules.

Highly stable palladium nanoparticles (Pd NPs) supported on a porous carbon aerogel (Pd/CA) prepared by a facile microwave reduction route is reported. The as-prepared Pd/CA composites were characterized by various techniques, viz. XRD, Raman, SEM-EDX, FE-TEM, BET, and TGA. The Pd NPs were found to disperse uniformly in the porous carbon matrix, which possesses a large surface area (851.8 m2 g-1) and pore volume (3.021 cm3 g-1). The Pd/CA composite was found to possess extraordinary electrocatalytic activity and excellent selectivity for simultaneous detection of dopamine (DA) and melatonin (ML). The Pd/CA-modified electrode exhibited a wide linear response range for electrochemical sensing of DA (0.01-100 µM) and ML (0.02-500 µM) with a detection limit of 0.0026 and 0.0071 µM, respectively. In addition, the electrochemical sensor reported herein was successfully applied for the detection of DA and ML in human serum and urine samples, revealing perspective practical applications.

Determination of 4-nitrophenol in water by use of a screen-printed carbon electrode modified with chitosan-crafted ZnO nanoneedles.

The toxicity and environmental pollution by nitro aromatic compounds in water samples is the most recognized problem in worldwide. Hence, we have developed a simple and highly sensitive electrochemical method for the determination of 4-nitrophenol (4-NP) in water samples based on a chitosan (CHT) crafted zinc oxide nanoneedles (ZnO NDs) modified screen printed carbon electrode. The CHT/ZnO NDs were characterized by Field emission scanning electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction technique. The CHT/ZnO NDs modified electrode showed an enhanced electrocatalytic activity and lower potential detection towards 4-NP, compared with other modified electrodes. Under optimum conditions, the differential pulse voltammetry (DPV) response of CHT/ZnO NDs modified electrode displayed a wide linear response range from 0.5 to 400.6µM towards the detection of 4-NP with a detection limit (LOD) of 0.23µM. The CHT/ZnO NDs modified electrode was used for specific and sensitive detection of 4-NP in presence of possible interfering species and common metal ions with long-term stability. In addition, the excellent analytical performance of the proposed sensor was successfully applied for determination of 4-NP in water samples.

One-Pot Green Synthesis of Graphene Nanosheets Encapsulated Gold Nanoparticles for Sensitive and Selective Detection of Dopamine.

We report a simple new approach for green preparation of gallic acid supported reduced graphene oxide encapsulated gold nanoparticles (GA-RGO/AuNPs) via one-pot hydrothermal method. The as-prepared composites were successfully characterized by using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction techniques (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM) and elemental analysis. The GA-RGO/AuNPs modified electrode behaves as a hybrid electrode material for sensitive and selective detection of dopamine (DA) in presence of ascorbic acid (AA) and uric acid (UA). The GA-RGO/AuNPs modified electrode displays an excellent electrocatalytic activity towards the oxidation of DA and exhibits a wide linear response range over the DA concentrations from 0.01-100.3 µM with a detection limit (LOD) of 2.6 nM based on S/N = 3. In addition, the proposed sensor could be applied for the determination of DA in human serum and urine samples for practical analysis.

A simple preparation of graphite/gelatin composite for electrochemical detection of dopamine.

In this study, we demonstrate a simple preparation of graphite (GR) sheets assisted with gelatin (GLN) polypeptide composite was developed for sensitive detection of dopamine (DA) sensor. The GR/GLN composite was prepared by GR powder in GLN solution (5mg/mL) via sonication process. The prepared GR/GLN composite displays well dispersion ability in biopolymer matrix and characterized via scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS) studies. The GR/GLN modified electrode showed an excellent electrocatalytic activity toward the oxidation of DA, suggesting that the successful formation of GR sheets crosslinked with the functional groups of GLN polypeptide. In addition, the GR/GLN modified electrode achieved a wide linear response ranging from 0.05 to 79.5µM with a detection limit of 0.0045µM. The calculated analytical sensitivity of the sensor was 1.36±0.02µAµM-1cm-2. Conversely, the modified electrode demonstrates a good storage stability, reproducibility and repeatability. In addition, the sensor manifests the determination of DA in human serum and urine samples for practical applications.

Highly stable biomolecule supported by gold nanoparticles/graphene nanocomposite as a sensing platform for H2O2 biosensor application.

A highly active and stable composite of hemin (HN) supported by reduced graphene oxide/gold nanoparticles (HN-RGO/AuNPs) was prepared by one-pot hydrothermal method. The physicochemical properties of the as-prepared composites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-vis spectroscopy, Raman spectroscopy and X-ray diffraction technique (XRD). The HN-RGO/AuNP-modified electrode shows a stable and well-defined, surface-confined redox couple at an apparent formal potential of -0.317 V vs. Ag|AgCl with a surface coverage value of 2.239 × 10-10 mol cm-2. Compared with HN, HN-GO and HN-RGO, the HN-RGO/AuNP-modified electrode exhibits excellent electrocatalytic activity towards hydrogen peroxide (H2O2). Under optimum conditions, the HN-RGO/AuNP-modified electrode shows a wide linear response ranges from 0.05 µM to 518.15 µM towards H2O2 with a fast response time (3 s). The calculated sensitivity and limit of detection (LOD) of the biosensor were 3.99 µA µM-1 cm-2 and 16 nM, respectively. In addition, the Michaelis-Menten constant value of the biosensor is 0.13 mM, which indicates the high affinity of HN towards the reduction of H2O2. The proposed biosensor displays high sensitivity and selectivity towards H2O2 in the presence of common biologically co-existing species. The biosensor shows an acceptable practical ability in human serum, contact lens solution and milk samples with an appreciable recovery.