Electrode Modification Using Alkyne Manganese Phthalocyanine and Click Chemistry for Electrocatalysis

In this work, azidobenzene diazonium salt is grafted onto a glassy carbon electrode (GCE) followed by clicking of manganese tetrahexynyl phthalocyanine for the electrocatalysis of hydrazine. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1,3‐dipolar cycloaddition reaction, catalyzed by a copper catalyst was utilized to ‘click’ the manganese tetrahexynyl phthalocyanine to the surface of the grafted GCE. This new platform was then characterized using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM) and X‐ray photoelectron spectroscopy (XPS). Based on the cyclic voltammetry calibration curve of electrocatalysis for hydrazine, the clicked Mn phthalocyanine electrode proved to be an effective sensor with a sensitivity of 27.38 µA mM^?1 and the limit of detection (LoD) of 15.4 pM which is a great improvement compared to other reported sensors for this analyte.     

Electrode Modification through Click Chemistry Using Ni and Co Alkyne Phthalocyanines for Electrocatalytic Detection of Hydrazine

This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5‐hexyn‐oxy) cobalt(II) phthalocyanine (complex 2 ) and tetrakis(5‐hexyn‐oxy) nickel(II) phthalocyanine (complex 3 ) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3‐dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP 2 ‐clicked‐GCE and NiP 3 ‐clicked‐GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc‐GCE was 6.09 μM, while the NiPc‐GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM⁻¹ for the CoPc‐GCE and 111.2 μA mM⁻¹ for the NiPc‐GCE.     

Click chemistry electrode modification using 4-ethynylbenzyl substituted cobalt phthalocyanine for applications in electrocatalysis

In this work, we report on the synthesis and applications of a new cobalt tetrakis 4-((4-ethynylbenzyl) oxy) phthalocyanine (3) for the detection of hydrazine. The glassy carbon electrode (GCE) was first grafted through diazotization, providing the GCE surface layer with azide groups. Thereafter, the 1,3-dipolar cycloaddition reaction, catalyzed by a copper(I) catalyst was used to “click” complex 3 to the grafted surface of GCE. The new platform was then characterized using cyclic voltammetry (CV), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). This work shows that 3 is an effective sensor with sensitivity of 91.5 μA mM^?1 and limit of detection of 3.28 μM which is a great improvement compared to other reported sensors for this analyte.     

Effect of detonation nanodiamonds on the electrocatalytic activity of asymmetric cobalt phthalocyanine: Covalent versus non-covalent linking

We report on the effect of detonation nanodiamonds (DNDs) on electrocatalytic properties of an asymmetrically substituted cobalt phthalocyanine (CoPc). The incorporation of DNDs onto cobalt phthalocyanine enhances its electrochemical behaviour. An asymmetrical CoPc alone, when π-π stacked (CoPc-DNDs(ππ)) or covalently linked (CoPc@DNDs) to DNDs is used to modify a glassy carbon electrode (GCE) for the electrocatalytic detection of hydrazine. In addition, the GCE was modified by sequentially adding CoPc and DNDs onto its surface, represented as GCE/CoPc-DNDs(seq) when CoPc is placed before DNDs on the electrode and GCE/DNDs-CoPc(seq) when DNDs are placed before CoPc, where seq represents sequential. The obtained catalytic rate for the detection of hydrazine on GCE/CoPc@DNDs was 9.3×10⁴ M⁻¹.s⁻¹ with a limit of detection as 0.33 μM. GCE/CoPc@DNDs gave better electrocatalytic activities when compared to its counterparts.     

Behavior of Palladium Nanoparticles in the Absence or Presence of Cobalt Tetraaminophthalocyanine for the Electrooxidation of Hydrazine

We report on the electrodeposition of palladium nanoparticles (PdNPs) on a glassy carbon electrode (GCE) and onto a poly‐CoTAPc‐GCE (CoTAPc=cobalt tetraamino phthalocyanine) surface. The electrodes are denoted as PdNPs‐GCE and PdNPs/poly‐CoTAPc‐GCE, respectively. PdNPs/poly‐CoTAPc‐GCE showed the best activity for the oxidation of hydrazine at the lowest potential of ?0.28 V and with the highest currents. The results were further supported by electrochemical impedance spectroscopy (EIS) which showed that there was less resistance to charge transfer for PdNPs/poly‐CoTAPc‐GCE compared to PdNPs‐GCE. The catalytic rate constant for hydrazine oxidation was 6.12×10⁸ cm³ mol^?1 s^?1 using PdNPs/poly‐CoTAPc‐GCE.     

Electrocatalytic Oxidation and Determination of Hydrazine at an AuCu Nanoparticles – Graphene – Ionic Liquid Composite Film Coated Glassy Carbon Electrode

Gold‐copper alloy nanoparticles (AuCu NPs) were electrodeposited on a graphene – ionic liquid composite film (EGN‐IL). The AuCu NPs showed high electrocatalysis to the oxidation of hydrazine with a catalytic reaction rate constant of about 5.0×10⁴ mol/Ls. In phosphate buffer solutions (pH 6.8) the oxidation current of hydrazine at 0.15 V (vs. SCE) at the resulting electrode (AuCu? EGN‐IL/GCE) was linear to its concentration in the range of 0.2–110 µM with a sensitivity of 56.7 µA/mM, and the detection limit was 0.1 µM (S/N=3). The electrode was successfully applied to the determination of waste water.     

Electrocatalytic Determination of Traces of Hydrazine by a Glassy Carbon Electrode Modified with Palladium‐Gold Nanoparticles

A glassy carbon electrode modified with palladium/gold nanoparticles was successfully prepared by an electrodeposition process. It efficiently oxidizes hydrazine at a low overpotential of ?0.26 V versus SCE. The Pd‐AuNPs with an average size of 50–80 nm are uniformly dispersed at the GCE. The Pd‐AuNPs/GCE was used for determination of hydrazine in phosphate buffer solution of pH 7.0. The amperometric current response of the electrode was increased linearly over a hydrazine concentration of 0.1–500 µM with a limit of detection of 0.07 µM .The prepared hydrazine sensor exhibited high sensitivity, good selectivity reproducibility and long term stability.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

Synthesis and characterisation of Ag-nanoparticles immobilised on ordered mesoporous carbon as an efficient sensing platform: application to electrocatalytic determination of hydrazine

In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N₂ adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results.     

Promotion Effect of Bismuth on Nickel Electrodeposition and Its Electrocatalysis to Glucose Oxidation

Metallic Bi and Ni were co‐deposited onto the surface of glass carbon electrode (GCE) from the electrolyte solution containing their respective nitrate to fabricate a Bi/Ni alloy modified GCE (Bi/Ni‐GCE). The purpose is to study the influence of Bi³⁺ on the deposition of Ni and that of deposited Bi on the electrocatalytic performance of Ni to glucose in alkali solution. The results show that both redox signal of Ni(OH)₂/NiOOH and Ni(OH)₂/NiOOH mediated electrocatalysis to glucose is remarkably increased in the presence of Bi. It seems that there is a synergistic effect between Bi and Ni on each other’s redox electrochemistry. It’s possible that the firstly deposited Bi on GCE surface helps to the following nucleation and growth of Ni, leading to the deposition of more metallic Ni on GCE surface. An extremely attractive feature of Bi/Ni‐GCE is reflected by the fast response time to the electrocatalytic oxidation of glucose. The electrode nearly responses immediately after glucose is added and it reaches a steady‐state level within only 2 seconds, demonstrating a good electrocatalytic property of Bi/Ni‐GCE. The calibration plot is linear over the wide concentration range of 0–5.8 mM with a sensitivity of 33.96 µA/mM and a correlation coefficient of 0.9985. The detection limit of the glucose was found to be 0.59 µM at a signal‐to‐noise ratio of 3. The fabricated Bi/Ni‐GCE was successfully employed to analyze the glucose level in blood samples, exhibiting high accuracy, strong resistance against inference and good reliability in the practical applications.     

A New Amperometric Hydrazine Sensor Based on Prussian Blue/Single‐walled Carbon Nanotube Nanocomposites

A slow reaction process has been successfully used to synthesize Prussian blue/single‐walled carbon nanotubes (PB/SWNTs) nanocomposites. Electrochemical and surface characterization by cyclic voltammetry (CV), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV‐vis absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) confirmed the presence of PB nanocrystallites on SWNTs. PB/SWNTs modified glassy carbon electrode (GCE) exhibits efficient electron transfer ability and high electrochemical response towards hydrazine. The fabricated hydrazine sensor showed a wide linear range of 2.0×10^?6–6.0×10^?3 M with a response time less than 4 s and a detection limit of 0.5 μM. PB/SWNTs modified electrochemical sensors are promising candidates for cost‐effective in the hydrazine assays.     

Hemin Functionalized Multiwalled Carbon Nanotubes as a Matrix for Sensitive Electrogenerated Chemiluminescence Cholesterol Biosensor

Based on hemin‐MWCNTs nanocomposite and hemin‐catalyzed luminol‐H₂O₂ reaction, a sensitive electrogenerated chemiluminescence (ECL) cholesterol biosensor was proposed in this paper. Firstly, hemin‐MWCNTs was prepared via π–π stacking and modified on the surface of GCE. Subsequently, cholesterol oxidase (ChOx) was adsorbed on the modified electrode to achieve a cholesterol biosensor. Hemin‐MWCNTs nanocomposite provided the electrode with a large surface area to load ChOx, and endowed the nanostructured interface on the electrode surface to enhance the performance of biosensor. The biosensor responded to cholesterol in the linear range from 0.3 µM to 1.2 mM with a detection limit of 0.1 µM (S/N=3).     

Electrocatalytic Activity of Nanocomposites of Sulphur Doped Graphene Oxide and Nanosized Cobalt Phthalocyanines

In this work we explore the electrocatalytic activity of nanocomposites of reduced sulphur doped graphene oxide nanosheets (rSDGONS) and cobalt phthalocyanine (CoPc) or cobalt tetra amino phthalocyanine (CoTAPc) towards hydrogen peroxide. Transmission electron microscopy, scanning electron microscopy, X‐ray photon spectroscopy, X‐ray diffraction, chronoamperometry, linear scan voltammetry and cyclic voltammetry were used to characterize the nanocomposites. Nanosized CoPc showed superior (in terms of currents) electrocatalytic oxidation and reduction of hydrogen peroxide compared to CoTAPc nanoparticles (CoTAPc NP ). The lowest detection limit was obtained for hydrogen peroxide oxidation on electrodes modified with CoPc NP ‐rSDGONS at 1.49 µM. The same electrode gave a high adsorption equilibrium constant of 1.27×10³ mol^?1 and a Gibbs free energy of ?17.71 kJ/mol, indicative of a spontaneous reaction on the electrode surface.     

A Simple and Sensitive Poly‐1,5‐Diaminonaphthalene Modified Sensor for the Determination of Sulfamethoxazole in Biological Samples

Sulfamethoxazole (SMZ), an antibacterial sulfonamide drug, has been selectively determined using poly‐1,5‐diaminonaphthalene (p‐DAN) modified glassy carbon electrode (GCE). The modified sensor was characterized by field emission scanning electron microscopy (FE‐SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). SMZ showed linear response in the concentration range of 0.5–150 µM by using square wave voltammetry (SWV) and the detection limit was found to be 0.05 nM with sensitivity of 0.085 µA µM^?1. The proposed sensor has been successfully employed to determine SMZ in the pharmaceutical tablets and human urine samples.     

Electrocatalytic Nitrite Determination Using Iron Phthalocyanine Modified Gold Nanoparticles

Electrochemical detection of nitrite was achieved via electrodeposition of gold nanoparticles (AuNPs) onto glassy carbon electrodes, followed by 3‐mercaptopropionic acid (MPA) self‐assembly, enabling attachment of an iron(III) monoamino‐phthalocyanine (FeMAPc) catalyst via amide bond formation. The use of scanning electron microscopy, energy dispersive X‐ray spectroscopy and ultraviolet‐visible spectroscopy realised surface characterisation while cyclic voltammetry and electrochemical impedance spectroscopy techniques were applied for electrochemical interrogation. The electrochemical behaviour of nitrite at the bare (GCE), AuNPs/GCE, FeMAPc/GCE and FeMAPc‐MPA/AuNPs/GCE was further scrutinised using differential pulse voltammetry in phosphate buffer solution (0.1 M PBS, pH 5.8). Overall the FeMAPc‐MPA/AuNPs/GCE resulted in sensitivity 14.5 nA/µM, which was double that of AuNPs/GCE, 2.4 times FeMAPc/GCE and 3.5 times the response at a bare GCE, with linear range 1.9 µM–2.04 mM (PBS, pH 5.8) and LOD 0.21 µM. An interference study revealed that the proposed sensor (FeMAPc‐MPA/AuNPs/GCE) exhibited a selective response in the presence of interfering anions and the analytical capability of the sensor was demonstrated via nitrite ion determination in real water samples.     

Carbon‐Based Electrodes for Sensitive Electroanalytical Determination of Aminonaphthalenes

The electroanalytical performance of bare glassy carbon electrodes (GCE) for the determination of 1‐aminonaphthalene (1‐AN) and 2‐aminonaphthalene (2‐AN) was compared with GCE modified by a Nafion permselective membrane or multiwalled carbon nanotubes and with other types of carbon‐based materials, carbon film and boron doped diamond. Nafion‐modified GCE gave the highest sensitivity and lowest detection limit (0.4 µmol L^?1) for differential pulse voltammetric determination of 1‐AN. Electrochemical impedance spectroscopy gave information about the processes at the electrode surface. Simultaneous determination of 1‐AN and 2‐AN in a mixture at GCE and their determination in model samples of river water is presented.     

Electrochemical Activation of Graphite Nanosheets Decorated with Palladium Nanoparticles for High Performance Amperometric Hydrazine Sensor

Herein, we have demonstrated a preparation of palladium nanoparticles on electroactivated graphite nanosheets modified screen printed carbon electrode (PdNPs‐EGNS/SPCE) by a simple electrochemical method. The well‐prepared electrocatalyst was potentially applied to the high performance electrocatalytic oxidation of hydrazine in neutral medium. The PdNPs‐EGNS novel composite was characterized by scanning electron microscope (SEM) and the average diameter and thickness of PdNPs and EGNS were found to be ～38 nm and 85 nm, respectively. The high performance electrocatalytic determination of hydrazine was performed by the amperometric i‐t method. The fabricated sensor displayed irreversible electrocatalytic oxidation of hydrazine with diffusion‐controlled electrode process. The oxidation of hydrazine at PdNPs‐EGNS/SPCE showed wider linear range 0.05–1415 µM and high sensitivity 4.382 µA µM^?1 cm^?2. The as‐prepared electrocatalyst achieved quick response towards hydrazine with a lower detection limit 4 nM.     

Preparation of 1H‐1,2,3‐Triazoles by Cuprous Ion Mediated Cycloaddition of Terminal Alkyne and Sodium Azide

1H‐1,2,3‐triazoles can be prepared in good yield by the reaction of terminal alkyne and sodium azide in the presence of cuprous chloride at a temperature higher than 70°C. The alkyne is unactivated and the reaction has to be carried out under inert gas. At room temperature, the reaction first gives a Cu(I)‐azide complex which is converted to a Cu‐alkyne complex when the temperature is raised to higher than 70°C. The reaction of Cu(I)‐alkyne complex and azide ion dissociated from or coordinated to Cu(I) then gives 1H‐1,2,3‐triazoles.     

Electrochemical Synthesis of β‐Cyclodextrin Functionalized Silver Nanoparticles and Reduced Graphene Oxide Composite for the Determination of Hydrazine

β‐cyclodextrin (β‐CD) functionalized silver nanoparticles (AgNPs) and reduced graphene oxide (RGO) via one step electrochemical potentiodyanamic method has been prepared. Scanning electron microscopy, Energy‐Dispersive X‐ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the role of β‐CD on preparation of AgNPs and RGO. RGO/β‐CD/AgNPs modified GCE showed good electrochemical activity towards electro‐oxidation of hydrazine in terms of decreasing the over potential and increasing the peak current. The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) of the modified electrode towards hydrazine were determined to be 0.66 and 0.97×10^?6 cm² s^?1, respectively. The LOD of our sensor was many folds lower than that of recommended concentration of hydrazine in drinking water by United States Environmental Protection Agency and World Health Organization. The sensor exhibited a wide linear range from 0.08 to 1110 µM and a very low detection limit (LOD) of 1.4 nM. In addition, the sensor selectively determined hydrazine even in the presence of common interferents.     

Determination of Sudan I Using Electrochemically Reduced Graphene Oxide

Electrochemically reduced graphene oxide (ER-GO) was prepared by reducing exfoliated graphene oxide sheets on a glassy carbon electrode (GCE). The voltammetric responses of Sudan I-IV were studied at the ER-GO modified GCE (ER-GO/GCE). Compared with chemically reduced graphene oxide (CR-GO) modified electrode (CR-GO/GCE), ER-GO/GCE showed higher voltammetric responses to Sudan I. The electrode had a linear response to Sudan I in the range of 0.04–8.0 µmol L^?1 and a detection limit of 0.01 µmol L^?1. The real sample determination indicated that the proposed method was reliable, effective, and sufficient.